ESOOld and nearly dead: gigantic galaxies, rich in red stars, cease starmaking from the center outward ESO
The immense galaxies known as ‘red and dead’ — due to the predominant color of their extremely old stars — may not be so lifeless after all. Together with his collaborators, Sandro Tacchella, from the Institute for Astronomy in Zurich, Switzerland, analyzed images of 22 of those galaxies and saw that those red giants are not inactive. Actually, they continue to generate stars, but in other regions. When young, the central regions of these galaxies gave birth to enormous numbers of stars. Later, starmaking activity was gradually transferred to ever more peripheral zones — a process estimated to take billions of years (Science, April 17, 2015). In another study, a group led by Andra Stroe, from the Leiden Observatory, in the Netherlands, as well as David Sobral, who works not only at Leiden but also at the University of Lisbon, Portugal, identified a phenomenon that could represent these galaxies “catching their breath”, albeit only momentarily. Mergers with smaller galaxies create shockwaves that spread like a tsunami, leading to the production of new generations of stars (Monthly Notices of the Royal Astronomical Society, April 23, 2015). It is possible, however, that the immense amount of gas released in this process will deplete the galaxy, making it even redder and deader.
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