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A recent investigation into a class of galaxies known as Compact Symmetric Objects (CSOs) has challenged previous assumptions about the nature of these objects. CSOs are active galaxies that host supermassive black holes at their cores, giving rise to two jets that travel in opposite directions at close to the speed of light. However, unlike other galaxies with similar jets, CSO jets are much more compact and do not extend to great distances. Until recently, astronomers believed that CSOs were young and that their jets would eventually travel out to greater distances.

Through a series of studies published in The Astrophysical Journal, a team led by Anthony Readhead at Caltech has concluded that CSOs are not young but rather have relatively short lifespans. Reviewing literature and past observations of over 3,000 CSO candidates, the team verified 64 as real CSOs and identified an additional 15. The team’s analysis indicates that CSOs expel jets for 5,000 years or less before dying out, leading to the belief that these objects are a distinct species with short life spans compared to other galaxies with bigger jets.

The researchers propose that the short-lived jets in CSOs are fueled by tidal disruption events (TDE) where a single star wanders too close to a supermassive black hole and gets devoured. This event releases a large amount of energy that is channeled into jets along the axis the black hole is spinning around. Readhead had originally proposed this hypothesis in the 1990s, but it went unnoticed until recent observational evidence began to support TDEs. The team’s findings provide new insights into the formation and evolution of CSOs and how they interact with supermassive black holes.

By analyzing a diverse collection of CSO radio images, the researchers were able to track how these objects evolve over time, creating a sort of photo album of a CSO’s life and observing how its jets change. Younger CSOs have shorter jets closer to the black holes, while older objects have jets that extend further out. While most CSO jets die out, the team estimates that one in 100 may go on to become long-lived like those of Cygnus A, a galaxy with particularly powerful jets. These long-lived jets likely result from galaxies merging with other galaxies, providing a large quantity of fuel for the supermassive black hole.

If these discoveries are confirmed with additional observations, CSOs could offer a new way to study how massive stars at the centers of galaxies interact with supermassive black holes. The team’s research has opened up a new avenue for studying supermassive black holes on shorter timescales, allowing for a deeper exploration of these enigmatic objects and the surprises they may hold. Readhead and his colleagues hope to learn more about the distinct origin of CSOs and how they came to be. This unique population of galaxies presents a wealth of opportunities for further investigation and understanding the complex interactions within our universe.

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