An Impostor Explosion

An artist's impression of a collision between two neutron stars releasing gravitational and electromagnetic waves.
Credit: NASA's Goddard Space Flight Center/CI Lab

These images from the Hubble Space Telescope show the fading light of the kilonova associated with the gravitational wave event GW170817. Credit: NASA and ESA Acknowledgment: A. Levan (U. Warwick), N. Tanvir (U. Leicester), and A. Fruchter and O. Fox (STScI)

Over many centuries of observing the night sky, astronomers have found only a single visible afterglow of a collision between neutron stars. For a few days in the summer of 2025, it seemed like observers may have found another of these treasured but elusive prizes; unfortunately, the promising candidate turned out to be a supernova in disguise.

A Rare Prize

When two neutron stars (the ultra-dense remnants of massive stellar explosions) spiral together and collide, the cataclysm is energetic enough to release strong gravitational waves, forge heavy elements, and briefly glow across the electromagnetic spectrum. These events are called kilonovae, and they’re quite rare; while we may have detected a handful at high energies, there is only one event for which astronomers managed to record both gravitational waves and an optical transient.

That one kilonova, found back in 2017, taught astronomers much about how heavy elements are formed and left the scientific community hungry for more data. Since then, each time a gravitational wave detector like LIGO reports that it may have spotted a neutron star merger, telescopes across the world scramble to look in the probable region of the sky, hoping to find the short-lived electromagnetic counterpart.

Too Good to Be True

On 18 August 2025, the LIGO/Virgo/KAGRA collaboration sent out an alert that it may have detected a neutron star–neutron star merger. The odds that their signal was real weren’t great, and the researchers gave it just a 29% chance of being a genuine astrophysical signal. Still, given the potential payoff of finding the next kilonova, several telescopes quickly began searches for the optical counterpart. The gravitational wave signal suggested that the event likely came from a curved patch of sky delightfully referred to as the “northern banana,” and after trawling that region for a few nights, astronomers hauled in 47 new transients. Any one of these could have been the kilonova, and all of them received extensive follow-up observations.

A team led by James Gillanders (University of Oxford) recently summarized some of these follow-up observations carried out with the Pan-STARRS and ATLAS telescopes. In the initial exciting few days after the alert went out, one candidate transient stood out as the most promising. Named AT2025ulz, it was first spotted by the Zwicky Transient Facility and initially started fading rapidly and changing colors, just as models of kilonovae predict. For four days, it seemed like the world may have witnessed its second-ever kilonova. But then the telescopes began their fifth night of observations.

The light curve of SN2025ulz. Note that the source appeared to grow brighter again after about 5 days.
Credit: Gillanders et al. 2025

Supernova Unmasked

A scatter plot showing a rapidly fading, then reversing and spiking, light curve.

The light curve of AT2025ulz, after fading steadily in the preceding days, suddenly turned upwards; in other words, whatever was causing the transient got brighter. Models of kilonova evolution predict no such brightening, but Type IIb supernovae are known to follow just this behavior. AT2025ulz showed itself to be another run-of-the-mill stellar explosion, not the sought-after fireworks of two neutron stars slamming together.

Frustrating as this particular result may be, the effort was far from wasted. The team could use their non-detection of the true kilonova to place limits on its timing and peak magnitude, assuming it existed in the first place. And, as gravitational wave detectors grow more sensitive and alerts like this more common, hindsight will likely frame this scramble as a dress rehearsal for an ultimately successful kilonova recovery effort. Until then, astronomers will keep searching, and will keep their guard up against cosmic impostors.

By Ben Cassese

Citation

“Pan-STARRS Follow-Up of the Gravitational-Wave Event S250818k and the Light Curve of SN2025ulz,” J. H. Gillanders et al 2025 ApJL 995 L27. doi: 10.3847/2041-8213/ae2125

Source: American Astronomical Society - AAS-Nova

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Astronomers Make First Radio Detection of Rare Supernova Type, Revealing Secrets of Stellar Death

A star explodes into a dense disk of helium-rich material, generating strong radio waves for the first time. How did this happen? One idea is that years before any explosion, a small star stripped of its hydrogen and made of mostly helium orbits an even smaller ultra-dense star made of neutrons. As the stars approach each other, the helium star begins to lose more and more mass to the neutron star, forming a chaotic disk of material around the system. Eventually, there is an explosion, with the exact cause unclear. The ejected material in the explosion slams into the disk of mass lost, creating shocks which produce strong radio emission. This emission was then observed by astronomers using the Very Large Array. Credit: NSF/AUI/NSF NRAO/B. Saxton

Baer Way Supernova
Credit: NSF/AUI/NSF NRAO/B. Saxton

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Astronomers using the U.S. National Science Foundation Very Large Array (NSF VLA) have made an unprecedented discovery, capturing the first-ever radio signals from a rare class of stellar explosion known as a Type Ibn supernova. This achievement brings fresh insight into the death throes of massive stars and provides a rare glimpse into the final years of a star’s life, previously hidden from view.

The supernova, designated SN 2023fyq, represents a unique opportunity to observe a massive star’s final act. Type Ibn supernovae result when a star explodes into helium-rich gas previously ejected from its surface. Using the NSF VLA’s powerful radio vision, astronomers tracked radio emissions from this explosion over a span of 18 months, uncovering compelling evidence about the environment around the dying star.

“We captured a rare, first-ever radio signal from a star exploding into helium-rich gas it shed shortly before the blast,” said Raphael Baer-Way, a graduate student at UVA working with Maryam Modjaz (UVA) and Poonam Chandra (NRAO) and primary investigator on the study. “Radio observations allowed us to ‘view’ the final decade of the star’s life before the demise. These observations revealed the star shedding its helium layers, including a significant five-year surge in mass loss immediately preceding the supernova, providing fresh evidence for binary-driven, exotic explosions.” This discovery reveals that the star underwent a dramatic period of mass loss, likely caused by the influence of a gravitationally bound stellar companion.

Radio and X-ray data revealed the density and extent of the helium-rich material ejected before the explosion. Astronomers determined that the star shed material at an astonishing rate — up to 0.4% of the mass of the sun per year — during a short-lived but intense phase leading up to the supernova explosion. This dynamic process aligns with predictions for stars in close binary systems and gives astrophysicists new, direct evidence of the mechanisms driving such rare supernovae.

Until now, the existence of dense material around most Type Ibn supernovae had only been inferred from optical studies. Dr. A.J. Nayana at UC Berkeley, a co-lead investigator, says “Our study probes the material ejected years before the explosion – revealing that t; he star underwent an intense phase of mass-loss in the final 0.7–3 years of its life.” By pinpointing the timeframe and magnitude of the mass loss, astronomers have filled a crucial gap in the story of how massive stars end their lives and enrich the Universe.

This landmark detection sets the stage for future studies of supernovae with radio telescopes, promising to deepen our understanding of the life cycles of stars and the forces that shape our galaxy. Dr. Wynn Jacobson-Galan at Caltech, another lead investigator and VLA program PI, says, “this study has opened up a whole new avenue for constraining the end points of certain massive stars and really highlights the need for systematic radio follow-up of similar events with incredible instruments like the VLA and GMRT.”

Source: National Radio Astronomy Observatory (NRAO)/News

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About NRAO

The National Radio Astronomy Observatory is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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The Hidden Efficiency of Stellar Interactions

Artist’s impression of the evolution of a binary system with mass transfer. The left panel represents the initial state, where two regular, main-sequence stars orbit each other. The middle panel shows the mass transfer process, where the more massive star evolves faster and expands, thereby throwing mass onto the other. The right panel shows the present-day configuration consisting of a stripped star and a rapidly rotating star. Credit: Navid Marvi, courtesy of the Carnegie Institution for Science

The observational constraints on the mass transfer efficiency are in conflict with theoretical models. The main panel shows the available constraints for each of the 16 binary star systems, which shows a preference for stars to accrete 30-90% of the transferred mass. The top panel shows histograms of the predictions of theoretical models. The rotationally limited model (in red) predicts very little mass accretion, namely below 10% of the transferred mass. The thermally limited model (in orange) predicts a bimodal distribution with an accretion efficiency of either below 20% or 100%. Both of these models, which are the main ones used in a larg.e number of theoretical studies and predictions for stellar populations, are therefore in conflict with the observations. © MPA

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When two stars orbit close together, one star can transfer material to its companion, dramatically changing both stars' evolution. However, how much of this transferred material actually stays with the receiving star has remained one of the biggest mysteries in binary star physics. Using a new sample of 16 carefully studied binary systems, MPA scientists have now discovered that binary stars are much more efficient at keeping transferred material than previously thought, with many systems retaining more than half of the mass that was donated. This finding challenges decades of theoretical assumptions and has profound implications for our understanding of stellar evolution, affecting everything from the types of supernovae we observe to the formation of gravitational wave sources, X-ray binaries, and exotic stellar objects like blue stragglers.

Most stars in the Universe are born in binary or multiple star systems, where two or more stars orbit around their common center of mass. When these stars orbit close enough together, over the course of their lifetimes, they can interact gravitationally and exchange material. This can dramatically alter the evolution of both stars, leading to exotic stellar objects, different types of supernovae, and the formation of compact objects like neutron stars and black holes. Therefore, binary interactions play a key role in shaping the stellar populations we observe.

The research team focused on a special type of binary system called Be+sdOB binaries, which consist of a "stripped" star that has lost its outer layers, and a rapidly rotating star that was spun up by accreting these outer layers (see Figure 1). These systems are particularly valuable for studying mass transfer because they represent clear examples of past binary interaction. The stripped star reveals how much mass was originally donated, while the other star shows how much was actually retained.

Previous studies have successfully measured the masses of both stars in 16 such systems using a combination of state-of-the-art observational techniques. Namely, high-resolution interferometry from the CHARA Array and VLTI/GRAVITY instruments creates a powerful virtual telescope by combining light from multiple telescopes, allowing them to measure the tiny separations and orbital motions of close binary stars. These interferometric measurements, combined with detailed spectroscopic observations, enabled precise mass determinations. By comparing these present-day masses with stellar evolution models, the team at MPA could determine how much mass must have been transferred and retained during the binary interaction.

The results are striking: half of the systems require that more than 50% of the transferred mass was retained by the receiving star. This is in stark contrast to theoretical models that assume only a few percent of transferred material can be kept, based on the idea that rapidly rotating stars cannot accept much additional mass due to centrifugal forces (see Figure 2).

The most likely explanation for this efficient mass transfer is that accretion disks around the receiving star can carry away angular momentum while allowing matter to fall onto the star. This process, well-known in other astrophysical contexts, appears to be much more important in binary star evolution than previously recognized.

These findings will force a major revision of binary evolution models and have wide-ranging implications. Many high-profile theoretical predictions about stellar evolution rely on the assumption that mass transfer is highly non-conservative, which these findings are in strong tension with. The results suggest that mass-gaining stars will be much more massive than currently predicted, leading to different populations of supernovae, white dwarfs, and gravitational wave sources. The orbital properties of post-interaction binaries will also be affected, which provides important constraints for understanding the formation of exotic stellar objects.

Source: Max Planck Institute for Astrophysics/Research Highlights

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Contacts:

Thibault Lechien
PhD student
Tel: 2001
lechien@mpa-garching.mpg.de

Selma E. de Mink
Director
Tel: 2041
sedemink@mpa-garching.mpg.de

Original publication

Thibault Lechien, Selma E. de Mink, Ruggero Valli, Amanda C. Rubio, Lieke A. C. van Son, Robert Klement, Harim Jin, and Onno Pols
Binary Stars Take What They Get: Evidence for Efficient Mass Transfer from Stripped Stars with Rapidly Rotating Companions

ApJL 990 L51

Source | DOI

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Signs of the stellar lifecycle Signs of the stellar lifecycle

NGC 1637

A spiral galaxy filling the view. Its disc is filled with bright red spots where stars are forming, dark reddish threads of dust that obscure light, and bluish glowing areas where older stars are concentrated. It has a large, glowing yellow oval area at the centre, from which two spiral arms wind through the galaxy’s disc. The bottom side of the disc is rounded while the top side is somewhat squared-off. Credit: ESA/Hubble & NASA, D. Thilker

The subject of this NASA/ESA Hubble Space Telescope Picture of the Week is NGC 1637, a spiral galaxy located 38 million light-years from Earth in the constellation Eridanus.

This image comes from an observing programme dedicated to studying star formation in nearby galaxies. Stars form in cold, dusty gas clouds that collapse under their own gravity. As young stars grow, they heat their nurseries through starlight, winds, and powerful outflows. Together, these factors play a role in controlling the rate at which future generations of stars form.

Evidence of star formation is scattered all around NGC 1637, if you know where to look. The galaxy’s spiral arms are dotted with what appear to be pink clouds, many of which are accompanied by bright blue stars. The pinkish colour comes from hydrogen atoms that have been excited by ultraviolet light from young, massive stars. This contrasts with the warm yellow glow of the galaxy’s centre, which is home to a densely packed collection of older, redder stars.

The stars that set their birthplaces aglow are comparatively short-lived, and many of these stars will explode as supernovae just a few million years after they’re born. In 1999, NGC 1637 played host to a supernova, pithily named SN 1999emsupe, that was lauded as the brightest supernova seen that year. When a massive star expires as a supernova, the explosion outshines its entire home galaxy for a short time. While a supernova marks the end of a star’s life, it can also jump start the formation of new stars by compressing nearby clouds of gas, beginning the stellar lifecycle anew.

Source: ESA/Hubble/potw.

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High School Student Creates Soundscape of Exploding Stars

A sound explosion of cosmic explosions: ZTF supernovae sonified

Vanya Agrawal creates her sonification with a computer and MIDI board.

More Videos

Vanya Agrawal discusses her experience of creating a sonification of supernova data

Agrawal's full 28-minute sonification of the ZTF supernova dataset.

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Using data from the Zwicky Transient Facility, Southern California high school student Vanya Agrawal creates new "space music."

In September 2023, Vanya Agrawal, a senior at Palos Verdes High School, was searching for a science research project. "I've been interested in music since I was very young, and, over the past few years, I've also become interested in physics and astronomy," Agrawal says. "I was planning on pursuing both as separate disciplines, but then I began to wonder if there might be a way to combine the two."

Enter data sonification. Just as researchers design graphs or diagrams or scatterplots to create a visual mapping of their data, they may also develop an audiomapping of their data by rendering it as sound. Instead of drawing a dot (or any other visual symbol) to correspond to a point of data, they record a tone.

Granted, this is highly unusual in scientific research, but it has been done. Her curiosity piqued, Agrawal soon found examples of these sonifications. For example, in 1994, an auditory researcher, Gregory Kramer, sonified a geoseismic dataset, resulting in detections of instrument error, while in 2014 the CEO and co-founder of Auralab Technologies, Robert Alexander, rendered a spectral dataset into sound and found that participants could consistently identify wave patterns simply by listening.

Do these scientific sonifications make you want to sit yourself down in a concert hall to be swept away by the music they create? Well, when you see a scatterplot of supernovae in an astrophysics journal, do you think, "What is that doing in an academic journal? It belongs on the wall of a museum!" Probably not often.

Here is where the artistic effort comes in: representing scientific information in ways that delight the eye or the ear. This was Agrawal's goal, using an astrophysical dataset to make music that could draw in nonscientific audiences and help them to engage with new discoveries about the universe.

Agrawal first approached Professor of Astronomy Mansi Kasliwal (PhD '11), a family friend, to see about finding an appropriate dataset to sonify. She was quickly put in touch with Christoffer Fremling, a staff scientist working with the Zwicky Transient Facility (ZTF) team. Using a wide-field-of-view camera on the Samuel Oschin Telescope at Caltech's Palomar Observatory, ZTF scans the entire sky visible from the Northern Hemisphere every two days, weather permitting, observing dynamic events in space.

Many of the dynamic events observed by ZTF are supernovae, the explosions of dying stars. In the dataset Agrawal received from Fremling of supernova observations from March 2018 to September 2023, there were more than 8,000 of these. She decided that each supernova detection would be one note in the music she was composing.

"I knew the things that I could modify about the music were when the note occurred, its duration, its pitch, its volume, and the instrument that played the note," Agrawal says. "Then it was a matter of looking at the parameters measured in the dataset of supernova observations and deciding which were most significant and how they should be matched up to musical features."

With Fremling's input, Agrawal decided that the five measurements associated with supernova observations that she would sonify would be discovery date, luminosity, redshift (a quantifiable change in the wavelength of light indicating the light source's distance from us), duration of explosion, and supernova type.

"Discovery date of a supernova has an obvious correlation with the time in which its associated note appears in the music," Agrawal says, "and matching the duration of a supernova with the duration of the note and the type of supernova with the type of instrument playing the note also made the most sense." As for the remaining parameters, Agrawal "flip-flopped back and forth with redshift and luminosity, which would go with pitch or volume. But I ultimately decided on having the luminosity correlate to volume because you can think of volume as the auditory equivalent to brightness. If something emits a dim light, that's like a quiet sound, but if it emits a bright light, that correlates to a loud sound. That left redshift to be translated into pitch."

Once parameters had been translated, the pitch values were modified to enhance the sound. Redshift had to be condensed into a tight range of pitches such that the result would be in the most audible range for human ears.

The initial result, according to Agrawal, was less than euphonius. Fremling, who had tried his own hand at setting down sounds in relationship to each supernova, had the same result: The music, he said, "did not sound good at all."

"I don't think I realized how many notes 8,000 actually is," Agrawal says. "I was definitely picturing it to be a lot slower and more spread out, but after converting the data to sound I heard how densely packed the notes were."

To achieve a sparser texture, Agrawal slowed the tempo of the sound file, extending its length to about 30 minutes, and then set about manipulating and enhancing the musicality of the piece. To ensure that the music would evoke outer space, Agrawal rounded pitches to fit into what is known as the Lydian augmented mode, a scale that begins with whole tones which, Agrawal says, "feel less settled and rooted than ordinary major or minor scales. This resembles the scales in sci-fi music, so I thought it would be beneficial for representing the vastness of space." Agrawal then added a percussion track, a chord track that harmonized dominant pitches in the dataset, and effects such as the sound of wind and distorted chattering.

"There is an element of subjectivity in this," Agrawal says, "because, of course, the music isn't what space actually sounds like, even before I began adding musical tracks. It's my interaction with the universe, my interpretation of it through sound. I would find it interesting to hear how other people sonify the same data, how they interact with the same universe."

Agrawal's composition has already been published on the ZTF website, along with a short video of supernova discoveries that uses portions of Agrawal's composition for background music. But Agrawal's imagination reaches well beyond her first composition: "Obviously the parameters will be different for every dataset, but this type of sonification can be done with any dataset. And with the right algorithms, sonifications can be created automatically and in real time. These compositions could be published on streaming services or played within planetariums, helping astrophysics discoveries to reach wider audiences."

Until those algorithms come along, Fremling, Agrawal, and the outreach coordinator of ZTF have created the resources and tutorials needed to enable anyone to sonify ZTF datasets. The aim is to build a library of sonifications that can be offered to educators, artists, science engagement centers, astronomy visualization professionals, and more to improve and enrich accessibility to science. All resources are available.

Of course, new data will come along to shift our perspective on supernovae, and as a consequence, musical compositions featuring them will change too. "Just within the last year or two we have found a new type of supernova, even though people have been studying supernovae since the 1940s and 1950s," Fremling says. Agrawal will need to introduce another instrument into her orchestra. Also, supernova data can be interpreted in different ways. For example, Fremling notes, "some types of supernovae are inherently always very similar in absolute luminosity. The only reason their luminosity varies in the dataset—which Agrawal has translated into volume in her composition—is because these supernovae are occurring at different distances from our observatory at Palomar."

Agrawal is bound for Washington University in St. Louis in fall 2024, planning to double major in music and astrophysics.

Try your own hand at sonifying supernovae!

Written by Cynthia Eller

Source: Caltech/News

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Contact:

Cynthia Eller
celler@caltech.edu

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Webb Finds Evidence for Neutron Star at Heart of Young Supernova Remnant

SN 1987A (NIRCam, MIRI and NIRSpec Images)

Credits: Image: NASA, ESA, CSA, STScI, Claes Fransson (Stockholm University), Mikako Matsuura (Cardiff University), M. Barlow (UCL), Patrick Kavanagh (Maynooth University), Josefin Larsson (KTH),

Images

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NASA’s James Webb Space Telescope has found the best evidence yet for emission from a neutron star at the site of a recently observed supernova. The supernova, known as SN 1987A, was a core-collapse supernova, meaning the compacted remains at its core formed either a neutron star or a black hole. Evidence for such a compact object has long been sought, and while indirect evidence for the presence of a neutron star has previously been found, this is the first time that the effects of high-energy emission from the probable young neutron star have been detected.

Supernovae — the explosive final death throes of some massive stars — blast out within hours, and the brightness of the explosion peaks within a few months. The remains of the exploding star will continue to evolve at a rapid rate over the following decades, offering a rare opportunity for astronomers to study a key astronomical process in real time.

Supernova 1987A

The supernova SN 1987A occurred 160,000 light-years from Earth in the Large Magellanic Cloud. It was first observed on Earth in February 1987, and its brightness peaked in May of that year. It was the first supernova that could be seen with the naked eye since Kepler's Supernova was observed in 1604.

About two hours prior to the first visible-light observation of SN 1987A, three observatories around the world detected a burst of neutrinos lasting only a few seconds. The two different types of observations were linked to the same supernova event, and provided important evidence to inform the theory of how core-collapse supernovae take place. This theory included the expectation that this type of supernova would form a neutron star or a black hole. Astronomers have searched for evidence for one or the other of these compact objects at the center of the expanding remnant material ever since.
Indirect evidence for the presence of a neutron star at the center of the remnant has been found in the past few years, and observations of much older supernova remnants — such as the Crab Nebula — confirm that neutron stars are found in many supernova remnants. However, no direct evidence of a neutron star in the aftermath of SN 1987A (or any other such recent supernova explosion) had been observed, until now.

Claes Fransson of Stockholm University, and the lead author on this study, explained: “From theoretical models of SN 1987A, the 10-second burst of neutrinos observed just before the supernova implied that a neutron star or black hole was formed in the explosion. But we have not observed any compelling signature of such a newborn object from any supernova explosion. With this observatory, we have now found direct evidence for emission triggered by the newborn compact object, most likely a neutron star.” Webb’s Observations of SN 1987A

Webb began science observations in July 2022, and the Webb observations behind this work were taken on July 16, making the SN 1987A remnant one of the first objects observed by Webb. The team used the Medium Resolution Spectrograph (MRS) mode of Webb’s MIRI (Mid-Infrared Instrument), which members of the same team helped to develop. The MRS is a type of instrument known as an Integral Field Unit (IFU).

IFUs are able to image an object and take a spectrum of it at the same time. An IFU forms a spectrum at each pixel, allowing observers to see spectroscopic differences across the object. Analysis of the Doppler shift of each spectrum also permits the evaluation of the velocity at each position.

Spectral analysis of the results showed a strong signal due to ionized argon from the center of the ejected material that surrounds the original site of SN 1987A. Subsequent observations using Webb’s NIRSpec (Near-Infrared Spectrograph) IFU at shorter wavelengths found even more heavily ionized chemical elements, particularly five times ionized argon (meaning argon atoms that have lost five of their 18 electrons). Such ions require highly energetic photons to form, and those photons have to come from somewhere.

“To create these ions that we observed in the ejecta, it was clear that there had to be a source of high-energy radiation in the center of the SN 1987A remnant," Fransson said. "In the paper we discuss different possibilities, finding that only a few scenarios are likely, and all of these involve a newly born neutron star.”

More observations are planned this year, with Webb and ground-based telescopes. The research team hopes ongoing study will provide more clarity about exactly what is happening in the heart of the SN 1987A remnant. These observations will hopefully stimulate the development of more detailed models, ultimately enabling astronomers to better understand not just SN 1987A, but all core-collapse supernovae.

These findings were published in the journal Science.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Source: NASA's James Webb Space Telescope/News

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About This Release

Credits:

Media Contact:

Bethany Downer
ESA/Webb, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Claes Fransson (Stockholm University)

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• "Emission lines due to ionizing radiation from a compact object in the remnant of Supernova 1987A" by C. Fransson et al.

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NASA's Roman to Use Rare Events to Calculate Expansion Rate of Universe

Supernova Refsdal (Hubble image)

Credits: Image: NASA, ESA, Steve A. Rodney (JHU), Tommaso Treu (UCLA), Patrick Kelly (UC Berkeley), Jennifer Lotz (STScI), Marc Postman (STScI), Zolt G. Levay (STScI), FrontierSN Team, GLASS Team, HFF Team (STScI), CLASH Team

Distant Supernova Multiply Imaged by Foreground Cluster
Illustration: NASA, ESA, Ann Feild (STScI), Joseph DePasquale (STScI)

Science: NASA, ESA, Steve A. Rodney (JHU), Tommaso Treu (UCLA), Patrick Kelly (UC Berkeley), Jennifer Lotz (STScI), Marc Postman (STScI), Zolt G. Levay (STScI), FrontierSN Team, GLASS Team, HFF Team (STScI), CLASH Team

Release Images

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Astronomers investigating one of the most pressing mysteries of the cosmos – the rate at which the universe is expanding – are readying themselves to study this puzzle in a new way using NASA’s Nancy Grace Roman Space Telescope. Once it launches by May 2027, astronomers will mine Roman’s wide swaths of images for gravitationally lensed supernovae, which can be used to measure the expansion rate of the universe.

There are multiple independent ways astronomers can measure the present expansion rate of the universe, known as the Hubble constant . Different techniques have yielded different values, referred to as the Hubble tension . Much of Roman’s cosmological investigations will be into elusive dark energy, which affects how the universe is expanding over time. One primary tool for these investigations is a fairly traditional method, which compares the intrinsic brightness of objects like type Ia supernovae to their perceived brightness to determine distances. Alternatively, astronomers could use Roman to examine gravitationally lensed supernovae. This method of exploring the Hubble constant is unique from traditional methods because it’s based on geometric methods, and not brightness.

“Roman is the ideal tool to let the study of gravitationally lensed supernovae take off,” said Lou Strolger of the Space Telescope Science Institute (STScI) in Baltimore, co-lead of the team preparing for Roman’s study of these objects. “They are rare, and very hard to find. We have had to get lucky in detecting a few of them early enough. Roman’s extensive field of view and repeated imaging in high resolution will help those chances.”

Using various observatories like NASA’s Hubble Space Telescope and James Webb Space Telescope, astronomers have discovered just eight gravitationally lensed supernovae in the universe. However, only two of those eight have been viable candidates to measure the Hubble constant due to the type of supernovae they are and the duration of their time-delayed imaging.

Gravitational lensing occurs when the light from an object like a stellar explosion, on its way to Earth, passes through a galaxy or galaxy cluster and gets deflected by the immense gravitational field. The light splits along different paths and forms multiple images of the supernova on the sky as we see it. Depending on the differences between the paths, the supernova images appear delayed by hours to months, or even years. Precisely measuring this difference in arrival times between the multiple images leads to a combination of distances that constrain the Hubble constant.

“Probing these distances in a fundamentally different way than more common methods, with the same observatory in this case, can help shed light on why various measurement techniques have yielded different results,” added Justin Pierel of STScI, Strolger’s co-lead on the program.

Finding the Needle in the Haystack

Roman's extensive surveys will be able to map the universe much faster than Hubble can, with the telescope “seeing” more than 100 times the area of Hubble in a single image.

“Rather than gathering several pictures of trees, this new telescope will allow us to see the entire forest in a single snapshot,” Pierel explained.

In particular, the High Latitude Time Domain Survey will observe the same area of sky repeatedly, which will allow astronomers to study targets that change over time. This means there will be an extraordinary amount of data – over 5 billion pixels each time – to sift through in order to find these very rare events.

A team led by Strolger and Pierel at STScI is laying the groundwork for finding gravitationally lensed supernovae in Roman data through a project funded by NASA’s Research Opportunities in Space and Earth Science (ROSES) Nancy Grace Roman Space Telescope Research and Support Participation Opportunities program.

“Because these are rare, leveraging the full potential of gravitationally lensed supernovae depends on a high level of preparation,” said Pierel. “We want to make all the tools for finding these supernovae ready upfront so we don’t waste any time sifting through terabytes of data when it arrives.”

The project will be carried out by a team of researchers from various NASA centers and universities around the country.

The preparation will occur in several stages. The team will create data reduction pipelines designed to automatically detect gravitationally lensed supernovae in Roman imaging. To train those pipelines, the researchers will also create simulated imaging: 50,000 simulated lenses are needed, and there are only 10,000 actual lenses currently known.

The data reduction pipelines created by Strolger and Pierel’s team will complement pipelines being created to study dark energy with Type Ia supernovae.

“Roman is truly the first opportunity to create a gold-standard sample of gravitationally lensed supernovae,” concluded Strolger. “All our preparations now will produce all the components needed to ensure we can effectively leverage the enormous potential for cosmology.”

The Nancy Grace Roman Space Telescope is managed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation by NASA's Jet Propulsion Laboratory and Caltech/IPAC in Southern California, the Space Telescope Science Institute in Baltimore, and a science team comprising scientists from various research institutions. The primary industrial partners are Ball Aerospace and Technologies Corporation in Boulder, Colorado; L3Harris Technologies in Melbourne, Florida; and Teledyne Scientific & Imaging in Thousand Oaks, California.

Source: Space Telescope Science Institute (STScI)/Press Release

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Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

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• Resource: Abstract of ROSES-2023 accepted proposal by L. Strolger et al., PDF (152.68 KB)
• Roman’s Key Science Themes

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Four Pulsars Discovered in New Survey

The supernova remnant 30 Doradus B encloses a pulsar at its center.
X-ray: NASA/CXC/Penn State Univ./L. Townsley et al.;
Optical: NASA/STScI/HST; Infrared: NASA/JPL/CalTech/SST;
Image Processing: NASA/CXC/SAO/J. Schmidt, N. Wolk, K. Arcand

A pilot survey using the world’s largest radio dish has led to the discovery of four pulsars, two of which are ultra-precise millisecond pulsars. This survey highlights the wealth of pulsars that await discovery at intermediate galactic latitudes.

An artist’s impression of a pair of pulsars.
Credit: Michael Kramer (Jodrell Bank Observatory, University of Manchester)

Small Stars with a Big Impact

When massive stars explode as supernovae, they can leave behind their extremely dense, collapsed cores in the form of neutron stars. Neutron stars spin rapidly and have strong magnetic fields, leading many of them to produce beams of radio emission along their poles. When these beams sweep across our field of view, we see brief, regular pulses of emission and call the objects pulsars.

Several thousand pulsars have been discovered in our galaxy, but there’s a need to find even more: pulsars provide a path to studying stellar evolution, the interiors of neutron stars, and even gravitational waves. Millisecond pulsars — those with the shortest rotation periods, around 10 milliseconds or less — are especially precious, as their pulses are exceptionally regular. By monitoring the arrival times of the pulses from many millisecond pulsars at once, researchers have found evidence for the gravitational wave background, which is thought to be the combined signals of millions of distant supermassive black hole binaries.

Pulse profiles of the four newly discovered pulsars.

Click to enlarge. Credit: Zhi et al. 2024

A Small FAST Survey

Where and how do we find pulsars? The word pulsar is short for pulsating radio source, and most pulsars are identified in surveys by their characteristic pulses of radio emission. Like most stars, pulsars are concentrated in the thin disk of our galaxy, but interstellar clouds of gas and dust in this region can scatter pulsar signals. Searching the area just above the galactic plane makes for easier pulsar discovery, and current evidence suggests that millisecond pulsars may be more common in these higher-latitude regions.

Using the Five-hundred Aperture Spherical Telescope (FAST) — the world’s largest radio dish — Qijun Zhi (Guizhou Normal University) and collaborators searched for pulsars in a small area of the sky about 5 degrees above the galactic midplane. The survey discovered four new pulsars and recovered all seven of the known pulsars in the search area. Of the four newly discovered pulsars, two are of the coveted millisecond variety, with rotation periods of 3.9 and 4.6 milliseconds. One of these two millisecond pulsars especially warrants further study, since it is bright enough to possibly be included in pulsar timing arrays in the future.

llustration of how galactic latitude is measured.
Credit: AAS Nova/Kerry Hensley

More Pulsars to Come

The pilot survey described in this study complements the efforts of other pulsar surveys. FAST is currently at work on the Commensal Radio Astronomy FAST Survey and the Galactic Plane Pulsar Survey, both of which aim to find pulsars at galactic latitudes below 10 degrees. These surveys have led to the discovery of roughly 800 pulsars so far, about 200 of which are millisecond pulsars.

Zhi and collaborators expect that many more pulsars await discovery at intermediate galactic latitudes, 5 to 15 degrees above the midplane of the Milky Way. Considering the success of their limited pilot study, the team expects that roughly 900 millisecond pulsars could be found in that region.

Citation

“Discovery of Four Pulsars in a Pilot Survey at Intermediate Galactic Latitudes with FAST,” Q. J. Zhi et al 2024 ApJ 960 79. doi:10.3847/1538-4357/ad0eca

By Kerry Hensley

Source: American Astronomical Society/AAS-Nova

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NASA's Hubble Finds Bizarre Explosion in Unexpected Place

Luminous Fast Blue Optical Transient (Artist's Concept)
Credits: Artwork: NASA, ESA, NSF's NOIRLab, Mark Garlick , Mahdi Zamani

Hubble Views Bright Outburst Far from Galaxies
Credits: Image: NASA, ESA, STScI, Ashley Chrimes (ESA-ESTEC/Radboud University)

Release Images

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A very rare, strange burst of extraordinarily bright light in the universe just got even stranger – thanks to the eagle-eye of NASA's Hubble Space Telescope.

The phenomenon, called a Luminous Fast Blue Optical Transient (LFBOT), flashed onto the scene where it wasn't expected to be found, far away from any host galaxy. Only Hubble could pinpoint its location. And, the results are leaving astronomers even more confounded. To start with, they don’t know what LFBOTs are. The Hubble results suggest they know even less by ruling out some possible theories.

LFBOTs are among the brightest known visible-light events in the universe – going off unexpectedly like camera flashbulbs. Only a handful have been found since the first discovery in 2018 – an event located about 200 million light-years away that was nicknamed "the Cow." Presently, LFBOTs are detected once per year.

After its initial detection, the latest LFBOT was observed by multiple telescopes across the electromagnetic spectrum, from X-rays to radio waves. Designated AT2023fhn and nicknamed "the Finch," the transitory event showed all the tell-tale characteristics of an LFBOT. It shined intensely in blue light and evolved rapidly, reaching peak brightness and fading again in a matter of days, unlike supernovae, which take weeks or months to dim.

But unlike any other LFBOT seen before, Hubble found that the Finch is located between two neighboring galaxies – about 50,000 light-years from a nearby spiral galaxy and about 15,000 light-years from a smaller galaxy.

"The Hubble observations were really the crucial thing. They made us realize that this was unusual compared to the other ones like that, because without the Hubble data we would not have known," said Ashley Chrimes, lead author of the Hubble paper reporting the discovery in an upcoming issue of the Monthly Notices of the Royal Astronomical Society (MNRAS). He is also a European Space Agency Research Fellow, formerly of Radboud University, Nijmegen, Netherlands.

While these awesome explosions have been assumed to be a rare type of supernova called core-collapse supernovae, the gargantuan stars that turn into supernovae are short-lived by stellar standards. Therefore, the massive progenitor stars don't have time to travel very far from their birthing place – a cluster of newborn stars – before exploding. All previous LFBOTs have been found in the spiral arms of galaxies where star birth is ongoing, but the Finch is not in any galaxy.

"The more we learn about LFBOTs, the more they surprise us," said Chrimes. "We've now shown that LFBOTs can occur a long way from the center of the nearest galaxy, and the location of the Finch is not what we expect for any kind of supernova."

The Zwicky Transient Facility – an extremely wide-angle ground-based camera that scans the entire northern sky every two days – first alerted astronomers to the Finch on April 10, 2023. Once it was spotted, the researchers triggered a pre-planned program of observations that had been on standby, ready to quickly turn their attention to any potential LFBOT candidates that arose.

Spectroscopic measurements made with the Gemini South telescope in Chile found that the Finch is a scorching 36,000 degrees Fahrenheit. Gemini also helped determine its distance from Earth so its luminosity could be calculated. Together with data from other observatories including NASA's Chandra X-ray Observatory and the National Science Foundation's ground-based Very Large Array radio telescopes, these findings confirmed the explosion was indeed an LFBOT.

The LFBOTs could be the result of stars being torn apart by an intermediate-mass black hole (between 100 to 1,000 solar masses). NASA's James Webb Space Telescope's high resolution and infrared sensitivity might eventually be used to find that the Finch exploded inside a globular star cluster in the outer halo of one of the two neighboring galaxies. A globular star cluster is the most likely place an intermediate-mass black hole could be found.

To explain the unusual location of the Finch, the researchers are considering the possibility that it is the result of a collision of two neutron stars, travelling far outside their host galaxy, that have been spiraling toward each other for billions of years. Such collisions produce a kilonova – an explosion 1,000 times more powerful than a standard nova. However, one very speculative theory is that if one of the neutron stars is highly magnetized – a magnetar – it could greatly amplify the power of the explosion even further to 100 times the brightness of a normal supernova.

"The discovery poses many more questions than it answers," said Chrimes. "More work is needed to figure out which of the many possible explanations is the right one."

Because astronomical transients can pop up anywhere and at any time, and are relatively fleeting in astronomical terms, researchers rely on wide-field surveys that can continuously monitor large areas of the sky to detect them and alert other observatories like Hubble to do follow-up observations.

A larger sample is needed to converge on a better understanding of the phenomenon, say researchers. Upcoming all-sky survey telescopes, such as the ground-based Vera C. Rubin Observatory, may be able to detect more, depending on the underlying astrophysics.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble and Webb science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

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NASA, ESA, STScI, NSF's NOIRLab, Ashley Chrimes (ESA-ESTEC/Radboud University)

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Webb Locates Dust Reservoirs in Two Supernovae

Dusty Supernovae (MIRI)
Credits: Science: NASA, ESA, CSA, Ori Fox (STScI), Melissa Shahbandeh (STScI)
Image Processing: Alyssa Pagan (STScI)

NGC 6496 (Kitt Peak National Observatory)
Credits: Image: KPNO, NSF's NOIRLab, AURA
Image Processing: Alyssa Pagan (STScI)

Release Images

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Researchers using NASA’s James Webb Space Telescope have made major strides in confirming the source of dust in early galaxies. Observations of two Type II supernovae, Supernova 2004et (SN 2004et) and Supernova 2017eaw (SN 2017eaw), have revealed large amounts of dust within the ejecta of each of these objects. The mass found by researchers supports the theory that supernovae played a key role in supplying dust to the early universe.

Dust is a building block for many things in our universe – planets in particular. As dust from dying stars spreads through space, it carries essential elements to help give birth to the next generation of stars and their planets. Where that dust comes from has puzzled astronomers for decades. One significant source of cosmic dust could be supernovae – after the dying star explodes, its leftover gas expands and cools to create dust.

“Direct evidence of this phenomenon has been slim up to this point, with our capabilities only allowing us to study the dust population in one relatively nearby supernova to date – Supernova 1987A, 170,000 light-years away from Earth,” said lead author Melissa Shahbandeh of Johns Hopkins University and the Space Telescope Science Institute in Baltimore, Maryland. “When the gas cools enough to form dust, that dust is only detectable at mid-infrared wavelengths provided you have enough sensitivity.”

For supernovae more distant than SN 1987A like SN 2004et and SN 2017eaw, both in NGC 6946 about 22 million light-years away, that combination of wavelength coverage and exquisite sensitivity can only be obtained with Webb’s MIRI (Mid-Infrared Instrument).

The Webb observations are the first breakthrough in the study of dust production from supernovae since the detection of newly formed dust in SN 1987A with the Atacama Large Millimeter/submillimeter Array (ALMA) telescope nearly a decade ago.

Another particularly intriguing result of their study isn’t just the detection of dust, but the amount of dust detected at this early stage in the supernova’s life. In SN 2004et, the researchers found more than 5,000 Earth masses of dust.

“When you look at the calculation of how much dust we’re seeing in SN 2004et especially, it rivals the measurements in SN 1987A, and it’s only a fraction of the age,” added program lead Ori Fox of the Space Telescope Science Institute. “It’s the highest dust mass detected in supernovae since SN 1987A.”

Observations have shown astronomers that young, distant galaxies are full of dust, but these galaxies are not old enough for intermediate-mass stars, like the Sun, to have supplied the dust as they age. More massive, short-lived stars could have died soon enough and in large enough numbers to create that much dust.

While astronomers have confirmed that supernovae produce dust, the question has lingered about how much of that dust can survive the internal shocks reverberating in the aftermath of the explosion. Seeing this amount of dust at this stage in the lifetimes of SN 2004et and SN 2017eaw suggests that dust can survive the shockwave – evidence that supernovae really are important dust factories after all.

Researchers also note that the current estimations of the mass may be the tip of the iceberg. While Webb has allowed researchers to measure dust cooler than ever before, there may be undetected, colder dust radiating even farther into the electromagnetic spectrum that remains obscured by the outermost layers of dust.

The researchers emphasized that the new findings are also just a hint at newfound research capabilities into supernovae and their dust production using Webb, and what that can tell us about the stars from which they came.

“There’s a growing excitement to understand what this dust also implies about the core of the star that exploded,” Fox said. “After looking at these particular findings, I think our fellow researchers are going to be thinking of innovative ways to work with these dusty supernovae in the future.”

SN 2004et and SN2017eaw are the first of five targets included in this program. The observations were completed as part of Webb General Observer program 2666 . The paper was published in the Monthly Notices of the Royal Astronomical Society on July 5.

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency), and CSA (Canadian Space Agency).

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• Science Paper by M. Shahbandeh, et al.
  

 

Source:NASA's James Webb Space Telescope/News

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A New Look at Gamma Rays from Our Galaxy’s Next-Door Neighbour

An ultraviolet image of the Andromeda Galaxy from NASA's Galaxy Evolution Explorer.
Credit: NASA/JPL-Caltech

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Title: On the Gamma-Ray Emission of the Andromeda Galaxy M31
Authors: Yi Xing et al.
First Author’s Institution: Shanghai Astronomical Observatory, Chinese Academy of Sciences
Status: Published in ApJL

Gamma rays are the highest-energy photons in our universe. Naturally, they come from some of the most extreme environments in the universe, such as pulsars, active galactic nuclei, supernovae, and potentially even dark matter. Though many gamma-ray sources have been detected both in the Milky Way and extragalactically, the nature of gamma-ray emission from our closest neighbouring galaxy, Andromeda (or Messier 31), remains somewhat of a mystery.

The Fermi Large Area Telescope (Fermi-LAT) is an instrument on the Fermi Gamma-ray Space Telescope that has been surveying the sky for high-energy gamma rays since 2008, with ample data taken on Andromeda throughout its flight. Many groups have analyzed these data, with more data giving more insight into what’s making these gamma rays.

Figure 1: Significance maps of Andromeda at energies from 0.1 to 500 gigaelectronvolts (left) and 2 to 500 gigaelectronvolts (right). The region of optical emission is represented by the white contour. The colorbar corresponds to test statistic, which is similar to significance. A test statistic of 25 corresponds to a detection. Green markers correspond to nearby sources found in the SIMBAD database. The left figure shows a hint of additional structure in the southeast region of Andromeda, but both point sources emerge out of the seemingly extended region only with the lowest energies cut out. Credit: Xing et al. 2023

To Extend or Not to Extend?

Up until today’s article, it looked like gamma rays from Andromeda were coming from a blob-like shape (i.e., extended emission) surrounding the centre of the galaxy (similar to Figure 1, left). This was particularly exciting, since extended structure in gamma-ray emission often suggests either a distribution of cosmic rays or the presence of a massive dark matter halo.

Cosmic rays are charged particles that travel at relativistic speeds through the universe but get easily diverted by magnetic fields, making it very difficult to trace their origin from Earth. Luckily, since there are processes that produce gamma rays from charged particles (hadronic processes), identifying regions of extended gamma rays can trace regions where populations of cosmic rays are interacting with their environments. On the other hand, clumps of massive dark matter located in the centre of Andromeda could decay or annihilate, producing gamma rays in the process.

Figure 2: A spectral energy distribution showing flux (quantity of gamma rays received) plotted against energy of Andromeda’s centre (black) and southeast (red) emission regions, along with the Milky Way’s galactic centre (blue). It is apparent that both sources are not only similar in brightness but are also producing significantly more gamma rays than our galactic centre. Click to enlarge. Credit: Xing et al. 2023

 
Where are the Gamma Rays Coming From?

A reanalysis of 14 years of Fermi-LAT data by the authors reveals that the emission of gamma rays isn’t extended after all. In fact, it seems that it’s constrained to two point sources: one located right at the centre of the galaxy and another ~20,000 light-years to the southeast (see Figure 1). This only became apparent when the authors cut out the lowest-energy gamma rays, which still make the data appear more or less extended when they’re included. Even more curiously, the authors found that both of these regions are significantly brighter than expected when compared to the gamma-ray emission of our own galactic centre (see Figure 2).

This new picture of Andromeda’s gamma rays changes a lot about our understanding of the galaxy. It’s no longer likely that Andromeda’s central gamma-ray hotspot is coming from a dark matter halo or cosmic ray distribution, so the authors looked to the Milky Way’s galactic centre to figure out what sorts of objects could be responsible for the gamma rays. One of the leading theories for our own galactic centre gamma rays is a population of old, unresolved objects, such as millisecond pulsars. However, in the case of Andromeda, at least 15,000 millisecond pulsars would be needed to account for the especially bright gamma-ray emission. While it’s still uncertain whether or not the centre of Andromeda can host this huge number of pulsars, we’ve only detected around 200 in the Milky Way’s centre, so this explanation seems unlikely.

The authors also investigate the southeast source that appeared in their new analysis. Since galaxies are pretty far apart from one another, the chance of finding two or more galaxies by coincidence in a circle drawn around both the central and southeast sources is only ~0.4%. This means that the emission is most likely coming from within Andromeda. As seen in Figure 2, the off-centre source is almost exactly the same brightness as Andromeda’s centre source (which is peculiar in its own right!), leading to the same problem of identifying sources capable of emitting such bright emission. After looking through X-ray and optical surveys, the authors determined that there weren’t any good counterparts for this region in other wavelengths either. Even considering the low probability of this being an extragalactic source behind Andromeda, there aren’t any known counterparts in the region of the sky where this hotspot is located.

The results are certainly unexpected and open up a whole new can of worms when it comes to figuring out the origin of the gamma rays in our neighbouring galaxy. Even though there are still a lot of unknowns, future observations and analyses of these newly constrained regions will help us understand how bright gamma rays are produced near the centres of galaxies and may even help us better understand our own galactic centre.

Original astrobite edited by Ivey Davis and Katya Gozman.

Source: American Astronomical Society - AAS Nova

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

 

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About the author, Samantha Wong:

I’m a graduate student at McGill University, where I study high-energy astrophysics. This includes studying all sorts of extreme environments in the universe like active galactic nuclei, pulsars, and supernova remnants with the VERITAS gamma-ray telescope.

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AI Finds that First Stars were Clustered Together

A schematic illustration of this research. Ejecta from the first supernovae (cyan, green, and purple objects surrounded by clouds of ejected material) enrich the primordial hydrogen and helium gas with heavy elements. If the first stars were born as multiple stellar systems, rather than as isolated single stars, elements ejected by different supernovae would be mixed together and incorporated into the next generation of stars. The characteristic chemical abundances in such a mechanism are preserved in the atmospheres of long-lived stars. The team invented a machine learning algorithm to distinguish between the observed stars (shown in red in the diagram) formed out of the ejecta of a single supernova and stars (shown in blue in the diagram) formed out of ejecta from multiple supernovae, based on measured elemental abundances from the spectra of the stars. (Credit: Kavli IPMU). Original size (673KB)

An international team has used artificial intelligence to analyze the chemical abundances of old stars and found indications that the very first stars in the Universe were born in groups rather than as isolated single stars. Now the team hopes to apply this method to new data from on-going and planned observation surveys to better understand the early days of the Universe.

After the Big Bang, the only elements in the Universe where hydrogen, helium, and lithium. Most of the other elements making up the world we see around us were produced by nuclear reactions in stars. Some elements are formed by nuclear fusion at the core of a star, and others form in the explosive supernova death of a star. Supernovae also play an important role in scattering the elements created by stars, so that they can be incorporated into the next generation of stars, planets, and possibly even living creatures.

The first generation of stars, the first to produce elements heavier than lithium, are of particular interest. But first-generation stars are difficult to study because none have ever been observed directly. It is thought that they have all already exploded as supernovae. Instead, researchers try to draw inferences about first-generation stars by studying the chemical signature the first generation of supernovae imprinted on the next generation of stars. Based on their composition, extremely metal-poor stars are believed to be stars formed after the first round of supernovae. Extremely metal-poor stars are rare, but enough have been found now to be analyzed as a group.

In this study, a team including members from the University of Tokyo/Kavli IPMU, National Astronomical Observatory of Japan, and University of Hertfordshire took a novel approach of using artificial intelligence to interpret elemental abundances in over 450 extremely metal-poor stars observed by telescopes including the Subaru Telescope. They found that 68% of the observed extremely metal-poor stars have a chemical fingerprint that is consistent with enrichment by multiple previous supernovae.

In order for the ejecta from multiple previous supernovae to get mixed together in a single star, the supernovae must have occurred in close proximity. This means that in many cases first-generation stars must have formed together in clusters rather than as isolated stars. This offers the first quantitative constraint based on observations for the multiplicity of the first stars.

Now the team hopes to apply this method to Big Data from current and future observing programs, such as the data expected from the Prime Focus Spectrograph on the Subaru Telescope.

These results appeared as Hartwig et al. “Machine Learning Detects Multiplicity of the First Stars in Stellar Archaeology Data” in The Astrophysical Journal on March 22, 2023.

 Related Links

• AI Finds that First Stars were Clustered Together (Subaru Telescope)
• Artificial intelligence finds the first stars were not alone (Kavli IPMU)

 Source: National Astronomical Observatory of Japan (NAOJ)/News

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