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Odd Relationship

December 17, 2015

There appears to be an odd relationship between a supermassive black hole and its surrounding galaxy. The black hole can help the galaxy give birth to new stars — but only up to a point. After that, the black hole may slow the rate of starbirth — or even stop it.

The first stage happens when the galaxy is taking shape. The black hole’s gravity helps pull enormous amounts of gas and dust into the galaxy’s center. Some of the material falls into the black hole, increasing its mass, which in turn increases its gravitational pull.

But a good bit of the infalling material forms a disk around the black hole. As this material spirals around the black hole, it’s heated to millions or billions of degrees. The super-hot disk radiates a lot of energy. It also creates powerful “winds” of particles that flow outward at a good fraction of the speed of light. This outflow sweeps away much of the gas in the galaxy’s central regions, shutting down the process of starbirth.

In fact, astronomers have recently seen that happening in two galaxies. In one, the winds carry an amount of energy that’s equal to a trillion Suns. In the other, the initial wind speed is a quarter of light-speed. The wind pushes away enough gas every year to make hundreds of stars as heavy as the Sun.

That supports the idea that black holes help galaxies give birth to stars early, then stop the process later on.

Script by Damond Benningfield, Copyright 2015

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