A Death Star

The universe can be a cruel place, but astronomers never knew it could be downright homicidal—at least for galaxies that have the bad luck to be in the crosshairs of a black hole.

For the first time, astronomers have observed a supermassive black hole blasting away at a nearby galaxy (which also contains a supermassive black hole at its center, though this one isn’t firing). “We’ve seen many jets produced by black holes, but this is the first time we’ve seen one punch into another galaxy,” said astronomer Dan Evans of the Harvard-Smithsonian Center for Astrophysics, who led the study. “This jet could be causing all sorts of problems for the smaller galaxy it is pummeling.”

Black holes are collapsed stars that are so dense, nothing that wanders within their gravitational sphere of influence, even light, can escape them. But black holes produce their own radiation, especially high-energy X-rays and gamma-rays, which shoot out from the star in the form of tightly collimated jets whose constituent particles travel at nearly the speed of light. When it hits another galaxy, as the jet of this “death star” is, the result is likely to be devastating for any planets lying in its line of fire, reacting kind of like an ant in a beam of sunlight focused by a lens, as this animation shows. As it happens, the target galaxy in this system lies 20,000 light years from the black hole—approximately the same distance as Earth lies from the center of the Milky Way. And yes, Virginia, our Milky Way does harbor a black hole, with 2 million times the mass of the Sun.

The two-galaxy system, named 3C321, lies 1.4 billion light years away from us in the constellation Serpens and was captured by the orbiting Chandra X-ray Observatory as well as the Hubble Space Telescope, the Spitzer Space Telescope, and the ground-based Very Large Array and MERLIN radio telescopes. The jet from the black hole began pounding the galaxy about 1 million years ago, the astronomers will report in The Astrophysical Journal.

For the galaxy being sprayed with lethal fire by the black hole’s jet, the consequences may not be all bad, however. The energy and radiation from the jet might trigger the formation of myriads of stars and planets, through the collapse of dust-and-gas clouds. In other words—and seasonally appropriate—out with the old, in with the new.
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