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.
How Scientists Traced the Flow of Matter Around a Dead Star Using X-rays
By studying changes in X-ray signals from Centaurus X-3, researchers at Bengaluru’s Raman Research Institute have found evidence of an unusual way in which matter reaches a neutron star. The discovery could change how scientists explain the radiation coming from this distant system.
An artistic impression of the high-mass X-ray binary system Centaurus X-3. Not to scale.
When a massive star dies, its core can collapse into an extremely dense object called a neutron star. Despite being only about the size of a city, it can have a mass comparable to that of the Sun. Its powerful gravity can pull matter away from a nearby companion star, releasing energy in the form of X-rays as the material falls towards it.
Scientists at Bengaluru’s Raman Research Institute (RRI) have studied these X-ray signals from Centaurus X-3, a star system about 24,000 light-years from Earth. By examining changes in the signals, the researchers identified a stream of matter flowing towards the neutron star and found evidence of a rotating disk of material around it. This is an unusual finding because such disks are not commonly expected in this type of star system. The discovery could help scientists better understand how matter moves around neutron stars and how these distant objects produce X-rays.
Star That Pulls in Matter
Centaurus X-3 is in the constellation Centaurus. It belongs to a class of systems known as high-mass X-ray binaries. These systems contain a neutron star and a massive companion star held together by gravity.
A neutron star forms when the core of a massive star collapses at the end of its life. It packs roughly the Sun’s mass into a sphere only about the size of a city. Its gravity is so strong that it can pull in material from a nearby companion star. As this material falls towards the neutron star, it releases enormous amounts of energy, including X-rays. Scientists study this radiation to understand how the material behaves and how the system works.
Centaurus X-3 is also a pulsar. Its neutron star rotates and sends out radiation from regions near its magnetic poles. As the star spins, these beams sweep across space. When a beam passes an observing satellite, the satellite detects a pulse of radiation, much as a lighthouse produces a repeating flash as it turns. These regular pulses provide scientists with a way to study the neutron star and its surroundings.
What the Changing Signals Revealed
The radiation from Centaurus X-3 does not come only from the neutron star itself. Some of it interacts with nearby material, including the surface of the companion star, gas flowing away from it and matter surrounding the neutron star. This material absorbs radiation and emits it again. Scientists call this secondary radiation.
The accretion stream falling onto the neutron star along its magnetic field lines.
Changes in this radiation can help researchers work out what is happening around the neutron star. However, Centaurus X-3 is so far away that telescopes cannot clearly distinguish its surrounding structures. It appears as a single point of light. Scientists must therefore piece together the system’s structure from the signals they receive.
Earlier observations had shown that the intensity of certain secondary X-ray emission lines changed as the neutron star rotated. An emission line is a feature in a spectrum that can reveal information about the material producing or interacting with the radiation. A research team led by Kinjal Roy of RRI examined four such emission lines in detail. The researchers found that the structure producing these changes must be rotating along with the neutron star.
The pattern helped them identify the likely source which is a stream of matter moving towards the neutron star.
Following the stream of matter
This stream is part of a process called accretion, in which a compact object draws in material from its surroundings. In Centaurus X-3, the stream carries matter from an accretion disk towards the neutron star. The disk is a rotating structure of gas and other material that moves around the star before being drawn inwards. The neutron star’s magnetic field then guides the incoming matter towards its magnetic poles.
The stream also changes what an observing satellite sees. As it moves around the neutron star, it can come between the satellite and the star, partially blocking the direct radiation. When this happens, the primary X-ray signal weakens. At the same time, radiation from the stream itself becomes stronger in the observed signal.
The researchers used these changing signals to connect the observed variations to the movement of matter around the neutron star. The evidence for an accretion stream also points to an accretion disk feeding it. This matters because scientists generally expect high-mass X-ray binaries to gather material in a different way.
Why an accretion disk matters
In many high-mass X-ray binaries, a neutron star captures gas directly from the stream of material blown away by its companion star. This is known as stellar-wind accretion. An accretion disk involves a different arrangement: material gathers into a rotating structure before flowing towards the neutron star. The findings from Centaurus X-3 indicate that this disk-based process is taking place in a system where it is not generally expected.
That difference matters when scientists calculate how the system produces and releases radiation. If their models leave out the disk, they may fail to account for some of the radiation coming from the surrounding material.
“Accretion disk is not expected to occur in [HMXBs] So, if an accretion disk is forming in this system, emission models have to be modified,” Roy said in the Department of Science and Technology’s announcement. He added that future models of Centaurus X-3 would need to account for radiation from the disk.
The research does not mean that scientists have directly photographed the disk. Instead, they have used the changing X-ray signals to infer the presence and behaviour of structures that remain too distant to resolve clearly. Published in The Astrophysical Journal, the study adds to the understanding of Centaurus X-3, one of the most widely studied binary pulsars. It also shows how small changes in radiation can reveal the movement of matter around objects that are otherwise beyond the reach of direct observation.
By identifying the flow responsible for the changing signals, the researchers have provided a more detailed picture of how this neutron star draws in material. That picture will help scientists refine their models of Centaurus X-3 and examine whether similar processes occur in other high-mass X-ray binaries.
A rocket launches over the ocean, illustrating the “Rocket Revolution” theme of World Space Week 2026 and the growing role of launch technology in space access. Representational image. Image credit: SpaceX/ Pexels
For most of the space age, rockets were built to fly once. After delivering a satellite to orbit, much of the vehicle was discarded. But that model is transforming as reusable boosters, smaller launch vehicles and shared launches are making space more accessible to companies, universities and countries beyond the traditional space powers.
This has become the focus of World Space Week 2026, observed from October 4 to 10 with the theme “Rocket Revolution.” The mission of World Space Week Association (WSWA) is to strengthen the link between space and society through public education, participation, and dialogue on the future of space activity using World Space Week as a focus.
The dates mark two milestones in space history: the launch of Sputnik 1 on October 4, 1957, and the entry into force of the Outer Space Treaty on October 10, 1967.
Rockets, Reused
SpaceX’s Falcon 9 has shown the potential of reusable rockets. Its first stage returns to Earth after launch and can fly again. The approach can reduce the need to build an entirely new rocket for every mission. Blue Origin’s New Glenn also has a reusable first stage, while Rocket Lab is developing a reusable version of its Electron launcher.
Smaller rockets and rideshare missions are opening another part of the market. A company with a small satellite no longer necessarily needs access to a large launcher or an entire rocket.
Nearly 15,000 Satellites are in Orbit
The OECD estimates that more than 14,000 operational satellites were in orbit at the end of 2025, rising to nearly 15,000 by mid-2026. Satellite observations supply more than 90% of the observations used in numerical weather prediction, according to the OECD. Earth-observation satellites also monitor crops, forests, oceans and cities, while their images can help map areas affected by floods and cyclones.
The global space economy was estimated at 550–600 billion dollars in 2025, with much of its value coming from services based on satellite communications, navigation and Earth-observation data.
India Opening Launch Sector
India is also moving towards a larger private space industry. In July 2026, Skyroot Aerospace’s Vikram-I became the first privately developed Indian rocket to conduct an orbital launch from Indian soil. It lifted off from Sriharikota on July 18 and placed two satellites, SCOPE and Grahaa, into low Earth orbit.
Interestingly, the Department of Space reported around 440 space-technology startups registered on the DPIIT Startup India portal as of August 2026. ISRO is also developing the Small Satellite Launch Vehicle (SSLV) for spacecraft weighing up to about 500 kg. A dedicated SSLV launch complex is being developed at Kulasekarapattinam in Tamil Nadu.
More spacecraft, More Orbital Risks
A busier space environment brings its own problems. About 45,860 pieces of space debris are regularly tracked, according to the OECD. Millions of smaller fragments are too difficult to monitor individually. A collision can create thousands more pieces and threaten other spacecraft.
Satellite operators therefore need to track nearby objects, avoid collisions and plan for spacecraft disposal after missions end. For World Space Week 2026, the “Rocket Revolution” theme points to a space industry that is moving beyond occasional government missions. Rockets are being reused, private companies are entering the launch business and satellites are becoming part of everyday infrastructure. The challenge that has to be tackled is the increasingly busy orbital environment usable for the next generation of missions.
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.