A Massive Elliptical Galaxy has Been Found to be an Avid Recycler
Approximately one billion light-years from Earth, a massive elliptical galaxy has been found to be an avid recycler, although not of plastic bottles. At its core, the supermassive black hole is blasting cold molecular gas, which is then falling into the black hole, and feeding the cycle again and again.
This kind of phenomenon is called a “fountain”, which is a galactic way to recycle star-forming material. Although it’s been a theory for a long time, it’s never been observed in its entirety…until now.
Astronomers discovered this intriguing scene in a galaxy at the heart of a cluster called Abell 2597.
Grant Tremblay from the Harvard-Smithsonian Center for Astrophysics stated that this is possibly the first system where they have found clear evidence for both cold molecular gas inflow toward the black hole and outflow or uplift from the jets that the black hole launches.
Tremblay added that this supermassive black hole at the centre of this giant galaxy functions like a mechanical pump in a fountain.
Of course, a black hole doesn’t actually spit out material. An active black hole “feeds”, material forms an accretion disc of swirling material that falls into it, similar to water swirling down a drain. However, not all the material ends up swallowed by the black hole.
Some of the material is funnelled towards the poles, perhaps through magnetic field lines, similar to how charged particles from solar wind travel along Earth’s magnetic field lines to generate aurora.
However, the dynamics of a black hole are different; rather than Aurora, they generate powerful jets of plasma, travelling almost at the speed of light into space, blasted out from their polar areas.
When it comes to this supermassive black hole powering Abell 2597’s brightest cluster galaxy (BCG), its jets blast cold molecular gas 9 kiloparsecs (30,000 light-years) into space.
This cold gas then rains back down into the reservoir that feeds into the black hole’s accretion disc – a wide filamentary nebula, with a mass equal to about 3 billion Suns, spanning 30 kiloparsecs (100,000 light-years) across in the galaxy’s centre.
Tremblay and his colleagues first observed this rain in 2016 by employing the Atacama Large Millimeter/submillimeter Array (ALMA). They saw molecules of carbon monoxide, some with temperatures as low as 13-23 Kelvin (-260 to -250 degrees Celsius, or -438 to -418 degrees Fahrenheit), falling towards the black hole.
The team has now linked it to earlier observations made using the MUSE instrument on the ESO’s Very Large Telescope. It saw the warmer gas being blasted into space by the black hole’s jets.
By using NASA’s Chandra X-ray Observatory to follow up with more observations they confirmed this link – making it the first evidence that the outflow and inflow are part of the same process.
In 2016, Tremblay explained that this extremely hot gas can quickly cool, condense, and precipitate similarly to how warm, humid air in Earth’s atmosphere can spawn rain clouds and precipitation.
Tremblay also stated that the newly condensed clouds then rain in on the galaxy, fuelling star formation and feeding its supermassive black hole.
Although this result is the first time these two parts of the process have been linked together, it’s quite possible that this is a common part of galactic evolution, according to the researchers. It could help us understand more about star formation, the way black holes feed, and the overall life cycle of galaxies.
The research has been published in The Astrophysical Journal and can be found on preprint resource arXiv.