An interesting theory from early 2015, before the first black
hole merger signal had been detected, drafts a compelling scenario, formulated by Madrid professor Juan Garcia - Bellido and postdoc Sebastien Clesse from RWTH Aachen University: maybe the universe is crowded with black holes of various sizes, remnants of large density fluctuations during the so - called inflation phase of the Big Bang.
Not exact matches
By timing the arrivals of the
signals at all three detectors, which differ by milliseconds, researchers were able to determine that the black
hole merger took place somewhere within a 60 - square - degree patch of sky in the Southern Hemisphere.
They'll help researchers hunt for gravitational wave
signals below 100 Hz, the frequency where traces of black
hole mergers can be found.
The detected
signal comes from the last 27 orbits of the black
holes before their
merger.
However, Marc Kamionkowski, a theoretical physicist at Johns Hopkins University in Baltimore, Maryland, says the
signal from the
merger of more - massive black
holes should be stronger and detectable from a greater distance.
This time, the subtle tremor of spacetime that
signaled the
merger also revealed a key feature of the black
holes: their spins, which were out of kilter.
We'll need to see more black
hole mergers before we can tell, though — the
signal doesn't give a clear answer either way.
LIGO's detection of this event, plus another, fainter
signal that also looks like a black
hole merger, means we can conclude that black
hole binaries this size can and do form in nature.
MAKING WAVES The first gravitational wave
signal detected by LIGO came from the
merger of two black
holes spiraling inward, as depicted in this numerical simulation.
The two
signals that have been produced so far came from the collision and
merger of two black
holes in some remote part of the universe.
Such events are the most energetic known; the power of the gravitational waves that they emit can briefly rival that of all the stars in the observable Universe combined.Black -
hole mergers are also among the cleanest gravitational - wave
signals to interpret.
The two US detectors, one in Washington and the other in Louisiana, saw the
signal of a black
hole merger just a few milliseconds apart, but with just two detectors the location of the source couldn't be pinned down.
Judy Racusin, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said during today's press conference that the Fermi team is «cautiously saying [the gamma - ray
signal] is potentially associated with the black
hole merger» detected by LIGO.
The LIGO press release mentions an estimation of black
hole merger rates — «about one every 10 years in a volume a trillion times the size of the Milky Way Galaxy» — based on how many
signals it's detected so far.
In 2016, the LIGO Scientific Collaboration reported the detection of two separate
signals of gravitational waves from the
merger of black
holes.
The very first detection of gravitational waves on 14 September 2015:
Signals received by the LIGO instruments at Hanford, Washington (left) and Livingston, Louisiana (right) and comparisons of these signals to the signals expected due to a black hole merger
Signals received by the LIGO instruments at Hanford, Washington (left) and Livingston, Louisiana (right) and comparisons of these
signals to the signals expected due to a black hole merger
signals to the
signals expected due to a black hole merger
signals expected due to a black
hole merger event.
Until that moment, gravitational wave detectors had only discerned the
merger of black
holes billions of light - years away, so to measure a weak
signal at a comparatively close distance came as a surprise.
The
signal also closely matched that predicted by supercomputer models of black -
hole mergers, said LIGO Scientific Collaboration spokeswoman Gabriela Gonzalez, a professor of physics and astronomy at Louisiana State University.
If the
signal LIGO had detected had been, say, neutron stars colliding and not black
holes, we would have had no complaints, but there's probably a very good chance you could see neutron star
mergers with other, conventional observational tools relying on light.
Indian scientists made direct contributions — ranging from designing algorithms used to analyse
signals registered by detectors to ascertain those from a gravitational wave to working out parameters like estimating energy and power radiated during
merger, orbital eccentricity and estimating the mass and spin of the final black
hole and so on.