Hubble discovers black hole beam promotes stellar flares

In a surprising discovery, astronomers using the NASA/ESA Hubble Space Telescope have discovered that the blowtorch-like jet from a supermassive black hole at the heart of a huge galaxy appears to cause stars to erupt along its path. The stars, called novae, are not captured inside the jet, but are apparently in a dangerous neighborhood nearby.

The research is published on the arXiv preprint server.

This discovery baffles researchers looking for an explanation. “We don’t know what’s going on, but it’s just a very exciting finding,” said lead author Alec Lessing of Stanford University. “This means there is something missing in our understanding of how black hole jets interact with their environment.”

A nova erupts in a two-star system where an aging, swollen normal star spills hydrogen onto a burned-out white dwarf companion star. When the dwarf has accumulated a surface layer of hydrogen a kilometer deep, this layer explodes like a giant nuclear bomb. The white dwarf is not destroyed by the nova eruption, which ejects its surface layer then begins siphoning fuel from its companion again, and the nova explosion cycle begins again.

Hubble found twice as many novae near the jet as elsewhere in the giant galaxy during the period studied. The jet is launched by a central black hole of 6.5 billion solar masses surrounded by a disk of swirling matter.

The black hole, full of infallible matter, launches a jet of plasma 3,000 light years long which crosses space at a speed close to that of light. Anything caught in the energy beam would sizzle. But being near its thundering flow is apparently also risky, according to new findings from Hubble.

The discovery of twice as many novae near the jet implies that there are twice as many nova-forming double star systems near the jet or that these systems erupt twice as often as similar systems elsewhere in the galaxy.

“There’s something the jet does to star systems wandering around. Maybe the jet somehow shoots hydrogen at the white dwarfs, causing them to erupt more frequently,” Lessing said.

“But it’s not clear that this is a physical surge. It could be the effect of the pressure of the light emanating from the jet. When you deliver hydrogen faster, you get flares faster. Something could double the rate of mass transfer on white dwarfs near the jet.

Another idea the researchers are considering is that the jet heats the dwarf’s companion star, causing it to overflow further and dump more hydrogen onto the dwarf. However, the researchers calculated that this heating is not significant enough to produce this effect.

“We’re not the first to say that there appears to be more activity around the M87 jet,” said co-investigator Michael Shara of the American Museum of Natural History in New York. “But Hubble showed this increased activity with far more examples and statistical significance than ever before.”

Shortly after Hubble’s launch in 1990, astronomers used its first-generation Faint Object Camera (FOC) to peer into the center of M87, where the monster black hole lurks. They noticed unusual things happening around the black hole.

Almost every time Hubble looked, astronomers saw bluish “transient events” that could be evidence of novae bursting like the flashes of nearby paparazzi cameras. But the FOC’s view was so narrow that Hubble astronomers couldn’t look away from the jet to compare with the region near the jet. For more than two decades, the results remained mysteriously tantalizing.

Compelling evidence of the jet’s influence on stars in the host galaxy was collected over a nine-month interval when Hubble observed with newer, larger cameras to count erupting novae. This presented a challenge to the telescope’s observing schedule, as it required revisiting M87 precisely every five days for another snapshot. Adding all the M87 images together led to the deepest images of M87 ever taken.

Hubble found 94 novae in the third of M87 that its camera can encompass. “The jet wasn’t the only thing we were looking at: we were looking at the entire inner galaxy. Once you trace all the known novae above M87, you no longer need statistics to convince you that there is an excess of novae along M87 It’s not rocket science We made the discovery just by looking at the images and, although we were really surprised, our statistical analyzes of the data confirmed what we have. clearly seen,” Shara said.

“We are witnessing an intriguing but puzzling phenomenon,” commented Chiara Circosta, an ESA researcher who studies the impact of the accretion of supermassive black holes on the galaxies that host them in the distant universe.

“I was very surprised by this discovery. Such detailed observations of nearby galaxies are valuable for expanding our understanding of how jets interact with their host galaxies and potentially affect star formation.”

This achievement is entirely due to Hubble’s unique capabilities. Images from ground-based telescopes lack the clarity needed to see novae deep within M87. They cannot detect stars or stellar flares near the galaxy’s core because the surroundings of the black hole are far too bright. Only Hubble can detect novae against the bright background of M87.

Novae are remarkably common in the universe. A nova erupts every day somewhere in M87. But since there are at least 100 billion galaxies in the visible universe, about a million novae erupt somewhere every second.