AstroTalk Episode April 20, 2017

The Arrythmic Beating of a Black Hole Heart

2:59pm - 3:27pm

A large elliptical galaxy, NGC 4696, located 145 light years from Earth, lurks at the heart of the Centaurus galaxy cluster. And hiding deep in the heart of NGC 4696, lurks a massive black hole. Even though black holes are known to devour matter around it, this particular black hole is pumping energy into the galaxy around it. The bursts of energy are thought to occur every 5 - 10 million years. The bursts create cavities in the hot gas that inhabits the space in between neighboring galaxies. Sonic booms, which have been measured to travel tens of thousands of light years, are also created when the black hole pumps out its energy. The process is being imaged by the Chandra Observatory in x-rays, Hubble in visible light, and in radio from the Very Large Array Telescope. When the images are combined, astronomers get a better picture of what is going on. Chandra was used to highlight 9 special cavities in the hot gas. Astronomers have also measured the "pitch" of the resonance in the cavities, and have marked it as having a note near middle C. The hot gas that fills the cluster of galaxies has allowed the sound to travel. The black hole bursts seem to be full of elements that are generated in previous supernova explosions in NGC 4696. Oddly, the energy coming from the black hole has prevented the gas around it from cooling. New stars form from cool gas, so the higher temperature of the gas has prevented large numbers of stars from forming in the vicinity of the black hole.

A different type of processing of the X-ray data reveals a sequence of curved and approximately equally spaced features in the hot gas. These may be caused by sound waves generated by the black hole’s repeated bursts. In a galaxy cluster, the hot gas that fills the cluster enables sound waves – albeit at frequencies far too low for the human hear to detect – to propagate.