Gravitational waves at galaxy edges

The edges of spiral galaxies may be one of the best places in the cosmos to look for gravitational waves, according to a new study.

This image from NASA’s Chandra X-ray Observatory shows the location of different elements in the Cassiopeia A supernova remnant including silicon (red), sulfur (yellow), calcium (green) and iron (purple). Each of these elements produces X-rays within narrow energy ranges, allowing maps of their location to be created. The blast wave from the explosion is seen as the blue outer ring. Astronomers study supernova remnants to better understand how stars produce and then disseminate many of the elements on Earth and in the cosmos at large.

A Chandra X-ray Observatory photograph of Cassiopeia A, the youngest supernova remnant in the Milky Way. Image Credit: NASA/CXC/SAO

Advertisement

The outskirts of spiral galaxies host a multitude of massive black holes and are consequently good places to search for gravitational waves, according to a new study.

Scientists from Rochester Institute of Technology made the discovery by looking at the visible precursors of black holes: supernovae with collapsing cores.

These ageing stars decay slowing, creating bright signatures in the electromagnetic spectrum.

Dark matter – the ‘missing’ Universe

They can then go on to become black holes, and one of the known sources of gravitational waves is colliding black holes.

Gravitational waves are warps in space-time caused by massive cosmic events, and were first predicted by Albert Einstein in his 1915 general theory of relativity.

The team behind the study used the Lick Observatory Supernova Search date to look at the supernovae rate in the edges of spiral galaxies.

They compared this with the rate of supernovae in known host galaxies and found comparable numbers.

Low levels of heavy elements in dwarf and satellite galaxies create good conditions for massive black holes to form.

Similar conditions in the outskirts of spiral galaxies create likely places for massive black holes to be found.

“If these core-collapse supernovae are the predecessors to the binary black holes detected by LIGO (Laser Interferometer Gravitational-wave Observatory), then what we’ve found is a reliable method of identifying the host galaxies of LIGO sources,” says Sukanya Chakrabarti, lead author and assistant professor in the RIT School of Physics and Astronomy.

Advertisement

“Because these black holes have an electromagnetic counterpart at an earlier stage in their life, we can pinpoint their location in the sky and watch for massive black holes.”