Constraining compact binary formation with gravitational wave observations

Lead Research Organisation: University of Glasgow
Department Name: School of Physics and Astronomy

Abstract

Black Holes and Neutron Stars are some of the strangest objects in the universe, containing more
mass than the Sun packed into a sphere only a few kilometres across. They are formed from the
remains of high mass stars, which burn their fuel quickly and end their lives in supernova
explosions which can outshine a whole galaxy. There are different types of supernova for different
types of stars: their masses, spins and composition all play a role in determining their eventual
fate, although the details are not fully understood yet.

What is left over after the supernova is an object so dense that its gravity
warps the space-time around it: a neutron star is thought to contain the densest possible
matter, denser than an atomic nucleus, which is the only material strong enough to support the star
against its own gravity. Even more extreme are black holes, which form when a star has even more mass,
and neutron star matter cannot support its weight. When this happens the star collapses into a black
hole, becoming so dense that not even light can escape the gravitational pull. At this point
an event horizon forms, hiding its contents from the rest of the universe. Since black holes do
not emit light, they are impossible for astronomers to find unless they are actively accreting material
from a companion star. But there is another way to detect them using a completely new astronomical
tool: gravitational waves.
According to Einstein's theory of General Relativity, when black holes and neutron stars are found
together in a binary system, the movement of so much matter in such a concentrated space creates
vibrations in space-time itself. These travel out across the universe at the speed of light, changing
the dimensions of everything they pass through, but invisible to the eye. Back on Earth, physicists
have long been searching for gravitational waves by making extremely precise distance measurements
using gravitational wave detectors.
So far no signs have been found, but soon the Advanced LIGO and Advanced Virgo detectors will become
operational with a sensitivity that ought to allow us to detect the gravitational waves from binary neutron
stars within hundreds of millions of light years from Earth, and out to even greater distances for the heavier
black hole binaries. The detectors are so sensitive that the change they can measure is equivalent of
varying the distance between the Sun and Saturn by a hair's breadth.
Encoded in the gravitational waves is information about the sources that emitted them, which will let us learn
about the masses and spins of neutron stars and black holes. By measuring many signals, we will be
able to piece together the physics that governs the evolution of massive stars, and how they end their
lives.

Planned Impact

The theory of General Relativity, and its non-intuitive and thought-provoking
predictions about the nature of space and time, has been a great source of
inspiration for many people's interest in physics and science in general.
Alongside quantum mechanics it is probably the most captivating aspect of
modern physics to the layman, as evidenced by the public knowledge of
concepts like black holes and E=mc^2. Although the general level of public understanding
of these is not highly developed, it can be the seed for encouraging an interest
in science in general and physics in particular.

The opening of the field of gravitational wave astronomy, toward which this
proposed research will make a significant contribution, is certain to further
increase the public interest in physics and astronomy. The direct detection
of gravitational waves in itself can be expected to attract a great deal
of attention for the field, as was the case with the recent announcement of possible
observation of primordial gravitational waves by the BICEP2 collaboration.
This will provide us with a superb opportunity to communicate to the public
the exciting science that will be possible with gravitational wave observatories in the future,
contributing to the public awareness and understanding of science. Encouraging this enthusiasm,
particularly in young people, will contribute to the choice of a STEM-related career for
many, providing the people most needed for a modern knowledge-based economy.
The University of Birmingham's School of Physics and Astronomy has an outstanding record
of public outreach activities which involve all members of academic staff and research
assistants, and the local community.

The training of young researchers within academia is also an important source of talented,
skilled workers for the commercial and government sectors. The University of Birmingham
encourages the development of skills such as quantitative research, communication and project
management in its staff and students, many of whom will ultimately leave academia.

Publications

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Related Projects

Project Reference Relationship Related To Start End Award Value
ST/M004090/1 13/09/2015 29/04/2017 £120,410
ST/M004090/2 Transfer ST/M004090/1 30/04/2017 12/09/2019 £88,153