Black holes are known to come in either small or large sizes, but new research brings us closer to confirming the existence of a "medium" black hole.
There are currently about a half-dozen candidates for medium black holes, but their existence is yet to be concretely determine, the University of Maryland reported. Now, scientists have uncovered evidence for a new intermediate-mass black hole that is about 5,000 times the mass of the sun, which is in between stellar mass black holes a few dozen times the mass of our sun and supermassive black holes that can be several billion times the sun's mass.
"Currently astronomers are confident that smaller (masses of a few times our sun) and supermassive black holes (a few million to a few billion) exist in the Universe. This work strengthens the argument for the existence of a third class of black holes, i.e., the middle-weight black holes," lead author Dheeraj Pasham told HNGN.
The new intermediate-mass black hole candidate, dubbed NGC1313X-1 is classified as an ultraluminous X-ray source and is one of the brightest sources seen in its neighborhood. The source of bright X-ray light in the distant universe has largely remained a mystery, but many scientists believe it can be traced back to intermediate-mass black holes actively drawing in matter and producing X-ray radiation.
Among the observed light, the researchers noticed two recurring flares that blinked at a surprisingly steady pace. These flashes may be caused by activity and the strong pull of gravity on matter close to the black hole. One of the flares blinked 27.6 times per minute and the other about 17.4 times per minute, creating a perfect 3:2 ratio that could reveal the object's mass.
"To make an analogy with acoustic instruments, if we imagine that stellar mass black holes are the violin and supermassive black holes are the double bass, then intermediate-mass black holes are the violoncello," said co-author Francesco Tombesi, an assistant research scientist in UMD's Department of Astronomy who has a joint appointment at NASA Goddard via the Center for Research and Exploration in Space Science and Technology.
The researchers hope identifying more ultraluminous X-ray sources that have 3:2 flashing ratios will lead to additional intermediate-mass black hole candidates to add to the list.
"NASA is soon to launch an X-ray satellite called Neutron Star Interior Composition ExploreR (NICER). NICER will be 1.5 times more sensitive than any of the current instruments to detect these 3:2 ratio X-ray flickering. Hence we anticipate to detect more such mid-sized black holes using the data from instruments on-board NICER. If we can build a census of these objects, we can start to learn more interesting things about the Universe like could these mid-sized black hole be the "seeds" for growing supermassive black holes when the Universe was very young .." Pasham told HNGN.
The findings were published in a recent edition of the Astrophysical Journal Letters.
