Giant black hole inside a tiny satellite galaxy of our Milky Way defies explanation

There is a black hole at the center of the dwarf galaxy. The image is from the ESA/ Gaia/DPAC.

Scientists don't know why a tiny galaxy at the outskirts of the Milky Way has a black hole at its center, similar to that of the larger one.

The universe is 820,000 light-years from Earth. The mass of the galaxy was thought to be between 15 and 30 million times the mass of our sun. The disk of the Milky Way is over 100,000 light-years wide and weighs as much as 1.5 trillion suns.

A new study has found that the black hole at the center of the little constellation, known as the little Leo I, is nearly as large as the one at the center of the entire Milky Way. Astronomers believed that giant black holes should correspond with the size of the galaxy.
Where do black holes lead?

Mara José Bustamante, an astronomer at the University of Texas, Austin, is the lead author of a new paper.
The discovery was made by chance. The University of Texas' McDonald Observatory's 2.7-meter Harlan Telescope was used to measure the amount of dark matter. The amount of dark matter in small galaxies is inferred from the motion of stars. The force of gravity is counteracted by dark matter. Scientists can measure its concentrations in the universe using the effects on the stars. The star's dark matter travels at a faster rate.
The team ran the data through their computer models and found that there was a black hole at the center of the system that was as heavy as 3 million suns. The black hole at the center of the Milky Way is 25% larger than the Sagittarius A*.

Karl Gebhardt, an astronomer at the University of Texas, Austin, and a co-author of the new study, said that the black hole in the small galaxy is about the size of the Milky Way's. The mass ratio is very large.

The results differ from previous calculations of dark matter. The previous studies were based on less precise data and didn't have access to the Austin team's powerful computers.

In previous studies, scientists didn't see the denser inner regions of the galaxy and focused on accessible information about a few individual stars. The data sets seemed to have a lot of slow stars. The dark matter in the inner regions was not revealed by the calculations. The amount of dark matter in the central regions is higher than in the fringes.

The study was published in December.

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