Astronomers have debated whether things go dark or whether there is a bright flash of light as a result of a collision between two black holes for some time now with most suggesting darkness ensues. However, an announcement from NASA suggests that its Fermi Gamma-ray Space Telescope may well have captured a burst of light following the collision of two black holes with masses about 30 times that of the sun.
NASA and Fermi may have seen a faint burst of light
In September of last year, the Fermi Gamma-ray Space Telescope observed a burst of light from the same region of sky that saw the collision of two black holes. The fact that the burst occurred less than a second after the known collision of two black holes in the same region of sky. While this is not conclusive evidence that the collision caused the burst of gamma-ray light, it certainly looks like that is indeed the case.
“This is a tantalizing discovery with a low chance of being a false alarm, but before we can start rewriting the textbooks, we’ll need to see more bursts associated with gravitational waves from black hole mergers,” study lead author Valerie Connaughton, of the National Space, Science and Technology Center in Huntsville, Alabama.
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NASA has enjoyed a run of new information and discoveries as a result of black holes this year with a large international team of scientists with the Laser Interferometer Gravitational-Wave Observatory (LIGO) directly detected gravitational waves for the first time. This discovery confirmed Einstein’s theory exactly a century after he put forth the idea (again, Einstein changed his mind a few times).
“With just one joint event, gamma rays and gravitational waves together will tell us exactly what causes a short GRB,” said Lindy Blackburn, a member of the LIGO Scientific Collaboration. “There is an incredible synergy between the two observations, with gamma rays revealing details about the source’s energetics and local environment and gravitational waves providing a unique probe of the dynamics leading up to the event.”
Black holes don’t radiate light but often the materials floating around space on their way into black holes does, and in galaxies that have monster black holes in the center, often the matter around them radiates to a level that makes them some of the brightest objects in the observable universe.
But that doesn’t mean that scientists expected light to be emitted from a collision.
“We weren’t actually expecting to see anything,” said Fermi team member Adam Goldstein, a gamma-ray astrophysicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama. His remarks were made recently at the April meeting of the American Physical Society in Salt Lake City, Utah.
Burst of light came 0.4 seconds after the black hole merger
Thanks to LIGO, that observation is beyond debate, but there is still a barely open window of contention.
Judy Racusin, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland was guardedly optimistic at the press conference when she said that the Fermi team is “cautiously saying [the gamma-ray signal] is potentially associated with the black hole merger.”
This unwillingness to be more sure of the event is due to the fact that the signal was weak and essentially caught in the “corner of the eye” of the Fermi satellite. Whether it was simply a weak burst in the first place or because it was captured in the periphery of Fermi’s sensors is anyone’s guess.
Goldstein puts the chance of a coincidental event where the black holes didn’t cause the burst of gamma-ray light at “one in 500 [chance].”
Goldstein and Racusin also pointed out that a recent paper released by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) team didn’t detect the burst. But they quickly pointed out that INTEGRAL was not necessarily designed to observe these types of bursts.
Goldstein said, it is “actually not very clear if [INTEGRAL] would have seen it or not.”
The two have yet to have their findings published, but have submitted their paper to the Astrophysical Journal where it is presently under peer review as per normal.
“It is important to note we would not have reported this event just by itself,” Goldstein said. “The reason we are publishing is because our data is public, obviously, and the most appropriate people to do this analysis [are in] the instrument team. And so there was particular pressure on us putting out a paper for this.”
“There [are] a lot of interesting ideas out there, and it was amazing how quickly those ideas were thrown together,” Racusin said. “The main idea is that you need to get some sort of matter outside those black holes, some sort of gas to accelerate. … I think it’s great how much theoretical speculation this has caused, and we’ll see, maybe, in the future [if any of them pan out] with better observations.”
“The question that everyone has is, ‘Are our observations and LIGO’s observations coming from the same object?'” Goldstein said. “And we cannot say definitely right now.”
Black hole observations are enjoying a banner year and more study and observations are certainly on their way.