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A simulation of the undulating black hole formed by the fusion of two smaller black holes
Simulation of the eXtreme Spacetimes project
By Adrian Cho
Three years ago, astrophysicists electrified the world when they detected gravitational waves – infinitesimal undulations in the same space – appearing when two gigantic black holes intertwined and merged at about 1, 3 billion light-years away. The ability to detect gravitational waves has opened a new window to the cosmos and since then physicists have spotted a dozen additional fusions in black holes and a fusion of two dense neutron stars. But physicists still had to use such observations to test the properties of the black holes themselves – until now.
A team of theoretical astrophysicists used data from this first event – spotted by paired instruments from the Laser Interferometer Observatory (LIGO) of Hanford, Washington, and Livingston, Louisiana – for probe the final black hole fused. By deciphering his oscillations in the same way that a pianist could think of a chord, they confirmed – albeit with a modest precision – a prediction of Albert Einstein."The theory of gravity is called the hairless theorem.
"This"It's really beautiful, you really want to see that, "says Daniel Holz, astrophysicist and member of the LIGO team at the University of Chicago, Illinois, who was not involved in the analysis.
A black hole is the ultra-intense gravitational field left when a sufficiently massive star collapses under its own weight at an infinitely small point. At a certain distance from the point, nothing can escape, not even the light, so that the black hole forms a sphere of ink. It has a definite mass – and huge – and it can turn like a vertex – usually at a fraction of the speed of light.
Otherwise, a black hole must be peculiar, says Einstein"s theory of gravity, general relativity. According to the theory, information falling in a black hole is lost. This means that a black hole can not retain any trace of its formation, says Saul Teukolsky, theoretical astrophysicist at Cornell University. This proscription is known as the Hairless Theorem, because the famous American theorist John Archibald Wheeler jokingly explained that black holes were as indistinguishable as bald pasta.
Testing the theorem is not easy. Astronomers have spotted isolated black holes, but they can not see their surfaces covered with hot gas. (It's the temperature of this hot gas that reveals the presence of a black hole.) Gravitational wave observations open up a new way of testing the theorem, since the violent fusion of black holes produces a bigger black hole that waves like a jell shaken. -O, radiant gravitational waves. Using the waves to measure the frequencies of these ephemeral oscillations is a way to test the theorem of the absence of hair.
Key cues are hidden in so-called harmonics, usually lower frequencies, which extinguish faster than the longest life. But measuring them seemed an impossible goal, because the researchers assumed they"We must wait until the initial chaos of the ring has calmed down. At this point, the harmonics would be undetectable for LIGO and its partner, the Virgo gravitational wave detector in Italy. However, last summer, Matthew Giesler, a graduate student at the California Institute of Technology in Pasadena, used simulations to show that the merger as a whole could be understood as the mere sum of the fundamental signals and accents of the principal. fashion. "It was a surprise for everyone," says Teukolsky.
When Teukolsky, Giesler and his colleagues reanalyzed the signal of the first fusion of black holes, they found the first harmonic, as they reported yesterday to Letters of physical examination. Its frequency and duration are in agreement with the predictions of general relativity and thus reinforce the theory of lack of hair. More precisely, they indicate a mass and a rotation that correspond to those of the computer simulations of the whole event, based on general relativity, to within 10%. This concordance reinforces the notion, inscribed in general relativity, that these are the only parameters that characterize the final black hole. "This"That's what I would call a real test of the hairlessness theorem, "says Teukolsky.
Holz nevertheless urges caution, noting that the evidence of the connotation is not"not strong enough to demand a definitive observation. "He"It's very exciting, but to say that they"Have we shown that the non-hair theorem is correct? I would not like"To put it finally, the goal is to measure multiple modes and show that they relate to each other as predicted by general relativity – or not. Such "black hole spectroscopy" may have to wait for the laser interferometer space antenna, a gravitational detector much more sensitive than scientists hope to launch in the early 2030s, Holz said.
But Teukolsky says the analysis suggests that black hole spectroscopy could be on hand sooner than that. Given the improvements in the sensitivity of LIGO detectors, he says,"It is possible that even a very powerful fusion of black holes can reveal several shades. "We could even hope to see something that"s almost twice as the first merger. "
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