What’s eating the stars out of our galaxy’s heart?

By Marcus Chown 

The centre of the Milky Way is darker than you’d expect – and not just because it’s home to a supermassive black hole

There's a hole at the centre of our galaxy (Image: <a href="Ciara Phelan">http://www.iamciara.co.uk/</a>There’s a hole at the centre of our galaxy (Image: http://www.iamciara.co.uk/

A LITTLE over 25,000 light years away lies the most mysterious place in the nearby universe. Jam-packed with colliding stars and cloaked in dust, it is the centre of our galaxy. At its very heart, we suspect, lurks a monstrous black hole more than 4 million times as massive as the sun. Known as Sagittarius A*, it is thought to rip stars apart, orchestrating stellar mayhem as it warps the very fabric of space and time.

Similar supermassive black holes are thought to exist at the centre of every galaxy. It is only now, by observing stars whirling about the monster closest to home, that we stand on the verge of confirming their existence once and for all. Not only that, we could also test Einstein’s general theory of relativity in the most extreme environment yet.

While the centre of our galaxy could serve as a lab for studying processes that occur in other galaxies, the first tantalising glimpses of it are throwing up surprises about our own. Recent observations have revealed that the heart of our galaxy harbours a second kind of hole – a region of space containing only a few young stars and mysteriously empty of older ones.

Previous scans of the Milky Way’s heart showed a few dozen young stars whose bright blue light is intense enough to shine through the shroud of dust. Astronomers expected them to be the tip of the stellar iceberg, their light overwhelming the faint glow emitted by vast numbers of more ancient stars.

That all changed when three teams independently got their hands on sensitive infrared telescopes capable of penetrating the dust shrouding the galactic centre. As they scanned the Milky Way, they counted thousands of old stars. But when they got very close to the galactic centre, the numbers plummeted, revealing a patch of space 3 light years across that was seriously lacking in stars (Astronomy & Astrophysics, vol 499, p 483).

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