An artist's impression based on Hubble Space Telescope observations of a 200,000-light-year-long "contrail" of stars behind an escaping black hole. Photo: Supplied / NASA, ESA, Leah Hustak (STScI)
A supermassive black hole travelling at incredible speed is leaving behind a track of newborn stars at a scale not seen before.
NASA said it was going too fast to swallow stars and, instead, flying through a halo of gas surrounding the host galaxy.
The result is "a never-before-seen 200,000-light-year-long 'contrail' of newborn stars, twice the diameter of our Milky Way galaxy".
The black hole was spotted by accident on NASA's Hubble Space Telescope.
"It didn't look like anything we've seen before," said Yale University professor of astronomy and physics Pieter van Dokkum, who first saw the streak.
The star trail was "quite astonishing, very, very bright and very unusual", he said.
Researchers believe gas is probably being shocked and heated from the black hole's movement, or it could be radiation from an accretion disk around it.
"Gas in front of it gets shocked because of this supersonic, very high-velocity impact of the black hole moving through the gas. How it works exactly is not really known," van Dokkum said.
So the star formations were the aftermath of the black hole's trail of cooled gas, he said.
The black hole weighs as much as 20 million Suns and is suspected to haved formed from the collisions of supermassive black holes when galaxies merged, dating as far back as 50 million years ago.
The theory is that initally two of them whirled around each other harmoniously before a third came into the picture and threw off the balance, sending this detected one on its own way at high speed.
To put it into perspective, NASA said it could travel from Earth to the Moon in 14 minutes.
The research paper has been published in The Astrophysical Journal Letters.
NASA said its Nancy Grace Roman Space Telescope - which is set to launch some time this decade and will attempt to address the mysteries of dark energy - might find more of these rare "star streaks" elsewhere in the universe.
A 200,000-light-year-long chain of young blue stars from supermassive black hole, which lies at the tip of the bridge at lower left. Photo: Supplied / NASA, ESA, Pieter van Dokkum (Yale); Image Processing: Joseph DePasquale (STScI)