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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NASA's Webb Makes First Detection of Heavy Element from Star Merger

Kilonova and Host Galaxy
Credits: Image: NASA, ESA, CSA, STScI, Andrew Levan (IMAPP, Warw)

Kilonova Emission Spectrum
Credits: Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)

Release Images

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A team of scientists has used multiple space and ground-based telescopes, including NASA’s James Webb Space Telescope, NASA’s Fermi Gamma-ray Space Telescope, and NASA’s Neil Gehrels Swift Observatory, to observe an exceptionally bright gamma-ray burst, GRB 230307A, and identify the neutron star merger that generated an explosion that created the burst. Webb also helped scientists detect the chemical element tellurium in the explosion’s aftermath.

Other elements near tellurium on the periodic table – like iodine, which is needed for much of life on Earth – are also likely to be present among the kilonova’s ejected material. A kilonova is an explosion produced by a neutron star merging with either a black hole or with another neutron star.

“Just over 150 years since Dmitri Mendeleev wrote down the periodic table of elements, we are now finally in the position to start filling in those last blanks of understanding where everything was made, thanks to Webb,” said Andrew Levan of Radboud University in the Netherlands and the University of Warwick in the UK, lead author of the study.

While neutron star mergers have long been theorized as being the ideal “pressure cookers” to create some of the rarer elements substantially heavier than iron, astronomers have previously encountered a few obstacles in obtaining solid evidence.

Kilonovas are extremely rare, making it difficult to observe these events. Short gamma-ray bursts (GRBs), traditionally thought to be those that last less than two seconds, can be byproducts of these infrequent merger episodes. (In contrast, long gamma-ray bursts may last several minutes and are usually associated with the explosive death of a massive star.)

The case of GRB 230307A is particularly remarkable. First detected by Fermi in March, it is the second brightest GRB observed in over 50 years of observations, about 1,000 times brighter than a typical gamma-ray burst that Fermi observes. It also lasted for 200 seconds, placing it firmly in the category of long duration gamma-ray bursts, despite its different origin.

“This burst is way into the long category. It’s not near the border. But it seems to be coming from a merging neutron star,” added Eric Burns, a co-author of the paper and member of the Fermi team at Louisiana State University.

The collaboration of many telescopes on the ground and in space allowed scientists to piece together a wealth of information about this event as soon as the burst was first detected. It is an example of how satellites and telescopes work together to witness changes in the universe as they unfold.

After the first detection, an intensive series of observations from the ground and from space, including with Swift, swung into action to pinpoint the source on the sky and track how its brightness changed. These observations in the gamma-ray, X-ray, optical, infrared, and radio showed that the optical/infrared counterpart was faint, evolved quickly, and became very red – the hallmarks of a kilonova.

“This type of explosion is very rapid, with the material in the explosion also expanding swiftly,” said Om Sharan Salafia, a co-author of the study at the INAF - Brera Astronomical Observatory in Italy. “As the whole cloud expands, the material cools off quickly and the peak of its light becomes visible in infrared, and becomes redder on timescales of days to weeks.”

At later times it would have been impossible to study this kilonova from the ground, but these were the perfect conditions for Webb’s NIRCam (Near-Infrared Camera) and NIRSpec (Near-Infrared Spectrograph) instruments to observe this tumultuous environment. The spectrum has broad lines that show the material is ejected at high speeds, but one feature is clear: light emitted by tellurium, an element rarer than platinum on Earth.

The highly sensitive infrared capabilities of Webb helped scientists identify the home address of the two neutron stars that created the kilonova: a spiral galaxy about 120,000 light-years away from the site of the merger.

Prior to their venture, they were once two normal massive stars that formed a binary system in their home spiral galaxy. Since the duo was gravitationally bound, both stars were launched together on two separate occasions: when one among the pair exploded as a supernova and became a neutron star, and when the other star followed suit.

In this case, the neutron stars remained as a binary system despite two explosive jolts and were kicked out of their home galaxy. The pair traveled approximately the equivalent of the Milky Way galaxy’s diameter before merging several hundred million years later.

Scientists expect to find even more kilonovas in the future due to the increasing opportunities to have space and ground-based telescopes work in complementary ways to study changes in the universe. For example, while Webb can peer deeper into space than ever before, the remarkable field of view of NASA’s upcoming Nancy Grace Roman Space Telescope will enable astronomers to scout where and how frequently these explosions occur.

“Webb provides a phenomenal boost and may find even heavier elements,” said Ben Gompertz, a co-author of the study at the University of Birmingham in the UK. “As we get more frequent observations, the models will improve and the spectrum may evolve more in time. Webb has certainly opened the door to do a lot more, and its abilities will be completely transformative for our understanding of the universe.”

These findings have been published in the journal Nature.

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.

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Space Telescope Science Institute, Baltimore, Maryland

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Space Telescope Science Institute, Baltimore, Maryland

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Source: NASA's James Webb Space Telescope/News

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Most distant detection of a black hole swallowing a star

PR Image eso2216a

Artist’s impression of a black hole swallowing a star

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Videos

 

PR Video eso2216a

Animation of a black hole swallowing a star

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Earlier this year, the European Southern Observatory’s Very Large Telescope (ESO’s VLT) was alerted after an unusual source of visible light had been detected by a survey telescope. The VLT, together with other telescopes, was swiftly repositioned towards the source: a supermassive black hole in a distant galaxy that had devoured a star, expelling the leftovers in a jet. The VLT determined it to be the furthest example of such an event to have ever been observed. Because the jet is pointing almost towards us, this is also the first time it has been discovered with visible light, providing a new way of detecting these extreme events.

Stars that wander too close to a black hole are ripped apart by the incredible tidal forces of the black hole in what is known as a tidal disruption event (TDE). Approximately 1% of these cause jets of plasma and radiation to be ejected from the poles of the rotating black hole. In 1971, the black hole pioneer John Wheeler [1] introduced the concept of jetted-TDEs as “a tube of toothpaste gripped tight about its middle,” causing the system to “squirt matter out of both ends.”

“We have only seen a handful of these jetted-TDEs and they remain very exotic and poorly understood events,” says Nial Tanvir from the University of Leicester in the UK, who led the observations to determine the object’s distance with the VLT. Astronomers are thus constantly hunting for these extreme events to understand how the jets are actually created and why such a small fraction of TDEs produce them.

As part of this quest many telescopes, including the Zwicky Transient Facility (ZTF) in the US, repeatedly survey the sky for signs of short-lived, often extreme, events that could then be studied in much greater detail by telescopes such as ESO’s VLT in Chile. “We developed an open-source data pipeline to store and mine important information from the ZTF survey and alert us about atypical events in real time,” explains Igor Andreoni, an astronomer at the University of Maryland in the US who co-led the paper published today in Nature together with Michael Coughlin from the University of Minnesota.

In February of this year the ZTF detected a new source of visible light. The event, named AT2022cmc, was reminiscent of a gamma ray burst — the most powerful source of light in the Universe. The prospect of witnessing this rare phenomenon prompted astronomers to trigger several telescopes from across the globe to observe the mystery source in more detail. This included ESO’s VLT, which quickly observed this new event with the X-shooter instrument. The VLT data placed the source at an unprecedented distance for these events: the light produced from AT2022cmc began its journey when the universe was about one third of its current age.

A wide variety of light, from high energy gamma rays to radio waves, was collected by 21 telescopes around the world. The team compared these data with different kinds of known events, from collapsing stars to kilonovae. But the only scenario that matched the data was a rare jetted-TDE pointing towards us. Giorgos Leloudas, an astronomer at DTU Space in Denmark and co-author of this study, explains that "because the relativistic jet is pointing at us, it makes the event much brighter than it would otherwise appear, and visible over a broader span of the electromagnetic spectrum."

The VLT distance measurement found AT2022cmc to be the most distant TDE to have ever been discovered, but this is not the only record-breaking aspect of this object. “Until now, the small number of jetted-TDEs that are known were initially detected using high energy gamma-ray and X-ray telescopes, but this was the first discovery of one during an optical survey,” says Daniel Perley, an astronomer at Liverpool John Moores University in the UK and co-author of the study. This demonstrates a new way of detecting jetted-TDEs, allowing further study of these rare events and probing of the extreme environments surrounding black holes.

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More information

This research was presented in a paper titled “A very luminous jet from the disruption of a star by a massive black hole” to appear in Nature (doi: 10.1038/s41586-022-05465-8)

The team is composed of Igor Andreoni (Joint Space-Science Institute, University of Maryland, USA [JSI/UMD]; Department of Astronomy, University of Maryland, USA [UMD]; Astrophysics Science Division, NASA Goddard Space Flight Center [NASA/GSFC], USA), Michael W. Coughlin (School of Physics and Astronomy, University of Minnesota, USA), Daniel A. Perley (Astrophysics Research Institute, Liverpool John Moores University, UK), Yuhan Yao (Division of Physics, Mathematics and Astronomy, California Institute of Technology, USA [Caltech]), Wenbin Lu (Department of Astrophysical Sciences, Princeton University, USA), S. Bradley Cenko (JSI/UMD; NASA/GSFC), Harsh Kumar (Indian Institute of Technology Bombay, India [IIT/Bombay]), Shreya Anand (Caltech), Anna Y. Q. Ho (Department of Astronomy, University of California, Berkeley, USA [UCB]; Lawrence Berkeley National Laboratory, USA [LBNL]; Miller Institute for Basic Research in Science, USA), Mansi M. Kasliwal (Caltech), Antonio de Ugarte Postigo (Université Côte d’Azur, Observatoire de la Côte d’Azur, France), Ana Sagués-Carracedo (The Oskar Klein Centre, Stockholm University, Sweden [OKC]), Steve Schulze (OKC), D. Alexander Kann (Instituto de Astrofisica de Andalucia, Glorieta de la Astronomia, Spain [IAA-CSIC]), S. R. Kulkarni (Caltech), Jesper Sollerman (OKC), Nial Tanvir (Department of Physics and Astronomy, University of Leicester, UK), Armin Rest (Space Telescope Science Institute, Baltimore, USA [STScI]; Department of Physics and Astronomy, The Johns Hopkins University, USA), Luca Izzo (DARK, Niels Bohr Institute, University of Copenhagen, Denmark), Jean J. Somalwar (Caltech), David L. Kaplan (Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee, USA), Tomás Ahumada (UMD), G. C. Anupama (Indian Institute of Astrophysics, Bangalore, India [IIA]), Katie Auchettl (School of Physics, University of Melbourne, Australia; ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions; Department of Astronomy and Astrophysics, University of California, Santa Cruz, USA), Sudhanshu Barway (IIA), Eric C. Bellm (DIRAC Institute, University of Washington, USA), Varun Bhalerao (IIT/Bombay), Joshua S. Bloom (LBNL; UCB), Michael Bremer (Institut de Radioastronomie Millimetrique, France [IRAM]), Mattia Bulla (OKC), Eric Burns (Department of Physics & Astronomy, Louisiana State University, USA), Sergio Campana (INAF-Osservatorio Astronomico di Brera, Italy), Poonam Chandra (National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune University, India), Panos Charalampopoulos (DTU Space, National Space Institute, Technical University of Denmark, Denmark [DTU]), Jeff Cooke (Australian Research Council Centre of Excellence for Gravitational Wave Discovery, Swinburne University of Technology, Hawthorn, Australia [OzGrav]; Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Australia [CAS]), Valerio D’Elia (Space Science Data Center - Agenzia Spaziale Italiana, Italy), Kaustav Kashyap Das (Caltech), Dougal Dobie (OzGrav; CAS), Jose Feliciano Agüí Fernández (IAA-CSIC), James Freeburn (OzGrav; CAS), Cristoffer Fremling (Caltech), Suvi Gezari (STScI), Matthew Graham (Caltech), Erica Hammerstein (UMD), Viraj R. Karambelkar (Caltech), Charles D. Kilpatrick (Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University, USA), Erik C. Kool (OKC), Melanie Krips (IRAM), Russ R. Laher (IPAC, California Institute of Technology, USA [IPAC]), Giorgos Leloudas (DTU), Andrew Levan (Department of Astrophysics, Radboud University, The Netherlands), Michael J. Lundquist (W. M. Keck Observatory, USA), Ashish A. Mahabal (Caltech; Center for Data Driven Discovery, California Institute of Technology, USA), Michael S. Medford (UCB; LBNL), M. Coleman Miller (JSI/UMD; UMD), Anais Möller (OzGrav; CAS), Kunal Mooley (Caltech), A. J. Nayana (Indian Institute of Astrophysics, India), Guy Nir (UCB), Peter T. H. Pang (Nikhef, The Netherlands; Institute for Gravitational and Subatomic Physics, Utrecht University, The Netherlands), Emmy Paraskeva (IAASARS, National Observatory of Athens, Greece; Department of Astrophysics, Astronomy & Mechanics, University of Athens, Greece; Nordic Optical Telescope, Spain; Department of Physics and Astronomy, Aarhus University, Denmark), Richard A. Perley (National Radio Astronomy Observatory, USA), Glen Petitpas (Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA), Miika Pursiainen (DTU), Vikram Ravi (Caltech), Ryan Ridden-Harper (School of Physical and Chemical Sciences — Te Kura Matu, University of Canterbury, New Zealand), Reed Riddle (Caltech Optical Observatories, California Institute of Technology, USA), Mickael Rigault (Université de Lyon, France), Antonio C. Rodriguez (Caltech), Ben Rusholme (IPAC), Yashvi Sharma (Caltech), I. A. Smith (Institute for Astronomy, University of Hawaii, USA), Robert D. Stein (Caltech), Christina Thöne (Astronomical Institute of the Czech Academy of Sciences, Czech Republic), Aaron Tohuvavohu (Department of Astronomy and Astrophysics, University of Toronto, Canada), Frank Valdes (National Optical Astronomy Observatory, USA), Jan van Roestel (Caltech), Susanna D. Vergani (GEPI, Observatoire de Paris, PSL Research University, France; Institut d’Astrophysique de Paris, France), Qinan Wang (STScI), Jielai Zhang (OzGrav; CAS).

The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration in astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as survey telescopes such as VISTA. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates APEX and ALMA on Chajnantor, two facilities that observe the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society.

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Contacts

Igor Andreoni
Joint Space-Science Institute, University of Maryland, NASA Goddard Space Flight Center
Greenbelt, MD, USA
Tel: +1 (626) 487-7545
Email: andreoni@umd.edu

Daniel Perley
Astrophysics Research Institute, Liverpool John Moores University
Liverpool, UK
Tel: +44 (0)745 6339330
Email: d.a.perley@ljmu.ac.uk

Nial Tanvir
Department of Physics and Astronomy, University of Leicester
Leicester, UK
Email: nrt3@leicester.ac.uk

Giorgos Leloudas
DTU Space, National Space Institute, Technical University of Denmark
Lyngby, Denmark
Email: giorgos@space.dtu.dk

Juan Carlos Muñoz Mateos
ESO Media Officer
Garching bei München, Germany
Tel: +49 89 3200 6176
Email: press@eso.org

Source: ESO/News

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How NASA’s Roman Telescope Will Scan for Showstopping Explosions

Illustration of a Kilonova

Following its launch no later than May 2027, NASA’s Roman Space Telescope will survey the same areas of the sky every few days. Researchers will mine these data to identify kilonovae – explosions that happen when two neutron stars or a neutron star and a black hole collide and merge. When these collisions happen, a fraction of the resulting debris is ejected as jets, which move near the speed of light. The remaining debris produces hot, glowing, neutron-rich clouds that forge heavy elements, like gold and platinum. Roman’s extensive data will help astronomers better identify how often these events occur, how much energy they give off, and how near or far they are. Credits: Artwwork: NASA, Joseph Olmsted (STScI)

Release Images/Release Video

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What happens when the densest, most massive stars – that are also super small – collide? They send out brilliant explosions known as kilonovae. Think of these events as the universe’s natural fireworks. Theorists suspect they periodically occur all across the cosmos – both near and far. Scientists will soon have an additional observatory to help follow up on and even scout these remarkable events: NASA’s Nancy Grace Roman Space Telescope, which is set to launch by May 2027.

The key actors in kilonovae are neutron stars, the central cores of stars that collapsed under gravity during supernova explosions. They each have a mass similar to the Sun, but are only about 6 miles (10 kilometers) in diameter. And when they collide, they send out debris moving near the speed of light. These explosions are also thought to forge heavy elements, like gold, platinum, and strontium (which gives actual fireworks their stunning reds). Kilonovae shoot those elements across space, potentially allowing them to end up in rocks forming the crust of terrestrial planets like Earth.

The astronomical community captured one of these remarkable kilonova events in 2017. Scientists at the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO) detected the collision of two neutron stars first with gravitational waves – ripples in space-time. Almost simultaneously, NASA’s Fermi Gamma-ray Space Telescope detected high-energy light. NASA quickly pivoted to observe the event with a broader fleet of telescopes, and captured the fading glow of the blast’s expanding debris in a series of images.

But the players in this example collided practically in our “backyard,” at least in astronomical terms. They lie only 130 million light-years away. There must be more kilonovae – and many that are farther flung – dotting our ever-active universe.

“We don’t yet know the rate of these events,” said Daniel M. Scolnic, an assistant professor of physics at Duke University in Durham, North Carolina. Scolnic led a study that estimates the number of kilonovae that could be discovered by past, present, and future observatories including Roman. “Is the single kilonova we identified typical? How bright are these explosions? What types of galaxies do they occur in?” Existing telescopes can’t cover wide enough areas or observe deeply enough to find more distant examples, but that will change with Roman.

Spotting More, and More Distant, Kilonovae

At this stage, LIGO leads the pack in identifying neutron star mergers. It can detect gravitational waves in all areas of the sky, but some of the most distant collisions may be too weak to be identified. Roman is set to join LIGO’s search, offering complementary qualities that help “fill out” the team. Roman is a survey telescope that will repeatedly scan the same areas of the sky. Plus, Roman's field of view is 200 times larger than the Hubble Space Telescope’s infrared view – not as vast as LIGO’s, but huge for a telescope that takes images. Its cadence will allow researchers to spot when objects on the sky brighten or dim, whether nearby or very far away.

Roman will provide researchers a powerful tool for observing extremely distant kilonovae. This is due to the expansion of space. Light that left stars billions of years ago is stretched into longer, redder wavelengths, known as infrared light, over time. Since Roman specializes in capturing near-infrared light, it will detect light from very distant objects. How distant? “Roman will be able to see some kilonovae whose light has traveled about 7 billion years to reach Earth,” explained Eve Chase, a postdoctoral researcher at Los Alamos National Laboratory in Los Alamos, New Mexico. Chase led a more recent study that simulated how differences in kilonovae ejecta can vary what we expect to observe from observatories including Roman.

There’s a second benefit to near-infrared light: It provides more time to observe these short-lived bursts. Shorter wavelengths of light, like ultraviolet and visible, disappear from view in a day or two. Near-infrared light can be gathered for a week or more. Researchers have been simulating the data to see how this will work. “For a subset of simulated kilonovae, Roman would be able to observe some more than two weeks after the neutron star merger occurred,” Chase added. “It will be an excellent tool for looking at kilonovae that are very far away.”

Soon, researchers will know far more about where kilonovae occur, and how often these explosions occur in the history of the universe. Were those that occurred earlier different in some way? “Roman will allow the astronomy community to begin conducting population studies along with a slew of new analyses on the physics of these explosions,” Scolnic said.

A survey telescope offers enormous possibility – and also a ton of data that will require precise machine learning. Astronomers are meeting this challenge by writing code to automate these searches. Ultimately, Roman’s massive data sets will help researchers unravel perhaps the greatest mysteries about kilonovae to date: What happens after two neutron stars collide? Does it produce a single neutron star, a black hole, or something else entirely? With Roman, we will gather the statistics researchers need to make substantial breakthroughs.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the Roman mission, with participation by NASA's Jet Propulsion Laboratory in Southern California, and will provide Roman’s Mission Operations Center. The Space Telescope Science Institute in Baltimore will host Roman’s Science Operations Center and lead the data processing of Roman imaging. Caltech/IPAC in Pasadena, California, will house Roman’s Science Support Center and lead the data processing of Roman spectroscopy.

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About This Release

Credits

Media Contact:

Claire Blome
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Permissions: Content Use Policy

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Related Links and Documents:

• Science paper by E. Chase et al
• Scence paper by D. Scolnic et al 

Source: HubbleSite/News

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Neil Gehrels Swift Observatory Gamma-Ray Burst associated with Kilonovae: ambushing the Standard Candle in its own nest

Illustration 1: NASA's Swift spacecraft spots its thousandth gamma-ray burst
Credit: MASA.

Gamma-Ray Bursts (GRBs) are the most luminous and explosive transient phenomena in the Universe after the Big Bang, but they are still puzzling phenomena regarding their emission mechanism even after more than 50 years from their discovery. A powerful tool for characterizing and classifying GRBs to allow them to be used as tracers of the expansion history of the Universe and to understand their mysterious and debated physical mechanisms has been recently presented by an international team of researchers led by Dr. hab. Maria Dainotti, Assistant Professor at Jagiellonian University, Poland and concurrently serving as Senior Research Scientist at RIKEN and affiliate Research Scientist at Space Science Institute, in Boulder, Colorado.

The new article, which has been accepted by the Astrophysical Journal, pays particular attention to the GRBs associated with Kilonovae, and to a sample called the Platinum sample for which the maximum redshift observed is 5, much more distant than the maximum redshift at which the SNe Ia have been observed.

Astronomers can only directly measure distances to objects that are close to Earth and can extrapolate the distances to objects farther out. All the objects that serve as rungs on the cosmological distance ladder have known luminosities and are referred to as "standard candles". Once the absolute luminosity of the standard candle is known, the distance to that object can be calculated based on its measured brightness. For example, the light of the same standard candle will appear dimmer when it is farther away. GRBs are so powerful that in a few seconds they emit the equivalent of the energy emitted by the Sun during its entire lifetime. Thus, it is possible to observe GRBs at incredibly large distances (a.k.a., high redshift), much further than standard candles like Ia-type supernovae (SNe Ia) that are observed at up to 11 billion light years. Using GRBs as a new type of standard candle will allow astronomers to study and comprehend cosmological issues that could change current models regarding the Universe's history and its evolution.

Despite decades of observations, a comprehensive model able to explain the underlying physical mechanisms and properties of these objects has not been reached yet. Many possible physical origins for GRBs have been proposed, like the explosion of an extremely massive star (the long duration GRBs) or the merging of two compact objects (the short duration GRBs). Many models about the progenitor responsible of powering GRBs have been proposed as well, such as a black hole, a neutron star (NS) or a rapidly rotating newly born NS with a high magnetific field (magnetar).

Kilonovae (in short: KNe) are astrophysical objects linked to short duration gamma-ray bursts, which are the result of explosions occuring after two very dense objects (for exampe, two neutron stars) merge together. The detection of X-ray emission at a location coincident with the given Kilonovae can also provide the missing observational link between short duration GRBs and gravitational wavesproduced by ssuch stellar mergers. The first detection of the Kilonovae associated with both gravitational waves emission and such a short GRB, namely GRB 170817, has opened a new era of observations and theoretical investigation. The missing piece to this long-standing story is the connection of KNe and the GRB observational correlations that Dainotti et al. now provide. 

Figure 2: The LX-T*X-Lpeak relation for the SGRB (short duration GRB) sample with separated KN-SGRB cases. We note here that all the KN-SGRBs (marked in yellow) fall below the best fitting plane. Credit: The Authors.

Even when all the GRBs are observed with the same satellite, in this case the NASA's Neil Gehrels Swift Observatory, the GRBs' features are seen to vary very widely over several orders of magnitude. This applies not only to the prompt emission (the main event in the gamma rays), but also to the extended afterglow phase (which follows the prompt emission and is seen over a wide range of wavelengths). Thus, the key point of the article by Dainotti et al., is the hunt for features which remain invariant according to peculiar classes of GRBs. 

Figure 3: Histograms of the distance from the Short Duration Plane for KN-SGRBs and SGRBs, considering the correction for selection biases and evolutionary effects. Credit: The Authors.

The team has found a 3-D correlation, i.e. a link between the following three variables that identifies a plane: duration of the X-ray plateau phase, its luminosity, and the luminosity of the peak prompt gamma ray feature. The distances of GRBs from a given class's plane allowed the authors to determine if GRBs belong to that particular class by showing different features related to this 3-D correlation. The Dainotti et al. study has also shown that although the GRBs-KNe events are a subsample of the larger class of short duration GRBs (red cuboids), they show some observational peculiarities: indeed, they all lie below the short fundamental plane as shown in Figure 2 (yellow truncated icosahedrons). In this analysis, selection biases and evolutionary effects (namely, how the variables change with distance or redshift) have been accounted for, and after correction for selection bias the 3D correlation for GRB-KNe is still tight together with the platinum sample, the tightest sample for the 3D correlation where only well-sampled determined features are taken into account. Thus, both the platinum and the GRBs-KNe plane seems to be the excellent tools for further cosmological studies.

In fact, the GRBs-KNe plane has the smallest observed distance from its plane, called the intrinsic scatter. Here this scatter is 29% smaller than a previous analysis, see Fig. 2, object of a NASA press in 2016, lead by Dr. Dainotti. We note that this finding has been reached in a natural way without assuming any observational criteria, as had been done in Dainotti et al. previous studies. This new result is thus a step much further ahead than previous analyses.

In addition, the separated KNe plane itself still has a very small distance from the 3D plane related to the KNe when evolution is accounted for, see Fig. 3. The smaller the distance is from the plane, the more useful the plane is to be used as a cosmological tool.

A great advantage of using the GRBs associated with Kilonovae is that the GRB-KNe events have a clearer physical emission process compared to other observational GRB classes. Thus, the leap forward in this study is that this sample has a physical grounding related to the fundamental plane relation regardless of the features of the plateau phase which can vary widely from one GRB to another.

Original publication: 

 

Prof. Maria Giovanna Dainotti, Aleksander Lenart, Giuseppe Sarracino, Shigehiro Nagataki, Salvatore Capozziello, Nissim Fraija; The X-ray fundamental plane of the Platinum Sample, the Kilonovae and the SNe Ib/c associated with GRBs, ApJ 2020 (DOI: 10.3847/1538-4357/abbe8a).

The research was conducted at the Department of High Energy Astrophysics of the Jagiellonian University’s Astronomical Observatory (OA UJ).

Contact:

Maria Giovanna Dainotti
Astronomical Observatory
Jagiellonian
M.Dainotti@oa.uj.edu.pl

 

Source: Astronomical Observatory of the Jagiellonian University

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