Never seen before: NASA says massive black hole leaving a trail of stars in its wake

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A supermassive black hole flying through space has left behind a trail of newborn stars twice as long as the Milky Way, a phenomenon researchers say they have never seen until now.

Researchers detailed the discovery, caught accidentally by the Hubble Space Telescope and announced on April 6, in a research paper published in The Astrophysical Journal Letters.

They say the trail of newborn stars is 200,000 light years long, while the runaway black hole weighs as much as 20 million suns and is travelling so fast it could get from the Earth to the moon in 14 minutes.

"This is pure serendipity that we stumbled across it," Pieter van Dokkum of Yale University said in a news release.

Van Dokkum says he was looking for globular star clusters in a nearby dwarf galaxy when he noticed a small streak.

"I immediately thought, 'Oh, a cosmic ray hitting the camera detector and causing a linear imaging artifact.' When we eliminated cosmic rays, we realized it was still there. It didn't look like anything we've seen before."

Researchers say the black hole may be moving so fast it is heating gas in front of it and in turn creating new star formations.

It could also be the result of radiation from an accretion disk around the black hole. An accretion disk is a hot disk of gas orbiting a black hole that serves as its main light source.

"We think we're seeing a wake behind the black hole where the gas cools and is able to form stars. So, we're looking at star formation trailing the black hole," van Dokkum said.

"What we're seeing is the aftermath. Like the wake behind a ship we're seeing the wake behind the black hole."

As for how the black hole managed to travel at such a high speed, the researchers say it could be the result of three supermassive black holes colliding with each other.

They say two galaxies likely merged about 50 million years ago, bringing two supermassive black holes to their centres that then spun around each other.

Another galaxy with its own black hole then came, with all three orbiting around each other until one finally flew out.

The researchers say follow-up observations using the James Webb Space Telescope and Chandra X-ray Observatory will confirm this theory.

Meanwhile, the upcoming Nancy Grace Roman Space Telescope, described as the wide-eyed cousin of Hubble, could reveal more star streaks elsewhere in the universe, the researchers say.