A tiny galaxy orbiting at the outskirts of the Milky Way appears to have a giant black hole at its center, comparable to that of the much larger Milky Way itself, and scientists are surprised.
The Leo I dwarf galaxy is some 820,000 light-years from Earth, and astronomers believe its mass was about 15 to 30 million times the mass of our sun. That's tiny compared to the Milky Way, which is estimated to weigh as much as 1.5 trillion suns and whose disk is over 100,000 light-years wide.
However, the study published in the latest issue of the Astrophysical Journal, unexpectedly found that at the heart of the little Leo I sits a black hole that is nearly as large as the one at the heart of the entire Milky Way. The discovery defies expectations as astronomers believed giant black holes grow from collisions between galaxies and should correspond with the galaxy's size.
"There is no explanation for this kind of black hole in dwarf spheroidal galaxies," María José Bustamante, an astronomy researcher at the University of Texas, and lead author of the new paper, said in a statement quoted by the Live Science website.
The discovery came as scientists originally set out to measure the amount of dark matter in Leo I using the Virus-W instrument on the University of Texas' 2.7-meter Harlan Telescope.
Virus-W measures the motion of stars in small galaxies around the Milky Way and infers the amount of dark matter in those galaxies from those motions.
Dark matter is the completely invisible material that resists gravity. Scientists can measure its concentrations in the universe based on its effects on orbits and velocities of nearby stars. The more dark matter in the star's orbit, the faster it travels.
When the team ran data gathered in the observations through their computer models, they found that Leo I appears to have basically no dark matter but a black hole at its center as heavy as 3 million suns. These findings surprised the scientists as the Sagittarius A* black hole at the center of the Milky Way is only 25% larger.
