Stephen Hawking’s black hole theorem has now been finally proven. First proposed in 1971, it said that the total area of the black hole event horizon can never go down or at least as big as the total area of both precursor black holes.
But scientists did not find any way to observe it against nature, until now. This has happened with LIGO’s first detection of gravitational waves.
Physicists at MIT and elsewhere now confirm Hawking’s black hole theorem for the first time. They did so with the help of observations of gravitational waves.
Their results appear in Physical Review Letters. The team of researchers, led by MIT fellow Maximiliano Isi, reconsidered the first signal, to see if they could get proof for the area theorem.
The scientists took a closer look at GW150914, the first gravitational wave signal detected by the Laser Interferometer Gravitational-wave Observatory (LIGO). Since LIGO, technology has advanced tremendously over the last few years. They began scanning the heavens for signs of gravitational waves way back in 2015.
GW150914 is the first gravitational wave signal spotted by LIGO. It came out from the collision of two black holes that generated a new baby black hole with ample amounts of energy that rippled across space-time as gravitational waves.
Scientists reanalyzed this signal from GW150914 before and after the cosmic collision. They finally came to the conclusion that the total event horizon area did not decrease after the merger.
Maximiliano Isi led the study. He is a NASA Einstein Postdoctoral Fellow in MIT’s Kavli Institute for Astrophysics and Space Research. Along with his colleague, they together developed a technique to extract the reverberations immediately following GW150914’s peak. This is the moment when the two-parent black holes collided to create a new black hole.
Using these new techniques, they were able to pick out specific frequencies, or the otherwise noisy aftermath of the collision. They later used it to calculate the final object’s mass and spin before they merged.
Stephen Hawking’s black hole theorem
It reinforces a series of fundamental insights regarding the mechanisms of a black hole. If Hawking’s black hole theorem holds true, then the horizon area of the new black hole should not be smaller than the total horizon area of its parent black holes.
The researchers team measured GW150914 before, during, and after the peak since a black hole’s mass and spin are directly related to the event horizon area.
It was found that before the merger, the two black holes had a total horizon area— an estimate roughly equal to about 235,000 square kilometres. One can say it was roughly nine times the area of Massachusetts.
The physicists reanalyzed the signal from GW150914 before and after the cosmic collision. They found that the total event horizon area actually did not decrease after the merger.
This team’s findings mark the first direct observational confirmation of Stephen Hawking’s black hole theorem.
So far it had been proven mathematically but was never examined in nature until now. The team now plans to further test other persistent theories of black hole mechanics.
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