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Nearby star cluster houses unusually large black hole

10 July 2024 at 18:20
Three panel image, with zoom increasing from left to right. Left most panel is a wide view of the globular cluster; right is a zoom in to the area where its central black hole must reside.

Enlarge / From left to right, zooming in from the globular cluster to the site of its black hole. (credit: ESA/Hubble & NASA, M. HΓ€berle)

Supermassive black holes appear to reside at the center of every galaxy and to have done so since galaxies formed early in the history of the Universe. Currently, however, we can't entirely explain their existence, since it's difficult to understand how they could grow quickly enough to reach the cutoff for supermassive as quickly as they did.

A possible bit of evidence was recently found by using about 20 years of data from the Hubble Space Telescope. The data comes from a globular cluster of stars that's thought to be the remains of a dwarf galaxy and shows that a group of stars near the cluster's core are moving so fast that they should have been ejected from it entirely. That implies that something massive is keeping them there, which the researchers argue is a rare intermediate-mass black hole, weighing in at over 8,000 times the mass of the Sun.

Moving fast

The fast-moving stars reside in Omega Centauri, the largest globular cluster in the Milky Way. With an estimated 10 million stars, it's a crowded environment, but observations are aided by its relative proximity, at "only" 17,000 light-years away. Those observations have been hinting that there might be a central black hole within the globular cluster, but the evidence has not been decisive.

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Black holes formed quasars less than a billion years after Big Bang

17 June 2024 at 21:56
Image of a glowing disk with a bright line coming out of its center.

Enlarge (credit: NASA, ESA, CSA, Joseph Olmsted (STScI))

Supermassive black holes appear to be present at the center of every galaxy, going back to some of the earliest galaxies in the Universe. And we have no idea how they got there. It shouldn't be possible for them to grow from supernova remnants to supermassive sizes as quickly as they do. And we're not aware of any other mechanism that could form something big enough that extreme growth wouldn't be necessary.

The seeming impossibility of supermassive black holes in the early Universe was already a bit of a problem; the James Webb Space Telescope has only made it worse by finding ever-earlier instances of galaxies with supermassive black holes. In the latest example, researchers have used the Webb to characterize a quasar powered by a supermassive black hole as it existed approximately 750 million years after the Big Bang. And it looks shockingly normal.

Looking back in time

Quasars are the brightest objects in the Universe, powered by actively feeding supermassive black holes. The galaxy surrounding them feeds them enough material that they form bright accretion disks and powerful jets, both of which emit copious amounts of radiation. They're often partly shrouded in dust, which glows from absorbing some of the energy emitted by the black hole. These quasars emit so much radiation that they ultimately drive some of the nearby material out of the galaxy entirely.

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