The gravitational wave background (also GWB
and stochastic background) is a random gravitational
wave signal produced by a large number of
weak, independent, and unresolved sources.It
is a possible target of gravitational wave
detection experiments.
The detection of such a background would have
a profound impact on early-universe cosmology
and on high-energy physics.
The emission of gravitational waves from astrophysical
sources can create a stochastic background
of gravitational waves.
For instance, a sufficiently massive star
at the final stage of its evolution will collapse
to form either a black hole or a neutron star
– in the rapid collapse during the final
moments of an explosive supernova event, which
can lead to such formations, gravitational
waves may theoretically be liberated.
Also, in rapidly rotating neutron stars there
is a whole class of instabilities driven by
the emission of gravitational waves.
Efforts to detect the gravitational wave background
are ongoing.
On 11 February 2016, the LIGO and Virgo collaborations
announced the first direct detection and observation
of gravitational waves, which took place in
September 2015.
In this case, two black holes had collided
to produce detectable gravitational waves.
This is the first step to discovery of the
GWB.
== Detection of gravitational waves ==
On 11 February 2016, the LIGO/EGO collaboration
announced the detection of gravitational waves,
from a signal detected at 10:51 UTC on 14
September 2015 of two black holes with masses
of 29 and 36 solar masses merging around 1.3
billion light years away.
The mass of the new black hole obtained from
merging the two was 62 solar masses.
Energy equivalent to 3 solar masses was emitted
as gravitational waves.
The signal was seen by both LIGO detectors,
in Livingston and Hanford, with a time difference
of 7 milliseconds due to the angle between
the two detectors and the source.
The signal came from the Southern Celestial
Hemisphere, in the rough direction of (but
much further away than) the Magellanic Clouds.
The confidence level of the discovery was
99.99994%.
== Future observations ==
Future gravitational waves observatories might
see primordial gravitational waves, relics
of the early universe, up to less than a second
after the Big Bang.
== See also ==
Cosmic microwave background
Cosmic neutrino background
