Vast black hole at heart of galaxy revealed by new telescopes

Astronomers have found firm evidence that there is a "supermassive" black hole lurking at the heart of the Milky Way.

Astronomers have found firm evidence that there is a "supermassive" black hole lurking at the heart of the Milky Way.

The black hole, called Sagittarius A*, or SgrA*, lies about 26,000 light years from Earth and has been identified with the help of new, powerful telescopes.

Based on the data from radio images, the black hole is 3.7 million times more massive than the Sun.

There is no danger that we, or the rest of the galaxy, are about to be sucked into it. Though SgrA* is vast, gravity falls off so quickly with distance that its pull on the average human is the same as the weight of just a few thousand bacteria.

The data, reported today in the science journal Nature, is derived from radio images of a star called S2, which orbits the galactic core once every 15 years, compared with the Earth and Sun, which take 230 million years to complete a galactic orbit together.

Astronomers say that new "adaptive optics" telescopes are letting them gaze 20 times more accurately at the distant, dusty centre of our galaxy.

"The power of adaptive optics may ... enable us to determine how material is funnelled into a supermassive black hole, or, in the case of the black hole in the Milky Way, why so little matter is consumed by it," said Karl Gebhardt, of the department of astronomy at the University of Texas, in Nature.

SgrA* is almost certainly not the closest black hole to the Earth, but it is by far the biggest in our galaxy. The discovery is in line with the fact that many of our neighbouring galaxies have black holes at their centres.

That, in turn, appears to be inevitable because the close packing of the stars at the centre of the galaxy tends to make them burn out and collapse together, first into "neutron" stars and then into black holes, which are objects so dense that even light cannot escape their gravitational pull.

Previously, scientists had not been able to rule out the possibility that Sgr A* was a collection of super-dense neutron stars, which are the result of large stars that have collapsed into dense, normal matter consisting only of neutrons – protons and electrons mashed together.

The new evidence was made possible by an instrument known as Naco, installed at the European Southern Observatory's 8.2-metre Yepun telescope in Chile last year. Naco allows the telescope's mirror to change shape to compensate for atmospheric distortion of starlight.

One of the astronomers, Thomas Ott, said: "When we included the latest Naco data in our analysis in May 2002, we could not believe our eyes. The star S2, which is the one currently closest to SgrA, had just performed a rapid swing-by near the radio source.

"We suddenly realised that we were actually witnessing the motion of a star in orbit around the central black hole, taking it incredibly close to that mysterious object."

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