QuoteWhen two black holes orbit each other, they eventually spiral inward and collide in one of the most violent phenomena in the universe. The event is so energetic that it significantly distorts the universe around it. It emits gravitational waves—ripples in the fabric of spacetime—that are strong enough to be detected with precision instruments on Earth even when they originate billions of light-years away.
These gravitational waves carry information about the event that physicists use to predict the size of the merger's resulting new, larger black hole—referred to as a remnant. But accurate predictions involve complex equations originally developed by Einstein as part of his theory of general relativity that require supercomputers to solve.
Now, a team of researchers led by physicists at Penn State has shown that there may be a simpler way, which also points toward a deeper understanding of the physics contained in those complex equations.
"The final black hole after a merger is ringing like a struck bell, and it radiates away more gravitational waves until it settles into a calm, stable state described by just two numbers—its final mass and spin," said Monica Rincon-Ramirez, a postdoctoral scholar in physics in the Penn State Eberly College of Science and the first author of the paper.
"The question we asked is: Can we predict what that final state looks like using arguments from thermodynamics?"
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The new work suggests that once the energy and angular momentum—a measure of the system's rotational motion—carried away by gravitational waves are properly accounted for, the final black hole appears to be the state that maximizes entropy, the measure of randomness in a system, tracking the natural tendency of the universe to go from a state of order to a state of chaos.
"Entropy is essentially a measure of disorder, or more precisely, of how many ways something can be arranged," said Vaishak Prasad, a postdoctoral researcher in astronomy and astrophysics at Penn State and an author of the paper.
"A messy room has high entropy—there are countless ways things can be strewn about. A perfectly tidy room has low entropy—there are only a few arrangements that count as 'tidy.' Nature tends to drift toward high-entropy states simply because there are more of them. Our results suggest that black hole mergers do something similar."
The team developed what they call the "maximum entropy conjecture for black hole mergers," which is strikingly similar to ordinary thermodynamics.
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QuoteAbstract:
The final state of a binary black hole merger is predicted with high precision by numerical relativity, but could there be a simple thermodynamic principle within general relativity that governs the selection of the remnant? Using post-Newtonian relations between the mass 𝑀 (including the binding energy) and angular momentum 𝐽 of quasicircular, nonspinning binaries, we uncover a puzzling result: When the binary's instantaneous 𝑀 and 𝐽 are mapped to those of a hypothetical Kerr black hole, the corresponding entropy exhibits a maximum during the evolution.
This maximum occurs at values of 𝑀 and 𝐽, strikingly close to those of the final remnant predicted by numerical relativity. Consistent behavior is observed when using the relation between 𝑀 and 𝐽 obtained from numerical relativity evolution.
Although this procedure is somewhat ad hoc, the agreement between the masses and spins of the final state obtained from numerical relativity and the results of this maximum entropy procedure is remarkable, with agreement to within a few percent when using either post-Newtonian or numerical relativity results for 𝑀 and 𝐽. These findings allow us to propose an entropy maximization conjecture for binary black hole mergers, hinting that thermodynamic principles may govern the selection of the final black hole state.
QuoteEvery time two black holes spiral together and merge, the resulting ripples in spacetime encode information about their masses and spins—the rate and direction at which each one rotates.
Astronomers can extract these properties from the gravitational-wave signal, but the picture is often incomplete: While some binaries formed from pairs of stars that lived and died together, others came together later, pulled into orbit by chance encounters in crowded stellar environments. Because these two pathways leave subtly different imprints on mass and spin, sifting through hundreds of detections to spot broader patterns has been a persistent challenge.
The first team's study, led by Cailin Plunkett at MIT, built a model that focuses on two well-measured spin parameters, capturing how a black hole's spin aligns with its orbital motion. The second study, led by Sharan Banagiri at Monash University in Australia, took a more open-ended approach, letting the data itself dictate how many distinct groups were present without assuming a particular formation story in advance.
Despite their different starting points, both teams identified a population of unusually massive black holes that stood apart from the rest, each roughly 40 times the mass of the sun or heavier.
Plunkett's team found that these heavyweights carry fast, randomly oriented spins consistent with black holes built from earlier mergers rather than stellar collapse. Banagiri's team reached a similar mass threshold and also found high spins in this group—though without the same clear signature of a merger origin. This prompted some caution about the interpretation.
Together, these findings offer some of the strongest evidence to date that a portion of observed black hole mergers are "second-generation" events, born from black holes that had already merged once before—rather than from the collapse of massive stars.
This distinction could ultimately help explain how black holes end up in a mass range otherwise thought to be off-limits, and how the seeds of the supermassive black holes at galaxies' centers might have grown. As gravitational-wave detectors grow more sensitive to these massive binaries, the boundaries between subpopulations could soon become clearer.
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An artist's impression of Uragasaurus kalasinensis. (Pakorn Chotchaiyaporn for Nilpanapan et al., Sci. Rep., 2026)
[F]rom a single vertebra found in a fossil bed in Thailand, researchers have identified a whole new species of giant dinosaur.
Its name is Uragasaurus kalasinensis, and it was a long-necked sauropod – the group of giant plant-eating dinosaurs, including Diplodocus and Brontosaurus – that lived in forests in Southeast Asia just before the Jurassic-Cretaceous transition, which began around 143 million years ago.
It's also the first formally named member of the long-necked dinosaur family Mamenchisauridae from northeastern Thailand.
"This discovery expands the known diversity of mamenchisaurid sauropods in Southeast Asia and provides new information on the geographic distribution and evolutionary history of the clade," writes a team led by paleontologist Apirut Nilpanapan of Mahasarakham University in Thailand.
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QuoteAbstract:
Mamenchisauridae is a group of long-necked non-neosauropodan eusauropod dinosaurs that were abundant in East Asia during the Middle to Late Jurassic, but their diversity and geographic distribution outside China remain poorly documented.
Here we describe Uragasaurus kalasinensis gen. et sp. nov., a new sauropod dinosaur from the Phu Kradung Formation of northeastern Thailand. The new taxon is based on a well-preserved anterior dorsal vertebra exhibiting a distinctive combination of characters, including a unique Y-shaped configuration formed by the intraprezygapophyseal and single intraprezygapophyseal laminae and a camellate internal pneumatic structure within the centrum revealed by computed tomography (CT).
Phylogenetic analyses recover the new taxon as an early-diverging member of Mamenchisauridae. This discovery represents the first formally named mamenchisaurid from Thailand and expands the known geographic distribution of the clade in Southeast Asia. The occurrence of this taxon in the Lower part of the Phu Kradung Formation also contributes to understanding faunal succession within the unit, supports an Upper Jurassic age for the lower part of the formation, and improves understanding of sauropod diversity in Southeast Asia during the Jurassic-Cretaceous transition.