The huge elliptical galaxy Abell 2597 that lies at the heart of one of the universe’s most massive galaxy clusters has revealed a cosmic secret to the evolution and lifespan of massive galaxies.
“Galaxy evolution can be pretty chaotic, and big galaxies like this tend to live hard and die young,” says Dr Timothy Davis, Ernest Rutherford Fellow and Lecturer here at Cardiff University in the department of Physics and Astronomy. who focuses on the evolution of galaxies, and how they assemble from the cosmic soup at high redshift to become the beautiful and diverse populations we see around us in the local universe.
For the first time, says Davis, 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 by drawing in vast stores of cold molecular gas and then spraying them back out again in an ongoing cycle.
Using the Atacama Large Millimetre/submillimetre Array (ALMA) of telescopes in Chile, the team, which includes researchers from Cardiff University, has observed a supermassive black hole acting like a ‘monumental fountain’ in the middle of a galaxy, named Abell 2597, over a billion light-years from Earth.
In the ESO image of Abell 2597, above, the background (blue) is from the NASA/ESA Hubble Space Telescope. The foreground (red) is ALMA data showing the distribution of carbon monoxide gas in and around the galaxy. The pull-out box shows the ALMA data of the “shadow” (black) produced by absorption of the millimeter-wavelength light emitted by electrons whizzing around powerful magnetic fields generated by the galaxy’s supermassive black hole. The shadow indicates that cold clouds of molecular gas are raining in on the black hole.
Galaxy evolution can be chaotic and messy, but it seems that streams of cold gas spraying out from the region around supermassive black holes may act to calm the storm. This is according to an international team of scientists who have provided the first clear and compelling evidence of this process in action.
According to the Cardiff researchers, this entire system operates via a self-regulating feedback loop. The incoming material provides power for the fountain as it “drains” toward the central black hole, like water entering the pump of a fountain. This 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 the galaxy’s expansive halo, where it eventually rains back in on the black hole, triggering the entire process anew.
By studying the location and motion of molecules of carbon monoxide (CO) with ALMA, which shine brightly in millimeter-wavelength light, the researchers were able to measure the motion of the gas as it falls in toward the black hole.
It is from these plumes of gas that new stars are formed in galaxies, and the researchers believe that the process they have observed could be common across the Universe and, more importantly, could be crucial to the development of massive galaxies like this one.
“The supermassive black hole at the center of this giant galaxy acts like a mechanical ‘pump’ in a water fountain,” said Grant Tremblay, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and lead author on the paper. “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.”
The Daily Galaxy via Cardiff University and The Conversation
Image credits: NRAO/AUI/NSF; D. Berry and image top of page: B. Saxton (NRAO/AUI/NSF)/G. Tremblay et al./NASA/ESA Hubble/ALMA (ESO/NAOJ/NRAO)