Origin of 'Mirach's Ghost' perplexes black hole scientists

By Rafi Letzter - Staff Writer 4 hours ago

There are two ways to build a supermassive black hole. But neither of them makes much sense.


About 10 million light-years from Earth, a blurry galaxy named Mirach's Ghost may help unravel a dark mystery: where the largest black holes in the universe came from. But this ghostly galaxy has also deepened the mystery surrounding these objects' births.

A black hole is a singularity, a region in space-time where matter has gotten too dense to sustain itself, and collapsed into a formless point. Supermassive black holes (SMBHs) are cosmic monsters, often weighing billions of times the mass of our sun, as compared to the mass of heavy stars that form ordinary black holes. They sit at the centers of large galaxies, sucking up gas and whipping stars around with their immense gravities. There's one at the center of the Milky Way and an even larger one at the center of the Virgo A galaxy that astronomers have photographed. But it's still not clear how these mammoth objects formed.

Physicists think there are two possibilities: Maybe SMBHs are ancient features of the universe, objects that directly collapsed out of the hot mass streaming through space after the Big Bang. Or perhaps they formed like every other black hole in the universe: as a result of the detonations of dying stars. If the latter explanation were correct, SMBHs would have started small and picked up additional mass over the course of eons by gobbling up dust and other stars.

"The problem is that in either case most black holes have grown significantly since their birth, swallowing up clouds of gas and dust that swirl around them," said Timothy Davis, an astrophysicist at Cardiff University in Wales. "This makes them heavier and makes it difficult to determine the mass they began their lives with."

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