Astronomers Have Seen A "Galactic Fountain" In Full Flow For The First Time

An artist's impression of the black hole in Abell 2597. NRAO/AUI/NSF; D. Berry

An international team of astronomers has detected what they say is a “colossal fountain” of gas coming from a black hole in a bright galaxy one billion light-years away.

A study describing the findings was published in The Astrophysical Journal. The team described how they used the Atacama Large Millimeter Array (ALMA) and Very Large Telescope (VLT) in Chile to observe a relatively close galaxy cluster called Abell 2597.

Looking at the brightest galaxy in this cluster, they found that the supermassive black hole at its core was firing out cold molecular gas into space, which then rained back onto the black hole. Such a vast system, with the “fountain” spanning 100,000 light-years, has never been seen before.

“This is possibly the first system 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,” Grant Tremblay of the Harvard-Smithsonian Center for Astrophysics, the study’s lead author, said in a statement from the European Southern Observatory (ESO). “The supermassive black hole at the centre of this giant galaxy acts like a mechanical pump in a fountain.”

It’s thought that this fountain system is self-regulating. The black hole sends material out into space in high-velocity jets of super-heated material, which then gradually falls back towards the black hole, providing power that increases its activity, and the process repeats.

“It’s like observing the rain cloud, rain, and puddle all at the same time,” Tremblay said in a statement from the National Radio Astronomy Observatory (NRAO). 

A composite image from ALMA (yellow), the VLT (red), and the Chandra X-ray Observatory (blue-purple) showing the black hole. Yellow is material falling in, and red is material flowing out. ALMA (ESO/NAOJ/NRAO), Tremblay et al.; NRAO/AUI/NSF, B. Saxton; NASA/Chandra; ESO/VLT

Despite being fired out in jets, the material is unable to escape the gravitational pull of the galaxy. The fountain is thought to contain about 3 billion solar masses of material. The gas that the black hole fires out tends to be warm, whereas the material that falls back towards it cools down to low temperatures of about -260°C (-435°F).

According to the researchers this process may be common in the universe, and could provide more information about how galaxies form. We’ve seen material flowing into or out of a galaxy before, but never both simultaneously like this, proving they are part of the same process.

“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,” the statement from the NRAO noted.

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