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Galactic Bubbles

July 24, 2013

The supermassive black hole at the center of the Milky Way galaxy is surrounded by millions of stars and by giant clouds of gas — material that should serve up a feast for the black hole. Yet for the most part, the black hole appears to be on a starvation diet. It occasionally ingests a few wisps of gas or a clump the size of an asteroid, but otherwise it’s quiet.

The black hole may be deprived of the rich buffet around it by the actions of the stars themselves. They may direct much of the gas away from the black hole and into intergalactic space.

The black hole’s gravity pulls in vast clouds of gas. But very little of the gas pours into the black hole itself. Instead, the clouds appear to slam together and break into smaller clumps, which collapse to form stars.

Radiation from the newborn stars, as well as the explosions of massive stars, blows away much of the remaining gas. The radiation also gives an electric charge to much of the gas, which is then funneled away by the vast magnetic field generated by the stars. This material is hemmed in by the galaxy’s disk, so it rises away from the disk.

Using a radio telescope in Australia, astronomers recently mapped this outflow of material. It creates vast bubbles that extend far above and below the disk — about 25,000 light-years in either direction. That acts as a release valve for the activity in the galaxy’s core — and keeps the black hole on a diet.

We’ll talk about another black hole in the Milky Way tomorrow.


Script by Damond Benningfield, Copyright 2013

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