Astronomers, using new imagery from the Hubble space telescope, have found a supermassive black hole at the center of one of the universe’s smallest known dwarf galaxies, calling into question some of our theories about how the universe was formed. The black hole at the center of the dwarf galaxy is about four times larger than the black hole that our own Milky Way revolves around — but amazingly, the dwarf galaxy is five hundred times smaller than the Milky Way, with a diameter of just 300 light years. “We don’t know of any other way you could make a black hole so big in an object this small,” says Anil Seth, lead author of the new research.
Dwarf galaxy M60-UCD1 consists of about 140 million stars, crammed into a space that’s just 300 light years across. Our own Milky Way, by comparison, is over 100,000 light years across and consists of about 200 billion stars. According to NASA, if you looked up at the night sky from within the dwarf galaxy you would see at least 1 million stars. Here on Earth, you can see just a few thousand. The image above (view larger) gives you some idea of what the night sky might look like, if we had a telescope on the surface of a planet in the dwarf galaxy. (Sadly it’s an artist’s rendering — the galaxy is 50 million light years distant, and thus too far away for Hubble to capture such details.)
While M60-UCD1 is undeniably very small, it isn’t its diminutive size that makes it notable — it’s the frickin’ huge black hole in the middle of it that has astronomers scratching their heads. It’s not unusual for a galaxy to have a supermassive black hole at the center of it — we think most galaxies have such a black hole — but we didn’t think it was possible for a dwarf galaxy to harbor a supermassive black hole. The black hole at the center of the Milky Way has a mass of around four million Suns, or about 0.01% of the galaxy’s entire mass. The M60-UCD1 black hole has the mass of 21 million Suns, or about 15% of the galaxy’s total mass. “That is pretty amazing, given that the Milky Way is 500 times larger and more than 1,000 times heavier than the dwarf galaxy M60-UCD1,” Seth says.
This is what the Milky Way looks like to an infrared telescope. Sadly, your human eyes can’t see anywhere near as many stars.
The only plausible explanation at the moment is that the dwarf galaxy used to be a full-fat galaxy with about 10 billion stars — but then it collided with another galaxy, M60, which pulled away most of its stars. M60 has its own, ginormous supermassive black hole with a mass of around 4.5 billion Suns. Long-term, astronomers believe that M60 and M60-UCD1 may eventually merge — and when that happens, the black holes will also merge. I’m not entirely sure what happens when two supermassive black holes merge, nor what such a monstrosity would be called, but it’s probably spectacular.
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