Photo: Astronomers have discovered that Leo I (inset), a small satellite galaxy of the Milky Way (main image), has a black hole almost as massive as that of the Milky Way. Credits: ESA / Gaia / DPAC; SDSS (box).

Astronomers at the McDonald Observatory at the University of Texas at Austin in the United States have discovered an unusually massive black hole at the heart of one of the Milky Way’s dwarf satellite galaxies, called Leo I. It is almost as massive as the hole. black of our galaxy, when in fact it is supposed to have smaller dimensions. The finding could redefine our understanding of how galaxies and all components of the universe evolve.

Leo I is a dwarf galaxy located in the constellation of Leo, which was only visually detected in the 1990s, because its proximity to the star Regulus, the brightest in the constellation, makes it difficult to visualize. Leo I forms the Local Group and is one of the farthest satellite galaxies of the Milky Way. It is also thought to be the youngest spheroidal dwarf galaxy in the Milky Way environment.

Although Leo I is 30 times smaller than the Milky Way, astronomers were surprised to observe that the black hole located in its center was huge, with practically the same mass as the one located in the heart of the Milky Way. According to a press release, they came to this conclusion by studying the dark matter profile of the satellite galaxy.

New results
The scientists used a unique instrument called VIRUS-W on the Harlan J. Smith Telescope to find out if the density of dark matter increases towards the center of the galaxy. To do this, they measured the gravitational attraction on the stars: the faster the stars move, the more dark matter they would have locked into their orbits. They also cross-checked the data with previous studies of the dwarf galaxy, conducted with telescopes and older technologies.

The results of the new study, published in The Astrophysical Journal, were conclusive: the distribution of dark matter indicates that in the center of the small galaxy there is a gigantic black hole with a great gravitational influence. In turn, toward the galactic center the amount of inferred dark matter locked within the orbits of the stars skyrocketed.

Apparently, a combination of specific biases and outdated technologies would have meant that previous research on Leo I did not show the incredible size of its central black hole, almost comparable to that of the Milky Way. The discovery is unprecedented, since what is expected is a black hole of much smaller dimensions.

Reference
Dynamical Analysis of the Dark Matter and Central Black Hole Mass in the Dwarf Spheroidal Leo I. M. J. Bustamante-Rosell, Eva Noyola, Karl Gebhardt, Maximilian H. Fabricius, Ximena Mazzalay, Jens Thomas and Greg Zeimann. The Astrophysical Journal (2021). DOI: https: //doi.org/10.3847/1538-4357/ac0c79