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NASA's exoplanet-hunting spacecraft TESS (Transiting Exoplanet Survey Satellite) has a new method for detecting worlds beyond the solar system. The technique relies on a phenomenon introduced by Einstein in his 1915 theory of gravity, general relativity, called gravitational microlensing.

The exoplanet in question is called Gaia23bra b. The first hints of this exoplanet were found in 2023 by the now-retired Gaia space telescope via the slight brightening of a star caused by a microlensing event.

TESS usually spots planets by the tiny drop in the light output from their parent star as they cross, or transit, its face. This technique is most effective for very large gas giants that orbit close to their star, so it most likely wouldn't work for Gaia23bra b, which has 1.6 times Jupiter's mass but orbits its star at a similar distance to Jupiter's orbit around the sun. Additionally, the transit method employed by TESS usually has a search radius of around 150 light-years. Gaia23bra b, however, orbits an orange dwarf star about 80 percent the size of the sun that is located 40,000 light-years away. Thus, to confirm the existence of this world, TESS had to learn a new trick.

"When TESS launched, no one expected it to ever be capable of finding this kind of planet," team member Diana Dragomir of the University of New Mexico said in a statement . "The discovery implies that there are probably other so-called microlensing planets hiding in TESS's data that we hadn't previously thought to look for."

Microlensing and the hunt for exoplanets

To understand what microlensing is, first we have to consider what general relativity says about the effect of objects with mass on space itself. Mass causes the very fabric of space and time, united as 4-dimensional spacetime, to warp. Gravity arises from that curvature. The greater the mass, the more extreme the warping and thus the greater the force of gravity.

Here is the cool part: light usually travels in a straight line, but when the very fabric of spacetime is curved, it has to follow that path. So when light from a background object passes a foreground object, the light bends around it. The bigger the mass and the closer to that mass the light passes, the more its path is curved. That means light from the same source can reach our telescopes at different times. This causes an amplification of the background source.

This phenomenon of gravitational lensing has been used to great effect to study ancient galaxies that would usually be too distant and faint to see when they are gravitationally lensed by foreground galaxy clusters.

A diagram shows an exaggerated microlensing situation (Image credit: NASA’s Goddard Space Flight Center/CI Lab) Obviously, planets have a heck of a lot less mass than clusters of galaxies, but they can still cause a slight gravitational lensing effect. That is micro-lensing, and it can be used to hunt planets.

Of the around 6,000 known exoplanets , only around 5 percent have thus far been discovered using microlensing. That is compared to around 75% found using the transit method TESS usually depends upon.

Gaia23bra b was first hinted at when it acted as a gravitational lens, passing between Earth and a background star, causing the ever-so-slight brightening of that star. The exciting thing about TESS successfully using microlensing is that this offers a complementary technique of exoplanet detection capable of detecting planets that the transit method might miss.

"With microlensing, we can find smaller planets with greater orbital distances, including worlds in the habitable zone of their star and even farther away," team member Mallory Harris of the University of New Mexico said. "Microlensing events happen once, and they're gone — they don't repeat. I like to joke that we'll probably find the first Earth analog with microlensing, and then wave at it as it goes by because we'll never see it again.

A diagram showing the search areas of three planet-hunting missions: NASA’s upcoming Nancy Grace Roman Space Telescope, the retired Kepler Space Telescope, and NASA’s TESS (Image credit: NASA’s Goddard Space Flight Center) And, if you will excuse the pun, the future is bright for microlensing. That is because it is one of the techniques that NASA's next project, the Nancy Grace Roman Telescope , will use.

Roman will scour the very heart of the Milky Way where stars are tightly packed together, hunting microlensing events which should be common in such a dense stellar region. NASA scientists predict that this will lead to Roman discovering around 1,000 microlensing exoplanets on top of the estimated 100,000 transiting worlds it is predicted to detect.

"This is a bit like a preview of the microlensing NASA's Nancy Grace Roman Space Telescope will do. The key to Roman's microlensing survey is its dense time coverage targeting the galactic bulge," team member Michael Fausnaugh of Texas Tech University said. "The TESS mission uniquely provides these rapid observations for stars in other parts of the galaxy, and pairing the two opens up prospects for understanding planet formation in a diverse population of stars.

"Since microlensing finds solar system-like planets, this offers a new chance to understand how planetary systems like our own vary in different regions of the galaxy."

The team's research was published on July 1 in The Astrophysical Journal Letters.

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Scientists have found evidence that gravitational waves from a spectacular black hole collision carry signals from the very edge of the newly formed black hole. If confirmed by future observations, the discovery could provide an entirely new way to investigate what happens in the immediate vicinity of a black hole without ever observing it directly.

In a new study, the researchers analyzed an exceptionally strong gravitational wave event known as GW250114. They identified a "direct wave," a subtle feature of the total gravitational wave signal predicted by theory but never previously detected in real data. The signal appears to contain information from extremely close to the black hole's event horizon , the boundary beyond which nothing, not even light, can escape.

The findings, published June 24 in the journal Nature , suggest that gravitational wave observatories may eventually allow astronomers to probe regions that have remained inaccessible since black holes were first predicted by Albert Einstein's theory of general relativity .

Listening to the edge of a black hole

Although astronomers have photographed the glowing material surrounding some supermassive black holes and have detected dozens of black hole mergers through gravitational waves, the event horizon itself has remained frustratingly difficult to study.

Unlike ordinary light, gravitational waves are tiny ripples in space-time produced when massive objects accelerate. They pass almost undisturbed through the universe, carrying information about violent cosmic events that would otherwise remain hidden.

According to study co-author Sizheng Ma , a postdoctoral researcher at the Perimeter Institute for Theoretical Physics in Canada, the newly identified signal offers a rare glimpse of what happens immediately after two black holes collide.

When two black holes merge, they release gravitational waves — ripples in the fabric of space time — throughout the universe. Studying these waves can provide information about the newly formed black hole. (Image credit: K. Thorne (Caltech) and T. Carnahan (NASA GSFC)) "When two black holes merge, they violently shake space-time itself," Ma told Live Science. "For a brief moment, the region very close to the newly formed black hole's horizon is swept into a fast, fading swirl."

Ma explained that the direct wave is the portion of the gravitational wave signal produced near the horizon and carries the imprint of that motion outward through space.

"That is why it is so interesting," he said. "It may let us 'listen' to what happens near the horizon, a region we cannot see directly with light."

A remarkable black hole collision

The team focused on GW250114, a black hole merger detected on Jan. 14, 2025, by the two Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in Hanford, Washington, and Livingston, Louisiana.

"Our earlier theoretical work predicted that black hole mergers should produce a direct-wave signal from the near-horizon region," Ma said. "The big question was whether this effect could actually be seen in real data."

GW250114 turned out to provide exactly the conditions needed to test that prediction.

"It was strong enough, clean enough, and close enough to the theoretical situation where this signal should be visible," he said.

To search for the elusive feature, the researchers first removed the best-understood part of the gravitational wave signal, which comes from the newly formed black hole settling down after the merger. Then, they examined the remaining data to determine whether it consisted only of detector noise or contained another physical signal.

"What we found was striking," Ma said. "The remaining signal followed the expected rhythm and fading pattern of a wave shaped by the region very close to the final black hole's horizon."

The team concluded that the leftover signal matches the behavior expected for a direct wave predicted by previous theoretical studies.

ESA's upcoming LISA mission will detect gravitational waves from space, offering even more insights into the mysterious ripples than Earth-based detectors currently can. (Image credit: All About Space/Getty Images) A new way to explore extreme gravity

The researchers stressed that their findings do not reveal what lies inside a black hole. Instead, they're providing a new observational tool for investigating the region immediately outside the event horizon.

"The gravitational wave data appear to carry an imprint from very close to the newly formed black hole's horizon — the famous point of no return," Ma said.

He explained that the measurements are consistent with space-time near the horizon being rapidly dragged around by the spinning black hole while the signal fades because of the intense gravitational field.

"For us, the exciting message is that gravitational waves may be giving us a new way to study the edge of a black hole using real observational data," Ma said.

Ma believes the method could eventually become useful for exploring ideas such as quantum gravity — which seeks to unite Einstein's theory of gravity with quantum mechanics — or the black hole information paradox, the longstanding puzzle of whether information that falls into a black hole is truly lost. However, it cannot test those questions directly yet.

"If quantum effects, or any deviations from the standard black-hole picture, leave a measurable imprint there, then direct waves could, in principle, help us search for them in the future," he said.

More observations will be needed

The researchers cautioned that the discovery is based on a single gravitational wave event. While GW250114 provided exceptionally favorable conditions, much stronger evidence will come only if similar signals are found in many additional black hole mergers.

"There are two main directions," Ma said. "The first is theory."

Current models capture the essential physics but remain simplified, and more realistic descriptions of black hole mergers will be needed.

"The second is observation," he added. "This result comes from one exceptionally loud and clean event, so the strongest confirmation would come from seeing the same kind of pattern in other black hole mergers."

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As gravitational wave observatories continue to improve and detect increasing numbers of mergers, researchers hope to determine whether direct waves are a universal feature of black hole collisions.

"If the pattern appears repeatedly in the way general relativity predicts," Ma said, "direct waves could become a new way to study black hole horizons or the regions very close to them, and to test Einstein's theory in one of the most extreme environments in the universe."

If future observations confirm the team's results, scientists may have gained something they have sought for decades: a direct observational window into the very edge of a black hole.

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