(Nanowerk News) There’s an invisible monster on the loose, hurtling through intergalactic space so fast that if it were in our solar system, it could travel from Earth to the Moon in 14 minutes. This supermassive black hole, weighing as much as 20 million Suns, has left behind a never-before-seen contrail of newborn stars 200,000 light years long, twice the diameter of our Milky Way galaxy. This may be the result of a rare and strange game of galactic pool among the three massive black holes.
Instead of devouring the stars in front of it, like cosmic Pac-Man, the fast black hole crashes into the gas in front of it to trigger the formation of new stars along narrow corridors. Black holes travel too fast to take time to snack. Nothing like this has ever been seen before, but it was captured accidentally by NASA’s Hubble Space Telescope.
“We thought we were looking at wake behind the black hole where gas cooled and was able to form stars. So we were looking at star formation that followed the black hole,” said Pieter van Dokkum of Yale University in New Haven. Connecticut. “What we see is the aftermath. Like waves behind a ship, we see waves behind a black hole.” The trail must contain many new stars, considering that the trail is almost half as bright as the parent galaxy it links to.
The black hole is located at one end of the column, which extends back to its parent galaxy. There is a very bright knot of ionized oxygen at the outer end of the column. The researchers believe that the gas may be shocked and heated from the motion of the black hole hitting the gas, or it could be radiation from the accretion disk around the black hole. “The gas in front of it is stung by the super high-velocity supersonic impact of the black hole moving through the gas. How it works is not known for certain,” van Dokkum said.
“It’s pure coincidence that we came across,” added van Dokkum. He was looking for globular star clusters in a nearby dwarf galaxy. “I just scanned through the Hubble images and then I saw that we have a little line. I immediately thought, ‘oh, cosmic rays are hitting the camera detector and causing linear imaging artifacts.’ When we eliminated the cosmic rays, we realized they were still there. They looked like nothing we’d ever seen before.”
Because it was so strange, van Dokkum and his team did follow-up spectroscopy with the WM Keck Observatories in Hawaii. He described the star trails as “quite astounding, very, very bright and very unusual.” This led to the conclusion that he was looking at the aftermath of a black hole flying through a halo of gas surrounding the parent galaxy.
This intergalactic rocket is likely the result of multiple supermassive black hole collisions. Astronomers suspect the first two galaxies merged perhaps 50 million years ago. It unites two supermassive black holes at the center. They revolve around each other as binary black holes.
Then another galaxy appeared with its own supermassive black hole. It follows the old idiom: “two companies and three crowds.” The three black holes mixed together lead to a chaotic and unstable configuration. One of the black holes robbed the momentum of the other two and was ejected from the host galaxy. The original binary may have remained intact, or a new interloper black hole may have replaced one of the two that were in the original binary, kicking off the previous companion.
When one black hole takes off in one direction, the binary black hole shoots up in the opposite direction. There is a visible feature on the opposite side of the parent galaxy that may be an escaped binary black hole. Indirect evidence for this is that there is no sign of an active black hole remaining in the galactic core. The next step is to make follow-up observations with NASA’s James Webb Space Telescope and the Chandra X-ray Observatory to confirm the black hole explanation.
NASA’s upcoming Nancy Grace Roman Space Telescope will have a wide-angle view of the universe at stunningly beautiful Hubble resolution. As a survey telescope, Roman observers may find more of these rare and improbable “star streaks” elsewhere in the universe. This may require machine learning to use algorithms that are really good at finding certain odd shapes in a sea of other astronomical data, according to van Dokkum.
Research paper to be published in Astrophysics Journal Letter (“Runaway Supermassive Black Hole Candidate Identified by Shock and Star Formation in Rise”).