The epic collision between two neutron stars in 2017 is indeed a scientific gift, continuing to inform scientists.
When the stars merged, gravitational waves spread throughout the universe; Now echoes of this event may support the long-standing hypothesis of black holes.
Astronomers studying the gravitational wave data believe they have found evidence of echoes – something that could only have happened in the presence of the 'quantum fluff' created by Hawking radiation.
“According to Einstein's general theory of relativity, nothing can escape from the gravity of a black hole when it passes the point of no return known as the event horizon,” said astronomer and physicist Nyaesh Afshordi of the University of Waterloo in Canada.
“This was the understanding of scientists for a long time, until Stephen Hawking used quantum mechanics to predict that quantum particles would slowly flow out of black holes, which we now call Hawking radiation.”
The most famous property of black holes is their extreme gravitational force. It is so intense that in general relativity, when something crosses a point called the event horizon, it is impossible to escape back. Even the fastest thing in the universe – electromagnetic radiation – cannot escape.
But quantum mechanics can explain the details of the universe in ways that general relativity cannot; according to Hawking's 1974 idea, a black hole emits something when you add quantum mechanics. This is a theoretical type of electromagnetic radiation, called Hawking radiation, respectively.
This theoretical radiation is similar to the spectrum of light emitted by heated objects obeying the rules of black body radiation, only in this case the black hole's super-heavy mass causes ultra-low energy waves to be emitted.
The existence of this radiation would mean that black holes are slowly evaporating, resolving the black hole information paradox; but just like gravitational waves, the radiation is still too weak to be detected.
Black hole models definitely show that Hawking radiation is real. But gravitational waves can change that. Because if Hawking radiation is real, there must be quantum 'fluff' around the black hole event horizon; and this fluff should cause gravitational waves.
“Scientists were unable to experimentally determine whether any matter was escaping black holes until the most recent detection of gravitational waves,” Afshordi said.
'If the quantum fluff responsible for Hawking radiation exists around black holes, gravitational waves can bounce off it, creating smaller gravitational wave signals after the main gravitational collision event, similar to repeating echoes.'
This is what Afshordi and his colleague, cosmologist Jahed Abedi of the Institute for Gravitational Physics. Max Planck in Germany, they were able to detect from gravity data. Their results are consistent with the simulated echo predicted by models of fuzzy black holes emitting Hawking radiation.
In fact, it is quite possible that our instruments are still not sensitive enough to detect Hawking radiation. And Afshordi admits that the signal the team found could actually just be noise in the data.
To figure this out, you need to look for similar signals in other gravitational wave datasets.
“Now that scientists know what we are looking for, we can look for more examples and get much more reliable confirmation of these signals,” Afshordi said.
“Such confirmation would be the first direct study of the quantum structure of spacetime.”
The study was published in the Journal of Cosmology and Astroparticle Physics.
Sources: Photo: physics.ucsb.edu/ Mondolithic Studios via Scientific American
