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Strangely Massive Black Hole Discovered in Milky Way Satellite Galaxy - SciTechDaily
Dec 03, 2021 2 mins, 19 secs

Astronomers at The University of Texas at Austin’s McDonald Observatory have discovered an unusually massive black hole at the heart of one of the Milky Way’s dwarf satellite galaxies, called Leo I.

Almost as massive as the black hole in our own galaxy, the finding could redefine our understanding of how all galaxies — the building blocks of the universe — evolve.

Unlike most dwarf galaxies orbiting the Milky Way, Leo I does not contain much dark matter.

Researchers measured Leo I’s dark matter profile — that is, how the density of dark matter changes from the outer edges of the galaxy all the way into its center.

In particular, the team wanted to know whether dark matter density increases toward the galaxy’s center.

McDonald Observatory astronomers have found that Leo I (inset), a tiny satellite galaxy of the Milky Way (main image), has a black hole nearly as massive as the Milky Way’s.

The result could signal changes in astronomers’ understanding of galaxy evolution.

“The models are screaming that you need a black hole at the center; you don’t really need a lot of dark matter,” Gebhardt said.

“You have a very small galaxy that is falling into the Milky Way, and its black hole is about as massive as the Milky Way’s.

The Milky Way is dominant; the Leo I black hole is almost comparable.” The result is unprecedented.

The finding could shake up astronomers’ understanding of galaxy evolution, as “there is no explanation for this kind of black hole in dwarf spheroidal galaxies,” Bustamante said.

The result is all the more important as astronomers have used galaxies such as Leo I, called “dwarf spheroidal galaxies,” for 20 years to understand how dark matter is distributed within galaxies, Gebhardt added. This new type of black hole merger also gives gravitational wave observatories a new signal to search for.

“If the mass of Leo I’s black hole is high, that may explain how black holes grow in massive galaxies,” Gebhardt said.

That’s because over time, as small galaxies like Leo I fall into larger galaxies, the smaller galaxy’s black hole merges with that of the larger galaxy, increasing its mass.

Built by a team at MPE in Germany, VIRUS-W is the only instrument in the world now that can do this type of dark matter profile studyJ

Noyola pointed out that many southern hemisphere dwarf galaxies are good targets for it, but no southern hemisphere telescope is equipped for it.

Reference: “Dynamical Analysis of the Dark Matter and Central Black Hole Mass in the Dwarf Spheroidal Leo I” by M.

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