Learning about Gravity Waves

Jess McIver‘s talk on Cosmic collisions observed with Advanced LIGO at last Thursday’s public monthly meeting was an eye-opener for me. I knew little about gravity waves and her talk was filled with fascinating facts. The following are some of the highlights for me.

Gravity waves are produced by asymmetric events like two black holes in close orbit around each other or a fast spinning neutron star with bumps on its surface.

The LIGO detectors are incredibly sensitive interferometers that can sense changes in length up to 10,000 times smaller than the width of a proton.

Schematic layout of a LIGO interferometer

There are 4 operational gravity wave detectors around the world: LIGO in Livingston Louisiana, another LIGO close by in Hanford Washington, GEO600 in Germany, and VIRGO in Italy. Another detector in Japan is expected to become operational within the next few months.

Gravity wave detectors are more like microphones than telescopes as they can pickup events from any direction in the sky. The current detection techniques assume that detectable events are rare so they don’t have to take into account two events at the same time in different parts of the sky.

It can be better to listen to gravity wave signals rather than using our eyes as is done with light-based astronomy. You can even download ringtones made from gravity wave sounds by The Albert Einstein Institute Hanover.

The strength of a gravity wave signals drops off proportionally with distance. This is quite different from how light works where the strength of the signal drops with the distance squared.  So there is hope in detecting ultra-distant gravitational waves. Improving the sensitivity of a detector by 100 times means we can see 100 times farther, rather than the 10 times farther that we could see with a light detector that was 100 times more sensitive. Very Cool! I had to look up more information on this one and found more details in this Forbes article.

Signals are found using matched filtering, in which data from detectors are cross-correlated with a theoretical waveforms constructed from Einstein’s general relativity equations applied to events like black-hole merges.

The gravitational-wave event GW150914 observed by LIGO

Gravity waves may be a good tool for exploring dark matter since dark matter is affected by gravity, but it may hard to detect signal from dark matter unless it clumps into compact objects like black holes or neutron stars.

The Gravitational Wave Open Science Center provides open data from gravitational-wave observatories, along with access to tutorials and software tools.

Citizen scientists all over the world are contributing to LIGO research with Gravity Spy.