A new study of a rare and short-lived type of galaxy has revealed that such objects harbor dormant supermassive black holes that briefly awaken to tear apart a massive star and devour its remains like a giant cosmic breakfast.
'Compact Symmetric Objects' or CSOs are active galaxies from which two jets emerge at almost the speed of light. These jets are common among active galactic nuclei (AGNs), which have supermassive black holes at their hearts that feed on surrounding gas and dust - but the jets from CSOs are different.
While jets from AGNs can extend 230,000 light-years in either direction, CSO jets are stunted and extend only about 1,500 light-years.
Scientists had previously theorized that CSO jets are short because they are newly formed or young. Now, a team led by scientists at the California Institute of Technology (Caltech) has determined that these jets simply have a short lifespan.
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"These CSOs are not young. You wouldn't call a 12-year-old dog young, even though it lived a shorter life than an adult human," team leader Anthony Readhead, professor emeritus of astronomy at Caltech, said in a statement. "These objects are a species all their own that live and die out over thousands of years, rather than the millions of years common in galaxies with larger jets."
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To solve the mystery of CSOs and discover their true nature, Readhead and colleagues spent two years searching 3,000 CSO candidates in previous literature and astronomical data from the Very Long Baseline Array (VLBA) and 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." [160 kilometers]', says Leeskop.
The team confirmed 64 of these candidates as CSOs and also discovered another 15 of these rare galaxies. Analyzing these social organizations, the team concluded that these rare types of galaxies only emit jets for 5,000 years or less and then disappear.
"The CSO jets are very energetic jets, but they seem to be shutting down," said team member Vikram Ravi, an assistant professor at Caltech. "The jets stop flowing from the source."
The team has identified a suspect in the emissions from these jets: they theorize that the core of CSOs are supermassive black holes that rip apart stars that get too close in so-called "tidal disruption events," or TDEs.
When stars venture too close to a black hole, the black hole's immense gravity generates powerful tidal forces within the stellar body. These tidal forces stretch the star vertically and flatten it horizontally, a process called "spaghettification."
This stellar noodle wraps around him, forming a disk of matter that is gradually eaten by the supermassive black hole. But black holes are messy eaters, and some of this stellar matter is channeled toward the poles of these cosmic monsters. From there, some of the material is blown away as jets. This TDE process is accompanied by incredibly bright light emissions that announce these feeding supermassive black holes to astronomers.
"We think a single star is torn apart, and all that energy is then channeled into jets along the axis around which the black hole rotates," Readhead explains. "The giant black hole starts out invisible to us, and then when it eats a star, boom! The black hole has fuel and we can see it."
However, it is not just any star that, as CSO, can be the messy cosmic meal that wakes up a black hole. The team thinks that a CSO only forms when a really massive star is torn apart by a supermassive black hole in a TDE.
"The TDEs we've seen before only lasted a few years," Ravi explained. "We think the remarkable TDEs that power CSOs last much longer because the disturbed stars are very large, very massive, or both."
Readhead and colleagues were also able to create a "cosmic family album" that shows how social organizations and their planes evolve over time. Younger CSOs have shorter jets that are closer to the central supermassive black hole, while older CSOs have longer jets that extend further away from the TDE's location.
The team found that while the vast majority of CSOs will go extinct, 1% of them will experience long-lived events with extended jets like those seen in Cygnus A, a distant supermassive black hole whose jets are aimed at Earth. class of objects called blazar.
In these 1 in 100 long-lived events, the researchers suggest that the central black hole is fueled by additional gas and dust provided by the host galaxy's merger with another galaxy.
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For Readhead, these findings confirm a theory he first put forward in the 1990s, when only three social organizations had been discovered. This idea was largely unrecognized by the broader scientific community when it was first proposed, but should gain momentum with this new evidence.
"The hypothesis was all but forgotten because years passed before the observational evidence for TDEs started to pile up," Readhead said. "These objects are indeed a distinct population with their own distinct origins, and it is now up to us to learn more about them and how they came to be.
"Being able to study these objects on time scales of years to decades rather than millions of years has opened the door to a whole new laboratory for studying supermassive black holes and the many unexpected and unpredictable surprises they bring."
The team's research was published last month in three studies in The Astrophysical Journal.
