Astronomers meeting in Seattle this week discussed new observations of the largest black hole known so far. It’s thought to contain a mass equal to 6.6 billion of our suns.
And it’s no wonder the black hole is so big. This black hole – whose mass had been previously estimated at 3 billion suns – is located in the center of a huge galaxy, or island of stars, known to us as M87. It’s thought to lie about 50 million light-years from our Earth. As we stand on Earth and look out at the stars, we see the M87 galaxy in the direction of the constellation Virgo (whose brightest star Spica will be near the moon from midnight to dawn on January 25 and 26). There are over 1,000 – perhaps as many as 2,000 – relatively nearby galaxies in this direction of space. M87 is the largest and brightest of these, which, in turn, form the heart of a still-larger cluster of galaxies known as our Local Supercluster.
You see, perhaps, that we are talking about a vast scale here – about huge galaxies, clusters of galaxies, and superclusters of galaxies. So it is no surprise that the giant elliptical galaxy M87 – the largest of the nearby galaxies – has a black hole at its heart that, in its turn, is now the largest one known.
Astronomer Karl Gebhardt of the University of Texas at Austin said, “It could swallow our solar system whole.”
Gebhardt and colleagues used a telescope on Mauna Kea in Hawaii to measure how fast stars orbit the black hole. From the observed speeds – up to almost 500 kilometers per second – they could then calculate the hole’s mass.
Six billion solar masses. A black hole that massive would have a very wide event horizon. That’s the edge from which nothing, not even light, can escape a black hole’s powerful gravity. How large is the event horizon of the black hole in M87? Think of our Earth’s orbit around the sun. Light from our sun takes 8 minutes to travel to Earth. Now think of the planet Neptune, officially the most distant known planet in our solar system, according to the International Astronomical Union. Light from our sun takes about 4 hours to travel to the orbit of Neptune. M87’s black hole has an event horizon about four times as large as Neptune’s orbit. Hence the idea that it could swallow our solar system whole.
Gebhardt told ScienceNOW that studying extreme black holes like the one in M87 gives astronomers their best chance of learning more about black hole physics in general. He said:
In fact, future observations of this object might finally help us prove that what we call black holes are really black holes. Until now, there has been no direct observational evidence at all for the existence of event horizons.
So the known universe has a new champion – weighing in at 6.6 billion times the mass of our sun – the black hole at the heart of M87 We’ll see how long this champion reigns, as astronomers use increasingly sophisticated tools to probe the space around us.