What a screaming black hole can tell us

tofayel ahmed
16 Oct, 2022
What a screaming black hole can tell us


In 2002, NASA's Chandra Telescope, an orbiting X-ray observatory, recorded the motion of hot gas in a cluster of galaxies 250 million light-years away.

No one has really noticed, except astronomers interested in X-ray emissions from galaxy clusters. Until NASA recently released sonification, which converts images into audible sounds.

It was... awful.

Great though. Conversion to sound involved taking the waves propagating in the cluster's hot gas and rescaling them into the human audible range. Perhaps the most amazing part of creating this scream was that..that was the whole process. That's because the waves propagating through the cluster's hot gas were literally sound waves. Sound waves are, after all, pressure waves that travel through media such as gases and liquids. We can hear someone speaking in our atmosphere because our vocal cords create pressure waves that we can hear. So what drives these pressure waves within the cluster's hot gas?

It's a black hole. Giant. The galaxy at the center of the cluster contains a supermassive black hole with millions of times the mass of the Sun. This black hole is not alone, but has a stream of gas swirling around it. This swirling gas motion raises its temperature to trillions of degrees, at which temperature the swirling gas creates enormous electric and magnetic fields. These fields direct some of the gas into a long, winding path that circumnavigates the boundaries of the black hole itself, before releasing it in the form of a long, thin jet. These jets are pushed tens of thousands of light-years away, far beyond the limits of their host galaxies.

Jet doesn't stop there. They penetrate the hot gas of the cluster of galaxies surrounding the central galaxy, heating it up and expanding it. That causes waves to spread across the galaxy cluster, causing screams seen in X-ray telescopes.

Through these waves, we can see that black holes can make themselves feel distant. The central black hole is huge, but insignificant compared to the massive mass of the entire cluster, it is by far the most powerful engine in the cluster.


This means that black holes directly influence the evolution of galaxies. Galaxies in galaxy clusters depend on hot gas around them. This gas continually rains down on the galaxy, giving it new material to build new generations of stars. As jets of black holes flit about, they heat and stir the gas, changing which galaxies are newly enriched and which starve.

Astronomers still don't fully understand the relationship between massive black holes and their surrounding clusters. All we know is that they evolved together, the cluster feeding new matter to the black hole, and the black hole responding by heating the cluster. But the details beyond this simple image remain vague.

I think i need to listen more.

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