Hannah Devlin - Third gravitational wave detection gives hints on dark matter and black holes
Ripples in the
fabric of spacetime triggered by the cataclysmic merger of two black holes more
than 3bn years ago have been detected by physicists. The observations
mark the third occasion that scientists have spotted gravitational waves – the
compression and stretching of space itself that was first predicted by
Einstein. The latest
detection, by the Laser Interferometer Gravitational-Wave Observatory, or Ligo,
has produced intriguing hints on the nature of black holes and, potentially,
dark matter. The faint hum,
picked up by Ligo’s twin instruments on 4 January 2017, could be traced back to
the violent collision more than 3bn years ago of two black holes with masses of
more than 31 and 19 times the mass of the sun, respectively. The two combined
to form a single black hole with a mass slightly less than 49 times that of the
sun and the leftover energy spilled out as deformations that spread outwards
across spacetime like ripples across a pond.
Ligo scientists
made the first historic observation of gravitational
waves in September 2015, using a pair of 4km-long perpendicular pipes,
one in Hanford, Washington state, the other in Livingston, Louisiana. A second
detection occurred three months later. With the third detection, scientists are
beginning to close in on their goal of using gravitational waves as a way of
observing ancient events that would be invisible to optical or radio
telescopes. Christopher Berry,
of the University of Birmingham and a researcher on the project, said: “We’re
not just in this business to detect gravitational waves. We’re really
interested in doing a new type of astronomy.” The detectors are
sensitive enough to pick up distortions as tiny as one thousandth of the
diameter of a proton in laser beams sent down Ligo’s tubes, and can even
crudely recreate the dynamics of the collisions.
The astronomers
believe their latest finding “provides clues about the directions in which the
black holes are spinning”. As pairs of black holes spiral inwards, heading
towards a collision, they also spin on their own axes. The latest observations
hint that these spins are misaligned. This could indicate that the pair of
black holes formed not from a binary star system, but from two independent
black holes that randomly came together in a dense primordial star cluster.
Black holes and
dark matter: