When two black holes merge into one, they sometimes leave behind ripples in space. These oscillations were first predicted by Albert Einstein more than a century ago, and are now helping scientists piece together the process that drives black hole mergers.
New research published in Letters from an Astrophysical Journal examined the ripples, or gravitational waves, from two black hole mergers that occurred in late 2024, each consisting of a pair of colliding black holes. The waves emitted from these events led the researchers to conclude that one black hole in each pair could be a “second generation” black hole, or one that had already emerged from a previous merger. With this discovery, they are beginning to understand how black hole systems grow in the dense environment of space.
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A good signal from a black hole merger
On October 11, 2024, a black hole merger occurred at a distance of approximately 700 million light years (GW241011); the two black holes weighed about 17 and 7 times the mass of our Sun, respectively, and the larger of the two had one of the fastest spins observed to date.
Then, on November 10, 2024, another merger (GW241110) brought together a separate pair of black holes, this time 2.4 billion light years away; the two weighed about 16 and 8 times the mass of our Sun, respectively, and the primordial black hole was the first observed to spin in the opposite direction to its orbit.
Using algorithmic methods and mathematical models, the researchers were able to interpret gravitational signals from both sources. mergers and observe key characteristics of detected black holes, such as their speed and rotation.
Hierarchies of black holes
Binary black hole merger
(Image credit: Carl Knox, OzGrav, Swinburne University of Technology)
However, what do these two mergers from last year have to do with each other? The connection, the researchers discovered, is that both can confirm the presence of “second generation” black holes.
This is because one black hole in each merger was larger and had a different spin orientation compared to its smaller partners. Given the difference in size between both mergers, the researchers suggested that the larger black holes were likely themselves created by previous mergers—a phenomenon called a “hierarchical merger.”
According to statement According to a new study, this happens when black hole systems are in dense environments, where the black holes are more likely to collide with each other and merge again and again.
“The unusual rotation configurations observed in GW241011 and GW241110 not only challenge our understanding of black hole formation, but also offer compelling evidence for hierarchical mergers in dense cosmic environments: they teach us that some black holes exist not just as isolated partners, but probably as members of a dense and dynamic crowd,” said Gianluca Gemme, a spokesman for the Virgo collaboration, which monitors the evolution of gravitational pull. Virgo waves. detector in Italy.
Testing Einstein's theories
By observing black hole mergers in October and November 2024, researchers were able to test predictions related to Einstein's theory general relativity and the work of mathematician Roy Kerr on the rotation of black holes.
According to the researchers, when a black hole's rapid rotation slightly deforms it, it leaves a distinctive fingerprint on its surface. gravitational waves he radiates. The huge difference in mass between black holes also creates a higher harmonic “hum” much like the overtones of musical instruments. One of these harmonics was observed during the October merger (GW241011), which is consistent with Einstein's theory.
Another way that rapidly spinning black holes help scientists is that they can be used to test the existence of hypothetical light elementary particles (called “ultralight bosons”) and how large they might be. If they exist, ultralight bosons could extract rotational energy from black holes, although there are still several unknown factors associated with these particles that have yet to be deciphered.
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