Most galaxies in the observable universe have supermassive black holes at their centers, which just sit there and do their thing, without moving much at all. However, certain circumstances could put these massive behemoths in motion, and NASA astronomers may just have found one.

Located in an elliptical galaxy about 3.9 billion light-years away (perhaps not in its center any more), the potential runaway candidate has a mass 160 million times that of the sun. It was identified using NASA’s Chandra X-ray Observatory and other space telescopes, including Hubble.

Read: Gravitational Waves Kick A Supermassive Black Hole Out Of Galactic Center

In terminology used by scientists, the black hole may have “recoiled” — a phenomenon that occurs when two relatively smaller supermassive black holes collide and merge to form a single, larger supermassive black hole. The collision produces gravitational waves that propagate more strongly in one direction than others, and the newly formed black hole would be pushed in the opposite direction from the stronger waves. This push would take the supermassive black hole out of the galaxy’s center.

Potential candidates for a recoiling supermassive black hole were first shortlisted using X-ray data from Chandra, because bright X-ray emissions are common to rapidly growing supermassive black holes. The galaxies with the bright X-ray emissions were then observed with the Hubble Space Telescope to see if any of them showed two peaks near their centers in optical images — one peak would indicate the recoiling black hole and the other the galactic center with its cluster of stars.

In the image above, the left inset is from Hubble data and shows two bright points in the middle of the galaxy. Though barely apart in the Hubble image, the distance between the two points — one the galactic center and the other the recoiling supermassive black hole — is about 3,000 light-years. Using data from Sloan Digital Sky Survey (all the galaxies selected from the Chandra observations were part of the survey) and the Keck telescope in Hawaii, the NASA team also concluded the black hole is moving at a different velocity from that of the galaxy.

According to a NASA statement, the outer regions of the galaxy itself show some disturbance, suggesting a relatively recent merger between two galaxies. That would fit well with the rest of the theory about the merger of the two supermassive black holes at their centers, leading to the recoil.

More weight is lent to the theory because the galaxy is producing stars at a high rate of several hundred solar masses every year. The star formation rate of galaxies is thought to be enhanced by mergers, especially if they contain recoiling black holes.

Read: How Does A Tiny Galaxy Host A Supermassive Black Hole?

However, another contending theory to explain the observations is that the galactic core has not one but two supermassive black holes, one of which is not growing rapidly enough to produce detectable radiation. Researchers prefer the recoiling theory, but need more data to support it further.

By studying the speed of the recoiling black hole, scientists can determine the rate and direction of the spin in the smaller black holes before they collided; properties otherwise very difficult to determine.

A paper describing the findings of the researchers is to be published in the Astrophysical Journal.