Scientists have managed to reveal a supermassive black hole in the center of a dwarf galaxy in the constellation Pech. UCD3 is part of the Cluster of the Furnace and belongs to a rare and unusual galactic class - ultra-compact dwarfs. The mass of such galaxies usually reaches several tens of millions of solar with a radius of no more than 300 light years. Because of the mass and size ratio, UCDs are considered the densest stellar systems in the universe.
The mass of the supermassive black hole in UCD3 is 3.5 million solar, which resembles a monster in the center of the Milky Way. The study used data from the SINFONI IR integrated spectrograph installed on one of the 8.2-meter instruments of the Very Large Telescope (Chile). An analysis of the observed spectra demonstrated a relationship between the dispersion of stellar velocities and the radius of the galaxy. The velocity dispersion determines the average change between the speed of the stellar line of sight and the average speed of the entire stellar population. In the presence of a massive body, like a black hole, gravity begins to affect the stars and accelerates them in different directions. As a result, the average speed does not grow, but the variance changes significantly. In a particular galaxy, the central velocity dispersion is so huge that it can only be explained by the presence of a massive black hole.
Optical image of the giant elliptical galaxy NGC 1399 and its satellite UCD3. Left: UCD3 image in the F606W filter taken by the Hubble telescope. Right: IR image of UCD3, extracted by the SINFONI spectrograph
After that, the researchers compared the dependence of speed and dispersion on dynamic models based on the assumption of the mass of a black hole. It turned out that a model with a mass of 3.5 million solar is best suited to observations. The possibility of the absence of a black hole was also considered, but the hypothesis was excluded with a statistical significance of 99.7%.
This is the fourth found hole of the UCD example and corresponds to 4% of the total galactic mass. The presence of massive black holes in such objects is an important argument in favor of the tidal origin of galaxies. That is, a medium-sized galaxy passed through a more massive and larger one at a certain evolutionary stage, which led to the loss of most of the stars due to the influence of tidal forces. The remaining compact core becomes an ultra-compact galaxy. But to confirm the hypothesis will need to find more supermassive holes in the UCD.