SPACE.com -- Highway of Stars Feeds Black Hole

Galaxy NGC 1097 and the structures that ESO researchers say feed a central black hole.

Black Holes: Most Galaxies May Not Have One

Monster Black Holes: How Galactic Collisions Fed Them

Black Holes Abundant, Varied in Early Universe, Detailed Study Shows

Scientist Claims First Direct Evidence of Black Hole


	Highway of Stars Feeds Black Hole By SPACE.com Staff posted: 11:07 am ET 14 August 2001

New research from a team of European scientists shows how a highway of stars might feed black holes that dominate the centers of many galaxies

New research from a team of European scientists shows how a highway of stars might feed black holes that dominate the centers of many galaxies.

Supermassive black holes, especially those in younger galaxies, consume surrounding matter voraciously. They don't suck their dinners in from great distances, consuming everything on the dinner table of the universe, as is often thought. Instead, black holes are simply opportunists. They will eat whatever is delivered to their plate, leaving no morsels. And no trace: Once consumed, not even light will escape a black hole.

More precisely, they attract anything that passes near enough to their gravitational grip.

Other supermassive black holes, like the one in our Milky Way Galaxy that is thought to be 2.6 million times as massive as our Sun, are strangely quiet.

So scientists wonder if black holes just dine less as they age, or if there is an on/off switch that toggles black holes from feast to famine throughout their lives. One leading idea is that galactic collisions were frequent in the early, crowded universe and so more material simply passed by the centers of growing galaxies.

But new observations made with the European Southern Observatory's Very Large Telescope reveal another mechanism that might be bringing food to the table.

By studying the motions of stars in three galaxies, researchers found "nuclear bars," highways of stellar movement that seem to act like giant spigots, allowing a flood of stars and other matter to flow from the outer parts of the galaxy into the gravitational embrace of the central black hole.

Swarm of bees

The scientists studied infrared light emitted by stars and gas in three relatively nearby galaxies, known as NGC 1097, NGC 1808 and NGC 5728.

The individual stars, as well as the swarm as a whole, move over time. Scientists describe the two separate but related movements as similar to the swarming of bees.

In each galaxy, a large bar of material that is thousands of light-years long efficiently sweeps the gas in the galaxy towards its core. When sufficient material has collected there, a smaller bar forms, nested within the larger bar.

Such a nuclear bar may then, at least in theory, take over and let the gas move further inwards towards the central black hole.

How fast and erratic the individual stars move within the swarm gives researchers a sense for what they call "dynamical temperature." Faster individual movement indicates a higher dynamical temperature in the system.

The observations yielded something unexpected. Near the centers of the galaxies, the scientists found a region where the dynamical temperature was cooler than computer models would have predicted. The likely reason, they say, is the presence of a newborn system of stars whose individual velocities have not yet had time to "heat up."

But like bees, these stars are probably restless.

"Soon it will heat up due to complex dynamical processes," said lead researcher Eric Emsellem of Centre de Recherche Astronomique de Lyon, France. "It is quite possible that some of these stars will eventually end up as food for the hungry black hole."

The study was discussed in a recent issue of the European journal Astronomy & Astrophysics.

Click here for more news and information about black holes.