Astronomers think they have found evidence for the existence of a black hole the size of Jupiter, which is just casually wandering the Milky Way like a gigantic interstellar traveler. 

While scientists aren't able to observe the black hole directly – it is, after all, an area of space nothing (including light) is able to escape – they have observed some unusual behavior around a celestial cloud they were tracking. 

"When I checked the ALMA [Atacama Large Millimeter/submillimeter Array] data for the first time, I was really excited because the observed gas showed obvious orbital motions, which strongly suggest an invisible massive object lurking," Shunya Takekawa, an astrophysicist at the National Astronomical Observatory of Japan (NAOJ), told New Scientist. 

According to Space.com, the team were watching two celestial clouds they've nicknamed Balloon and Stream 26,000 light-years from the center of the Milky Way. In most instances, they are formed by gas crashing into a supernova or another celestial cloud – in either case, astronomers expect the cloud to expand or leave a V-shape motif. Not, as they've seen now, streams of gas orbiting around a central point.

From these movements, they have calculated that the object attracting the gas is 30,000 times the mass of the Sun and roughly the size of Jupiter. The most likely explanation, therefore, is an intermediate-mass black hole.

Medium-sized black holes such as these are quite a rare celestial phenomenon. Most are either small (relatively speaking) and the product of a star collapse or very big (aka supermassive black holes), which are thought to be formed when the galaxy they are in first appears. 

Astronomers believe there are two more potential black holes of an intermediate size lurking close to the center of the Milky Way. However, for now, the evidence for this third intermediate-mass black hole is suggestive rather than conclusive, Avi Loeb from Harvard University told New Scientist.

"One would like to detect a telltale signature of a black hole, such as a jet, broad emission line due to relativistic motions, or non-thermal radiation in the X-ray or radio bands," Loeb added.

The data has yet to be peer-reviewed but is available to read on the pre-print server arXiv.