About 10 million light years from Earth, a fuzzy galaxy called Mirach’s Ghost can help unravel a dark mystery: where the universe’s largest black holes come from. But this ghostly galaxy has also deepened the mystery surrounding the births of these objects.
A black hole is a singularity, a region in space time where matter has become too dense to support itself and has collapsed into a point without form. Supermassive black holes (SMBH) are cosmic monsters, often weighing billions of times the mass of our sun, compared to the mass of heavy stars that form common black holes. They sit in the centers of great galaxies, suck gas and whip stars with their immense gravities. There’s one in the center of the Milky Way galaxy and an even bigger one in the center of the Virgo A galaxy than astronomers have photographed. But it is still unclear how these gigantic objects were formed.
Physicists believe there are two possibilities: perhaps SMBHs are ancient features of the universe, objects that directly collapsed from the hot mass that flowed through space afterward. the big bang. Or perhaps they formed like any other black hole in the universe: as a result of the detonations of dying stars. If the last explanation were correct, the SMBHs would have started small and would accumulate additional mass over the eons, gobbling up dust and other stars.
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“The problem is that, in any case, most black holes have grown significantly since birth, swallowing 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 with which they started their lives.”
So Davis and his colleagues went looking for the smallest SMBHs they could find.
These little supermasses, he told Live Science, “have not had the opportunity to consume large amounts of material in their past, [so in studying them we are] get closer to revealing what SMBHs must have looked like when they were formed. “
The researchers studied SMBH at the center of the “Mirach’s Ghost” galaxy (so named because of land the galaxy is seen as an apparition near the star Mirach), using a new technique to determine its mass.
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Based on data from the Atacama Large Millimeter / submillimeter Array (ALMA) in Chile, the researchers measured the velocity of the carbon monoxide gas as it spun toward the SMBH at the center of the Mirach Phantom Galaxy.
“Like the water that passes around a plug hole, this gas goes faster and faster as it gets closer to the black hole,” Davis said.
That eddy is a product of the mass of the black hole, so the speed of the eddy, accurately measured, can tell researchers how much the black hole weighs. ALMA images, with a resolution of 1.5 light years (very detailed for such a distant object), made this possible. They discovered that this SMBH has a mass less than 1 million times greater than that of our sun: a baby by SMBH standards. Based on estimates of how much it has grown since birth, it probably weighed less than 500,000 times the mass of our sun when it was born, Davis said.
The researchers found that does not prove that any of the origin stories is correct. But it does tip the balance against the direct collapse model, completely discarding the more extreme versions of the direct collapse theory. Some direct collapse theories do not allow such small SMBHs to form.
Still, the origin of black holes is a mystery. One problem: Other observations have shown that very large SMBHs existed in their current form very shortly after the Big Bang, challenging our assumptions about how fast black holes can grow.
“We know of two main ways to make SMBH, and neither of them can make black holes of this size directly. Instead, they must have been born smaller and grown to these prodigious sizes. This is really difficult to do, as there is a limit about how much a black hole can swallow in the time available since the universe was created, “Davis said. “Our work reinforces this problem. We have shown that any mechanism that produces SMBH allows them to have a mass less than 500,000 times the mass of our sun when they are born.”
While that tips the balance against the theory of direct collapse, no theory offers good explanations for where such a small SMBH could have come from. The eventual response will likely involve some significant modifications to one of the models that physicists currently have.
So now physicists know a little more about what young SMBHs look like. But they are still not sure where they came from. The article describing the black hole in the center of the Mirach Phantom was published today (July 14) in the Monthly Notices of the Royal Astronomical Society.
Originally published in Live Science.