From the Heart

The Darwin Lecture for the National Astronomy Meeting 2007 was given by Dr. Reinhard Genzel. He spoke about the black hole which sits at the centre of the Milky Way, our own galaxy.

Early infrared astronomy showed very fast motions in the central mass of the galaxy. 20 years later we still agree with these early results but now have other data which confirms the existence of Sagittarius A*, the black hole in the middle of the Milky Way.

VLBA measurements have shown that Sgr A* does not move with respect the centre of the galaxy. Observations of nearby stars orbiting Sgr A* have velocities which suggest it is a supermassive black hole. There is relatively low amounts of gas spiraling onto Sagittarius A*, perhaps because in such active regions, supernovae have blown away much of it away.

Although this is by far the closest supermassive black hole, it is still hard to study because there are many thick clouds of interstellar dust, which absorb visible light, between us and Sgr A*. Astronomers rely on X-rays, radio waves, and other wavelengths of energy to study the Milky Way’s core.

The object is 8,000 parsec away (~27,000 light years) and is thought to have a mass of around 3 million times that of the Sun. That’s big! It is believed tha this beast of a black hole holds in its gravity more than 100 of the galaxies most massive and energetic OB Stars within just a few light years and these stars may be the evidence that gives it away, as seen in this animation.

Sgr A* also has the peculiar property that it experiences a periodic burst of brightness every few hours, for an hour or so. This may be the result of it swallowing up material and releasing energy or even of objects careeering into each other as they in turn infall into this monstrous gravity guzzler.

Reinhard Genzel has been working on this object for some time, amongst other things, and so his talk on thse subject was excellent. It was a pleasure to hear someone speak on a topic that doesn’t end up being an utter mystery or controversy for a change. That’s not to say that Sgr A* is all wrapped up, because it certainly isn’t. This is an object that will remain a topic of intense study for some time and no doubt Genzel will be at the front of it.