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A Black Hole has been Burping for 100 Million Years

Black holes are incredibly massive objects that can be found at the center of galaxies. They have a gravitational pull so strong that nothing, not even light, can escape them. When anything made of simple matter gets too close, like a planet, star, or gas cloud, it is inevitably consumed by the black hole. However, black holes do not immediately consume their prey; instead, they "play with their food" like a fussy child, sometimes spewing out light.

In the center of a galaxy cluster, black holes can create enormous cavities in the hot gas at the cluster's center through these burps and jets, which are called radio bubbles. To study black holes, astronomers rely on observing the light that comes from the environment surrounding them, as the black holes themselves do not emit light.

A recent study published in Astronomy and Astrophysics examined a supermassive black hole that was burping out mysterious radio bubbles, using the National Science Foundation's Green Bank Telescope. The lead author, Jack Orlowski-Scherer, described the burp as a violent release of energy that occurs when a black hole is fed.

Supermassive black holes are found in the centers of large galaxies and are present in every large galaxy, including those at the heart of galaxy clusters. The environment at the heart of a galaxy cluster is extreme, with scorching plasma that can reach temperatures up to 50 million degrees Celsius. Over time, the plasma radiates x-rays, and as it cools, stars can form. However, black holes can emit jets of heated material from their centers, preventing star formation through a process called black hole feedback. These jets are powerful enough to push away the hot gas in the center of the galaxy cluster, creating vast radio bubbles.

The black hole feedback loop is a complex process that involves enormous energy to move gas, and astrophysicists are trying to determine where all that energy comes from. A graphic from the team at the Space Science Telescope Institute describes this process, but it's not as straightforward as it seems. To understand the energy source, researchers probed the radio bubbles, which led them to the galaxy cluster MS0735.

Using the Green Bank Telescope, the world's largest fully steerable radio telescope located in West Virginia, the team aimed the MUSTANG-2 receiver, a type of camera called a continuum receiver that operates across multiple channels, at MS0735. This cluster is known for having an enormously massive black hole in its center, and the jets coming from the black hole are one of the most powerful active galactic nucleus eruptions ever recorded. The eruption has been going on for over 100 million years and has released as much energy as hundreds of millions of gamma-ray bursts.

Lead author Orlowski-Scherer noted that the team is looking at one of the most energetic outbursts ever seen from a supermassive black hole. The jets are the likely cause behind the radio bubbles, which prevent star formation. However, how the jets work is unknown, but they somehow provide the heat needed to prevent it. The authors of the paper explain that "jets are the main drivers of ICM (Intra-Cluster Medium) reheating, although the exact mechanism is not clear yet."

The team studied the region using MUSTANG-2's power to peer into the bubbles. They took advantage of the Sunyaev-Zeldovich (SZ) effect, a subtle distortion of the Cosmic Microwave Background (CMB), sometimes called the echo from the Big Bang. The SZ effect registers as a slight thermal pressure at 90 GigaHertz, where MUSTANG-2 can sense it. The radio waves in this band have wavelengths from one to ten millimeters.

NASA's Chandra X-ray Observatory (left image) and the GBO's MUSTANG-2 instrument (right image) have captured observations that reveal enormous cavities excavated by powerful radio jets (green contours) expelled from the black hole located at the center of galaxy cluster MS0735. The gray circles highlight these cavities. The Naval Research Laboratory's VLA Low-band Ionosphere and Transient Experiment (VLITE) back end used on the National Radio Astronomy Observatory's (NRAO) Very Large Array (VLA) also performed observations and provided the green contours in both images. The study, led by Orlowski-Scherer et al. in 2022, presents the deepest high-fidelity SZ observations yet of the inside of the bubbles. The SZ effect helps distinguish between thermal pressure causes and non-thermal pressure and relativistic electron causes, allowing for a more nuanced understanding of the cause of the cavities, which includes both thermal and non-thermal sources.

According to Tony Mroczkowski, an astronomer with the European Southern Observatory who was part of this new research, "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." Although this isn't the first time that astrophysicists have studied these radio bubbles, the observations in this new study are the most detailed yet, revealing a more complete picture of the system. Tracy Clarke, an astronomer at the U.S. Naval Research Laboratory and VLITE Project Scientist who co-authored a previous radio study of this system, explains, "We knew this was an exciting system when we studied the radio core and lobes at low frequencies, but we are only now beginning to see the full picture."

Galaxy clusters play a crucial role in the Universe's structure formation, and their continuous growth through mergers and accretion results in some of their energy remaining non-thermal. This non-thermal energy comes from turbulence and bulk motion, and researchers aim to determine how much of a cluster's pressure support is not thermal to better understand how the gas in the intra-cluster medium reaches equilibrium, a process known as virialization that ultimately leads to star formation.

One of the key issues related to this problem is black hole feedback, which can prevent star formation. To address this, scientists are studying the thermal and non-thermal pressures that support the radio bubbles in clusters, using tools like the GBT/MUSTANG-2 receiver across multiple frequencies. By examining the role of turbulence, magnetic fields, and cosmic rays in supporting these bubbles, researchers hope to gain a clearer understanding of the complex environment in galaxy clusters.

According to Orlowski-Scherer, "This work will help us better understand the physics of galaxy clusters and the cooling flow feedback problem that has vexed many of us for some time."

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