Astronomers discover strangely massive black hole in Milky Way satellite galaxy

Date:
December 1, 2021
Source:
University of Texas at Austin
Summary:
Astronomers 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.



FULL STORY ========================================================================== 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. The work is published in a recent issue of The Astrophysical Journal.


==========================================================================
The team decided to study Leo I because of its peculiarity. 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. They did this by measuring its gravitational
pull on the stars: The faster the stars are moving, the more matter
there is enclosed in their orbits.

In particular, the team wanted to know whether dark matter density
increases toward the galaxy's center. They also wanted to know whether
their profile measurement would match previous ones made using older
telescope data combined with computer models.

Led by recent UT Austin doctoral graduate Mari'a Jose' Bustamante,
the team includes UT astronomers Eva Noyola, Karl Gebhardt and Greg
Zeimann, as well as colleagues from Germany's Max Planck Institute for Extraterrestrial Physics (MPE).

For their observations, they used a unique instrument called VIRUS-W on McDonald Observatory's 2.7-meter Harlan J. Smith Telescope.

When the team fed their improved data and sophisticated models into a supercomputer at UT Austin's Texas Advanced Computing Center, they got
a startling result.

"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 mass ratio is
absolutely huge. The Milky Way is dominant; the Leo I black hole is
almost comparable." The result is unprecedented.

The researchers said the result was different from the past studies
of Leo I due to a combination of better data and the supercomputer
simulations. The central, dense region of the galaxy was mostly unexplored
in previous studies, which concentrated on the velocities of individual
stars. The current study showed that for those few velocities that were
taken in the past, there was a bias toward low velocities. This, in turn, decreased the inferred amount of matter enclosed within their orbits.

The new data is concentrated in the central region and is unaffected
by this bias. The amount of inferred matter enclosed within the stars'
orbits skyrocketed.

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 study. Noyola pointed out that many southern hemisphere dwarf galaxies are good targets
for it, but no southern hemisphere telescope is equipped for it. However,
the Giant Magellan Telescope (GMT) now under construction Chile was,
in part, designed for this type of work. UT Austin is a founding partner
of the GMT.

========================================================================== Story Source: Materials provided by University_of_Texas_at_Austin. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
*
Leo_I,_a_tiny_satellite_galaxy_of_the_Milky_Way,_has_a_black_hole_nearly
as_massive_as_the_Milky_Way's ========================================================================== Journal Reference:
1. M. J. Bustamante-Rosell, Eva Noyola, Karl Gebhardt, Maximilian H.

Fabricius, Ximena Mazzalay, Jens Thomas, Greg Zeimann. Dynamical
Analysis of the Dark Matter and Central Black Hole Mass in the
Dwarf Spheroidal Leo I. The Astrophysical Journal, 2021; 921 (2):
107 DOI: 10.3847/1538- 4357/ac0c79 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211201112011.htm

--- up 2 weeks, 6 days, 2 hours, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)