A new investigation into an obscure class of galaxies known as Compact Symmetric Objects, or CSOs, has revealed that these objects are not entirely what they seem. CSOs are active galaxies that host supermassive black holes at their cores. Out of these monstrous black holes spring two jets traveling in opposite directions at nearly the speed of light. But in comparison to other galaxies that boast fierce jets, these jets do not extend out to great distances-they are much more compact. For many decades, astronomers suspected that CSOs were simply young and that their jets would eventually travel out to greater distances.
Now, reporting in three different papers in The Astrophysical Journal, a Caltech-led team of researchers has concluded that CSOs are not young but rather lead relatively short lives.
"These CSOs are not young," explains Anthony (Tony) Readhead, the Robinson Professor of Astronomy, Emeritus, who led the investigation. "You wouldn't call a 12-year-old dog young even though it has lived a shorter life than an adult human. These objects are a distinct species all of their own that live and die out in thousands of years rather than the millions of years that are common in galaxies with bigger jets."
In the new studies, the team reviewed literature and past observations of more than 3,000 CSO candidates, verifying 64 as real and identifying an additional 15 CSOs. All these objects had been previously observed by the National Radio Astronomy Observatory's Very Long Baseline Array (VLBA), funded by the National Science Foundation (NSF), and some had been observed by other high-resolution radio telescopes. "The VLBA observations are the most detailed in astronomy, providing images with details equivalent to measuring the width of a human hair at a distance of 100 miles," Readhead says.
The team's analysis concludes that CSOs expel jets for 5,000 years or less and then die out. "The CSO jets are very energetic jets but they seem to shut off," says Vikram Ravi, assistant professor of astronomy at Caltech and a co-author of one of the studies. "The jets stop flowing from the source."
As for what is fueling the short-lived jets, the scientists believe the cause is a tidal disruption event (TDE), which occurs when a single star wanders too close to a supermassive black hole and is devoured.
"We think that a single star gets ripped apart, and then all that energy is channeled into jets along the axis the black hole is spinning around," Readhead says. "The giant black hole starts out invisible to us, and then when it consumes a star, boom! The black hole has fuel, and we can see it."
