The Gravitational-Wave Transient Catalog 4.0, pictured, is a record of cosmic mergers detected between 2015 and 2024 by the LIGO, Virgo, and KAGRA gravitational wave observatories. Each panel is a time and frequency signature of an individual event — the merger of two black holes, two neutron stars, or one of each, somewhere out in the cosmos. Credit: Ryan Nowicki / Bill Smith / Karan Jani
More than a century after Albert Einstein predicted them, gravitational waves are transforming astronomy. Ripples in space-time produced by colliding black holes and neutron stars are now being detected routinely, revealing a universe filled with violent mergers and cosmic echoes that have travelled billions of years to reach Earth.
A Ripple Across the Cosmos
When the densest objects in the universe collide, the impact does not simply end with the destruction or merger of stars. It sends ripples through the very fabric of space and time.
These ripples—known as gravitational waves—spread outward at the speed of light, crossing galaxies and cosmic voids for millions or even billions of years. By the time they reach Earth, they are unimaginably faint distortions of space itself.
Yet scientists have learned how to detect them.
Image by Gerd Altmann from Pixabay
A global network of observatories now monitors these tiny disturbances: the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States, the Virgo detector in Italy, and the Kamioka Gravitational Wave Detector (KAGRA) in Japan. Together, these instruments form one of the most sensitive scientific experiments ever constructed, capable of detecting distortions smaller than the width of a proton.
Through them, astronomers have begun to “listen” to the universe.
And what they are hearing is astonishing.
A Universe Filled with Collisions
The LIGO–Virgo–KAGRA (LVK) Collaboration has now released the latest compilation of gravitational-wave detections, to appear in a special issue of Astrophysical Journal Letters. The findings suggest that the cosmos is reverberating with collisions far more frequently than scientists once imagined.
The newly released Gravitational-Wave Transient Catalog-4.0 (GWTC-4) includes detections from part of the observatories’ fourth observing run, conducted between May 2023 and January 2024.
In just nine months, the detectors recorded 128 new gravitational-wave candidates—signals that likely originated from extreme astrophysical events occurring hundreds of millions or billions of light-years away.
This newest batch more than doubles the size of the gravitational-wave catalog, which previously contained 90 candidates from earlier observing runs.
“The beautiful science that we are able to do with this catalog is enabled by significant improvements in the sensitivity of the gravitational-wave detectors as well as more powerful analysis techniques,” says Nergis Mavalvala, a member of the LVK collaboration and dean of the MIT School of Science.
Albert Einstein /Credit: Wikipedia
What began in 2015 with the first historic detection has now become a steady stream of discoveries.
“In the past decade, gravitational wave astronomy has progressed from the first detection to the observation of hundreds of black hole mergers,” says Stephen Fairhurst, professor at Cardiff University and spokesperson for the LIGO Scientific Collaboration. “These observations enable us to better understand how black holes form from the collapse of massive stars, probe the cosmological evolution of the universe and provide increasingly rigorous confirmations of the theory of general relativity.”
When Black Holes Dance
Most gravitational waves detected so far originate from binary black holes—pairs of black holes locked in orbit around each other.
Over time, gravity draws them closer together. As they spiral inward, they release enormous amounts of energy in the form of gravitational waves. In the final fraction of a second, the two objects merge in a titanic collision, forming a single, larger black hole.
These cosmic dances are among the most energetic events in the universe.
Black holes themselves are born when massive stars collapse at the end of their lives, compressing enormous amounts of matter into regions so dense that not even light can escape.
Many form in pairs. When they eventually collide, the event sends gravitational waves surging through space.
The first such detection, announced in 2016, confirmed a century-old prediction of Einstein’s theory of general relativity. Since then, dozens—and now hundreds—of similar events have been observed.
But the latest catalog shows that the universe is far more diverse than scientists once believed.
Pushing the Edges of Black Hole Physics
The newly detected signals reveal a remarkable variety of cosmic systems.
Among them are the heaviest black hole binaries ever detected, systems where the masses of the two black holes are strikingly unequal, and pairs spinning at astonishing speeds.
“The message from this catalog is: We are expanding into new parts of what we call ‘parameter space’ and a whole new variety of black holes,” says Daniel Williams, a research fellow at the University of Glasgow. “We are really pushing the edges, and are seeing things that are more massive, spinning faster, and are more astrophysically interesting and unusual.”
Image by Iris,Helen,silvy from Pixabay
One particularly dramatic signal—GW231123_135430—appears to have originated from two enormous black holes, each roughly 130 times the mass of the Sun. Most previously observed mergers involved black holes closer to 30 solar masses.
The extraordinary size of these objects suggests they may themselves have formed from earlier black hole mergers—a kind of cosmic generational chain.
Another remarkable event, GW231028_153006, revealed a binary in which both black holes are spinning at around 40 percent of the speed of light.
And in GW231118_005626, scientists detected an unusually uneven pair where one black hole is roughly twice as massive as the other.
“One of the striking things about our collection of black holes is their broad range of properties,” says Jack Heinzel, an MIT graduate student who contributed to the catalog’s analysis. “Some of them are over 100 times the mass of our sun, others are as small as only a few times the mass of the sun. Some black holes are rapidly spinning, others have no measurable spin.”
“We still don’t completely understand how black holes form in the universe,” he adds, “but our observations offer a crucial insight into these questions.”
The observatories use L-shaped interferometers with arms several kilometers long. Laser beams travel down these tunnels and reflect back to their source.
If a gravitational wave passes through the detector, it slightly stretches one arm while compressing the other, changing the distance the light travels by an incredibly tiny amount.
These changes can be smaller than one-thousandth the diameter of a proton.
Even with such advanced technology, detections remain unpredictable.
Image by Stefan Keller from Pixabay
“You can’t ever predict when a gravitational wave is going to come into your detector,” says Amanda Baylor, a graduate student at the University of Wisconsin–Milwaukee who worked on the signal search. “We could have five detections in one day, or one detection every 20 days. The universe is just so random.”
Recent upgrades have dramatically improved the detectors’ reach. LIGO can now detect signals from neutron star collisions up to one billion light-years away, and black hole mergers far beyond that.
Testing Einstein’s Ultimate Theory
Gravitational waves are not only revealing spectacular cosmic events. They are also providing some of the most extreme tests ever conducted of Einstein’s theory of general relativity.
Black holes themselves are one of the most extraordinary predictions of the theory.
“Black holes are one of the most iconic and mind-bending predictions of general relativity,” says Aaron Zimmerman, associate professor of physics at the University of Texas at Austin.
When two black holes collide, he explains, they “shake up space and time more intensely than almost any other process we can imagine observing.”
One particularly powerful signal—GW230814_230901—allowed scientists to analyze the structure of the gravitational wave in exceptional detail.
“So far, the theory is passing all our tests,” Zimmerman says. “But we’re also learning that we have to make even more accurate predictions to keep up with all the data the universe is giving us.”
Measuring the Expansion of the Universe
Gravitational waves are also becoming powerful tools for answering one of cosmology’s biggest questions: how fast the universe is expanding.
Astronomers measure this expansion using the Hubble constant, but different methods have produced conflicting results.
Gravitational waves offer an independent approach.
“Merging black holes have a really unique property: We can tell how far away they are from Earth just from analyzing their signals,” says Rachel Gray, a lecturer at the University of Glasgow.
“So, every merging black hole gives us a measurement of the Hubble constant, and by combining all of the gravitational wave sources together, we can vastly improve how accurate this measurement is.”
Using the current gravitational-wave catalog, scientists estimate that the universe is expanding at roughly 76 kilometers per second per megaparsec.
For now, the uncertainty remains large—but future detections could sharpen the measurement significantly.
Image by Johnson Martin from Pixabay
Listening to the Future
Only a decade ago, gravitational waves were purely theoretical signals.
Today, they are transforming astronomy.
With every new detection, scientists gain another glimpse into the hidden life of the universe: the birth of black holes, the evolution of galaxies, and the behavior of gravity under the most extreme conditions imaginable.
“Each new gravitational-wave detection allows us to unlock another piece of the universe’s puzzle in ways we couldn’t just a decade ago,” says Lucy Thomas, a postdoctoral researcher at the Caltech LIGO Lab.
“It’s incredibly exciting to think about what astrophysical mysteries and surprises we can uncover with future observing runs.”
The instruments on Earth are quiet, their lasers moving silently down vacuum tunnels. But far beyond our galaxy, black holes continue to collide.
And with each collision, the universe sends out another ripple—another echo across the cosmos—waiting for us to hear it.
EP Staff is the editorial team at EdPublica, an independent media organisation focused on science, education, environment and public policy. The team produces evidence-based news, features, explainers and analysis on issues that shape society and everyday life.
The accretion of material from an evaporating second-generation giant planet accreting on a white dwarf star | Credit: Snehalata Sahu
A planet orbiting once every 4 days around a white dwarf star HS 0209+0832 – about 270 light years in the direction of the constellation Pisces – is steadily losing its atmosphere to its host star. While many stars in solar systems beyond our own often feed on their planets, this particular star feeds on its own ashes.
The gaseous planet HS 0209+0832 b was discovered in 2024, when the Transiting Exoplanet Survey Satellite, a NASA space telescope, found it orbiting the white dwarf star over the course of four days. The new study followed through with detailed observations from TESS data, NASA’s space-based Far Ultraviolet Spectroscopic Explorer, in addition to the ESO’s mountain-based Very Large Telescope, to study the star’s atmosphere and in turn inferring some chemistry occurring in the planet.
In a study published in the journal Nature Astronomy on Monday and funded by NASA, European Research Council, Fundación Occident and the Instituto de Astrofísica de Canarias, an international team of astronomers have reported imprints of niobium, a heavy element, in the atmosphere of a white dwarf star.
Astronomers predict the transiting young planet around the dead star is supplying that niobium back to its host. The sighting is evidence of a “second generation” planet, one of many candidates identified over several years, manifesting in a myriad different ways from spent gas ejected in the wake of stellar deaths.
It adds to a known coterie of planets now found orbiting dead stars, astronomers are busy studying to spot signs of life.
What are white dwarf stars?
White dwarves are an exotic stars, and are all that’s left off giant stars shedding their large gaseous skin in violent deaths. Our sun is destined one day to transform into a white dwarf, but only after swelling in size some five billion years from now to become a red giant when it will eclipse past the earth’s orbit. It would take several million years after that for the red giant sun to shed its gaseous exterior to become a white dwarf.
Planets if any, found orbiting these dead stars may have likely migrated from the new solar system’s outer reaches. All that’s left off the progenitor star’s past are imprints of light metals and other elements on the white dwarf’s atmosphere. Such planets have previously been spotted orbiting pulsars, a kind of neutron star, back in 1992. In fact, its discovery had marked the first ever detection of any planet orbiting a star beyond our sun.
Elements such as niobium don’t typically form in the core of stars like our sun. Chemical production usually limits to elements lighter than or until iron, with its 26 protons and 30 neutrons. Beyond that, slamming an extra proton or neutron will cause those to split, leaving iron to be the last element to be directly forged.
Niobium, with 41 protons and 52 neutrons, is thought to be born after absorbing slow passing neutrons when the red giant star dies to form a white dwarf star. This niobium hitches a ride along with rest of the contents of the red giant star, farther into the outer reaches of the system after the formation of the white dwarf.
These contents could create a new disc of circumstellar material with dust and gas that could condense one day to form new planets. The “second generation” planet found orbiting the white dwarf star from the new study, could have been born this way.
Alternatively, it may have been a planet in the outskirts like Neptune, migrating inwards, and enriching itself with niobium-rich star material.
Either way, the planet got too close to its host star, which is irradiating its newfound niobium-rich atmosphere, stripping it away and devouring it.
While it’s likely not a candidate planet for life as we know it to be found, it’s discovery can help ascertain how such worlds are formed in the aftermath of a star’s various phases of evolution.
Representational image of astronauts collecting lunar samples as international missions prepare for a new era of Moon exploration. Image credit: NASA
The Artemis Accords now have 76 signatories, expanding the international framework around the next phase of lunar exploration. For India, the milestone comes weeks after NASA invited the Indian Space Research Organisation (ISRO) to participate in its planned Moon Base programme.
Albania, Croatia, Côte d’Ivoire and San Marino joined the Accords in September, taking participation to 76 countries. NASA says nearly 40% of the world’s nations are now part of the framework, which sets principles for peaceful, transparent and responsible exploration of the Moon, Mars and beyond.
India became the 27th signatory in June 2023. At the India-US Civil Space Joint Working Group meeting in Bengaluru in August, NASA invited ISRO to participate in its Moon Base programme. The two countries also agreed to advance discussions on open scientific-data sharing under the Accords.
India is among the 76 countries that have signed the Artemis Accords, a framework for peaceful and responsible exploration of the Moon and beyond. Source: NASA
India’s Moon Base opportunity
The invitation does not specify what India will contribute. NASA has said every Artemis Accords signatory can participate through scientific payloads, technology demonstrations, CubeSats and other capabilities. Any specific Indian contribution would require further agreements.
India, however, is developing its own increasingly ambitious lunar programme. ISRO’s Chandrayaan-4 is planned as a lunar sample-return mission, designed to collect samples from the Moon’s polar region and bring them back to Earth. Chandrayaan-5/LUPEX, being developed with Japan’s JAXA, will study lunar polar volatiles in situ.
These missions could give India experience and scientific capabilities relevant to a future international lunar infrastructure.
ISRO Shaping the Data Conversation
Scientific data could be another area of Indian participation. In May 2026, ISRO led an initial Artemis Accords discussion on advancing open-data practices. NASA subsequently held two workshops focused on making lunar scientific data more accessible, interoperable and reproducible across countries.
That is significant as more lunar missions target the same regions. Shared standards could allow researchers to combine observations from different spacecraft instead of treating each mission’s data separately.
Moon – Space Coperation
India-US space cooperation is also expanding into human spaceflight. ISRO’s 2025–26 annual report records that Indian astronaut Shubhanshu Shukla travelled to the International Space Station in June 2025 as part of the Axiom-4 mission and conducted seven microgravity experiments. ISRO also held discussions with NASA on potential cooperation related to Gaganyaan.
The Artemis relationship therefore sits alongside an existing programme of India-US cooperation, including the NASA-ISRO Synthetic Aperture Radar (NISAR) mission.
What Changes for India?
The significance of the 76-country milestone lies in the network developing around it. The Artemis Accords cover scientific-data sharing, interoperability, non-interference between missions, emergency assistance and protection of historically significant lunar sites. NASA says signatories are now working through technical meetings and workshops to put these principles into practice.
For India, that creates several possible avenues: contributing technology or science to NASA’s Moon Base effort, sharing lunar data, and working with a growing group of countries on standards for increasingly crowded lunar operations. What India’s specific contribution to the Moon Base remains undecided. But with Chandrayaan-4, LUPEX and its human-spaceflight programme advancing alongside deeper NASA cooperation, India is entering the next phase of lunar exploration with its own capabilities already taking shape.
A dense field of stars, gas and dust surrounds the centre of the Milky Way in this infrared view from the James Webb Space Telescope. The region includes the environment around Sagittarius A* and nearby stars such as IRS 3. Image credit: ESA/Webb, NASA & CSA, F. Peißker, J. Lu, F. Yusef-Zadeh, N. B. Sabha, C. Chan
A dying star nearing the end of its life is shedding material into space just 0.55 light-years from the Milky Way’s central black hole. And somehow, some of that material is holding on. New observations from the James Webb Space Telescope have revealed water and oxygen-rich dust surrounding IRS 3, an evolved star living remarkably close to Sagittarius A*, the supermassive black hole at the heart of our galaxy.
The finding gives astronomers a rare view of what happens when an ordinary stage of stellar evolution unfolds in an anything-but-ordinary neighbourhood.
A Dying Star Beside a Black Hole
IRS 3 is an asymptotic giant branch (AGB) star, a late stage in the life of stars like this one. As such stars age, they swell, cool and lose material through powerful stellar winds. IRS 3 is doing exactly that. Gas and dust are streaming away from the star, creating a large envelope around it.
The star sits only about 0.55 light-years from Sagittarius A*. That may sound distant, but on the scale of the Galactic Centre it is remarkably close. Earth is about 26,000 light-years away from the same black hole.
A series of observations zooms from the Milky Way’s central region to IRS 3, the dying star located about 0.55 light-years from Sagittarius A*. The JWST infrared view reveals the crowded environment around the star and the Milky Way’s central black hole. Image credit: ESA/Webb, NASA & CSA, F. Peißker, J. Lu, F. Yusef-Zadeh, N. B. Sabha, C. Chan
Around Sagittarius A* is a crowded, energetic environment filled with intense radiation, dense gas and powerful gravitational forces. Astronomers have long wondered how stars manage to evolve and shed material there. IRS 3 is offering an answer.
Webb Finds Water in the Stellar Outflow
NASA‘s James Webb Space Telescope looked at IRS 3 using its Mid-Infrared Instrument, or MIRI. Infrared observations are particularly useful here because the dust surrounding the star glows strongly at these wavelengths.
The observations revealed oxygen-rich dust in the star’s envelope. They also produced the first detection of water in this material. This does not mean Webb found a pool, cloud or droplets of water. The water exists as molecules mixed into the hot gas and dust surrounding the star.
That distinction matters because molecules can be vulnerable in the harsh environment around the Galactic Centre. Radiation can break them apart, while the conditions around a supermassive black hole can affect the material being expelled by nearby stars. Yet water molecules are present around IRS 3.
The Star is Feeding Its Surroundings
IRS 3 is losing material rapidly as it approaches the end of its life. Researchers estimate that the star is shedding roughly the mass of Earth every 18 days. That enormous outflow is important beyond IRS 3 itself.
When evolved stars lose their outer layers, they return material to the space between stars. The gas carries elements produced during the star’s lifetime, while newly formed dust becomes part of the reservoir from which future cosmic structures can emerge. IRS 3 is therefore caught in a familiar cycle of stellar life: a star is dying, but the material it releases can become part of something else.
What makes this case unusual is that the recycling process is happening almost next door to a supermassive black hole.
How Much Can Survive Here?
The observation does not mean that the black hole has little influence on its surroundings. Sagittarius A* still creates an extreme environment, and the researchers are interested precisely because IRS 3 shows that stellar material can persist within it.
“Galactic centres are among the most extreme environments,” said Florian Peißker of the University of Cologne, the study’s lead author to media. With Webb, researchers can now examine the material around stars such as IRS 3 in much greater detail and ask how stellar winds, dust formation and molecular chemistry behave so close to a black hole. The answer emerging from IRS 3 is intriguing: the environment may be extreme, but it does not necessarily shut down the chemistry of a dying star.
For IRS 3, the end of its stellar life is already underway. Its outer layers are drifting away into the Galactic Centre, carrying dust, molecules and the chemical ingredients of future cosmic systems with them. Even in the shadow of the Milky Way’s central black hole, a dying star is still leaving something behind.