Medium-sized black holes have been shown to exist for the first time in history, providing additional information concerning the properties of the strangest objects in the Universe.

Black holes were believed to exist in just two sizes - (relatively) small, and supermassive. The largest bodies are found at the core of every major galaxy, including our own Milky Way. These massive features have masses many millions or billions of times larger than the Sun. Stellar-sized black holes, the smallest of these objects, form from the final collapse of a star, a few dozen times larger than our stellar companion.
 
Medium-sized black holes, with masses between 100 and a few thousand times more than the Sun, remained elusive for decades. One of the challenges in finding these bodies was the difficulty of accurately determining the mass of the enigmatic objects. Now, researchers believe they have precisely measured the mass of a medium-sized black hole for the first time.

The Cigar Nebula, otherwise known as M82, lies 12 million light years from Earth. The family of stars is home to a black hole, observed by astronomers to have a mass of 428 solar masses, plus or minus 100. However, some astronomers believe M82 X-1 could be as light as 20 solar masses.

Before University of Maryland (UMD) researchers made this measurement, astrophysicists had long debated the reasons objects like this one were so rare, or even non-existent.

"Astronomers have been asking, do these objects exist or do they not exist? What are their properties? Until now we have not had the data to answer these questions," Richard Mushotzky, astronomy professor at UMD, and co-author of the study, said.

Dheeraj Pasham, a graduate student of astronomy at UMD, led the research that revealed the mass of the object.

Black holes are objects with a gravitational pull so great that not even light can escape its surface. The mysterious bodies are invisible to anyone attempting to observe them from outside. However, their gravitational pull on surrounding matter may be detected, indicating the presence of an unseen massive body. As material spirals into the black hole, radiation created from motion around the mass can be seen by observers. This structure displayed a pair of lights on each side of the black hole, plashing at 5.1 and 3.3 times each second. This produces a 3:2 ratio, like the beats in the Beatles song "Mean Mr. Mustard." Astronomers used this pattern to calculate the mass of the object.

Astrophysicists are still debating how middleweight black holes form, and if they exhibit properties like their smaller - and much larger - cousins.

The family of stars in which this body lies is classified as a starburst galaxy, where millions of young stars are being born. The Cigar Galaxy is the nearest one of these structures to the Earth.

Analysis if the middleweight black hole in M82 was detailed in the journal Nature.