Black holes' effects on nearby stars eyed

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GREENBELT, Md., Feb. 28 (UPI) -- U.S. astronomers say they have identified a curious correlation between the mass of a galaxy's central black hole and the velocity of stars around it.

A team led by Francesco Tombesi at NASA's Goddard Space Flight Center in Greenbelt, Md., said a type of outflow driven by the black hole appears to be both powerful enough and common enough to explain this link between a black hole's mass and the movement of stars in a vast, roughly spherical structure known as a bulge surrounding it and beyond the boundary where matter is consumed by it.

Most large galaxies contain a central black hole, but galaxies hosting more massive black holes also possess those bulges that contain, on average, faster-moving stars.

This suggested some sort of feedback mechanism between a galaxy's black hole and its star-formation processes, astronomers said, but they could not explain how a monster black hole's activity, while strongly consuming surrounding matter in a region several times larger than our solar system, could influence a galaxy's bulge, which encompasses regions roughly a million times larger.

"This was a real conundrum. Everything was pointing to super-massive black holes as somehow driving this connection, but only now are we beginning to understand how they do it," Tombesi said.

The researchers examined 42 nearby active galaxies using the European Space Agency's XMM-Newton satellite and found so-called "ultra-fast outflows" of gas and energetic particles, flows the astronomers have dubbed UFOs.

"Although slower than particle jets, UFOs possess much faster speeds than other types of galactic outflows, which makes them much more powerful," Tombesi said.

"They have the potential to play a major role in transmitting feedback effects from a black hole into the galaxy at large."