Examining a molecular cloud with enigmatic motion, a team led by researchers in Japan has found signs of stray black hole hiding in the Milky Way.

It is difficult to find black holes, because they are completely black. In some cases black holes cause effects which can be seen.

Theoretical studies have predicted that 100 million to one billion black holes should exist in the Milky Way, although only 60 or so have been identified through observations to date.

"We found a new way of discovering stray black holes," said one of the researchers Tomoharu Oka, Professor at Keio University in Japan.

The researchers used the ASTE Telescope in Chile and the 45-m Radio Telescope at Nobeyama Radio Observatory, both operated by the National Astronomical Observatory of Japan, to observe molecular clouds around the supernova remnant W44, located 10,000 light-years away from us.

A supernova is the explosion of a star — the largest explosion that takes place in space, according to NASA.

The primary goal of the researchers was to examine how much energy was transferred from the supernova explosion to the surrounding molecular gas, but they happened to find signs of a hidden black hole at the edge of W44, said the study published in Astrophysical Journal Letters.

During the survey, the team found a compact molecular cloud with enigmatic motion.

To investigate the origin of this cloud, named the "Bullet", the team performed intensive observations of the gas cloud.

The data indicated that the Bullet seems to jump out from the edge of the supernova remnant with immense kinetic energy.

"Most of the Bullet has an expanding motion with a speed of 50 km/s, but the tip of the Bullet has a speed of 120 km/s," Masaya Yamada, a graduate student at Keio University, said.

"Its kinetic energy is a few tens of times larger than that injected by the W44 supernova. It seems impossible to generate such an energetic cloud under ordinary environments," Yamada added.

The researchers believe that a dark and compact gravity source, possibly a black hole, has an important role in the formation of the Bullet.