This image, captured by the Very Long Baseline
Array (VLBA), shows the Compact Symmetric Object (CSO) known as
J1734+0926. The red blobs are the ends of a powerful bipolar jet
emanating from an unseen black hole.Credit: M.L. Lister/Purdue University
This illustration shows how Compact Symmetric
Objects, or CSOs, likely form. When a single, massive star wanders too
close to a black hole (left), it is devoured. This causes the black hole
to shoot out an ultrafast, bipolar jet (center). The jet extends
outward and its hot ends glow with radio emissions (right). Credit: B. Saxton/NRAO/AUI/NSF
This image, taken by the Very Long Baseline Array (VLBA), shows two
supermassive black holes, which appear as the blobs with red strips. The
black holes are in the center of an elliptical galaxy. Colors represent
different spectral slopes in radio emission, with red showing the most
dense regions surrounding the black holes. The black hole on the right
has likely recently devoured a massive star, which caused it to shoot
out two ultrafast jets. The ends of those jets appear as green blobs
above and below the black hole. This object, called J0405+3803, is
referred to as a Compact Symmetric Object (CSO), because its jets are
relatively close-in (or compact), compared to other black holes with
much larger jets.Credit: H.L. Maness/Grinnell College
Cosmic objects called Compact Symmetric Objects (CSOs) likely form when a single, massive star wanders too close to a supermassive black hole and is shredded to pieces. The process, highlighted in this animation, results in fierce bipolar jets that last up to 5,000 years. Credit: B. Saxton/NRAO/AUI/NSF
Radio observations of Compact Symmetric Objects (CSOs) provide new clues about their origins
Readhead first suspected that CSOs might be fueled by TDEs back in the 1990s, but he says the idea went largely unnoticed by the scientific community. "The hypothesis was all but forgotten because years went by before observational evidence began to mount for TDEs," he says. At the time of his original hypothesis, only three CSOs had been found.
Fast forward to 2020. Readhead, who had paused his studies of CSOs to delve into different problems in radio astronomy, decided it was time to revisit the topic. He gathered some of his colleagues together on Zoom, and they decided to comb through literature and weed out objects that had been misclassified as CSOs. Over the next two years, the team investigated more than 3,000 CSO candidates, narrowing the group down to only dozens that had the criteria to be real CSOs.
Ultimately, a picture began to emerge of CSOs as an entirely distinct family with jets that die out much sooner than their gigantic brethren, such as those of the extremely powerful Cygnus A, a galaxy that shoots out extremely powerful jets that glow brightly at radio wavelengths. These jets stretch to distances of about 230,000 light-years in each direction and last tens of millions of years. In contrast, the CSO jets extend to about 1,500 light-years at most and die out by about 5,000 years.
According to the astronomers, the CSO jets likely form when a supermassive black hole snacks on not just any star, but a substantial one.
"The TDEs we've previously seen only lasted for a few years," Ravi says. "We think that the remarkable TDEs powering CSOs last far longer because the disrupted stars are very large in size, very massive, or both."
By analyzing the varied collection of CSO radio images, the researchers say they can trace how the objects age over time, almost like looking at a photo album of a CSO's life to observe how its jets evolve. The younger CSOs have shorter jets that are closer to the black holes, while the older objects have jets that extend further out from their black hole. Though most of the jets die out, the scientists estimate that one in 100 will go onto to become long-lived like those of Cygnus A. In those rare cases, the galaxies are likely merging with other galaxies, a turbulent process that provides a large quantity of fuel.
If the discoveries of Readhead and his team are confirmed with additional observations, the CSOs will provide a whole new avenue for studying how massive stars at the centers of galaxies interact with supermassive black holes.
"These objects are indeed a distinct population with their own distinct origin, and it is up to us now to learn more about them and how they came to be," Readhead says. "Being able to study these objects on timescales 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 hold."
The three studies are, "Compact Symmetric Objects - I Towards a Comprehensive Bona Fide Catalog," "Compact Symmetric Objects – II Confirmation of a Distinct Population of High-Luminosity Jetted Active Galaxies," and "Compact Symmetric Objects – III Evolution of the High-Luminosity Branch and a Possible Connection with Tidal Disruption Events." The studies were funded by NSF, NASA, Caltech, the Max Planck Institute for Radio Astronomy in Bonn, Germany, and the European Research Council.
Fast forward to 2020. Readhead, who had paused his studies of CSOs to delve into different problems in radio astronomy, decided it was time to revisit the topic. He gathered some of his colleagues together on Zoom, and they decided to comb through literature and weed out objects that had been misclassified as CSOs. Over the next two years, the team investigated more than 3,000 CSO candidates, narrowing the group down to only dozens that had the criteria to be real CSOs.
Ultimately, a picture began to emerge of CSOs as an entirely distinct family with jets that die out much sooner than their gigantic brethren, such as those of the extremely powerful Cygnus A, a galaxy that shoots out extremely powerful jets that glow brightly at radio wavelengths. These jets stretch to distances of about 230,000 light-years in each direction and last tens of millions of years. In contrast, the CSO jets extend to about 1,500 light-years at most and die out by about 5,000 years.
According to the astronomers, the CSO jets likely form when a supermassive black hole snacks on not just any star, but a substantial one.
"The TDEs we've previously seen only lasted for a few years," Ravi says. "We think that the remarkable TDEs powering CSOs last far longer because the disrupted stars are very large in size, very massive, or both."
By analyzing the varied collection of CSO radio images, the researchers say they can trace how the objects age over time, almost like looking at a photo album of a CSO's life to observe how its jets evolve. The younger CSOs have shorter jets that are closer to the black holes, while the older objects have jets that extend further out from their black hole. Though most of the jets die out, the scientists estimate that one in 100 will go onto to become long-lived like those of Cygnus A. In those rare cases, the galaxies are likely merging with other galaxies, a turbulent process that provides a large quantity of fuel.
If the discoveries of Readhead and his team are confirmed with additional observations, the CSOs will provide a whole new avenue for studying how massive stars at the centers of galaxies interact with supermassive black holes.
"These objects are indeed a distinct population with their own distinct origin, and it is up to us now to learn more about them and how they came to be," Readhead says. "Being able to study these objects on timescales 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 hold."
The three studies are, "Compact Symmetric Objects - I Towards a Comprehensive Bona Fide Catalog," "Compact Symmetric Objects – II Confirmation of a Distinct Population of High-Luminosity Jetted Active Galaxies," and "Compact Symmetric Objects – III Evolution of the High-Luminosity Branch and a Possible Connection with Tidal Disruption Events." The studies were funded by NSF, NASA, Caltech, the Max Planck Institute for Radio Astronomy in Bonn, Germany, and the European Research Council.
Written by Whitney Clavin
Source: Caltech/News
Contact:
Whitney Clavin
(626) 395‑1944
wclavin@caltech.edu
