Friday, August 22, 2025

Noteworthy nearby spiral

A spiral galaxy seen face-on. Its centre is a bright glowing yellow. The galaxy’s spiral arms contain sparkling blue stars, pink spots of star formation, and dark threads of dust that follow the arms. Credit: ESA/Hubble & NASA, R. Chandar, J. Lee and the PHANGS-HST team

Today’s NASA/ESA Hubble Space Telescope Picture of the Week offers a closeup of a nearby spiral galaxy. The subject is NGC 2835, which lies 35 million light-years away in the constellation Hydra (The Water Snake).

A previous Hubble image of this galaxy was released in 2020, and the NASA/ESA/CSA James Webb Space Telescope turned its gaze toward NGC 2835 in recent years as well. Do you see anything different between today’s image of NGC 2835 and the previously released versions? Overall, NGC 2835 looks quite similar in all of these images, with spiral arms dotted with young blue stars sweeping around an oval-shaped centre, where older stars reside.

This image differs from previously released images because it incorporates new data from Hubble that captures a specific wavelength of red light called H-alpha. The regions that are bright in H-alpha emission can be seen along NGC 2835’s spiral arms, where dozens of bright pink nebulae appear like flowers in bloom. Astronomers are interested in H-alpha light because it signals the presence of several different types of nebulae that arise during different stages of a star’s life. Newborn massive stars create nebulae called H II regions that are particularly brilliant sources of H-alpha light, while dying stars can leave behind supernova remnants or planetary nebulae that can also be identified by their H-alpha emission.

By using Hubble’s sensitive instruments to survey 19 nearby galaxies, researchers aim to identify more than 50 000 nebulae. These observations will help to explain how stars affect their birth neighbourhoods through intense starlight and winds.



Thursday, August 21, 2025

Examining Earendel: Is the Most Distant Lensed Star Actually a Cluster?

WST image of the galaxy cluster WHL0137-08 (left) and a beautifully lensed high-redshift galaxy called the Sunrise Arc (right). A label indicates the location of Earendel, a source that has been interpreted as the most distant lensed single star.
Image: NASA, ESA, CSA, D. Coe (STScI/AURA for ESA; Johns Hopkins University), B. Welch (NASA’s Goddard Space Flight Center; University of Maryland, College Park). Image processing: Z. Levay


Record-Breaking Discovery

In 2022, astronomers using the Hubble Space Telescope reported the discovery of the most distant single star candidate ever seen, now pinpointed to have a redshift of z = 5.926. The star, named Earendel, is an incredible beacon from the first billion years of the universe, standing out brilliantly from the red smear of its host galaxy, the Sunrise Arc.

But there’s a catch — at the distances involved, distinguishing between one star and many isn’t easy, and Earendel might not actually be just one star. New research uses stellar population modeling to explore the possibility that what has been touted as a single star is really a cluster.

JWST spectra of Earendel (top) and 1b (bottom), along with the best-fitting models
Credit:Pascale et al. 2025

The Light of Earendel, Our Most Beloved Star… Cluster?

The question sounds simple: does the light from Earendel resemble that of one star, or does it more closely align with the emission from a collection of many stars? What complicates matters is that Earendel’s light has been warped and magnified by an intervening galaxy cluster in a process called gravitational lensing. Because the degree of magnification isn’t known precisely, it’s not clear exactly how large the source is — leaving wiggle room for Earendel to be one or many stars.

To investigate Earendel’s identity, Massimo Pascale (University of California, Berkeley) and collaborators fit a simple stellar population model to JWST Near-Infrared Spectrograph (NIRSpec) spectra of both Earendel and another source in the Sunrise Arc called 1b, which is widely accepted to be a star cluster. The model varied the age of the cluster, its metallicity, the amount of dust it contains, and other factors. To make the modeling more rigorous, the team also used three different stellar population model libraries.

Both Earendel and 1b were well fit by all three stellar population models, supporting the hypothesis that Earendel is a cluster. Earendel and 1b share certain similarities, such as metallicity (less than 10% of the Sun’s), stellar surface density (high, rivaling the maximum density seen in the local universe), and age (more than 30 million years old).

Metallicity and formation age of star clusters in the local universe, in the Milky Way and Magellanic Clouds, and at high redshifts. Credit: Pascale et al. 2025

Given the potential ages and metallicities of the two sources, it’s possible that both Earendel and 1b are the precursors to today’s globular clusters. These clusters may fit into an evolutionary sequence that connects other lensed star clusters, such as the redshift z = 10.2 Cosmic Gems clusters and the z = 1.4 Sparkler clusters.

While this work demonstrates that Earendel could be a cluster, it doesn’t prove that it is. Doing so is challenging, especially since certain features predicted to exist for a single star might be beyond our observational capabilities, or they could be reproduced by clusters with certain properties. The authors pointed to one smoking-gun signal for Earendel being a single, massive star: brightness fluctuations due to microlensing by stellar winds. So far, no such variability has been found, and the cluster hypothesis remains viable.

By Kerry Hensley

Citation

“Is Earendel a Star Cluster?: Metal-Poor Globular Cluster Progenitors at z ∼ 6,” Massimo Pascale et al 2025 ApJL 988 L76. doi:10.3847/2041-8213/aded93



Wednesday, August 20, 2025

Rare quadruple star system could unlock mystery of brown dwarfs

An artist's impression of the UPM J1040−3551 system against the backdrop of the Milky Way as observed by Gaia. On the left, UPM J1040−3551 Aa & Ab appears as a distant bright orange dot, with an inset revealing these two M-type stars in orbit. On the right, in the foreground, a pair of cold brown dwarfs – UPM J1040−3551 Ba & Bb – orbit each other for a period of decades while collectively circling UPM J1040−3551 Aab in a vast orbit that takes over 100,000 years to complete. Credit: Jiaxin Zhong/Zenghua Zhang
Licence type: Attribution (CC BY 4.0)

The "exciting" discovery of an extremely rare quadruple star system could significantly advance our understanding of brown dwarfs, astronomers say.

These mysterious objects are too big to be considered a planet but also too small to be a star because they lack the mass to keep fusing atoms and blossom into fully-fledged suns.

In a new breakthrough published in the Monthly Notices of the Royal Astronomical Society (MNRAS), astronomers have now identified an extremely rare hierarchical quadruple star system consisting of a pair of cold brown dwarfs orbiting a pair of young red dwarf stars, located 82 light-years from Earth in the constellation Antlia.

The system, named UPM J1040−3551 AabBab, was identified by an international research team led by Professor Zenghua Zhang, of Nanjing University.

The researchers made their discovery using common angular velocity measured by the European Space Agency’s Gaia astrometric satellite and NASA\s Wide-field Infrared Survey Explorer (WISE), followed by comprehensive spectroscopic observations and analysis.

That’s because this wide binary pair need more than 100,000 years to complete one orbit around each other, so their orbital motion cannot be seen in years. Researchers therefore had to analyse how they are moving towards the same direction with the same angular velocity.

In this system, Aab refers to the brighter stellar pair Aa and Ab, while Bab refers to the fainter substellar pair Ba and Bb.

"What makes this discovery particularly exciting is the hierarchical nature of the system, which is required for its orbit to remain stable over a long time period," said Professor Zhang.

"These two pairs of objects are orbiting each other separately for periods of decades, while the pairs are also orbiting a common centre of mass over a period of more than 100,000 years."

The two pairs are separated by 1,656 astronomical units (au), where 1 au equals the Earth-Sun distance. The brighter pair, UPM J1040−3551 Aab, consists of two nearly equal-mass red dwarf stars, which appear orange in colour when observed in visible wavelengths.

With a visual magnitude of 14.6, this pair is approximately 100,000 times fainter than Polaris (the North Star) in visible wavelengths. In fact, no red dwarf star is bright enough to be seen with the naked eye – not even Proxima Centauri, our closest stellar neighbour at 4.2 light-years away. To make UPM J1040−3551 Aab visible without optical aid, this binary pair would need to be brought to within 1.5 light-years of Earth, placing it closer than any star in our current cosmic neighbourhood.

The fainter pair, UPM J1040−3551 Bab, comprises two much cooler brown dwarfs that emit virtually no visible light and appear roughly 1,000 times dimmer than the Aab pair when observed in near-infrared wavelengths, where they are most easily detected.

The close binary nature of UPM J1040−3551 Aab was initially suspected due to its wobbling photocentre during Gaia's observations and confirmed by its unusual brightness – approximately 0.7 magnitude brighter than a single star with the same temperature at the same distance, as the combined light from the nearly equal-mass pair effectively doubles the output.

Similarly, UPM J1040−3551 Bab was identified as another close binary through its abnormally bright infrared measurements compared to typical brown dwarfs of its spectral type. Spectral fitting analysis strongly supported this conclusion, with binary templates providing a significantly better match than single-object templates.

Dr Felipe Navarete, of the Brazilian National Astrophysics Laboratory, led the critical spectroscopic observations that helped characterise the system components.

Using the Goodman spectrograph on the Southern Astrophysical Research (SOAR) Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF NOIRLab, Dr Navarete obtained optical spectra of the brighter pair, while also capturing near-infrared spectra of the fainter pair with SOAR's TripleSpec instrument.

"These observations were challenging due to the faintness of the brown dwarfs," said Dr Navarete, "but the capabilities of SOAR allowed us to collect the crucial spectroscopic data needed to understand the nature of these objects."

Their analysis revealed that both components of the brighter pair are M-type red dwarfs with temperatures of approximately 3,200 Kelvin (about 2,900°C) and masses of about 17 per cent that of the Sun.

The fainter pair are more exotic objects: two T-type brown dwarfs with temperatures of 820 Kelvin (550°C) and 690 Kelvin (420°C), respectively.

Brown dwarfs are small and dense low-mass objects, with the brown dwarfs in this system having sizes similar to the planet Jupiter but masses estimated to be 10-30 times greater. Indeed, at the low end of this range these objects could be considered "planetary mass" objects.

"This is the first quadruple system ever discovered with a pair of T-type brown dwarfs orbiting two stars," said Dr MariCruz Gálvez-Ortiz of the Center for Astrobiology in Spain, a co-author of the research paper.

"The discovery provides a unique cosmic laboratory for studying these mysterious objects."

Unlike stars, brown dwarfs continuously cool throughout their lifetime, which changes their observable properties such as temperature, luminosity, and spectral features.

This cooling process creates a fundamental challenge in brown dwarf research known as the "age-mass degeneracy problem".

An isolated brown dwarf with a certain temperature could be a younger, less massive object or an older, more massive one – astronomers cannot distinguish between these possibilities without additional information.

"Brown dwarfs with wide stellar companions whose ages can be determined independently are invaluable at breaking this degeneracy as age benchmarks," explained Professor Hugh Jones, of the University of Hertfordshire, a co-author of the research paper.

"UPM J1040−3551 is particularly valuable because H-alpha emission from the brighter pair indicates the system is relatively young, between 300 million and 2 billion years old."

The team believes the brown dwarf pair (UPM J1040−3551 Bab) could potentially be resolved with high-resolution imaging techniques in the future, enabling precise measurements of their orbital motion and dynamical masses.

"This system offers a dual benefit for brown dwarf science," said co-researcher Professor Adam Burgasser, of the University of California San Diego.

"It can serve as an age benchmark to calibrate low-temperature atmosphere models, and as a mass benchmark to test evolutionary models if we can resolve the brown dwarf binary and track its orbit."

The discovery of the UPM J1040−3551 system represents a significant advancement in he understanding of these elusive objects and the diverse formation paths for stellar systems in the neighbourhood of the Sun.




Media contacts:

Sam Tonkin (Submitted by)
Royal Astronomical Society
Mob: +44 (0)7802 877 700

press@ras.ac.uk

Science contacts:

Professor Zenghua Zhang
Nanjing University

zz@nju.edu.cn



Further information

The paper ‘Benchmark brown dwarfs – I. A blue M2 + T5 wide binary and a probable young M4 + [T7 + T8] hierarchical triple’ by Zenghua, Zhang et al. has been published in Monthly Notices of the Royal Astronomical Society. DOI:10.1093/mnras/staf895.



Notes for editors

About the Royal Astronomical Society

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

The RAS organises scientific meetings, publishes international research and review journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.

Keep up with the RAS on
 Instagram, Bluesky, LinkedIn, Facebook and YouTube.

'Most massive black hole ever discovered' is detected

The Cosmic Horseshoe gravitational lens. The newly discovered ultramassive blackhole lies at the centre of the orange galaxy. Far behind it is a blue galaxy that is being warped into the horseshoe shaped ring by distortions in spacetime created by the immense mass of the foreground orange galaxy. Credit:NASA/ESA
Licence type: Attribution (CC BY 4.0)

Astronomers have discovered potentially the most massive black hole ever detected.

The cosmic behemoth is close to the theoretical upper limit of what is possible in the universe and is 10,000 times heavier than the black hole at the centre of our own Milky Way galaxy.

It exists in one of the most massive galaxies ever observed – the Cosmic Horseshoe – which is so big it distorts spacetime and warps the passing light of a background galaxy into a giant horseshoe-shaped Einstein ring.

Such is the enormousness of the ultramassive black hole, it equates to 36 billion solar masses, according to a new paper published today in Monthly Notices of the Royal Astronomical Society.

It is thought that every galaxy in the universe has a supermassive black hole at its centre and that bigger galaxies host bigger ones, known as ultramassive black holes.

“This is amongst the top 10 most massive black holes ever discovered, and quite possibly the most massive,” said researcher Professor Thomas Collett, of the University of Portsmouth.

“Most of the other black hole mass measurements are indirect and have quite large uncertainties, so we really don't know for sure which is biggest. However, we’ve got much more certainty about the mass of this black hole thanks to our new method.”

Researchers detected the Cosmic Horseshoe black hole using a combination of gravitational lensing and stellar kinematics (the study of the motion of stars within galaxies and the speed and way they move around black holes).

The latter is seen as the gold standard for measuring black hole masses, but doesn't really work outside of the very nearby universe because galaxies appear too small on the sky to resolve the region where a supermassive or ultramassive black hole lies.

Adding in gravitational lensing helped the team “push much further out into the universe”, Professor Collett said.

“We detected the effect of the black hole in two ways – it is altering the path that light takes as it travels past the black hole and it is causing the stars in the inner regions of its host galaxy to move extremely quickly (almost 400 km/s).

“By combining these two measurements we can be completely confident that the black hole is real.”

Lead researcher, PhD candidate Carlos Melo, of the Universidade Federal do Rio Grande do Sul (UFRGS) in Brazil, added: “This discovery was made for a 'dormant' black hole – one that isn’t actively accreting material at the time of observation.

“Its detection relied purely on its immense gravitational pull and the effect it has on its surroundings.

“What is particularly exciting is that this method allows us to detect and measure the mass of these hidden ultramassive black holes across the universe, even when they are completely silent.”

Another image of the Cosmic Horseshoe, but with the pair of images of a second background source highlighted. The faint central image forms close to the black hole, which is what made the new discovery possible. Credit: NASA/ESA/Tian Li(University of Portsmouth)
Licence type: Attribution (CC BY 4.0)

The Cosmic Horseshoe black hole is located a long way away from Earth, at a distance of some 5 billion light-years.

“Typically, for such remote systems, black hole mass measurements are only possible when the black hole is active,” Melo said. “But those accretion-based estimates often come with significant uncertainties.

“Our approach, combining strong lensing with stellar dynamics, offers a more direct and robust measurement, even for these distant systems.”

The discovery is significant because it will help astronomers understand the connection between supermassive black holes and their host galaxies.

“We think the size of both is intimately linked,” Professor Collett added, “because when galaxies grow they can funnel matter down onto the central black hole.

“Some of this matter grows the black hole but lots of it shines away in an incredibly bright source called a quasar. These quasars dump huge amounts of energy into their host galaxies, which stops gas clouds condensing into new stars.”

Our own galaxy, the Milky Way, hosts a 4 million solar mass black hole. Currently it's not growing fast enough to blast out energy as a quasar but we know it has done in the past, and it may will do again in the future.

The Andromeda Galaxy and our Milky Way are moving together and are expected to merge in about 4.5 billion years, which is the most likely time for our supermassive black hole to become a quasar once again, the researchers say.

An interesting feature of the Cosmic Horseshoe system is that the host galaxy is a so-called fossil group.

Fossil groups are the end state of the most massive gravitationally bound structures in the universe, arising when they have collapsed down to a single extremely massive galaxy, with no bright companions.

“It is likely that all of the supermassive black holes that were originally in the companion galaxies have also now merged to form the ultramassive black hole that we have detected,” said Professor Collett.

“So we're seeing the end state of galaxy formation and the end state of black hole formation.”

The discovery of the Cosmic Horseshoe black hole was somewhat of a serendipitou discovery. It came about as the researchers were studying the galaxy’s dark matter distribution in an attempt to learn more about the mysterious hypothetical substance.

Now that they’ve realised their new method works for black holes, they hope to use data from the European Space Agency’s Euclid space telescope to detect more supermassive black holes and their hosts to help understand how black holes stop galaxies forming stars.
highlights


Media contacts:

Sam Tonkin (Submitted by)
Royal Astronomical Society
Mob: +44 (0)7802 877 700

press@ras.ac.uk

Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877 699

press@ras.ac.uk

Science contacts:

Carlos Melo
UFRGS

crmc.melo@gmail.com

Professor Thomas Collett
University of Portsmouth

thomas.collett@port.ac.uk



Further information

The paper ‘Unveiling a 36 Billion Solar Mass Black Hole at the Centre of the Cosmic Horseshoe Gravitational Lens’ by Carlos Roberto and Thomas Collett et al. has been published in Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/staf1036.



Notes for editors

About the Royal Astronomical Society

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

The RAS organises scientific meetings, publishes international research and review journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.

Keep up with the RAS on
Instagram, Bluesky, LinkedIn, Facebook and YouTube.


Tuesday, August 19, 2025

Comet’s Water Mirrors Earth’s Oceans, Strengthening Life-Origin Theory

Origins of Earth’s Water. Terrestrial H2O is thought to have been delivered several billion years ago, by a combination of cometary, asteroidal, and meteoritic impacts. In contrast to previous findings, new work using the ALMA telescope shows that the isotopic (D/H) ratio in Earth’s water is consistent with delivery by Halley-type comets. Credit: NASA / Theophilus Britt Griswold

ALMA maps showing the distribution of ordinary water (H₂O) and heavy water (HDO) in comet 12P/Pons-Brooks. The contours indicate how strong the signals are, with higher contours showing stronger detections. The small panels in the upper right display the strength of the water signals at the comet’s center. The lower left shows ALMA’s resolution for these observations, while the lower right indicates the direction toward the Sun and the comet’s path through space. Credit: M. Coordiner et al. - ALMA (ESO/NAOJ/NRAO)

A. I. generated illustration showing a comet approaching Earth.
Credit: N. Lira - ALMA (ESO/NAOJ/NRAO)



ALMA observations of Halley-type comet 12P/Pons-Brooks reveal water with the same isotopic signature as Earth’s oceans

New observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have revealed that water in the Halley-type comet 12P/Pons-Brooks has an isotopic composition virtually identical to that of Earth’s oceans. This finding strengthens the theory that comets may have played a crucial role in delivering water, and possibly some of the molecular ingredients for life, to our young planet.

Earth’s water is thought to have arrived billions of years ago through impacts by comets, asteroids, and meteorites. While previous measurements in many comets showed significant differences from Earth’s water, the new results provide the strongest evidence yet that at least some Halley-type comets carried water with the same chemical “fingerprint” as that found on our planet.

Using ALMA’s exceptional sensitivity and imaging capabilities, an international team led by Martin Cordiner (NASA’s Goddard Space Flight Center) mapped, for the first time, the spatial distribution of both ordinary water (H₂O) and heavy water (HDO, containing deuterium) in a comet’s coma—the cloud of gas surrounding its nucleus. These observations, made as 12P/Pons-Brooks approached the Sun, were combined with infrared measurements from NASA’s Infrared Telescope Facility (IRTF) to determine the ratio of deuterium to hydrogen (D/H) with unprecedented precision for a comet of this class.

Remarkably, the D/H ratio—(1.71 ± 0.44) × 10⁻⁴—is the lowest ever measured in a Halley-type comet and falls at the lower end of all cometary values, matching Earth’s oceans. “Comets like this are frozen relics left over from the birth of our Solar System 4.5 billion years ago,” said Cordiner. “Since Earth is believed to have formed from materials lacking water, comet impacts have long been suggested as a source of Earth’s water. Our new results provide the strongest evidence yet that at least some Halley-type comets carried water with the same isotopic signature as that found on Earth, supporting the idea that comets could have helped make our planet habitable.”

“By mapping both H2O and HDO in the comet’s coma, we can tell if these gases are coming from the frozen ices within the solid body of the nucleus, rather than forming from chemistry or other processes in the gas coma,” said NASA’s Stefanie Milam, co-author of the study.

The detection of faint heavy water signals so close to the nucleus—never before mapped in a comet—was only possible thanks to ALMA’s unmatched imaging power.

Scientific Paper




Additional Information

The research paper appeared in Nature Astronomy as "A D/H ratio consistent with Earth’s water in Halley-type comet 12P from ALMA HDO mapping" by M. Coordiner et al.

This text is based on the
original press release by the National Radio Astronomy Observatory (NRAO), an ALMA partner on behalf of North America.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan, and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of ALMA's construction, commissioning, and operation.



Contacts:

Nicolás Lira
Education and Public Outreach Officer
Joint ALMA Observatory, Santiago - Chile
Phone:
+56 2 2467 6519
Cel: +56 9 9445 7726
Email: nicolas.lira@alma.cl

Jill Malusky
Public Information Officer
NRAO
Phone:
+1 304-456-2236
Email: jmalusky@nrao.edu

Yuichi Matsuda
ALMA EA-ARC Staff Member
NAOJ
Email:
yuichi.matsuda@nao.ac.jp

Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Phone:
+49 89 3200 6670
Email: press@eso.org


Monday, August 18, 2025

NSF VLBA Peers Into the “Eye of Sauron” to Solve Cosmic Neutrino Mystery

View Inside The Jet Of A Blazar
Looking inside the plasma jet cone of the blazar PKS 1424+240 with a radio telescope of the National Science Foundation’s Very Long Baseline Array (NSF VLBA). Credit: NSF/AUI/NRAO/B. Saxton/Y.Y. Kovalev et al.



Unprecedented radio observations reveal why a distant blazar appears sluggish yet blazes in high-energy gamma rays and neutrinos

Using the U.S. National Science Foundation National Radio Astronomy’s Very Long Baseline Array (NSF NRAO VLBA), an international team of astronomers has solved a decade-long puzzle about one of the brightest cosmic neutrino sources in the sky. Their findings, published today in Astronomy & Astrophysics Letters, reveal that the blazar PKS 1424+240 – dubbed the “Eye of Sauron” for its striking appearance – points its powerful jet almost directly at Earth, creating an extreme cosmic lighthouse effect.

Located billions of light-years away, PKS 1424+240 had long baffled astronomers. Despite appearing to have a slow-moving plasma jet in radio observations, it blazes as one of the brightest sources of high-energy gamma rays and cosmic neutrinos ever detected. This contradiction, known as the “Doppler factor crisis,” has challenged scientists’ understanding of how these extreme cosmic accelerators work.

“The NSF VLBA’s extraordinary resolution has allowed us to peer directly into the heart of this cosmic monster,” said Yuri Kovalev, lead author of the study and Principal Investigator of the ERC-funded MuSES project at the Max Planck Institute for Radio Astronomy. “We discovered that this blazar’s jet is aimed at us with pinpoint precision – within just 0.6 degrees of our line of sight.”

The breakthrough came from 15 years of ultra-high-resolution observations using the NSF VLBA, which consists of ten 25-meter radio telescopes stretching from Hawaii to the U.S. Virgin Islands. By combining 42 separate images collected from 2009 to 2025 as part of the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) program, the team created an unprecedented deep view of the blazar’s inner structure.

“This is like looking at car headlights from the Moon – the NSF VLBA’s incredible precision made it possible,” said Jack Livingston, a co-author at the Max Planck Institute for Radio Astronomy. “What we found was a nearly perfect toroidal magnetic field structure threading the jet of plasma,” added Daniel Homan, co-author and professor of Denison University. Alexander Plavin, co-author and research fellow of Harvard University, continued, “It’s creating what looks remarkably like the Eye of Sauron from Tolkien’s Lord of the Rings.”

The extreme alignment of PKS 1424+240’s jet toward Earth creates a relativistic “searchlight” effect, amplifying its brightness by a factor of 30 or more through special relativity. This explains why the source appears as one of the brightest neutrino emitters detected by the IceCube Neutrino Observatory in Antarctica, despite its plasma jet appearing to move slowly in radio images.

The discovery demonstrates the critical role of Very Long Baseline Interferometry (VLBI) in solving cosmic mysteries. The NSF VLBA connects radio telescopes across a continent-sized baseline, creating a virtual telescope with the highest resolution available in astronomy – sharp enough to read a newspaper in New York from Los Angeles.

The research strengthens the connection between relativistic plasma jets, high-energy neutrinos, and the magnetic fields that shape cosmic particle accelerators, marking a significant milestone in multimessenger astronomy – the study of the universe using multiple types of cosmic signals.

You can read the press release from the Max-Planck Institute for Radio Astronomy here.




Background Information:

A blazar is a type of active galactic nucleus powered by a supermassive black hole that launches jets of plasma moving at nearly the speed of light. What makes blazars special is their orientation: one of their jets points within about 10 degrees of Earth, making them appear exceptionally bright and allowing scientists to study extreme physical processes.

The original paper:

Y. Kovalev, A. B. Pushkarev, J. L. Gomez, D. C. Homan, M. L. Lister, J. D. Livingston, I. N. Pashchenko, A. V. Plavin, T. Savolainen, S. V. Troitsky: Looking into the Jet Cone of the Neutrino-Associated Very High Energy Blazar PKS 1424+240, A&A Letters, August 12, 2025 (DOI: 10.1051/0004-6361/202555400)

https://doi.org/10.1051/0004-6361/202555400



Preprint: https://arxiv.org/abs/2504.09287

Further Information/Links:

Multi-messenger Studies of Extragalactic Super-colliders (MuSES), ERC Grant:
https://www.mpifr-bonn.mpg.de/muses

Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE) program:
https://www.cv.nrao.edu/MOJAVE/

Max Planck Institute for Radio Astronomy (MPIfR): http://www.mpifr-bonn.mpg.de/2169/en

Center for Astrophysics – Harvard & Smithsonian (CFA):
https://www.cfa.harvard.edu/

Denison University (DU): https://denison.edu/academics/astronomy

Very Long Baseline Array (VLBA): https://science.nrao.edu/facilities/vlba

European Research Council (ERC): https://erc.europa.eu/homepage



About NRAO:

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

About the VLBA:

The NSF Very Long Baseline Array is a system of ten identical 25-meter radio telescopes operating as a single instrument. Stretching 5,000 miles from Mauna Kea, Hawaii, to St. Croix in the U.S. Virgin Islands, the VLBA provides the highest resolution images available in astronomy.

Images and additional resources are available at:
https://public.nrao.edu/news/


Sunday, August 17, 2025

NASA’s Hubble Uncovers Rare White Dwarf Merger Remnant

This is an illustration of a white dwarf star merging into a red giant star. A bow shock forms as the dwarf plunges through the star’s outer atmosphere. The passage strips down the white dwarf’s outer layers, exposing an interior carbon core. Artwork: NASA, ESA, STScI, Ralf Crawford (STScI)




An international team of astronomers has discovered a cosmic rarity: an ultra-massive white dwarf star resulting from a white dwarf merging with another star, rather than through the evolution of a single star. This discovery, made by NASA’s Hubble Space Telescope’s sensitive ultraviolet observations, suggests these rare white dwarfs may be more common than previously suspected.

“It's a discovery that underlines things may be different from what they appear to us at first glance,” said the principal investigator of the Hubble program, Boris Gaensicke, of the University of Warwick in the United Kingdom. “Until now, this appeared as a normal white dwarf, but Hubble's ultraviolet vision revealed that it had a very different history from what we would have guessed.”

A white dwarf is a dense object with the same diameter as Earth, and represents the end state for stars that are not massive enough to explode as core-collapse supernovae. Our Sun will become a white dwarf in about 5 billion years.

In theory, a white dwarf can have a mass of up to 1.4 times that of the Sun, but white dwarfs heavier than the Sun are rare. These objects, which astronomers call ultra-massive white dwarfs, can form either through the evolution of a single massive star or through the merger of a white dwarf with another star, such as a binary companion.

This new discovery, published in the journal Nature Astronomy, marks the first time that a white dwarf born from colliding stars has been identified by its ultraviolet spectrum. Prior to this study, six white dwarf merger products were discovered via carbon lines in their visible-light spectra. All seven of these are part of a larger group that were found to be bluer than expected for their masses and ages from a study with ESA’s Gaia mission in 2019, with the evidence of mergers providing new insights into their formation history.

Astronomers used Hubble’s Cosmic Origins Spectrograph to investigate a white dwarf called WD 0525+526. Located 128 light-years away, it is 20% more massive than the Sun. In visible light, the spectrum of WD 0525+526’s atmosphere resembled that of a typical white dwarf. However, Hubble’s ultraviolet spectrum revealed something unusual: evidence of carbon in the white dwarf’s atmosphere.

White dwarfs that form through the evolution of a single star have atmospheres composed of hydrogen and helium. The core of the white dwarf is typically composed mostly of carbon and oxygen or oxygen and neon, but a thick atmosphere usually prevents these elements from appearing in the white dwarf’s spectrum.

When carbon appears in the spectrum of a white dwarf, it can signal a more violent origin than the typical single-star scenario: the collision of two white dwarfs, or of a white dwarf and a subgiant star. Such a collision can burn away the hydrogen and helium atmospheres of the colliding stars, leaving behind a scant layer of hydrogen and helium around the merger remnant that allows carbon from the white dwarf’s core to float upward, where it can be detected.
WD 0525+526 is remarkable even within the small group of white dwarfs known to be the product of merging stars. With a temperature of almost 21,000 kelvins (37,000 degrees Fahrenheit) and a mass of 1.2 solar masses, WD 0525+526 is hotter and more massive than the other white dwarfs in this group.

WD 0525+526’s extreme temperature posed something of a mystery for the team. For cooler white dwarfs, such as the six previously discovered merger products, a process called convection can mix carbon into the thin hydrogen-helium atmosphere. WD 0525+526 is too hot for convection to take place, however. Instead, the team determined a more subtle process called semi-convection brings a small amount of carbon up into WD 0525+526’s atmosphere. WD 0525+526 has the smallest amount of atmospheric carbon of any white dwarf known to result from a merger, about 100,000 times less than other merger remnants.

The high temperature and low carbon abundance mean that identifying this white dwarf as the product of a merger would have been impossible without Hubble’s sensitivity to ultraviolet light. Spectral lines from elements heavier than helium, like carbon, become fainter at visible wavelengths for hotter white dwarfs, but these spectral signals remain bright in the ultraviolet, where Hubble is uniquely positioned to spot them.

“Hubble's Cosmic Origins Spectrograph is the only instrument that can obtain the superb quality ultraviolet spectroscopy that was required to detect the carbon in the atmosphere of this white dwarf,” said study lead Snehalata Sahu from the University of Warwick.

Because WD 0525+526’s origin was revealed only once astronomers glimpsed its ultraviolet spectrum, it’s likely that other seemingly “normal” white dwarfs are actually the result of cosmic collisions — a possibility the team is excited to explore in the future.

“We would like to extend our research on this topic by exploring how common carbon white dwarfs are among similar white dwarfs, and how many stellar mergers are hiding among the normal white dwarf family,” said study co-leader Antoine Bedrad from the University of Warwick. “That will be an important contribution to our understanding of white dwarf binaries, and the pathways to supernova explosions.”

The Hubble Space Telescope has been operating for more than three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.



Saturday, August 16, 2025

NuSTAR Observes A Flaring Star

An image of a coronal mass ejection from the Sun, taken by the Solar Dynamics Observatory in 2015. The star that NuSTAR observed, BD-08 6022, is a G-type star, making it very similar to our own Sun. Image credit: NASA/Goddard/SDO
. Download Image

During the past week, NuSTAR responded to a Director’s Discretionary Time request for a rapid follow-up of a bright stellar flare reported by the Einstein Probe Wide-field X-ray Telescope (EP-WXT) on August 2, 2025. Stellar flares are explosive releases of magnetic energy on active stars that heat plasma and accelerate particles, producing bright, rapidly evolving X-ray emission. A growing number of studies have found that some flares are accompanied by brief episodes of strong X-ray absorption, when cool, dense ejecta lifted from the low corona crosses the line of sight and temporarily boosts photoelectric opacity. Such ejecta can naturally arise if a coronal mass ejection (CME) is launched: clumpy prominences and filament material in the CME front and wake may partially cover the X-ray source, suppressing low-energy photons while higher-energy X-rays continue to escape, and producing sharp spectral hardening and energy-dependent dips. NuSTAR is ideal for probing transient X-ray absorption and searching for hard-X-ray signatures of CME-driven obscuration. By tracking spectral hardness and effective column density through the flare decay, the observations will constrain the geometry and dynamics of the absorber and evaluate the CME interpretation. Combined with EP discovery data and ongoing monitoring, this NuSTAR dataset is expected to place stringent hard-X-ray constraints on this event and provide a template for rapid characterization of similar nearby stellar flares.

Authors: Yifan Hu (Imperial College London, UK)



Ultra-High-Energy Neutrino Emission on the Extragalactic Express: A Mystery

Radio image from MeerKAT of a galaxy nicknamed Phaedra, one of three main suspects in a hunt for a neutrino emitter.
Adapted from Filipović et al. 2025

Title: ASKAP and VLASS Search for a Radio-Continuum Counterpart of Ultra-High-Energy Neutrino Event KM3–230213A
Authors: M. D. Filipović et al.
First Author’s Institution: Western Sydney University
Status: Published in ApJL

The Scene of the Crime

On Galentine’s Day this year, an ultra-high-energy neutrino attempted to sneak through the Mediterranean Sea, likely expecting she wouldn’t be caught. The odds were in her favor; neutrinos, ghostly particles with no electric charge and infinitesimal mass, only very rarely interact with matter. However, what she failed to account for was the awaiting undersea neutrino detector, KM3NeT, and the clever lepton within who would finally notice her. She slammed into the lepton, spewing charged particles everywhere at speeds greater than the speed of light in the water. While no particle can outrun a photon in a vacuum, water slows light down, giving us the familiar effect of refraction; similar to supersonic jets creating a boom when they break the sound barrier, these charged particles produced a distinctive blue light, known as Cherenkov light, exposing the neutrino’s position to astronomers and physicists everywhere. Busted.

The Investigation Begins

However, the neutrino was only the messenger; of even more interest is the astrophysical object that produced her. It’s not easy to generate such a high-energy particle, and no one can create a neutrino from thermal emission alone, indicating that wherever she originated, something extreme was going on. To date, only three astrophysical sources have been caught emitting neutrinos at all, and none of them are extragalactic: the Sun, although this is old news (in the 1960s, detections of solar neutrinos showed definitively that the Sun is powered by nuclear fusion, resolving the issue of how the Sun has burned long enough for life to evolve on Earth); the nearest core-collapse supernova to our galaxy in modern times, SN 1987A; and the galactic plane.

Theoretical models predict a much wider variety of objects, including extragalactic sources, to produce neutrinos, usually via cosmic-ray production: supernova remnants, star-forming galaxies, gamma-ray bursts, supermassive black holes (which are found at the centers of most galaxies), active galactic nuclei (a particularly fussy subset of supermassive black holes that are eating their host galaxies), and blazars (an extreme subset of active galactic nuclei that emit jets of radio light directly at Earth). The reason we have not detected their predicted neutrino emission is that neutrino astronomy is a new field, extragalactic sources are super far away, and neutrinos are both difficult to detect and difficult to trace back to their origin.

Rounding Up Suspects

With this in mind, today’s authors embark on a quest to catch the culprit, starting in the radio band. Radio emission, like neutrino emission, is usually an indicator of non-thermal radiative processes, and one such process, synchrotron radiation (emitted by relativistic electrons getting spun around in powerful magnetic fields), can be distinguished from other types of radiation based on its radio characteristics. Conveniently, the region our neutrino hails from is spanned by multiple radio surveys conducted with the Very Large Array (VLA) and the Australian Sub-Kilometer Compact Array Pathfinder (ASKAP), and so our authors use these surveys to round up all the radio riffraff. Unfortunately, the long wavelengths of radio photons and the scarcity of neutrinos result in reduced resolution for both compared to traditional optical telescopes, and our authors find over a thousand radio emitters in the region. Of course, no one can question that many sources, so our authors limit their investigation to objects with at least two radio brightness measurements, which can be used to calculate the brightness as a function of radio wavelength (the spectral energy distribution, which tells us about what type of radiation we see) and/or as a function of time (a light curve, which tells us if our source is variable). Our authors settle on a lineup of 10 likely blazars, any of whom could have emitted our ultra-high-energy neutrino, as well as a shortlist of prime suspects warranting further investigation: Phaedra, a spiral galaxy; Hebe, a radio galaxy; and Narcissus, an unusual compact radio emitter (see Figure 1).

Figure 1: Radio emission detected by ASKAP in the region of the sky in which the neutrino originated. Every yellow dot should be considered suspect, but the three colored squares identify the primary guilty parties: Phaedra (in blue), Hebe (in yellow), and Narcissus (in pink). Credit: Filipović et al. 2025

Phaedra: A Spiral Galaxy with a Secret?

Phaedra (Figure 2), the most radio-luminous in the area, exhibits plenty of behavior typical of a galaxy guilty of neutrino emission. For starters, she has two regions of highly concentrated radio emission, and these regions are offset from her center, making them look suspiciously like active galactic nucleus jets, which are excellent particle accelerators. Furthermore, infrared observations suggest she is a starburst galaxy, churning out stars faster than a bestselling author with a team of ghostwriters churns out books. This intense star formation could have easily been triggered by jet activity. Even more suspiciously, she is closely associated with an X-ray binary, and where there are high-energy photons, there are likely to be other high-energy particles like neutrinos and cosmic rays. Phaedra’s prospects of beating the neutrino emission allegations are not looking good; these high-energy phenomena produce buckets of high-energy particles, and even if they produce only cosmic rays, the cosmic rays are bound to crash into the surrounding dense gas and photons, creating neutrinos anyway.

Figure 2: Radio image of Phaedra, one of our suspects. The east and west components are the likely radio jets, and the third bright blob is the radio counterpart to the X-ray binary, SXPS J062657.7-082939. Adapted from Filipović et al. 2025

Hebe: A Simple Radio Galaxy, or Something More?

Hebe (Figure 3), the nearest extended radio source, isn’t exactly innocent-looking either. She is one of a triplet of galaxies sharing a common envelope, like peas in an extragalactic pod. Galaxies, unlike peas, however, are so massive that they can’t help but interact dynamically in such close quarters, causing a commotion that could totally produce ultra-high-energy neutrinos. She likely also has an active galactic nucleus jet, giving her the same neutrino-wielding powers as Phaedra.

Figure 3: An infrared image of Hebe that clearly shows the common envelope surrounding the triplets. The white contour lines denote levels of polarized intensity, which indicate the presence of a magnetic field. Adapted from Filipović et al. 2025

Narcissus: Double Active Galactic Nucleus?

Our final suspect, Narcissus (Figure 4), consists of not one, but two active galactic nuclei. One appears to exhibit the classic synchrotron spectral energy distribution, and the other is likely a blazar, based on his notable radio variability and infrared observations.

Figure 4: Infrared image of Narcissus, with the purple contours outlining the two radio sources that are likely active galactic nuclei. Adapted from Filipović et al. 2025

Solving the Mystery

So, who really emitted the ultra-high-energy neutrino? For now, our authors can’t jump to any firm conclusions — they’d never risk condemning an innocent galaxy — but they will continue to closely monitor the suspects and gather more evidence. In the meantime, Phaedra, Hebe, and Narcissus should find themselves a good defense attorney experienced in neutrino emission cases.

Original astrobite edited by Sandy Chiu.




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.



About the author, Chloe Klare:

I’m a PhD student in astronomy and astrophysics at Penn State (with a physics minor, so I get to use my semester spent in QFT for something!). I study active galactic nuclei (in the radio!), and I’m currently looking for baby synchrotron jets in active galactic nuclei.


Friday, August 15, 2025

Webb Narrows Atmospheric Possibilities for Earth-sized Exoplanet TRAPPIST-1 d

This artist’s concept depicts planet TRAPPIST-1 d passing in front of its turbulent star, with other members of the closely packed system shown in the background. The TRAPPIST-1 system is intriguing to scientists for a few reasons. Not only does the system have seven Earth-sized rocky worlds, but its star is a red dwarf, the most common type of star in the Milky Way galaxy. If an Earth-sized world can maintain an atmosphere here, and thus have the potential for liquid surface water, the chance of finding similar worlds throughout the galaxy is much higher. In studying the TRAPPIST-1 planets, scientists are determining the best methods for separating starlight from potential atmospheric signatures in data from NASA’s James Webb Space Telescope. The star TRAPPIST-1’s variability, with frequent flares, provides a challenging testing ground for these methods. Credits/Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)



The exoplanet TRAPPIST-1 d intrigues astronomers looking for possibly habitable worlds beyond our solar system because it is similar in size to Earth, rocky, and resides in an area around its star where liquid water on its surface is theoretically possible. But according to a new study using data from NASA’s James Webb Space Telescope, it does not have an Earth-like atmosphere.

“Ultimately, we want to know if something like the environment we enjoy on Earth can exist elsewhere, and under what conditions. While NASA’s James Webb Space Telescope is giving us the ability to explore this question in Earth-sized planets for the first time, at this point we can rule out TRAPPIST-1 d from a list of potential Earth twins or cousins,” said Caroline Piaulet-Ghorayeb of the University of Chicago and Trottier Institute for Research on Exoplanets (IREx) at Université de Montréal, lead author of the study published in The Astrophysical Journal.

Planet TRAPPIST-1 d

The TRAPPIST-1 system is located 40 light-years away and was revealed as the record-holder for most Earth-sized rocky planets around a single star in 2017, thanks to data from NASA’s retired Spitzer Space Telescope and other observatories. Due to that star being a dim, relatively cold red dwarf, the “habitable zone” or “Goldilocks zone” – where the planet’s temperature may be just right, such that liquid surface water is possible – lies much closer to the star than in our solar system. TRAPPIST-1 d, the third planet from the red dwarf star, lies on the cusp of that temperate zone, yet its distance to its star is only 2 percent of Earth’s distance from the Sun. TRAPPIST-1 d completes an entire orbit around its star, its year, in only four Earth days.

Webb’s NIRSpec (Near-Infrared Spectrograph) instrument did not detect molecules from TRAPPIST-1 d that are common in Earth’s atmosphere, like water, methane, or carbon dioxide. However, Piaulet-Ghorayeb outlined several possibilities for the exoplanet that remain open for follow-up study.

“There are a few potential reasons why we don’t detect an atmosphere around TRAPPIST-1 d. It could have an extremely thin atmosphere that is difficult to detect, somewhat like Mars. Alternatively, it could have very thick, high-altitude clouds that are blocking our detection of specific atmospheric signatures — something more like Venus. Or, it could be a barren rock, with no atmosphere at all,” Piaulet-Ghorayeb said.

The Star TRAPPIST-1

No matter what the case may be for TRAPPIST-1 d, it’s tough being a planet in orbit around a red dwarf star. TRAPPIST-1, the host star of the system, is known to be volatile, often releasing flares of high-energy radiation with the potential to strip off the atmospheres of its small planets, especially those orbiting most closely. Nevertheless, scientists are motivated to seek signs of atmospheres on the TRAPPIST-1 planets because red dwarf stars are the most common stars in our galaxy. If planets can hold on to an atmosphere here, under waves of harsh stellar radiation, they could, as the saying goes, make it anywhere.

“Webb’s sensitive infrared instruments are allowing us to delve into the atmospheres of these smaller, colder planets for the first time,” said Björn Benneke of IREx at Université de Montréal, a co-author of the study. “We’re really just getting started using Webb to look for atmospheres on Earth-sized planets, and to define the line between planets that can hold onto an atmosphere, and those that cannot.”

The Outer TRAPPIST-1 Planets

Webb observations of the outer TRAPPIST-1 planets are ongoing, which hold both potential and peril. On the one hand, Benneke said, planets e, f, g, and h may have better chances of having atmospheres because they are further away from the energetic eruptions of their host star. However, their distance and colder environment will make atmospheric signatures more difficult to detect, even with Webb’s infrared instruments.

“All hope is not lost for atmospheres around the TRAPPIST-1 planets,” Piaulet-Ghorayeb said. “While we didn’t find a big, bold atmospheric signature for planet d, there is still potential for the outer planets to be holding onto a lot of water and other atmospheric components.”

“As NASA leads the way in searching for life outside our solar system, one of the most important avenues we can pursue is understanding which planets retain their atmospheres, and why,” said Shawn Domagal-Goldman, acting director of the Astrophysics Division at NASA Headquarters in Washington. “NASA’s James Webb Space Telescope has pushed our capabilities for studying exoplanet atmospheres further than ever before, beyond extreme worlds to some rocky planets – allowing us to begin confirming theories about the kind of planets that may be potentially habitable. This important groundwork will position our next missions, like NASA’s Habitable Worlds Observatory, to answer a universal question: Are we alone?”

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 CSA (Canadian Space Agency).

To learn more about Webb, visit: https://science.nasa.gov/webb




About This Release

Credits:

Media Contact

Hannah Braun
Space Telescope Science Institute, Baltimore

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents


Thursday, August 14, 2025

NASA Roman Core Survey Will Trace Cosmic Expansion Over Time

These two images, taken one year apart by NASA's Hubble Space Telescope, show how the supernova designated SN 2018gv faded over time. The High-Latitude Time-Domain Survey by NASA’s Nancy Grace Roman Space Telescope will spot thousands of supernovae, including a specific type that can be used to measure the expansion history of the universe. Credits/Image: NASA, ESA, Martin Kornmesser (ESA), Mahdi Zamani (ESA/Hubble), Adam G. Riess (STScI, JHU), SH0ES Team

This infographic describes the High-Latitude Time-Domain Survey that will be conducted by NASA’s Nancy Grace Roman Space Telescope. The survey’s main component will cover over 18 square degrees — a region of sky as large as 90 full moons — and see supernovae that occurred up to about 8 billion years ago. Credits/Illustration: NASA-GSFC

This sonification that uses simulated data from NASA’s OpenUniverse project shows the variety of explosive events that will be detected by NASA’s Nancy Grace Roman Space Telescope and its High-Latitude Time-Domain Survey. Different sounds represent different types of events, as shown in the key at right. A single kilonova seen about 12 seconds into the video is represented with a cannon shot.

The sonification sweeps backward in time to greater distances from Earth, and the pitch of the instrument gets lower as you move outward. (Cosmological redshift has been converted to a light travel time expressed in billions of years.). Credits/Sonification: Martha Irene Saladino (STScI), Christopher Britt (STScI) - Visualization: Frank Summers (STScI) - Designer: NASA, STScI, Leah Hustak (STScI)



NASA’s Nancy Grace Roman Space Telescope will be a discovery machine, thanks to its wide field of view and resulting torrent of data. Scheduled to launch no later than May 2027, with the team working toward launch as early as fall 2026, its near-infrared Wide Field Instrument will capture an area 200 times larger than the Hubble Space Telescope’s infrared camera, and with the same image sharpness and sensitivity. Roman will devote about 75% of its science observing time over its five-year primary mission to conducting three core community surveys that were defined collaboratively by the scientific community. One of those surveys will scour the skies for things that pop, flash, and otherwise change, like exploding stars and colliding neutron stars.

Called the High-Latitude Time-Domain Survey, this program will peer outside of the plane of our Milky Way galaxy (i.e., high galactic latitudes) to study objects that change over time. The survey’s main goal is to detect tens of thousands of a particular type of exploding star known as type Ia supernovae. These supernovae can be used to study how the universe has expanded over time.

“Roman is designed to find tens of thousands of type Ia supernovae out to greater distances than ever before,” said Masao Sako of the University of Pennsylvania, who served as co-chair of the committee that defined the High-Latitude Time-Domain Survey. “Using them, we can measure the expansion history of the universe, which depends on the amount of dark matter and dark energy. Ultimately, we hope to understand more about the nature of dark energy.”

Probing Dark Energy

Type Ia supernovae are useful as cosmological probes because astronomers know their intrinsic luminosity, or how bright they inherently are, at their peak. By comparing this with their observed brightness, scientists can determine how far away they are. Roman will also be able to measure how quickly they appear to be moving away from us. By tracking how fast they’re receding at different distances, scientists will trace cosmic expansion over time.

Only Roman will be able to find the faintest and most distant supernovae that illuminate early cosmic epochs. It will complement ground-based telescopes like the Vera C. Rubin Observatory in Chile, which are limited by absorption from Earth’s atmosphere, among other effects. Rubin’s greatest strength will be in finding supernovae that happened within the past 5 billion years. Roman will expand that collection to much earlier times in the universe’s history, about 3 billion years after the big bang, or as much as 11 billion years in the past. This would more than double the measured timeline of the universe’s expansion history.

Recently, the Dark Energy Survey found hints that dark energy may be weakening over time, rather than being a constant force of expansion. Roman’s investigations will be critical for testing this possibility.

Seeking Exotic Phenomena

To detect transient objects, whose brightness changes over time, Roman must revisit the same fields at regular intervals. The High-Latitude Time-Domain Survey will devote a total of 180 days of observing time to these observations spread over a five-year period. Most will occur over a span of two years in the middle of the mission, revisiting the same fields once every five days, with an additional 15 days of observations early in the mission to establish a baseline.

“To find things that change, we use a technique called image subtraction,” Sako said. “You take an image, and you subtract out an image of the same piece of sky that was taken much earlier — as early as possible in the mission. So you remove everything that’s static, and you’re left with things that are new.”

The survey will also include an extended component that will revisit some of the observing fields approximately every 120 days to look for objects that change over long timescales. This will help to detect the most distant transients that existed as long ago as one billion years after the big bang. Those objects vary more slowly due to time dilation caused by the universe’s expansion.

“You really benefit from taking observations over the entire five-year duration of the mission,” said Brad Cenko of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, the other co-chair of the survey committee. “It allows you to capture these very rare, very distant events that are really hard to get at any other way but that tell us a lot about the conditions in the early universe.”

This extended component will collect data on some of the most energetic and longest-lasting transients, such as tidal disruption events — when a supermassive black hole shreds a star — or predicted but as-yet unseen events known as pair-instability supernovae, where a massive star explodes without leaving behind a neutron star or black hole.

Survey Details

The High-Latitude Time-Domain Survey will be split into two imaging “tiers” — a wide tier that covers more area and a deep tier that will focus on a smaller area for a longer time to detect fainter objects. The wide tier, totaling a bit more than 18 square degrees, will target objects within the past 7 billion years, or half the universe’s history. The deep tier, covering an area of 6.5 square degrees, will reach fainter objects that existed as much as 10 billion years ago. The observations will take place in two areas, one in the northern sky and one in the southern sky. There will also be a spectroscopic component to this survey, which will be limited to the southern sky.

“We have a partnership with the ground-based Subaru Observatory, which will do spectroscopic follow-up of the northern sky, while Roman will do spectroscopy in the southern sky. With spectroscopy, we can confidently tell what type of supernovae we’re seeing,” said Cenko.

Together with Roman’s other two core community surveys, the High-Latitude Wide-Area Survey and the Galactic Bulge Time-Domain Survey, the High-Latitude Time-Domain Survey will help map the universe with a clarity and to a depth never achieved before.

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 in Southern California; Caltech/IPAC in Pasadena, California; the Space Telescope Science Institute in Baltimore; and a science team comprising scientists from various research institutions. The primary industrial partners are BAE Systems, Inc. in Boulder, Colorado; L3Harris Technologies in Melbourne, Florida; and Teledyne Scientific & Imaging in Thousand Oaks, California.




About This Release

Credits:

Media Contact:

Christine Pulliam
Space Telescope Science Institute, Baltimore

Permissions: Content Use Policy