So yesterday I posted about exactly how big a 12 billion solar mass black hole appears to be. But I didn’t get into the followup question of, “So why is this new black hole exciting?” Here’s why this is cool, and surprising.
The weird thing about this black hole isn’t so much how massive it is. The problem is how massive and young it is. Fist, some quick background about “lookback time”:
When we look out at the night sky we’re really looking back in time because light only travels as a fixed speed (about 300,000 km / sec). Putting this in human terms, a km is about 10 football fields laid out end to end. If you shine a flashlight from one end of those football fields to the other it takes about 3 microseconds to to the other end. This is about how long an old 300 Mhz computer takes to do a single math operation. This sounds small, but distance get large. It takes about 8 minutes for light to cover the distance from the Earth to the Sun. In the case of this blackhole, the light that we’re seeing traveled for 12 billion years before it reached out telescopes. So what we’re really doing is using this supermassive black hole to look back in time almost all the way to Big Bang. We can add this to observations of other black holes that we can observe that are closer to us (and therefore from a time when the Unvierse was older) to build up a “family tree” of all of the black holes in the Universe.
Above is an example of lookback time from the WMAP team, which is a satellite that studies the light emitted from the time right after the Big Bang occurred that I really like.
So the black hole is really young, but it’s also really big. The next question is “how it get that there?” If you look in the figure above, the first stars only formed about 400 million years after the Big Bang. You can’t grow a supermassive black hole in a few hundred million years; it just can’t eat enough stars and gas fast enough to grow to something like 12 billion solar masses. This means that the black hole is a “primoridal” leftover from whatever extreme physics was goign on during the first moments after the Big Bang. Physicists and astronomers have been working hard for decades now to try to understand the evolution of the Universe. One picture is the “hierarchical” model, where you build really big black holes by merging together smaller (but still really massive) black holes. But you still need some time to make this happen. I think that having a really young, really massive black hole may start to wear this picture of the evolution of the Universe around the edges a bit.