Using three X-ray space telescopes - ESA's XMM-Newton, JAXA's Suzaku and NASA's Chandra - Japanese astronomers have discovered that the black hole at the centre of our galaxy was much more active 300 years ago, when it gorged on a large feast of nearby stars (for full details, see ESA's press release).
Imagine looking for a black object on a black background, and you will appreciate the difficulty in observing black holes! However, when a star or gas falls in towards a black hole, it gets extremely hot - millions of degrees centigrade hot! Anything at this temperature will give off X-ray radiation. So the best way to find a black hole is to look for X-rays in space - the tell-tell sign of something falling towards a black hole.
Not only that, but those X-rays can reflect off clouds of gas... which is exactly what has been observed. A cloud of gas near the centre of our galaxy suddenly brightened. What astronomers believed happened is that the black hole at the centre of the galaxy had a big feast which released large amounts of X-rays. Those X-rays then travelled for 300 years until they collided with the neighbouring gas cloud and caused it to glow. And now, we are just seeing that gas cloud glow.
This means that, if we had X-ray space telescopes 300 years ago, we would have been able to witness the black hole at the centre of the Milky-way enjoying its feast!
We have seen the super-massive black-hole at the centre of the Milky-way feed before, but the feast 300 years ago was a million times bigger than anything we have seen in recent times.
If you want to know more about black hole, why not watch our planetarium show Black-holes: the other side of infinity?