Scientists have reported that presence of such black holes that are neither very large nor very small.
For a long time, scientists were aware of only two types of black holes. One of the types is about the masses of only 10 times that of our sun and the other is about the masses of 10 billion suns, which are also known as supermassive black holes, i.e. there are only two extremes. Supermassive black holes are present at the heart of galaxies while small galaxies are present elsewhere in the galaxies. Supermassive black holes have immense gravity taking in the material from the surroundings and release powerful X-rays.
“Exactly how intermediate-sized black holes would form remains an open issue,” said Dominic Walton of the California Institute of Technology, Pasadena. “Some theories suggest they could form in rich, dense clusters of stars through repeated mergers, but there are a lot of questions left to be answered.”
Now, astronomers utilized NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, and have reported ultraluminous X-ray sources, or ULXs that takes the material of a normal star, which is not as big as that of supermassive black holes. Moreover, they are also present throughout the galaxies not at the heart. They are found to be of 100-1000 times the masses of our sun.
These ULXs have been spotted in two places; in the Circinus galaxy (as shown in the first image) and in the spiral galaxy called NGC 1313, or the Topsy Turvy galaxy (as shown in the second image).
“It’s possible that these objects are ultraluminous because they are accreting material at a high rate and not because of their size,” said Matteo Bachetti of the Institut de Recherche en Astrophysique et Planétologie. “If intermediate-mass black holes are out there, they are doing a good job of hiding from us.”
Do Black Holes Come in Size Medium? – NASA (http://goo.gl/mEj7VP)
Matteo Bachetti, Vikram Rana, Dominic J. Walton, Didier Barret, Fiona A. Harrison, Steven E. Boggs, Finn E. Christensen, William W. Craig, Andrew C. Fabian, Felix Fürst, Brian W. Grefenstette, Charles J. Hailey, Ann Hornschemeier, Kristin K. Madsen, Jon M. Miller, Andrew F. Ptak, Daniel Stern, Natalie A. Webb, & William W. Zhang (2013). The ultraluminous X-ray sources NGC 1313 X-1 and X-2: a broadband study with NuSTAR and XMM-Newton arXiv arXiv: 1310.0745v3
D. J. Walton et al. (2013). An Extremely Luminous and Variable Ultraluminous X-ray Source in the Outskirts of Circinus Observed with NuSTAR arXiv arXiv:1310.2633