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Thursday, 16 June 2016
Second gravitational wave detected from ancient black hole collision
Following February’s historic announcement, LIGO has again spotted ripples in the fabric of spacetime, from the collision of a second set of black holes
This image depicts two black holes just moments before they collided and
merged with each other, releasing energy in the form of gravitational
waves.
Illustration: Numerical Simulations: S. Ossokine/A. Buonanno/Max Planck
Institute/SXS project. Visualization: T. Dietrich/R. Haas/Max Planck
Institute
Physicists have detected ripples in the fabric of spacetime that were
set in motion by the collision of two black holes far across the
universe more than a billion years ago.
The event marks only the second time that scientists have spotted
gravitational waves, the tenuous stretching and squeezing of spacetime
predicted by Einstein more a century ago.
The faint signal received by the twin instruments of the Laser
Interferometer Gravitational Wave Observatory (LIGO) in the US revealed
two black holes circling one another 27 times before finally smashing
together at half the speed of light.
The cataclysmic event saw the black holes, one eight times more
massive than the sun, the other 14 times more massive, merge into one
about 21 times heavier than the sun. In the process, energy equivalent
to the mass of the sun radiated into space as gravitational waves.
An animated gravitational waves explainer from the University of Birmingham.
“This is confirmation that there’s a real population of black holes
out there waiting to be detected in the future,” said John Veitch, an
astrophysicist on the LIGO team at the University of Birmingham.
In February, researchers on the instrument made the historic announcement that they had picked up gravitational waves for the first time.
The twin pieces of equipment, one in Hanford, Washington state, the
other in Livingston, Louisiana, recorded the ripples in September 2015
as minuscule distortions in laser beams sent down 4km-long tubes. The
detectors are so sensitive they can pick up changes in length one
thousandth the diameter of a proton.
Writing in the journal Physical Review Letters
on Wednesday, the LIGO team describes how a second rush of
gravitational waves showed up in their instrument a few months after the
first, at 3.38am UK time on Boxing Day morning 2015. An automatic
search detected the signals and emailed the LIGO scientists within
minutes to alert them.
Why discovering gravitational waves changes everything“Everyone was still flabbergasted by the first discovery. We were
writing up papers and preparing for them to be released when we had this
second one. We thought ‘phew!’, it’s definitely real!” said Veitch.
Another apparent signal received in October has not yet been verified.
The
latest signals arrived at the Livingston detector 1.1milliseconds
before they hit the Hanford detector, allowing scientists on the team to
roughly work out the position of the collision in the sky. At least one
of the black holes was spinning.
Closed for upgrade work in January this year, LIGO is expected to
switch back on in the autumn with improvements that will nearly double
the amount of the universe it can observe.
According to Will Farr, another LIGO researcher at Birmingham, pairs
of black holes slam into one another on average once every 15 minutes in
the observable universe.
“For me, the first detection broke everything wide open, but there
was always the possibility that we had got phenomenally lucky. With the
second signal it’s clear we are starting to see a population. We are
going to see many of more of these in the next run,” he said.
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