Chapter 10 in Begelman & Rees discusses the proof of General and Special
Theories of Relativity. We have examined the observational and experimental
evidence of general and special relativity in Unit 1, so there is no need to
repeat all that information. However, there are some very exciting news that
can be added to this chapter – gravitational waves have been discovered in
2016, after a 50 year long search!
When binary BHs (or neutron stars) merge to form a larger black hole, they
emit gravitational waves. The dominant frequency of the gravitational waves is
inversely proportional to the mass. This means that lower the mass, higher the
frequency of the gravitational waves.
You will find all the information that you are expected to know in this
article and the video below:
Here is another link where Brian Greene explains the discovery of
gravitational waves:
Information to watch for:
What are gravitational waves?
If something “jostles” spacetime, gravitational waves can be produced (term
that Brian Green used). This can occur when two neutron stars or black holes
orbit one another and when they merge. Gravitational waves that are produced
in such an event will squeeze and stretch spacetime as they travel through
the universe.
What is the name of the observatory that discovered the first gravitational
waves?
LIGO – Laser Interferometer Gravitational-Wave Observatory (LIGO). It
consists of one observatory in Washington State and one in Louisiana.
How much did the Earth expand and contract as the gravitational waves that
we detected passed by us?
By about the width of an atomic nucleus; space stretched by one part in
1021
and we were able to detect this!
What collided to produce these gravitational waves?
Two black holes with masses 29 and 36 Msun
.
What is the resulting mass of the merged object?
The mass of the merged object is 62 Msun
. This is less than the
sum of the two objects by 3 Msun
.
Where did the missing 3 Msun
go?
The missing mass was converted into energy and released in the form of gravitational waves.