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Space and Physics

How Black Holes Destroy Star Formation

author

Stephen Luntz

Freelance Writer

clockJul 8 2014, 03:57 UTC
1442 How Black Holes Destroy Star Formation
NASA Artist's conception of a supermassive black hole emitting jets of radiation

Having a really large black hole at the center of your galaxy is bad for star formation, but it is only now that astronomers have confirmed the reason why.

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While it is easy to imagine supermassive black holes eating so voraciously they grab all the material in a galaxy before, or after, it forms into stars, that isn't the problem. Getting too close to a black hole is fatal, but the area they feed from is a tiny portion of the galaxy. On the other hand, it has been known for a while certain galaxies have had their molecular hydrogen driven out, with the black holes at their core the most likely culprit. 

Since stars need cold hydrogen to form, the galaxies where this occurs are largely static, dull places with little star formation going on. While models have been created to explain how the gas is driven out, we've lacked observational support.

In Naturethe University of Sheffield's Professor Clive Tadhunter reveals evidence that the outflow of charged particles from the core of the Seyfert galaxy IC 5063 is hitting the warm molecular gas in the galaxy's western lobe. The gas is being accelerated to speeds of 2 million km/h relative to the galactic disk.

Seyfert galaxies have very bright nuclei that resemble quasars, but the surrounding galaxy is visible. The black holes at their core are large even by the standards of supermassive black holes. IC 5063 is one of the closer, and therefore more studied, Seyfert galaxies.

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The theory that jets from black holes are driving material from the outskirts of the galaxy is not new, but direct evidence has been lacking. The fact that the giant hole at the center of Seyfert IC 5063 is capable of having such effects does not prove that this is the driving force wherever galaxies have had their gas expelled. Nevertheless, the paper notes, “These results demonstrate the general feasibility of accelerating molecular outflows in fast shocks driven by active nuclei.”

"Much of the gas in the outflows is in the form of molecular hydrogen, which is fragile in the sense that it is destroyed at relatively low energies,” says Tadhunter. “It is extraordinary that the molecular gas can survive being accelerated by jets of electrons moving at close to the speed of light."

The Milky Way is expected to collide with the Andromeda Galaxy in 5 billion years. The amalgamation of the two black holes along with the disruption in gas from the collision could induce an very active galactic nucleus, potentially leading to jets powerful enough to expel the surviving hydrogen gas from both galaxies, and resulting in diminished star formation.


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