Astronomers using the Atacama Large Millimetre/submillimetre Array (ALMA) have observed a supermassive black hole acting like a ‘monumental fountain’ in the middle of a giant elliptical galaxy in Abell 2597, a phenomenally bright group of about 50 galaxies located over a billion light-years from Earth. At the center of this huge galaxy, known as Abell 2597 BCG, the supermassive black hole is drawing in vast stores of cold molecular gas and then spraying them back out again in an ongoing cycle.
Composite image of the galaxy cluster Abell 2597 showing the fountain-like flow of gas powered by the supermassive black hole in the central galaxy. The yellow is ALMA data of the cold gas. The red is data from ESO’s Very Large Telescope showing the hot hydrogen gas in the same region. The extend purple is the extended hot, ionized gas as imaged by NASA’s Chandra X-ray Observatory. Image credit: ALMA / ESO / NAOJ / NRAO / Tremblay et al / AUI / NSF / B. Saxton / NASA / Chandra / VLT.
“The supermassive black hole at the center of Abell 2597 BCG acts like a mechanical ‘pump’ in a water fountain,” said lead author Dr. Grant Tremblay, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics.
“This is one of the first systems in which we find clear evidence for both cold molecular gas inflow toward the black hole and outflow or uplift from the jets that the black hole launches.”
This entire system operates via a self-regulating feedback loop.
The infalling material provides power for the fountain as it ‘drains’ toward the central black hole, like water entering the pump of a fountain.
This infalling gas then causes the black hole to ignite with activity, launching high-velocity jets of super-heated material that shoot out of the galaxy. As it travels, this material pushes out clumps and streamers of gas into Abell 2597 BCG’s expansive halo, where it eventually rains back in on the black hole, triggering the entire process anew.
In total, about three billion solar masses of molecular gas is part of this fountain, forming a filamentary nebula that spans the innermost 100,000 light-years of the galaxy.
In a 2016 study by the same team, the researchers were able to verify the interconnection between the black hole and the galactic fountain by observing the region across a range of wavelengths, or portions of the spectrum.
By studying the location and motion of molecules of carbon monoxide with ALMA, which shine brightly in millimeter-wavelength light, the astronomers could measure the motion of the gas as it falls in toward the black hole.
Earlier data revealed warm, ionized gas being expelled from Abell 2597 BCG — essentially the plume of the fountain.
The new ALMA observations found clumps of cold, molecular gas in precisely the same locations as the warm gas seen in the earlier observations.
The observations also very convincingly support the hypothesis that the warm ionized and cold molecular nebulas are one-in-the-same, with the warm ionized gas merely being the ‘shell’ around the cold molecular cores that churn within this galaxy-scale fountain. This multiwavelength approach offers an uncommonly complete picture of this system.
“It’s like observing the rain cloud, rain, and puddle all at the same time,” Dr. Tremblay said.
“While this is just one observation of one galaxy, we speculate that we may be observing a process that is common in galaxies and fundamental to their evolution.”
“Galaxy evolution can be pretty chaotic, and big galaxies like this tend to live hard and die young. For the first time we have been able to observe the full cycle of a supermassive black hole fountain, that acts to regulate this process, prolonging the life of galaxies,” said co-author Dr. Timothy Davis, of Cardiff University.
The findings appear in the Astrophysical Journal (arXiv.org preprint).
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G.R. Tremblay et al. 2018. A Galaxy-scale Fountain of Cold Molecular Gas Pumped by a Black Hole. ApJ 865, 13; doi: 10.3847/1538-4357/aad6dd
