A black hole is burping radiation and scientists are trying to find out why
An international collaboration of researchers used observations from the Green Bank Telescope (GBT) to find out more about a supermassive black hole that mysteriously gives out bubbles of radiation, a press release said.
Supermassive black holes are often seen at the heart of galaxy clusters in the centers of enormous galaxies. The atmospheres of these galaxy clusters are filled with hot plasma that can exceed temperatures of 50 million degrees Celsius. Over long periods of time, these temperatures cool down relatively, which allows the formation of new stars.
In some circumstances, though, the supermassive black hole can reheat the gas that surrounds it by sending out violent outbursts from its center. This process, called feedback, can prevent the cooling down of the atmosphere and the subsequent formation of a star.
Why do scientists study feedback from black holes?
Jets of radiation that are part of the feedback from a supermassive black hole can carve out large cavities inside the hot plasma of the galaxy clusters. As the gas moves farther from the cluster center, it is replaced by large bubbles that can emit radiation, the press release said.
Displaying such large volumes of gas needs massive amounts of energy. However, scientists haven't still figured out the source of this energy, and by studying what remains in these cavities, astronomers hope to find out how they are formed.
What did the researchers find?
The international collaboration of researchers from institutes in Italy, Germany, Russia, Canada, and the U.S. used the MUSTANG-2 receiver on the Green Bank Telescope located in West Virginia to image the galaxy cluster MS0735 constellation Camelopardalis, located 2.6 billion light years away from us.
During their observation, the researchers used the Sunyaev-Zeldovich (SZ) effect, which looks at the subtle distortion in the cosmic microwave background (CMB) radiation due to scattering by hot electrons in the gas of a galaxy cluster. The CMB was emitted 380,000 years thousand years after the Big Bang. The SZ effect signal as observed by the MUSTANG-2 receivers on the GBT telescope primarily measures thermal pressure, the press release said.
"With the power of MUSTANG-2, we are able to see into these cavities and start to determine precisely what they are filled with, and why they don’t collapse under pressure," said Tony Mroczkowski, an astronomer with the European Southern Observatory, who was part of the international collaboration.
The images taken by the collaboration are the deepest SZ images of the thermodynamic state of cavities in a galaxy cluster. These new images support the previous findings that at least part of the pressure support in the cavities comes from non-thermal sources such as cosmic rays, turbulence, and also the magnetic field to a limited extent.
However, the research team also found that the pressure support within the bubbles is likely more nuanced than previously thought. By complementing their observations with that of NASA's Chandra X-ray Observatory, the researchers also obtained complementary views of the gas observed by MUSTANG-2.
"We’re looking at one of the most energetic outbursts ever seen from a supermassive black hole,” said Jack Orlowski-Scherer, another researcher associated with the study “This is what happens when you feed a black hole and it violently burps out a giant amount of energy.”
The research findings were published in the journal Astronomy and Astrophysics
Mechanical feedback from active galactic nuclei is thought to be the dominant feedback mechanism quenching cooling flows and star formation in galaxy cluster cores. It, in particular, manifests itself by creating cavities in the X-ray emitting gas, which are observed in many clusters. However, the nature of the pressure supporting these cavities is not known.
Aims. Using the MUSTANG-2 instrument on the Green Bank Telescope (GBT), we aimed to measure thermal Sunyaev-Zeldovich (SZ) effect signals associated with the X-ray cavities in MS0735.6+7421, a moderate-mass cluster that hosts one of the most energetic active galactic nucleus outbursts known. We used these measurements to infer the level of nonthermal sources of pressure that support the cavities, such as magnetic fields and turbulence, as well as relativistic and cosmic ray components.
Results We show that the SZ signal associated with the cavities is suppressed compared to the expectations for a thermal plasma with temperatures of a few tens of keV. The smallest value of the suppression factor, f, that is consistent with the data is ∼0.4, lower than what has been inferred in earlier work. Larger values of f are possible once the contribution of the cocoon shock surrounding the cavities is taken into account.
Conclusions. We conclude that in the “thermal” scenario when half of the pressure support comes from electrons with a Maxwellian velocity distribution, the temperature of these electrons must be greater than ∼100 keV at 2.5σ confidence. Alternatively, electrons with nonthermal momentum distribution could contribute to the pressure, although existing data do not distinguish between these two scenarios. The baseline model with cavities located in the sky plane yields a best-fitting value of the thermal SZ signal suppression inside cavities of f ∼ 0.5, which, at face value, implies a mix of thermal and nonthermal pressure support. Larger values of f (up to 1, i.e., no thermal SZ signal from the cavities) are still possible when allowing for variations in the line-of-sight geometry.
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