Black hole takes 'light snack'

By BBC News Online science editor Dr David Whitehouse

An animation of the fast-moving stars at the centre of our galaxy shows up clearly the location where a massive black hole is thought to reside.

The alternating pictures on this page were produced by Professor Andrea Ghez, of the University of California, who made two sets of observations of the galactic core two months apart.

The bright points that oscillate indicate the changed positions of high-velocity stars circling within two light-weeks of the very heart of the Milky Way.

But it is the faint object which does not move that catches the eye. Professor Ghez believes this is recently emitted light coming from superhot gas falling into a supermassive black hole.

Ghez uses the advanced optics of the Keck on Hawaii

The centre of our galaxy is a strange and dramatic place. Gigantic rotating gas rings can be seen there, as well as stars travelling in excess of 1,000 kilometres per second around a very massive central object.

The presence of a black hole there has been suspected for some time because of the nature of the faint radiation coming from the location and the motion of the fast-moving stars.

Sustained observation has allowed astronomers to pinpoint with unprecedented accuracy the hole's location, known as Sagittarius A* (Sgr A*). It is about 26,000 light-years from Earth.

Professor Ghez: "This is still a very quiet black hole"

And Professor Andrea Ghez, herself, has provided the best estimate yet of the mass of the object - about 2.6 million times that of the Sun.

But her images, obtained using the 10-metre Keck telescope on Hawaii, also give an eloquent demonstration of what is happening in this extraordinary region of space.

They indicate the black hole at Sgr A* is going through what appears to be a new "feeding" phase, pulling in more gas.

"If we do think the black hole is going through a slightly larger feeding phase at the moment, it is tiny compared to what other galaxies are doing," she told the BBC Science programme Horizon. "In fact, this is still a very quiet black hole in spite of the fact that there might be new emission from it."