Dormant supermassive black holes are briefly awakened by shattered stars

A new investigation into a mysterious class of galaxies known as compact symmetric objects, or CSOs, has revealed that these objects are not quite what they seem. CSOs are active galaxies that host supermassive black holes at their cores. From these massive black holes, two jets are released, traveling in opposite directions at speeds approaching the speed of light. But compared to other galaxies with fierce jets, these jets do not extend over great distances, they are much more compact.

For many decades, astronomers had suspected that CSOs were just young, and that their planes would eventually travel to greater distances. Now, reports in three different newspapers in Astrophysical Journala team of researchers led by the California Institute of Technology concluded that civil society organizations are not young but rather live relatively short lives.

“These CSOs are not young,” explains Anthony (Tony) Redhead, Robinson Professor Emeritus of Astronomy, who led the investigation. “You can't call a 12-year-old dog a miniature even though it has lived a shorter life than an adult human. These creatures are their own distinct species that live and die over thousands of years, not millions.” Years are common in galaxies with larger jets.”

In the new studies, the team reviewed the literature and previous observations of more than 3,000 CSO candidates, verifying that 64 were genuine and identifying an additional 15 CSOs. All of these objects have been previously observed by the National Radio Astronomy Observatory's Very Long Baseline Array (VLBA), and some have been observed by other high-resolution radio telescopes.

“The VLBA observations are the most detailed in astronomy, providing images with detail equivalent to measuring the width of a human hair at a distance of 100 miles,” says Redhead.

The team's analysis concludes that CSOs ward off planes for 5,000 years or less and then die.

“CSO jets are very active jets but they seem to stop working,” says Vikram Ravi, assistant professor of astronomy at Caltech and co-author of one of the studies. “Jets stop flowing from the source.”

As for what's fueling the short-lived jets, scientists think the culprit is a tidal disruption event (TDE), which occurs when a single star wanders too close to a supermassive black hole and is eaten.

“We think one star gets torn apart, and then all that energy is funneled into jets along the axis around which the black hole rotates,” Redhead says. “A giant black hole starts out invisible to us, and then when it devours a star, there's an explosion. The black hole has fuel, and we can see it.”

Redhead was the first to suspect that CSOs might be supported by TDEs in the 1990s, but he says the idea has gone largely unnoticed by the scientific community. “The hypothesis was almost forgotten, because years passed before observational evidence for TDEs began to accumulate,” he says. At the time of his original hypothesis, only three civil society organizations had been found.

Fast forward to 2020. Redhead, who had paused his CSO studies to delve into various problems in radio astronomy, decided it was time to revisit the topic. He got some colleagues together on Zoom, and they decided to dig through the literature and weed out things that were mislabeled as CSOs. Over the next two years, the team investigated more than 3,000 CSO candidates, narrowing the pool to just a dozen who had the necessary criteria to be a true CSO.

Eventually, the picture of CSOs began to emerge as a quite distinct family of jets that were dying out much sooner than their giant brethren, such as that of the very powerful Cygnus A, a galaxy that spews out extremely powerful jets that glow brightly at radio wavelengths. . These jets extend to distances of about 230,000 light-years in each direction and last tens of millions of years. In contrast, CSO jets extend to about 1,500 light-years at most and disappear after about 5,000 years.

According to astronomers, CSO jets likely form when a supermassive black hole attacks not just any star, but a massive star.

“The TDEs we saw previously only lasted a few years,” says Ravi. “We believe that the magnificent TDEs that fuel the CSOs last much longer because the disrupted stars are either very large in size, very massive, or both.”

By analyzing the diverse array of radio images of CSOs, researchers say they can track how objects age over time, much like looking through a photo album of a CSO's life to observe how its jets evolve. Younger CSOs have shorter jets that are closer to black holes, while older objects have jets that extend farther from their black hole.

Although most jets die, scientists estimate that one in 100 will go on to become as long-lived as the one in Cygnus A. In those rare cases, galaxies will likely merge with other galaxies, a turbulent process that creates a large space of Galaxies. Fuel quantity.

If Redhead and his team's findings are confirmed by additional observations, CSOs will provide an entirely new way to study how massive stars at the centers of galaxies interact with supermassive black holes.

“These objects are actually a distinct group with their own distinct origin, and it's now up to us to learn more about them and how they came to be,” says Redhead. “The ability to study these objects on timescales of years to decades rather than millions of years has opened the door to an entirely new laboratory for studying supermassive black holes and the many surprising and unexpected surprises they hold.”