Astronomers Determine Brown Dwarf Age Using Tiny Stellar Pulsations

An illustration of a star and a brown dwarf in a binary system.
Generated with ChatGPT by the University of Hawaiʻi .

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Results Test Brown Dwarf Theory challenging astrophysicists

Maunakea, Hawaiʻi – Astronomers using W. M. Keck Observatory on Maunakea, Hawaiʻi Island, have measured one of the most precise ages yet for a Sun-like star hosting a brown dwarf companion. The result offers a powerful new test of how brown dwarfs cool and evolve over time, helping to address a long-standing challenge in astrophysics.

The study focused on the nearby system HR 7672, which includes a Sun-like star and a faint brown dwarf companion. Using Keck Observatory’s Keck Planet Finder (KPF), the team detected subtle oscillations in the star’s surface, ripples that revealed its age to be 2.3 billion years.

Because the brown dwarf formed alongside the star, this precise stellar age serves as a benchmark for the companion’s evolution, offering a rare chance to directly test theoretical models of brown dwarf cooling.

“The 18% age uncertainty establishes the HR7672 system as a valuable benchmark for years to come,” said Yaguang Li, lead author and researcher at the University of Hawaiʻi at Mānoa.

The study, led by the University of Hawaiʻi Institute for Astronomy, is published in The Astrophysical Journal.

A Two-Decade Scientific Arc

The HR 7672 system has played a historic role in the study of substellar objects. The companion, known as HR 7672B, was first discovered by researcher Michael Liu, co-author and professor at the University of Hawaiʻi Institute for Astronomy. HR 7672B was the first directly imaged brown dwarfs orbiting a Sun-like star.

Using Keck Observatory’s Near-Infrared Camera (NIRC2) and the telescope’s Adaptive Optics system to correct for atmospheric blurring, Liu obtained a sharper image of the brown dwarf, which is 2,000 times fainter than its bright host star.

“Pioneering observations with Keck Observatory helped illuminate the so-called “brown dwarf desert,” the scarcity of such companions around Sun-like stars at close separations,” said Liu.

Now, more than two decades later, a new generation of Keck Observatory instrumentation continues to advance that legacy. Using ultra-precise measurements of the host star with the Keck Planet Finder (KPF) instrument, astronomers detected tiny stellar pulsations that reveal the star’s internal structure and age with unprecedented precision.

“The unique fast-readout mode of the Keck Planet Finder makes it the only instrument in the Northern Hemisphere capable of sampling oscillations on such short timescales,” added Li.

Testing How Brown Dwarfs Cool Over Time

Brown dwarfs are failed stars that are too small to sustain stable hydrogen fusion, so they gradually cool and fade as they age. Their brightness, therefore, depends sensitively on both their mass and age. However, astronomers have had difficulty testing theoretical models of this cooling, in part because reliable ages are rarely available.

Now, with this new and precise age measurement, combined with HR 7672B’s well-known luminosity and mass, the system becomes an exceptional “benchmark” for testing brown dwarf evolutionary models.

Comparing the observations with six different theoretical cooling models, the team found the best agreement with the most recent models that incorporate updated interior physics. Without the new data, the team would not have been able to distinguish this model from the five other possibilities.

These results demonstrate that high-precision stellar ages are essential for understanding substellar evolution — and show that precision spectroscopy with the next generation of observations will finally provide this information.

“Yaguang’s research has made this object even more valuable for our theoretical understanding of brown dwarfs,” said Liu.

As a next step, the researchers plan to generalize this method to a broader set of benchmark systems and test brown dwarf evolutionary models across different regimes.

Source: W. M. Keck Observatory/News

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Related Links
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• Science Paper.
• University of Hawaiʻi Release

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Media Contact:

Meagan O’Shea
moshea@keck.hawaii.edu

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“Superkilonova” A Star So Nice, It Explodes Twice

Artist interpretation depicts a hypothesized event known as a superkilonova. Initially, a massive star explodes in a supernova, which generates elements like carbon and iron (left). In the aftermath, two neutron stars are born, at least one of which is believed to be less massive than our Sun (middle). The neutron stars spiral together, sending gravitational waves rippling through the cosmos, before merging in a dramatic kilonova (right). Kilonovae seed the universe with the heaviest elements, such as gold at platinum, which glow in red light as depicted in the animation. Credit: Caltech/K. Miller and R. Hurt (IPAC)

Double Cosmic Explosion

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Potential first-of-a-kind may have produced gravitational waves and light

Maunakea, Hawaiʻi – A team of astronomers using a variety of telescopes, including the W. M. Keck Observatory on Maunakea, Hawaiʻi Island, have discovered a possible “Superkilonova” that exploded not once but twice, evidence that this oddball event may be a first-of-a-kind superkilonova, or a kilonova spurred by a supernova. Such an event has been hypothesized but never seen.

When the most massive stars reach the ends of their lives, they blow up in spectacular supernova explosions, which seed the universe with heavier elements such as carbon and iron. Another type of explosion—the kilonova—occurs when a pair of dense, dead stars called neutron stars smash together, forging even heavier elements, such as gold and uranium. The heavy elements created by both of these explosions are among the basic building blocks of stars and planets.

So far, only one kilonova has been unambiguously confirmed to date, a historic event known as GW170817, which took place in 2017. In that case, two neutron stars smashed together, sending ripples in space-time known as gravitational waves, as well as light waves, across the cosmos. The cosmic blast was detected in gravitational waves by the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO) and its European partner, the Virgo gravitational-wave detector, and in light waves by dozens of ground-based and space telescopes around the world.

The curious case of the kilonova candidate, AT2025ulz, is complex, and thought to have stemmed from a supernova blast that went off hours before, ultimately obscuring astronomers’ view and making the case more complicated.

“At first, for about three days, the eruption looked just like the first kilonova in 2017,” said Mansi Kasliwal, professor of astronomy at The California Institute of Technology and director of Palomar Observatory. “Everybody was intensely trying to observe and analyze it, but then it started to look more like a supernova, and some astronomers lost interest. Not us.”

The study, led by The California Institute of Technology, is published in The Astrophysical Journal Letters.

In August 2025, a new gravitational-wave signal was picked up by The Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo in Italy. Within minutes, an alert was issued to the astronomical community containing a rough map of the source signaling to researchers that gravitational waves had been registered from what appeared to be a merger between two objects, with at least one of them being unusually tiny.

After first being identified by the Zwicky Transient Facility at Palomar Observatory, Kasliwal coordinated with Keck Observatory staff astronomer Michael Lundquist to launch a rapid Target of Opportunity (ToO) observation of AT2025ulz, a process that allows scientists to request immediate access for short-lived cosmic events. Mansi’s ToO request enabled the immediate spectroscopic follow-up using the Low-Resolution Imaging Spectrograph (LRIS).

“Keck Observatory provided the imagery and spectroscopy via our Low-Resolution Imaging Spectrograph (LRIS) Instrument to measure the host extinction and redshift of the galaxy as well as looking at the spectroscopic evolution,” Lundquist said. “This highlights Keck Observatory’s Target of Opportunity capability to rapidly respond to transient alerts and deliver the spectroscopic data needed to explore potential multi-messenger associations.”

The observations confirmed that the eruption of light had faded fast and glowed at red wavelengths—just as GW170817 had done eight years earlier. In the case of the GW170817 kilonova, the red colors came from heavy elements like gold; these atoms have more electron energy levels than lighter elements, so they block blue light but let red light pass through.

Then, days after the blast, AT2025ulz started to brighten again, turn blue and show hydrogen in its spectra, all signs of a supernova not a kilonova (specifically a “stripped-envelope, core-collapse” supernova). Supernovae from distant galaxies are generally not expected to generate enough gravitational waves to be detectable by LIGO and Virgo, whereas kilonovae are. This led some astronomers to conclude that AT2025ulz was triggered by a typical, ho-hum supernova and not in fact related to the gravitational-wave signal.

What Might Be Going On?

Kasliwal says that several clues tipped her off that something unusual had taken place. Though AT2025ulz did not resemble the classic kilonova GW170817, it also did not look like an average supernova. Additionally, the LIGO–Virgo gravitational-wave data had revealed that at least one of the neutron stars in the merger was less massive than our Sun, a hint that one or two small neutron stars might have merged to produce a kilonova.

Neutron stars are the leftover remains of massive stars that explode as supernovae. They are thought to be around the size of San Francisco (about 22 to 30 kilometers across) with masses that range from 1.2 to about 3 times that of our Sun. Some theorists have proposed ways in which neutron stars might be even smaller, with masses less than the Sun’s, but none have been observed so far.

Theorists invoke two scenarios to explain how a neutron star could be that small. In one, a rapidly spinning massive star goes supernova, then splits into two tiny, sub-solar neutron stars in a process termed fission. In the second scenario, called fragmentation, the rapidly spinning star again goes supernova, but this time a disk of material forms around the collapsing star. The lumpy disk material coalesces into a tiny neutron in a manner similar to how planets form.

With LIGO and Virgo having detected at least one sub-solar neutron star, it is possible, according to theories proposed by co-author Brian Metzger of Columbia University that two newly formed neutron stars could have crashed into each other, erupting as a kilonova that sent gravitational waves rippling through the cosmos. As the kilonova churned out heavy metals, it would have initially glowed in red light as ZTF and other telescopes observed. The expanding debris from the initial supernova blast would have obscured the astronomers’ view of the kilonova. In other words, a supernova may have birthed twin baby neutron stars that then merged to make a kilonova.

“The only way theorists have come up with to birth sub-solar neutron stars is during the collapse of a very rapidly spinning star,” Metzger says. “If these ‘forbidden’ stars pair up and merge by emitting gravitational waves, it is possible that such an event would be accompanied by a supernova rather than be seen as a bare kilonova.”

But while this theory is tantalizing and interesting to consider, the research team stresses that there is not enough evidence to make firm claims. The only way to test the superkilonovae theory is to find more.

“Future kilonovae events may not look like GW170817 and may be mistaken for supernovae,” Kasliwal says. “We can look for new possibilities in data like this, but we do not know with certainty that we found a superkilonova. The event, nevertheless, is eye o,brpening.”

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Source: W. M. Keck Observatory/News

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About LRIS

The Low Resolution Imaging Spectrometer (LRIS) is a very versatile and ultra-sensitive visible-wavelength imager and spectrograph built at the California Institute of Technology by a team led by Prof. Bev Oke and Prof. Judy Cohen and commissioned in 1993. Since then it has seen two major upgrades to further enhance its capabilities: the addition of a second, blue arm optimized for shorter wavelengths of light and the installation of detectors that are much more sensitive at the longest (red) wavelengths. Each arm is optimized for the wavelengths it covers. This large range of wavelength coverage, combined with the instrument’s high sensitivity, allows the study of everything from comets (which have interesting features in the ultraviolet part of the spectrum), to the blue light from star formation, to the red light of very distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in 2011 for research determining that the universe was speeding up in its expansion.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaiʻi feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. For more information, visit: www.keckobservatory.org

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Astronomers Discover the First Gravitationally Lensed Superluminous Supernova

SN 2025wny

Gravitationally lensed superluminous supernova
An artist’s interpretation of light from a supernova passing through a gravitational lens, reaching Earth at different times.
Credit: Oskar Klein Center, University of Stockholm / Samuel Avraham & Joel Johansson.

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Maunakea, Hawaiʻi – An international team of astronomers using a combination of ground-based telescopes, including the W. M. Keck Observatory on Maunakea, Hawaiʻi Island, has discovered the first-ever spatially resolved, gravitationally lensed superluminous supernova. The object, dubbed SN 2025wny, offers a rare look at a stellar cataclysm from the early Universe and provides a striking confirmation of Einstein’s theory of general relativity.

SN 2025wny lies so far away that its light has traveled 10 billion years to reach Earth; the Universe was just 4 billion years old when the explosion occurred. Normally, a supernova at this distance would be far too faint to detect from the ground. But two foreground galaxies act as a natural gravitational “magnifying glass,” boosting the supernova’s brightness by a factor of 50 and splitting it into distinct, spatially separated images.

“This is nature’s own telescope,” says Joel Johansson, lead author from the Oskar Klein Centre, Stockholm University. “The magnification lets us study a supernova at a distance where detailed observations would otherwise be impossible.”

The study, led by Stockholm University, is published in The Astrophysical Journal Letters.

An artist’s interpretation of light from a supernova passing through a gravitational lens, reaching Earth at different times.
Credit: Oskar Klein Center, University of Stockholm / Samuel Avraham & Joel Johansson.

A new method to probe the expansion of the universe

Because each of the multiple lensed images takes a slightly different path around the intervening galaxies, their arrival times differ. Measuring these time delays provides a powerful, independent method to determine the Hubble constant—the rate at which the Universe is expanding.

A major unsolved problem in modern cosmology is the Hubble tension—the growing mismatch between measurements of the Universe’s expansion rate made from the early Universe versus those made from nearby objects. The disagreement suggests that our current cosmological model may be incomplete. Strongly lensed supernovae like SN 2025wny offer a new, independent way to measure this expansion rate through time-delay differences between the lensed images, helping determine whether the tension reflects new physics or limitations in existing methods.

“A lensed supernova with multiple, well-resolved images provides one of the cleanest ways to measure the expansion rate of the Universe,” says Ariel Goobar of the Oskar Klein Centre. “SN 2025wny is an important step toward resolving one of cosmology’s most significant challenges.”

A surprising and exceptionally hot explosion

Superluminous supernovae are extremely bright, rare explosions. SN 2025wny stands out even in this elite category: its early ultraviolet light, stretched into optical wavelengths by cosmic expansion, revealed an exceptionally hot, brilliant event.

The supernova’s intense brightness illuminated its host galaxy, allowing astronomers to identify narrow absorption lines from elements such as carbon, iron, and silicon. These fingerprints point to a low-metallicity, star-forming dwarf galaxy—exactly the kind of environment thought to produce superluminous supernovae during the Universe’s youth.

How the Discovery Was Made

The discovery relied on a chain of cutting-edge observatories working together on scientific breakthroughs. The Zwicky Transient Facility (ZTF) at Palomar Observatory in California first detected the explosion during its nightly monitoring of the sky. The Nordic Optical Telescope (NOT) on La Palma in the Canary Islands provided early spectroscopy of the transient, Liverpool Telescope (LT) also on La palma provided four separate images of SN 2025wny, and Keck Observatory ultiumately provided the decisive spectra that confirmed both the supernova type and its extreme distance.

Yu-Jing Qin, a postdoctoral researcher at Caltech, led a series of spectroscopic observations using Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS), targeting each of the individual supernova images and the lensing galaxies.

The Keck spectra revealed a forest of narrow absorption lines from the supernova’s host galaxy – the fingerprints of elements such as carbon, iron and silicon – which nailed down the redshift and nature of the event.

“The spectrum taken with LRIS provides the most convincing measurement of its distance/redshift and pinpointed its classification as a superluminous supernova, which is a rare subclass. We were really impressed by the data quality and are pursuing further observations using other Keck instruments,” said Qin.

These rapid-response observations were enabled by Keck Observatory’s Target of Opportunity (ToO) policy, which allows scientists to request immediate access for short-lived cosmic events.

“It’s always exciting to get a request for a very rapid response to a transient event like this,” said John O’Meara, Chief Scientist and Deputy Director for Keck Observatory. “Keck was ready to respond, and we were happy to deliver and participate in this breakthrough.”

What Comes Next?

SN 2025wny demonstrates that strongly lensed supernovae at very high redshifts can be discovered and resolved with today’s surveys—a crucial proof of concept ahead of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST), which is expected to uncover hundreds more.

Follow-up observations with the Hubble Space Telescope and James Webb Space Telescope are already underway. These data will refine the gravitational lens model, map the multiple images with exceptional precision, and ultimately measure the time delays needed for a new, independent determination of the Hubble constant.

The extraordinary magnification also offers an unprecedented view into how such extreme explosions work and how stars evolved in the early Universe.

Source: W.M. Keck Observatory/Science News

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About LRIS

The Low Resolution Imaging Spectrometer (LRIS) is a very versatile and ultra-sensitive visible-wavelength imager and spectrograph built at the California Institute of Technology by a team led by Prof. Bev Oke and Prof. Judy Cohen and commissioned in 1993. Since then it has seen two major upgrades to further enhance its capabilities: the addition of a second, blue arm optimized for shorter wavelengths of light and the installation of detectors that are much more sensitive at the longest (red) wavelengths. Each arm is optimized for the wavelengths it covers. This large range of wavelength coverage, combined with the instrument’s high sensitivity, allows the study of everything from comets (which have interesting features in the ultraviolet part of the spectrum), to the blue light from star formation, to the red light of very distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in 2011 for research determining that the universe was speeding up in its expansion.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaiʻi feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. For more information, visit: www.keckobservatory.org

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Supernova’s ‘Trapped’ Jet Reveals Source of Fast X-ray Transient

This image shows the cosmic field in which the fast X-ray transient EP 250108a, and the supernova that followed it, were detected by Einstein Probe (EP) in early 2025. Using a combination of telescopes, including the W. M. Keck Observatory, a team of astronomers studied the evolving signal of EP 250108a/SN 2025kg to uncover details about its origin. Their analysis reveals that fast X-ray transients can result from the ‘failed’ explosive death of a massive star. Credit: International Gemini Observatory/NOIRLab/NSF/AURA.

Maunakea, Hawaiʻi – An international team of astrophysicists using W. M. Keck Observatory on Maunakea, Hawaiʻi Island have uncovered a possible origin of fast X-ray transients (FXTs) — mysterious, fleeting bursts of X-rays that have long puzzled astronomers.

Using a combination of telescopes around the globe and in space, the team studied the closest FXT associated with the explosive death of a massive star, or supernova, ever observed. A geyser of high-energy particles, or jet, trapped inside a supernova produced the FXT, the scientists discovered.

When jets burst through a massive star’s onion-like layers, they generate gamma-ray bursts (GRBs), the most powerful and luminous explosions in the universe. When the jets are stifled, however, they emit lower levels of energy, which astronomers can detect only from X-ray signals. The new observations now point to these “failed” jets as a source of the emission, explaining the historically elusive phenomena.

This finding marks a significant step in understanding the diverse landscape of cosmic explosions — bridging the gap among FXTs, GRBs and supernovae.

A pair of studies, led by Northwestern University and the University of Leicester in England, has been accepted by The Astrophysical Journal Letters.

“Since the 1970s, astronomers have detected FXTs — blasts of X-rays from distant galaxies that can last from seconds to hours,” said Northwestern’s Jillian Rastinejad, lead author of one of the studies. “But their origin sources have remained a long-standing mystery. Our work definitively shows that FXTs can originate from the explosive death of a massive star. It also supports a causal link between GRB-supernovae and FXT-supernovae, in which GRBs are produced by successful jets, and FXTs are produced by trapped weak jets.”

The team utilized the various time zones and locations of its members to gather and analyze the data, passing it along to the next time zone to make decisions on the next night of observations.

“The result? A massive and beautiful stream of data collected from facilities large and small, on the ground and in space, chronicling this event’s first month. It takes really special events to motivate such a global effort, and this FXT was one,” said Northwestern’s Wen-fai Fong, a senior author on the study.

This sequence of images shows the fading light of the supernova SN 2025kg, which followed the fast X-ray transient EP 250108a, a powerful blast of X-rays that was detected by Einstein Probe (EP) in early 2025. Using a combination of telescopes, including the W. M. Keck Observatory, a team of astronomers studied the evolving signal of EP 250108a/SN 2025kg to uncover details about its origin. Their analysis reveals that fast X-ray transients can result from the ‘failed’ explosive death of a massive star. Credit: International Gemini Observatory/NOIRLab/NSF/AURA.

Spectroscopy obtained from Keck Observatory’s Low-Resolution Imaging Spectrometer (LRIS) revealed that SN 2025kg is a Type Ic-BL supernova—an especially fast and powerful kind of stellar explosion. By analyzing the light, scientists measured how quickly the star’s material was ejected (nearly 19,000 kilometers per second or about 11,800 miles per second) and gained insight into the immense energy released during the blast.

“The fact that Keck Observatory was able to respond quickly to a transient of interest was pivotal to understanding the composition and speed of the supernova ejecta, and how much material was shed,” said Fong. “Its nimble capabilities were particularly important at later times when the source was fainter and only detectable with the most sensitive ground-based spectrographs.”

“This result highlights the important role Keck Observatory plays with observatories across the globe and in space,” added John O’Meara, chief scientist and deputy director at the observatory. “The international team has really pulled out all the stops to characterize and understand this new type of transient.”

“The fact that Keck Observatory was able to respond quickly to a transient of interest was pivotal to understanding the composition and speed of the supernova ejecta, and how much material was shed,” said Fong. “Its nimble capabilities were particularly important at later times when the source was fainter and only detectable with the most sensitive ground-based spectrographs.”

“This result highlights the important role Keck Observatory plays with observatories across the globe and in space,” added John O’Meara, chief scientist and deputy director at the observatory. “The international team has really pulled out all the stops to characterize and understand this new type of transient.”

An explosive neighbor

Although astronomers have detected FXTs for decades, the limited number of discoveries prevented detailed studies. But now, scientists have a new space-based tool, called the Einstein Probe, which is dedicated to the search. Launched in January 2024 by the Chinese Academy of Sciences in partnership with the European Space Agency and the Max Planck Institute for Extraterrestrial Physics, the Einstein Probe carries two scientific instruments, specially designed to observe X-ray sources.

“FXTs have long fascinated us but their study has relied on a small number of events that were discovered in serendipitous ways,” Fong said. “The Einstein Probe has revolutionized this field by increasing the number of known events by ten-fold in just a year of operations. Thus, it is not only filling in the previously sparse landscape of FXTs, but also making our picture of that landscape crisper, bringing facets of these explosions into focus that we had not imagined before.

Shortly after its launch, the Einstein Probe captured the most nearby FXT, associated with a supernova, to date. Dubbed EP 250108a, the FXT was located 2.8 billion light-years away from Earth, within the river-like constellation Eridanus. Its close proximity to Earth gave astronomers an unprecedented opportunity to observe the event’s evolution.

To track this evolving behavior, the team captured the event’s signal across multiple wavelengths. The Gemini South telescope at the International Gemini Observatory provided near-infrared data, the Gemini North telescope atop Maunakea provided optical data, the MMT Observatory in Arizona provided the infrared images, and the James Webb Space Telescope provided highly sensitive infrared data.

Failed jet, big breakthrough

By analyzing the rapidly evolving signal of EP 250108a, the scientists concluded the object is likely a “failed” GRB. Although EP 250108a is similar to a jet-driven explosion, its jets did not break through the outer layer of the dying star. Instead, the jets remained trapped inside.

“Through decades of scientific study, we know that jets can successfully plow through a dying star’s outer layers, and we view them as GRBs,” Rastinejad said. “In our study, we found this ‘trapped’ jet outcome is more common in massive star explosions than jets that successfully emerge from the star.”

The researchers now plan to use datasets provided by the Vera C. Rubin Observatory that will show how stars and their explosive deaths change over time. These insights could help reveal the inner workings of FXTs and many other exotic cosmic events.

Related Links:

• Science Paper by Rastinejad et. al

Source: W. M. Keck Observatory/News

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Biggest Boom Since the Big Bang: Hawaiʻi-Based Astronomers Uncover the Most Energetic Explosions In The Universe Yet Discovered

Artist’s concept of the formation of Extreme Nuclear Transients (ENTs)
Credit: W. M. Keck Observatory / Adam Makarenko

Releasing more energy than 100 supernovae, Extreme Nuclear Transients (ENTs) are the most energetic transients yet observed

Maunakea, Hawaiʻi – Astronomers using data from the W. M. Keck Observatory on Maunakea, Hawaiʻi Island discovered the most energetic cosmic explosions discovered to date, naming the new class of events “extreme nuclear transients” (ENTs). These extraordinary phenomena occur when massive stars—at least three times heavier than our Sun—are torn apart after wandering too close to a supermassive black hole. Their disruption releases vast amounts of energy visible across enormous distances.

The team’s findings were detailed today in the journal Science Advances.

“We’ve observed stars getting ripped apart as tidal disruption events for over a decade, but these ENTs are different beasts, reaching brightnesses nearly ten times more than what we typically see,” said Jason Hinkle, who led the study as the final piece of his doctoral research at the University of Hawaiʻi’s Institute for Astronomy (IfA). “Not only are ENTs far brighter than normal tidal disruption events, but they remain luminous for years, far surpassing the energy output of even the brightest known supernova explosions.”

The immense total energy output of these ENTs are truly unprecedented. The most energetic ENT studied, named Gaia18cdj, emitted an astonishing 25 times more energy than the most energetic supernovae known. While typical supernovae emit as much energy as the Sun does in its 10 billion-year lifetime, ENTs radiate the energy of 100 Suns.

ENTs were first uncovered when Hinkle began a systematic search of public surveys for long-lived flares emanating from the centers of galaxies. He identified two unusual flares in data from the European Space Agency’s Gaia mission that were detected in 2016 and 2018.

“Gaia doesn’t tell you the physics of the event, just that something changed in brightness,” said Hinkle. The discovery launched a multi-year follow-up campaign to figure out what these sources were.

Meanwhile, a third event with similar properties was discovered in 2020 by the Zwicky Transient Facility (ZTF) and reported independently by two teams in 2023. Using data from the Keck Observatory Archive (KOA) for this new ZTF object showed it was similar to the two Gaia ENTs, adding strong support that ENTs are a distinct new class of extreme astrophysical events.

Drawing on observations from a wide array of ground- and space-based telescopes, the team determined these extraordinary events could not be supernovae because they release far more energy than any known stellar explosion. The sheer energy budget, combined with their smooth and prolonged light curves, firmly pointed to an alternative mechanism: accretion onto a supermassive black hole.

However, ENTs differ significantly from normal black hole accretion, when materials surrounding the black hole heat up and emit light and typically show irregular and unpredictable changes in brightness. The smooth and long-lived flares of ENTs indicate a distinct physical process—the gradual accretion of a disrupted star by a supermassive black hole.

Benjamin Shappee, Associate Professor at IfA and study co-author, emphasized the implications: “ENTs provide a valuable new tool for studying massive black holes in distant galaxies. Because they’re so bright, we can see them across vast cosmic distances—and in astronomy, looking far away means looking back in time. By observing these prolonged flares, we gain insights into black hole growth during a key era known as cosmic noon, when the universe was half its current age when galaxies were happening places—forming stars and feeding their supermassive black holes 10 times more vigorously than they do today.”

The rarity of ENTs, occurring at least 10 million times less frequently than supernovae, makes their detection challenging and dependent on sustained monitoring of the cosmos. Future observatories like the Vera C. Rubin Observatory and NASA’s Nancy Grace Roman Space Telescope promise to uncover many more of these spectacular events, revolutionizing our understanding of black hole activity in the distant, early universe.

“These ENTs don’t just mark the dramatic end of a massive star’s life,” stated Hinkle. “They illuminate the processes responsible for growing the largest black holes in the universe.”

Source: W. M. Keck Observatory/Science News

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Related Links:

• Keck Observatory Archive (KOA)
• Science Paper by Jason Hinkle et al.
• NASA Press Release
• University of Hawaiʻi News

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Media Contact:

Meagan O’Shea
moshea@keck.hawaii.edu

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Gargantuan Black Hole Jets Are Biggest Seen Yet

An artist’s illustration of the longest black hole jet system ever observed. Nicknamed Porphyrion after a mythological Greek giant, these jets span roughly 7 megaparsecs, or 23 million light-years. That is equivalent to lining up 140 Milky Way galaxies back-to-back. Porphyrion dates back to a time when our universe was less than half its present age. During this early epoch, the wispy filaments that connect and feed galaxies, known as the cosmic web, were closer together than they are now. Consequently, this colossal jet pair extended across a larger portion of the cosmic web compared to similar jets in our nearby universe. Porphyrion’s discovery thus implies that jets in the early universe may have influenced the formation of galaxies to a greater extent than previously believed. Image credit: E. Wernquist / D. Nelson (IllustrisTNG Collaboration) / M. Oei

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The jumbo jets blast hot plasma well beyond their own host galaxy

Maunakea, Hawaiʻi – Astronomers have spotted the biggest pair of black hole jets ever seen, spanning 23 million light-years in total length. That’s equivalent to lining up 140 Milky Way galaxies back to back.

“This pair is not just the size of a solar system, or a Milky Way; we are talking about 140 Milky Way diameters in total,” says Martijn Oei, a Caltech postdoctoral scholar and lead author of the new study. “The Milky Way would be a little dot in these two giant eruptions.”

The study, which includes data from W. M. Keck Observatory on Maunakea, Hawaiʻi, published online today in the journal Nature and will be featured on the cover of the print issue tomorrow, September 19.

The jet megastructure, nicknamed Porphyrion after a giant in Greek mythology, dates to a time when our universe was 6.3 billion years old, or less than half its present age of 13.8 billion years. These fierce outflows—with a total power output equivalent to trillions of suns—shoot out from above and below a supermassive black hole at the heart of a remote galaxy.

Prior to Porphyrion’s discovery, the largest confirmed jet system was Alcyoneus, also named after a giant in Greek mythology. Alcyoneus, which was discovered in 2022 by the same team that found Porphyrion, spans the equivalent of around 100 Milky Ways. For comparison, the well-known Centaurus A jets, the closest major jet system to Earth, spans 10 Milky Ways.

The latest finding suggests that these giant jet systems may have had a larger influence on the formation of galaxies in the young universe than previously believed. Porphyrion existed during an early epoch when the wispy filaments that connect and feed galaxies, known as the cosmic web, were closer together than they are now. That means enormous jets like Porphyrion reached across a greater portion of the cosmic web compared to jets in the local universe.

“Astronomers believe that galaxies and their central black holes co-evolve, and one key aspect of this is that jets can spread huge amounts of energy that affect the growth of their host galaxies and other galaxies near them,” says co-author George Djorgovski, professor of astronomy and data science at Caltech. “This discovery shows that their effects can extend much farther out than we thought.”

Lurking in the Past

To find the galaxy from which Porphyrion originated, the team used the Giant Metrewave Radio Telescope in India along with ancillary data from a project called Dark Energy Spectroscopic Instrument, which operates from Kitt Peak National Observatory in Arizona. The observations pinpointed the home of the jets to a hefty galaxy about 10 times more massive than our Milky Way.

The team then used the Keck Observatory to show that Porphyrion is 7.5 billion light-years from Earth.

“Up until now, these giant jet systems appeared to be a phenomenon of the recent universe,” Oei says. “If distant jets like these can reach the scale of the cosmic web, then every place in the universe may have been affected by black hole activity at some point in cosmic time,” Oei says.

Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS) also revealed that Porphyrion emerged from what is called a radiative-mode active black hole, as opposed to one that is in a jet-mode state. When supermassive black holes become active—in other words, when their immense forces of gravity tug on and heat up surrounding material—they are thought to either emit energy in the form of radiation or jets. Radiative-mode black holes were more common in the young, or distant, universe, while jet-mode ones are more common in the present-day universe.

The fact that Porphyrion came from a radiative-mode black hole came as a surprise because astronomers did not know this mode could produce such huge and powerful jets. What is more, because Porphyrion lies in the distant universe where radiative-mode black holes abound, the finding implies there may be a lot more colossal jets left to be found.

Porphyrion: Largest Known Black Hole Jet System
Credit: Caltech - Vimeo

Ongoing Mysteries

How the jets can extend so far beyond their host galaxies without destabilizing is still unclear.

“Martijn’s work has shown us that there isn’t anything particularly special about the environments of these giant sources that causes them to reach those large sizes,” says Hardcastle, who is an expert in the physics of black hole jets. “My interpretation is that we need an unusually long-lived and stable accretion event around the central, supermassive black hole to allow it to be active for so long—about a billion years—and to ensure that the jets keep pointing in the same direction over all of that time. What we’re learning from the large number of giants is that this must be a relatively common occurrence.”

As a next step, Oei wants to better understand how these megastructures influence their surroundings. The jets spread cosmic rays, heat, heavy atoms, and magnetic fields throughout the space between galaxies.

Oei is specifically interested in finding out the extent to which giant jets spread magnetism.

“The magnetism on our planet allows life to thrive, so we want to understand how it came to be,” he says. “We know magnetism pervades the cosmic web, then makes its way into galaxies and stars, and eventually to planets, but the question is: Where does it start? Have these giant jets spread magnetism through the cosmos?”

Source: W. M. Keck Observatory/Science News

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About LRIS

The Low Resolution Imaging Spectrometer (LRIS) is a very versatile and ultra-sensitive visible-wavelength imager and spectrograph built at the California Institute of Technology by a team led by Prof. Bev Oke and Prof. Judy Cohen and commissioned in 1993. Since then it has seen two major upgrades to further enhance its capabilities: the addition of a second, blue arm optimized for shorter wavelengths of light and the installation of detectors that are much more sensitive at the longest (red) wavelengths. Each arm is optimized for the wavelengths it covers. This large range of wavelength coverage, combined with the instrument’s high sensitivity, allows the study of everything from comets (which have interesting features in the ultraviolet part of the spectrum), to the blue light from star formation, to the red light of very distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in 2011 for research determining that the universe was speeding up in its expansion.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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Faintest Known Star System Orbiting the Milky Way Discovered from Hawaiʻi

An image of uma3/u1, a tiny cluster of ancient stars captured by CFTH
Credit: CFHT/S. Gwyn

Maunakea, Hawaiʻi - A team of astronomers led by the University of Victoria and Yale University has detected an ancient star system traveling around our galaxy named Ursa Major III / UNIONS 1 (UMa3/U1) – the faintest and lowest-mass Milky Way satellite ever discovered, and possibly one of the most dark matter-dominated systems known.

The team conducted the study from Hawaiʻi using two Maunakea Observatories on Hawaiʻi Island – W. M. Keck Observatory and Canada-France-Hawaiʻi Telescope (CFHT) – as well as the University of Hawaiʻi Institute for Astronomy Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) on Haleakalā, Maui; the findings are published in a recent edition of The Astrophysical Journal.

“UMa3/U1 is located in the Ursa Major (Great Bear) constellation, home of the Big Dipper. It is in our cosmic backyard, relatively speaking, at about 30,000 light-years from the Sun,” says Simon Smith, an astronomy graduate student at University of Victoria and lead author of the study. “UMa3/U1 had escaped detection until now due to its extremely low luminosity.”

Observations reveal the stellar system is tiny, with only about 60 stars that are over 10 billion years old spanning just 10 light years across. UMa3/U1 has an extremely low mass – at 16 times the mass of the Sun, it is 15 times less massive than the faintest suspected dwarf galaxy.

UMa3/U1 was first detected using data obtained from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS) at CFHT and Pan-STARRS.

The team then studied the star system in finer detail using Keck Observatory’s Deep Imaging Multi-Object Spectrograph (DEIMOS) and confirmed UMa3/U1 is a gravitationally-bound system, either a dwarf galaxy or a star cluster.

“There are so few stars in UMa3/U1 that one might reasonably question whether it’s just a chance grouping of similar stars. Keck was critical in showing this is not the case,” says co-author Marla Geha, professor of astronomy and physics at Yale University. “Our DEIMOS measurements clearly show all the stars are moving through space at very similar velocities and appear to share similar chemistries.”

Hidden in this deep sky image (left) is Uma3/U1, a miniscule group of stars (right) bound together by their own gravity (and possibly even dark matter!) in orbit around the Milky Way. Credit: CFHT/S. Gwyn (right) / S. Smith (left)

“Excitingly, a tentative spread in velocities among the stars in the system may support the conclusion that UMa3/U1 is a dark matter-dominated galaxy – a tantalizing possibility we hope to scrutinize with more Keck observations,” says Yale University graduate student Will Cerny, the second author of the study.

How these stars have managed to stay a tight-knit group is remarkable. One possible explanation is that dark matter may be keeping them together.

“The object is so puny that its long-term survival is very surprising. One might have expected the harsh tidal forces from the Milky Way’s disk to have ripped the system apart by now, leaving no observable remnant,” says Cerny. “The fact that the system appears intact leads to two equally interesting possibilities. Either UMa3/U1 is a tiny galaxy stabilized by large amounts of dark matter, or it’s a star cluster we’ve observed at a very special time before its imminent demise.”

With the former scenario, achieving direct confirmation of UMa3/U1 as a faint, ancient, dark matter-dominated satellite star system would be an exciting feat because it would support a prediction in the leading theory for the universe’s origin. Under the Lambda Cold Dark Matter (LCDM) model, scientists hypothesize that when galaxies like the Milky Way first formed, they created a gravitational pull during their assembly process that attracted hundreds of satellite star systems which continue to orbit galaxies today.

A companion study on UMa3/U1’s implications on the LCDM theory has been accepted for publication in The Astrophysical Journal and is available in preprint format on arXiv.org.

“Whether future observations confirm or reject that this system contains a large amount of dark matter, we’re very excited by the possibility that this object could be the tip of the iceberg – that it could be the first example of a new class of extremely faint stellar systems that have eluded detection until now,” says Cerny.

Conclusive evidence of the presence or lack of dark matter in UMa3/U1 is key to determining whether the star system is a dwarf galaxy or a star cluster. Until its classification becomes clear, Ursa Major III / UNIONS 1 has two names. Ultra-faint Milky Way satellites are typically named after the constellation they are discovered in (in this case, Ursa Major) whereas ultra-faint star clusters are generally named after the survey project they were discovered in (UNIONS).

While this star system’s identity is still ambiguous, UMa3/U1 paves the way for new perspectives in cosmology.

“This discovery may challenge our understanding of galaxy formation and perhaps even the definition of a ‘galaxy’,” says Smith.

Source: W. M. Keck Observatory/News

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About DEIMOS

The DEep Imaging and Multi-Object Spectrograph (DEIMOS) boasts the largest field of view (16.7arcmin by 5 arcmin) of any of the Keck Observatory instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. Astronomers study fields of distant galaxies with DEIMOS, efficiently probing the most distant corners of the universe with high sensitivity.

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About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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A Hundred Million Suns

SN 2023ixf occurred in a spiral arm of the pinwheel galaxy near several star-forming regions.
Credit: Travis Deyoe, Mount Lemmon SkyCenter, University of Arizona

Maunakea, Hawai – Accounts of supernovae – exploding stars – go back thousands of years, and while we know today these events create the building blocks of life itself, there are still unanswered questions about the conditions that cause a star to explode.

Researchers from the Weizmann Institute of Science have now made major headway in better understanding these fascinating phenomena. Using multiple telescopes, including W. M. Keck Observatory on Maunakea, Hawaiʻi Island, they were able to gather data from a once-in-a-lifetime supernova called SN 2023ixf. Their findings are published in today’s edition of the journal Nature.

Until recently, supernovae were considered rare with known occurrences in the Milky Way happening once a century at best, lighting up the night sky with the intensity of 100 million suns; the last observable explosion in our galaxy took place hundreds of years ago.

Advances in telescope technology have since helped identify supernovae in distant galaxies, supplying more data than was previously possible. Still, the same problem persists; since explosions can’t be predicted, astrophysicists are like space archeologists, usually arriving at the scene after the event and trying to piece together information from the remains.

“That’s what makes this particular supernova different,” says PhD student Erez Zimmerman of Prof. Avishay Gal-Yam’s group at Weizmann. “We were able – for the very first time – to closely follow a supernova while its light was emerging from the circumstellar material in which the exploding star was embedded.”

The discovery was equivalent to getting to the scene of the crime while the crime was still taking place.

A composite image taken with the Liverpool Telescope showing the location of SN 2023ixf, a red supergiant supernova (the most blue object in the rectangle) that occurred 22 million light-years from Earth in the Pinwheel Galaxy. Credit: E. Zimmerman et al., Weizmann Institute of Science/Liverpool Telescope.

The scientists admit they were lucky. Gal-Yam’s team applied for research time on NASA’s Hubble Space Telescope, hoping to gather ultraviolet (UV) spectral data on any supernova interacting with its environment. Instead, they got the chance to witness in real-time one of the closest supernovae in decades: a red supergiant exploding in a neighboring galaxy called Messier 101, also known as the Pinwheel Galaxy.

Koichi Itagaki, an amateur astronomer from Japan, discovered SN 2023ixf and reported it on a Friday night, which was in the middle of the weekend in Israel (the work week in Israel is Sunday-Thursday) and right before the weekend in Baltimore’s Space Telescope Science Institute – the operations center for the Hubble Telescope. Complicating things even further, it took place two days before Zimmerman’s wedding. But his team quickly conducted follow-up observations of the supernova, pulling an all-nighter on Friday and delivering the necessary measurements to NASA in the nick of time.

“It’s very rare, as a scientist, that you have to act so swiftly,” says Gal-Yam. “Most scientific projects don’t happen in the middle of the night, but the opportunity arose, and we had no choice but to respond accordingly.”

Not only did they succeed in getting Hubble to assume the right coordinates and angle for recording the necessary data, but because of the explosion’s relative proximity, it turned out Hubble had already made recordings in this sector of the universe many times before. Turning to the NASA archives, Gal-Yam’s team and many other groups were able to acquire data from before the star’s eventual demise – when it was still just a red supergiant in its final stages of life – thus creating the most complete portrait of a supernova ever: a composite of its last days and death.

Observations of SN 2023ixf consisted of UV and X-ray data from NASA’s Hubble and Swift satellites, as well as many of the best telescopes across the globe.

This included spectra captured using three of Keck Observatory’s instruments – the Keck Cosmic Web Imager (KCWI), Deep Imaging and Multi-Object Spectrograph (DEIMOS), and Low Resolution Imaging Spectrometer (LRIS) – with each instrument offering a unique view of the supernova and how it changed over time.

The compilation of high-quality space- and ground-based data enabled the researchers to map out the two outer layers of the exploding star and come up with an extraordinary hypothesis.

“Calculations of the circumstellar material emitted in the explosion, as well as this material’s density and mass before and after the supernova, create a discrepancy, which makes it very likely that the missing mass ended up in a black hole that was formed in the aftermath of the explosion – something that’s usually very hard to determine,” says PhD student Ido Irani of Gal-Yam’s team.

“Stars behave very erratically in their senior years,” says Gal-Yam. “They become unstable and we usually cannot be sure which complex processes occur within them because we always start the forensic process after the fact, when much of the data has already been lost.”

“This study presents a unique opportunity to better understand the mechanisms that lead to the conclusion of a star’s life and the eventual formation of something entirely new,” said Zimmerman.

Scientists may never find out what will happen to the matter that made up Messier 101’s former red supergiant. However, the later stages of the supernova are ongoing and new data are still coming in, which means this study, along with follow-up studies of SN 2023ixf, could provide more insight into these explosive events.

Source: W. M. Keck Observatory

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About KCWI

The Keck Cosmic Web Imager (KCWI) is designed to provide visible band, integral field spectroscopy with moderate to high spectral resolution formats and excellent sky-subtraction. The astronomical seeing and large aperture of the telescope enables studies of the connection between galaxies and the gas in their dark matter halos, stellar relics, star clusters, and lensed galaxies. KCWI covers the blue side of the visible spectrum; the instrument also features the Keck Cosmic Reionization Mapper (KCRM), extending KCWI’s coverage to the red side of the visible spectrum. The combination of KCWI-blue and KCRM provides simultaneous high-efficiency spectral coverage across the entire visible spectrum. Support for KCWI was provided by the National Science Foundation, Heising-Simons Foundation, and Mt. Cuba Astronomical Foundation. Support for KCRM was provided by the National Science Foundation and Mt. Cuba Astronomical Foundation.

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About DEIMOS

The DEep Imaging and Multi-Object Spectrograph (DEIMOS) boasts the largest field of view (16.7arcmin by 5 arcmin) of any of the Keck Observatory instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. Astronomers study fields of distant galaxies with DEIMOS, efficiently probing the most distant corners of the universe with high sensitivity.

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About LRIS

The Low Resolution Imaging Spectrometer (LRIS) is a very versatile and ultra-sensitive visible-wavelength imager and spectrograph built at the California Institute of Technology by a team led by Prof. Bev Oke and Prof. Judy Cohen and commissioned in 1993. Since then it has seen two major upgrades to further enhance its capabilities: the addition of a second, blue arm optimized for shorter wavelengths of light and the installation of detectors that are much more sensitive at the longest (red) wavelengths. Each arm is optimized for the wavelengths it covers. This large range of wavelength coverage, combined with the instrument’s high sensitivity, allows the study of everything from comets (which have interesting features in the ultraviolet part of the spectrum), to the blue light from star formation, to the red light of very distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in 2011 for research determining that the universe was speeding up in its expansion.

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About W. M. Keck Observatory/News

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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Astronomers Capture Direct Image of Ancient Galaxy Recycling Gas to Make New Stars

Artist’s illustration of mammoth-1, a massive ancient galaxy recycling gas to sustain its growth in the early universe.
Credit: Tsinghua University

Maunakea, Hawaiʻi – Astronomers have found direct evidence showing ancient galaxies were able to sustain star formation by recycling gas from previous stars to birth new generations of stars. This recycled gas could have been enough to supply all the material needed for galaxies in the early universe to grow, shedding new light on the evolution of galaxies and stars.

The findings, which include data from two Maunakea Observatories on Hawaiʻi Island – W. M. Keck Observatory and Subaru Telescope – are published in the journal Science.

Gas provides the material galaxies need to form new stars. When stars die in supernova explosions, they can expel gas out of a galaxy. To continue forming stars, a galaxy requires a steady supply of gas streaming into it. But it has been unclear if star formation is driven by a supply of pristine new gas, which consists mostly of hydrogen with a little helium – among the lightest elements in the universe – or if galaxies are able to recycle the gas from previous generations of supernovae, which would contain heavier elements produced by nuclear fusion in stars.

To answer this question, an international team of researchers led by Tsinghua University snapped a direct image of MAMMOTH-1, a massive nebula in a galaxy cluster that existed 11 billion years ago.

Using Keck Observatory’s Keck Cosmic Web Imager (KCWI) and Subaru Telescope, the team detected signs of hydrogen, helium, and carbon extending out to 300,000 light-years around MAMMOTH-1. The ratios of the elements are similar to what is seen in the Sun today; this is surprising for such an ancient protogalaxy, whose composition is expected to more closely resemble the pristine state of new gas.

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Artist’s animation depicting direct observations of recycled gas spiraling into the MAMMOTH-1 protogalaxy, fueling more star formation. Credit: Tsinghua University

Source:  W. M. Keck Observatory/News

 

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The team was also able to map the motion of the gas, which showed the gas enriched with heavy elements is flowing back into the galaxy, delivering about 700 times the mass of the Sun in recycled gas each year. This amounts to much more than what is needed to fuel the star formation rate seen in MAMMOTH-1, which is about 81 times the mass of the Sun each year, thus indicating that the recycled gas alone is enough to sustain star formation in the protogalaxy. “Our observations give a first hint that recycled inflows might be an ubiquitous supply mechanism for massive star-forming galaxies in the early universe,” said Zheng Cai of Tsinghua University, the Principal Investigator of this study and co-author of the paper.

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About KCWI

The Keck Cosmic Web Imager (KCWI) is designed to provide visible band, integral field spectroscopy with moderate to high spectral resolution formats and excellent sky-subtraction. The astronomical seeing and large aperture of the telescope enables studies of the connection between galaxies and the gas in their dark matter halos, stellar relics, star clusters, and lensed galaxies. Support for this project was provided by the National Science Foundation, Heising-Simons Foundation, and Mt. Cuba Astronomical Foundation.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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First Detection of Radio Waves from a Type Ia Supernova

Artist's rendition of SN 2020eyj, a white dwarf star that went supernova after pulling material from a helium companion star. Credit: W. M. Keck Observatory/Adam Makarenko

Maunakea, Hawaiʻi – A team of astronomers led by Stockholm University has discovered an unusual Type Ia supernova – or thermonuclear supernova – called SN 2020eyj. Not only did they make the first detection of such a supernova in radio waves, follow-up observations from W. M. Keck Observatory on Maunakea, Hawaiʻi Island also showed strong emission lines of helium.

This marks the first confirmed Type Ia supernova triggered by a white dwarf star that pulled material from a companion star with an outer layer consisting primarily of helium; normally, in the rare cases where the material stripped from the outer layers of the donor star could be detected in spectra, this was mostly hydrogen.

Type Ia supernovae are important for astronomers since they are used to measure the expansion of the universe. However, the origin of these explosions has remained an open question. While it is established that the explosion is caused by a compact white dwarf star that somehow accretes too much matter from a companion star, the exact process and the nature of the progenitor is not known.

The new discovery of supernova SN 2020eyj is evidence the companion star was a helium star that had lost much of its material just prior to the explosion of the white dwarf.

The study, which includes data from Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS), is published in today’s issue of the journal Nature.

First Detection of Radio Waves from a Type Ia Supernova from Keck Observatory on Vimeo.

Artist’s impression of SN2020eyj, a double star system with a compact white dwarf star accreting matter from a helium-rich donor companion, surrounded by dense and dusty circumstellar material. It was the interaction of the exploded star and the material left over from this companion that gave rise to the strong radio signal and the conspicuous helium lines in the optical spectra of SN 2020eyj. Credit: W. M. Keck Observatory/Adam Makarenko

“Once we saw the signatures of strong interaction with the material from the companion, we tried to also detect it in radio emission,” says Erik Kool, a postdoc at Stockholm University’s Department of Astronomy and lead author of the paper. “The detection in radio is the first one of a Type Ia supernova – something astronomers have tried to do for decades.”

Supernova 2020eyj was first spotted by the Zwicky Transient Facility at Palomar Observatory near San Diego where the Oskar Klein Centre at Stockholm University are members.

“The Nordic Optical Telescope on La Palma was fundamental for following up this supernova,” says Jesper Sollerman, a professor at Stockholm University’s Department of Astronomy and co-author of the paper. “As were spectra from the large Keck telescope in Hawaiʻi that immediately revealed the very unusual helium-dominated material around the exploded star.”

“This is clearly a very unusual Type Ia supernova, but still related to the ones we use to measure the expansion of the universe,” adds co-author Joel Johansson from the Department of Physics at Stockholm University. “While normal Type Ia supernovae appear to always explode with the same brightness, this supernova tells us that there are many different pathways to a white dwarf star explosion.”

Source: W.M.Keck Observatory/Science News

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About LRIS

The Low Resolution Imaging Spectrometer (LRIS) is a very versatile and ultra-sensitive visible-wavelength imager and spectrograph built at the California Institute of Technology by a team led by Prof. Bev Oke and Prof. Judy Cohen and commissioned in 1993. Since then it has seen two major upgrades to further enhance its capabilities: the addition of a second, blue arm optimized for shorter wavelengths of light and the installation of detectors that are much more sensitive at the longest (red) wavelengths. Each arm is optimized for the wavelengths it covers. This large range of wavelength coverage, combined with the instrument’s high sensitivity, allows the study of everything from comets (which have interesting features in the ultraviolet part of the spectrum), to the blue light from star formation, to the red light of very distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in 2011 for research determining that the universe was speeding up in its expansion.

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About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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First Ever 3D Map of Messier 87 Galaxy Assembled

An image of the M87 galaxy captured with nasa's hubble space telescope.

Credit: NASA, ESA, Hubble Heritage Team (STScI/AURA); Acknowledgment: P. Cote (Herzberg Institute of Astrophysics), E. Baltz (Stanford University)

Maunakea, Hawaiʻi – A UC Berkeley-led team of astronomers has for the first time measured the three-dimensional shape of Messier 87 (M87), one of the biggest and closest elliptical galaxies to us. New data from W. M. Keck Observatory on Maunakea in Hawaiʻi show M87 isn’t perfectly symmetrical after all, but rather triaxial – similar to the uneven shape of a potato.

The study is published in The Astrophysical Journal Letters.

Located about 55 million light-years away from Earth in the constellation Virgo, M87 is close enough to see using binoculars or a small telescope. As with most celestial objects viewed from our vantage point, M87 appears flat.

The galaxy’s true form revealed itself through the lens of Keck Observatory’s cutting-edge instrument called the Keck Cosmic Web Imager (KCWI), which captures 3D data as opposed to the traditional 2D image or spectrum from conventional instruments.

The researchers used KCWI along with star brightness measurements of M87 from NASA’s Hubble Space Telescope to assemble a 3D view of the motion of stars orbiting M87’s supermassive black hole, named Pōwehi by Larry Kimura, a Hawaiian language professor at the University of Hawaiʻi at Hilo. This provided fresh insight into the galaxy’s shape and allowed the team to calculate with higher precision Pōwehi’s mass, which came out to about 5.4 billion times the mass of the Sun. Previous measurements taken in 2017 when the Event Horizon Telescope (EHT) snapped a direct image of Pōwehi found its mass to be about 6.5 billion solar masses.

Pōwehi means ‘embellished dark source of unending creation’ in Hawaiian and is the world’s first black hole to have its picture taken using EHT’s network of telescopes around the planet, including two Maunakea Observatories – the James Clerk Maxwell Telescope and the Submillimeter Array.

A photo of the huge elliptical galaxy M87 [left] is compared to its three-dimensional shape as gleaned from meticulous observations made with the Hubble and Keck telescopes [right]. Because the galaxy is too far away for astronomers to employ stereoscopic vision, they instead followed the motion of stars around the center of M87, like bees around a hive. This created a three-dimensional view of how stars are distributed within the galaxy. Credit: NASA, ESA, Joseph Olmsted (STScI), Frank Summers (STScI), Chung-Pei Ma (UC Berkeley)

While KCWI was unable to resolve the individual stars due to M87’s great distance from Earth, it was able to obtain spectra that revealed the range of the stars’ velocities as they whizzed around Pōwehi.

“It’s sort of like looking at a swarm of 100 billion bees that are going around in their own happy orbits,” said Chung-Pei Ma, a UC Berkeley professor of astronomy and of physics who led the research team. “Though we are looking at them from a distance and can’t discern individual bees, we are getting very detailed information about their collective velocities. It’s really the superb sensitivity of this spectrograph that allowed us to map out M87 so comprehensively.”

Ma, UC Berkeley graduate student and lead author of the study Emily Liepold, and Jonelle Walsh at Texas A&M University pointed the Keck II telescope at 62 locations across the galaxy and captured KCWI spectra of stars covering a region spanning 70,000 light years across. Gravity in the central 3,000 light-years of this region is largely dominated by Pōwehi. This marked the first time KCWI has been used to reconstruct the geometry of a distant galaxy.

“The Keck data are so good that we can measure the intrinsic shape of M87 along with the black hole at the same time,” said Ma. “We made the first measurement of the actual 3D shape of the galaxy. And since we allowed the swarm of bees to have a more general shape than just a sphere or disk, we have a more robust dynamical measurement of the mass of the central black hole that is governing the bees’ orbiting velocities.”

Ma’s team was also able to measure M87’s rotation, which clocks in at a relatively sedate 25 kilometers per second.

The new findings pave the way for an exciting investigation into M87 that wasn’t possible before – determining Pōwehi’s spin.

“Now that we know the direction of the net rotation of stars in M87 and have an updated mass of the black hole, we can combine this information with the amazing data from the EHT team to constrain the spin,” said Ma. “This may point toward a certain direction and range of spin for the black hole, which would be remarkable.”

Source: W. M. Keck Observatory

 

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Learn more:

• “3D Picture of Galaxy M87 Helps Pin Down Mass of the Black Hole at its Core” – UC Berkeley Press Release April 13, 2023
• “Giant Galaxy Seen in 3D by NASA’s Hubble Space Telescope and Keck Observatory” – STScI Press Release, April 13, 2023

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About KCWI

The Keck Cosmic Web Imager (KCWI) is designed to provide visible band, integral field spectroscopy with moderate to high spectral resolution formats and excellent sky-subtraction. The astronomical seeing and large aperture of the telescope enables studies of the connection between galaxies and the gas in their dark matter halos, stellar relics, star clusters, and lensed galaxies. Support for this project was provided by the National Science Foundation, Heising-Simons Foundation, and Mt. Cuba Astronomical Foundation.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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