An artist's rendition of the galaxies Akira (right) and Tetsuo (left) © Kavli IPMU

Are ‘red geysers’ the solution to an old-galaxy mystery?

Scientists discover supermassive black hole phenomenon that stops ageing galaxies from producing new stars.

Did you know that even galaxies become less fertile with age? It has long been known that many galaxies stop producing new stars once they get to a certain point in their lifespan, but the reasons have thus far remained a mystery. Now, scientists from the University of Tokyo and the University of Oxford have published a paper in the journal Nature that might offer an explanation – a phenomenon called ‘red geysers’.

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What are ‘red geysers’?

Sadly these galactic red geysers have nothing to do with the hot water fountains on Iceland. Instead, the term is used for galaxies that don’t produce new stars, so-called quiescent galaxies, and contain a supermassive black hole.  These black holes create strong interstellar winds that sporadically heat up their surrounding gases and suppress the formation of young, blue stars, which is why they appear red.

Why can’t they form new stars?

The problem is not that the raw material needed to form stars is somehow used up, in fact quiescent galaxies have plenty of the necessary gas available, so another solution is needed.

“Stars form from the gas, a bit like the drops of rain condense from the water vapour,” says co-author Dr Michele Cappellari, from the Department of Physics at Oxford University. “In both cases one needs the gas to cool down, for condensation to occur. But we could not understand what was preventing this cooling from happening in many galaxies,”

But the discovery of interstellar winds in ‘red geysers’ offers a neat explanation to the phenomenon – they heat up the gas so much that it can’t cool down enough to condense into a star.

A galactic survey gave the answer

Using the SDSS-IV MaNGA galaxy survey, the team created multidimensional galaxy maps showing the outer appearance of galaxies as well as the movement of stars and gas inside. They then modelled the winds and movement of gases for the galaxy Akira as an example. It showed huge winds coming from a supermassive black hole at its core with enough energy to heat the ambient gases and block star formation.

This red geyser behaviour modelled in Akira is surprisingly common and the scientists reckon it is applicable to other quiescent galaxies.

Time for an intergalactic weather forecast: Watch out youngsters, Akira will be dry with a strong and hot breeze…

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