Astronomers find tail of stray black hole lurking in Milky Way

Japanese researchers have found evidence suggesting there is a trail of a stray black hole hiding in our galaxy.

Japanese researchers may have found a new way to uncover 'quiet black holes'

An artist's impression of the black hole. The strong gravity of the hole drags gas in a narrow stream. (Keio University)

Researchers may have found a "quiet black hole" lurking in our galaxy.

Black holes, regions of space with intense gravity, where nothing — not even light — can escape, are difficult to detect.

But if a star is nearby, the black hole will consume its gas, which heats up as it is pulled inward, forming a disk. That process emits intense radiation, making the black hole detectable.

However, some black holes don't interact with stars. If no radiation is emitted, how can we find them?

These types of objects, dubbed "quiet black holes," are difficult to find. In July 2016, University of Alberta researchers found a source of radio waves emitting from a binary star system may be one of these unique objects, which was a first. It was very slowly pulling in material from a nearby star, making it hard to detect. 

Now, a team of Japanese astronomers may have found a new way to find these sneaky celestial objects.

The researchers, studying a molecular cloud — an accumulation of dust and gas — surrounding W44, a remnant of a supernova 10,000 light-years away, have stumbled on a surprise: the cloud was moving in a strange way.

The cloud — which they dubbed the Bullet — was moving more than 100 kilometres a second, twice the speed of sound in interstellar space. Not only that, but it was moving backward, compared to the rotation of the Milky Way.

This image illustrates the emissions around the supernova remnant W44. (Yamada et al., Keio University, NAOJ)

The researchers used two telescopes to investigate: the 45-metre radio telescope at Nobeyama Radio Observatory and the ASTE Telescope in Chile, both operated by the National Astronomical Observatory of Japan. They found that the Bullet extends out of W44 with incredible kinetic energy.

"Most of the Bullet has an expanding motion with a speed of 50 kilometres a second, but the tip of the Bullet has a speed of 120 kilometres a second," Masaya Yamada, a graduate student at Keio University in Japan and author of the study, said in a statement.

Explosion or 'irruption'?

The researchers theorized this was occurring under the influence of a black hole.

The astronomers aren't quite certain how the Bullet has formed, but have two theories.

One, the "explosion model," is that the expanding shell of W44 passes a static black hole that pulls the gas towards it. The gas then explodes, shooting towards our line of sight. If this is the case, the black hole would be about 3.5 times the mass of our sun.

A second theory, the "irruption model," is that a black hole moving at high speed is dragging gas along with it, forming a stream. In this case, the black hole would be a whopping 36 times the mass of our sun.

Astronomers believe that 100 million to one billion black holes should exist in our Milky Way. Only about 60 have been found. 

The Japanese astronomers say that perhaps with this new observation, these "quiet black holes," as they are known, may be detectable.


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