Astronomers have spotted a massive black hole in a galaxy a lot smaller than ours. This incredibly large black hole sits at the middle of one of the smallest known galaxies.

M60-UCD1 is a dwarf galaxy that has a whole bunch of stars in a relatively small amount of space. 140 million stars make up the galaxy that has a diameter of just 300 light-years.

Doesn’t sound small does it? It is when you compare to our own galaxy, the Milky Way. A diameter of 300 light years is just 1/500th of our own galaxy’s diameter.

NASA describes what it would be like to live in the galaxy. “If you lived inside this dwarf galaxy, the night sky would dazzle with at least 1 million stars visible to the naked eye. Our nighttime sky as seen from Earth’s surface shows 4,000 stars.”

University of Utah astronomer Anil Seth was lead author on an international study of the dwarf galaxy. The study was published in today’s issue of the journal Nature.

Seth said in a statement, “We don’t know of any other way you could make a black hole so big in an object this small.”

“There are a lot of similar ultracompact dwarf galaxies, and together they may contain as many supermassive black holes as there are at the centers of normal galaxies.”

Seth and his fellow astronomers compiled data from the Hubble space Telescope along with the Gemini North 8-meter optical and infrared telescope in Hawaii to observe the dwarf galaxy and gauge the black hole’s mass. The Hubble took measurements of the galaxy’s diameter and stellar density while Gemini watched for motions affected by the enormous black hole.

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How does M60-UCD1’s black hole compare to the Milky Way’s? The black hole at the center of our galaxy has the mass of around 4 million suns. That’s 0.01% of our galaxy’s total mass. M60-UCD1’s black hole on the other hand, has the mass of 21 million suns. That equals a whopping 15% of the tiny galaxy’s 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 said.

NASA touched on one potential explanation in its press release.

One explanation is that M60-UCD1 was once a large galaxy containing 10 billion stars, but then it passed very close to the center of an even larger galaxy, M60, and in that process all the stars and dark matter in the outer part of the galaxy were torn away and became part of M60.

The University of Utah put together a video showing how this would have happened.

Formation of Dwarf Galaxy M60-UCD1 from The University of Utah on Vimeo.

Image credit: NASA. Image is an artist representation.

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