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The Universe Is Ringing

How gravitational waves from colliding black holes are opening an entirely new way of exploring the cosmos

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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.

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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.

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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.

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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.

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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.

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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.”

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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.”

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Catching a Whisper in Space-Time

Detecting gravitational waves requires extraordinary precision.

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.

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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.”

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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.

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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.

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Space & Physics

NASA announces crew of Artemis III at live event

Artemis III will be the agency’s next human space exploration mission paving the way for humanity’s planned return to the moon in 2028.

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The Artemis III crew poses for an official portrait (from left: Andre Douglas, Luca Parmitano, Randy Bresnik, Frank Rubio). Credit: NASA/Bill Stafford

At 20:30 hours IST yesterday, NASA’s Johnson Space Center in Houston, Texas held a live event their engineers, scientists, the astronaut corps and the media attended. The space agency officially announced the crew of Artemis III, the agency’s next human space exploration mission, paving the way for humanity’s planned return to the moon in 2028, over fifty years after the Apollo program.

Half-way through the hour-long presentation, Jared Isacson, the NASA administrator, walked to the dais to announce the all-men crew of Artemis III: NASA mission commander Randy Bresnik, mission specialists Andre Douglas and Frank Rubio, and European Space Agency pilot Luca Parmitano, an Italian national. 

Three of the astronauts excluding Douglas, a US Coast Guard reserve, are both spaceflight and military veterans. Bresnik, a US marine colonel and test pilot clocking 7,000 hours, commanded the International Space Station. So did Parmitano, the first Italian commander of the station, and who survived a 2013 spacewalk when water abruptly filled his helmet and had an asteroid named after him. Rubio, a US army helicopter pilot, holds the record for the longest time spent in space. 

NASAs Artemis III Announcement 38 40 screenshot

Screengrab from the YouTube livestream of the event at NASA Johnson Space Center, Houston, Texas. Credit: NASA

Mission timeline

The mission could take off in the second-half of 2027. Originally,  NASA planned Artemis III to be the first soft-landing lunar mission since 1972’s Apollo 17, with a slated launch date in 2028. However, in March, the agency updated mission timelines, with the mission relegated for testing its mission critical docking mechanism, ahead of Artemis IV’s planned soft-landing that year.

The crew will fly aboard a Space X Orion capsule into low-earth orbit. Unlike its predecessor, Artemis III won’t leave earth orbit and conduct a flyby past the moon. Instead, it will test life support systems and docking with Artemis’ era lunar landers, built by private space companies Space X and Blue Origin, the Starship Human Landing System (HLS) and the Blue Moon respectively. In addition, Artemis III will carry on science experiments, including using instrumentation to test effects of atmospheric drag upon the spacecraft, amidst hostile space weather.

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The Apollo and Artemis-era lunar landers drawn to scale. Credit: NASA

Lunar landers 

There has been skepticism whether the Blue Moon lunar lander’s launch schedule would be affected, in the aftermath of last week’s mishap involving New Glenn, the flagship rocket of Jeff Bezos-owned Blue Origin, exploding during a hot-static test ahead of its slated launch of Amazon’s satellites. The explosion destroyed the company’s custom-developed launchpad at Cape Canaveral Space Force Station in Florida. However, the company CEO, David Limp, posted on X, they’ll return to full-swing operations latest before the end of this year.

Whereas Starship HLS, the other lunar lander design, will feature a variant of the Starship rocket, with the latter design being still tested over repeated space flights in the past year. 

Either lunar landers designed to ferry astronauts from lunar orbit to the surface, and back. In a future Artemis mission, the astronauts, who will ride aboard Space X’s Orion crew module from earth, will dock with the lander in lunar orbit, before transferring to the lander module. 

It’s unclear which lander design’s slated to make the soft-landing attempt in Artemis IV. 

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Engineers Develop Dual-Mode Propulsion System for Next-Generation Small Satellites

MIT engineers have developed a dual-mode propulsion system that combines chemical and electric thrusters, giving small satellites greater flexibility in space

Joe Jacob

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MIT researchers testing a dual-mode propulsion system designed to power next-generation small satellites using a shared propellant tank.
MIT-developed electrospray thrusters prepared for NASA's Green Propulsion Dual Mode mission, a demonstration of next-generation propulsion technology for CubeSats. Photo: Amelia Bruno/MIT News

Dual-mode propulsion system technology developed by MIT engineers could give small satellites the ability to perform both powerful manoeuvres and fuel-efficient long-distance travel using a single propellant source.

Small satellites have transformed space research by making missions cheaper and more accessible. Yet they continue to face a fundamental limitation: propulsion.

Traditional chemical thrusters provide powerful bursts of speed but consume large amounts of fuel. Electric propulsion systems, on the other hand, are highly efficient but generate only gentle thrust over long periods. Spacecraft designers have typically had to choose between the two.

Engineers at the Massachusetts Institute of Technology (MIT) now believe they have found a way to combine both approaches in a single compact system, potentially giving small satellites the agility of much larger spacecraft.

The breakthrough centres on a special propellant capable of powering both chemical and electric thrusters from the same fuel tank.

“If you can have chemical and electrical propulsion in one small package, it’s the best of both worlds,” said Amelia Bruno, lead author of the study and a former postdoctoral researcher in MIT’s Department of Aeronautics and Astronautics, in a media statement.

“This opens the door for small satellites to do even more science, more observations, and more interesting missions, all on a smaller and cheaper platform.”

The findings have been published in the Journal of Propulsion and Power.

Dual-Mode Propulsion System Combines Two Technologies

The MIT team tested a propellant known as Advanced SpaceCraft Energetic Non-Toxic propellant, or ASCENT. Originally developed by the U.S. Air Force as a safer alternative to hydrazine, ASCENT was designed for chemical propulsion systems.

Researchers discovered that the same propellant can also power miniature electric propulsion devices known as electrospray thrusters.

These tiny thrusters use electric fields to charge particles within a liquid propellant and eject them into space, creating precise and fuel-efficient thrust. While chemical thrusters are ideal for rapid manoeuvres, electrospray systems are better suited for gradual course corrections and long-duration journeys.

By enabling both systems to share a single fuel source, the technology could significantly reduce the size and complexity of propulsion systems aboard CubeSats and other small spacecraft.

Dual-Mode Propulsion System Could Expand Deep-Space Missions

Dual-mode propulsion system can expand deep-space missions. The implications extend beyond Earth orbit.

CubeSats have become popular for scientific research and technology demonstrations, but their limited propulsion capabilities have restricted their use in deep-space missions.

According to Paulo Lozano, the Miguel Alemán Velasco Professor of Aeronautics and Astronautics at MIT, the new system could change that.

“We could send CubeSats to Mars, or the asteroid belt, where they could make the journey slowly, using electrospray thrusters,” he said.

“You could then use your chemical thrusters to quickly move to look at interesting features. You could have a lot more flexibility to do a lot more things.”

Testing the Technology

To evaluate the propellant’s performance, the researchers filled small CubeSat reservoirs with ASCENT and tested them in a vacuum chamber designed to simulate conditions in space.

During the experiments, electrospray thrusters powered by ASCENT successfully generated thrust for extended periods, in some cases operating continuously for up to 100 hours.

NASA Mission Will Put the Technology to the Test

The next major test will come later this year.

MIT researchers are working with NASA on the Green Propulsion Dual Mode mission, a CubeSat that will carry both chemical and electrospray thrusters powered by a single propellant tank. Scheduled for launch in November, the mission will be the first demonstration of such a system in a small spacecraft.

If successful, the mission could help pave the way for a new generation of versatile satellites capable of switching between rapid manoeuvres and highly efficient long-distance travel.

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India Semiconductor Mission: ‘It’s Not About Fabs. It’s About Building An Entire Ecosystem’

India Semiconductor Mission is reshaping the country’s chip ambitions. Neelkanth Mishra explains the opportunities, challenges and long-term strategy.

Dipin Damodharan

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Neelkanth Mishra, Chief Economist at Axis Bank and member of the India Semiconductor Mission advisory committee, speaking about India's semiconductor ambitions and chip ecosystem.
From extreme ultraviolet lithography to the economics of fabrication, semiconductors sit at the intersection of advanced science and industrial complexity. Neelkanth Mishra unpacks where India stands today, the constraints it faces, and the strategic choices that will define its place in the global chip ecosystem. Image: Dipin Damodharan/EdPublica
India Semiconductor Mission is at the centre of the country's efforts to build a globally competitive chip ecosystem
Photo by Christian Wiediger/Unsplash

Let me start with asking something out of curiosity – how did you get interested in semiconductors in the first place?

When I joined Credit Suisse First Boston in 2003 in Singapore, the person who hired me was heading Asia technology research and was also the lead analyst for semiconductor foundries such as TSMC and UMC. I was hired to cover IT services, but he wanted help in building the semiconductor research franchise.

That led me to start reading about how chips are made. At that time, the industry was transitioning from 130-nanometer to 90-nanometer nodes, and copper was being introduced to replace aluminum due to resistance issues. There were challenges around yields because copper was seeping into substrates. I remember writing my first note around this issue after going through technical papers.

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That note became quite popular, and it gave me the confidence to continue covering semiconductors. I spent a lot of time travelling to Taiwan, studying DRAM cycles, capex cycles, node transitions, and the broader global semiconductor ecosystem. Eventually, I moved to Taipei and began covering chip design companies such as MediaTek.

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At that time, were you also tracking what was happening in India?

India has had chip design activity for a long time, even in the 1990s. Companies like Texas Instruments, Cadence, and Synopsys were recruiting from Indian campuses. Many engineers built long careers in these firms.

However, India did not have domestic chip manufacturing or strong Indian-owned chip design companies. By the mid-2000s, global firms such as Nvidia, Broadcom, and Intel began setting up design centres in India. So the design ecosystem was growing, but it was largely driven by global companies.

It is only in the last four to five years that more serious efforts have begun toward building Indian-owned capabilities.

So what changed in the last few years? Was it policy, or something else?

Policy has played a role. The Design Linked Incentive (DLI) scheme has been an important catalyst. We are seeing some early success. At the same time, there is also an evolutionary factor at play. Engineers who moved abroad 20–25 years ago are now at a stage where they have both the experience and financial capacity to take entrepreneurial risks. Many also want to return to India.

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Another important factor is the growth of India’s electronics manufacturing ecosystem. As assembly volumes increase, there is greater awareness of what products need to be designed. Without that visibility into OEM pipelines, it is difficult to design chips.

Schemes like PLI for electronics manufacturing have helped build that awareness and ecosystem. As downstream industries grow, upstream opportunities in chip design also become clearer.

As US is good at designing chips, Taiwan and South Korea are good at manufacturing There’s always this question – should India focus on design, manufacturing, or packaging?

There is no either/or. India needs to participate across the value chain.

We already have a natural advantage in chip design, with about 20% of global design engineers based in India. Design is also less capital-intensive compared to manufacturing. In a $10 chip, $5–6 of value is captured by the designer, and in some cases even more.

At the same time, semiconductor manufacturing is a geopolitical necessity. It is not just a commercial issue but also a matter of national security. That is why governments provide significant subsidies for fabs.

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However, manufacturing is a low-return business globally. Only a few companies like TSMC and Samsung have consistently generated returns above their cost of capital. Much of the value in the ecosystem is captured by design firms and by capital equipment suppliers, which operate in highly concentrated markets.

Therefore, India must build capabilities across the chain—from design to manufacturing to equipment and materials—if it wants meaningful value capture.

When we talk about building an ecosystem, how complex is that in reality?

It is extremely complex. The industry has multiple layers of specialization. For example, electronic design automation (EDA) tools are dominated by a few companies. Lithography, especially extreme ultraviolet, is controlled by a single company globally. Equipment for deposition, wafer slicing, and testing is also concentrated among a handful of firms.

Even the chemicals used in wafer cleaning are highly sophisticated and require extraordinary purity. A single wafer can take months to manufacture, involving hundreds of process steps.

So when we talk about semiconductors, it is not just about fabs. It is about building an entire ecosystem—equipment, materials, design, testing, and packaging. This is why it is a 15–20 year journey at least.

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Image credit: Taiwan Semiconductor Manufacturing Co., Ltd

What about talent? Are we ready from a skills perspective?

In general, skilling in India is more of a demand problem than a supply problem. If there is sufficient demand, the industry tends to create the supply.

For example, there is already discussion about developing tens of thousands of chip testing engineers in India, and that is achievable. However, for cutting-edge technologies, there is a need for deeper investment in research.

As we move toward more advanced nodes—such as 7 to 12 nanometers—we will require significant high-end research capabilities. Countries like China took over 25 years to reach that level.

We need to invest not just in near-commercial research (TRL 6–9) but also in fundamental research (TRL 1–4), which creates long-term intellectual property. Government initiatives like the Anusandhan National Research Fund are steps in that direction, but overall R&D spending needs to increase.

What role should industry play in R&D?

Industry participation is essential. The government can catalyse investment, but companies will invest when they see potential returns.

We have seen this in pharmaceuticals, where Indian firms moved into R&D after reaching limits in generics. A similar shift can happen in semiconductors, but it will require scale, capital, and long-term commitment.

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Where do startups fit into this picture?

Startups will have a significant role, particularly in chip design. Manufacturing is extremely capital-intensive, requiring billions of dollars in investment, which limits the role of startups.

However, in design and innovation, startups can play an important part. Many innovations in the semiconductor ecosystem originate from smaller firms, which are later acquired or integrated into larger companies.

To produce a globally competitive company, you need a large ecosystem of startups, experimentation, and risk-taking.

Coming to policy – what did India learn from ISM 1.0?

ISM 1.0 (India Semiconductor Mission) was a learning curve for everyone. It helped the government understand how to evaluate proposals, support companies, and manage operational challenges.

There were practical issues—from customs procedures affecting sensitive equipment to ensuring uninterrupted power supply. Semiconductor manufacturing requires extremely high reliability, and even a brief power outage can cause significant losses.

Another important learning is that the global industry is now more comfortable working with India. While India may not yet be the first choice, confidence has improved due to visible commitment and progress.

This increased comfort allows India to be more ambitious with ISM 2.0.

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Photo by Laurel and Michael Evans/Unsplash

How important is policy stability?

Policy continuity is very important because these are long-term projects. Global firms value consistency in decision-making and relationships.

There is also a growing effort to ensure continuity in leadership within government institutions, which helps build expertise and trust over time.

Do we need a dedicated semiconductor research institution like IMEC?

There are existing efforts, such as the facility in Mohali, which supports defence-related applications. There are also discussions around creating IMEC-like research centres.

However, over time, the private sector will need to take a larger role in research. Government support is critical in the early stages, but for sustained innovation and competitiveness, industry-led initiatives are more effective. The government can act as the binding force or the catalyst that brings people to the table; however, I believe it is ultimately better if the private sector takes the lead. This creates a natural incentive for innovation and rigorous research. Beyond a certain point, government support becomes both fiscally unfeasible and operationally undesirable

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If we look ahead 20 years, where do you see India?

On the design side, India can become much more significant. It is possible to see 10–15 large chip design companies and many smaller firms emerging.

On the manufacturing side, we could have several large fabs and potentially global players establishing operations in India, especially if a strong domestic design ecosystem develops.

For example, companies like TSMC tend to follow innovation ecosystems. If Indian design firms grow in scale and sophistication, it could attract global manufacturing investments.

Neelkanth Mishra, Chief Economist at Axis Bank and member of the India Semiconductor Mission advisory committee, speaking about India's semiconductor ambitions and chip ecosystem.

Let me end with this – can India produce a company like Nvidia?

It is possible, but it requires a large ecosystem. Many Indians already occupy senior roles in global semiconductor companies and are involved in cutting-edge design work.

To create a company of that scale, you need risk capital, entrepreneurial ambition, and a large number of startups. In other markets, hundreds of firms compete, and one eventually emerges as a dominant player.

So it is not about a single effort—it is about building an ecosystem where many experiments take place, and success emerges from that.

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