. Galaxy death occurs when the core ceases making new stars. However, the outer regions continue to produce new stars according to a release from the ESA/Hubble Information Centre. Astronomers revealed for the first time how stars formed in dead galaxies many billions of year ago. ESO’s Very Large Telescope and NASA/ESA Hubble Space Telescope revealed that these galaxies still made stars at their edges three billion years ago, after which the universe began to form (Big Bang). The star formation seems to have stopped in galaxies’ cores. This is because the stars are then quenched and spread to their outer regions. This latest research was published in Science by the researchers. Star formation appears to have been slowed down in the inner galaxies, and spread out to the outer regions. Credit: ESA/Hubble, ESO. How can massive galaxies slowdown? The mystery of how large, inactive, elliptical galaxy clusters that are so common today in the Universe have lowered their star-formation rates has long been a major part of astronomy. These massive galaxies are sometimes called “spheroids” because they have an unusual shape. They have approximately ten times the star density in their central regions than our Milky Way and a mass of ten-tenths of our galaxy. These massive galaxies are called’red-and-dead’ by astronomers because of their abundance of old red stars and very few young blue stars. They also have no signs of star formation. According to the estimated age of these red stars, they stopped creating new stars around ten billions of years ago. The extinction of star formation occurred at the height of the Universe’s star-formation, at which time several galaxies still formed stars at twenty times the current pace. Sandro Tacchella of ETH, Eidgenossische Technische Hochschule – Swiss Federal Institute of Technology, Zurich, Switzerland is the lead author of this article. He stated that massive dead spheroids account for half of all stars the Universe produced over its lifetime. Without understanding how galaxies came to be, we cannot say that we know how the Universe developed and evolved into what we see today. Tachella and her team observed 22 galactics from three billion years after the big Bang. They covered a wide range of masses. To view the galaxies, they used the Hubble Space Telescope’s WFC3 (“Wide Field Camera 3”) camera. Camera captured detailed images in near-infrared to reveal the distribution of older stars within active star-forming galaxies. The SINFONI instrument, which is part of ESO’s Very Large Telescope, was also used to capture light from galaxies. This allowed them to pinpoint the locations where new stars are being created. Marcella Carollo from ETH Zurich was also a co-author. She said that “Hubble could show us in incredible detail how stars are distributed inside these galaxies.” This accuracy was also possible with SINFONI, which allowed us to locate patches of starformation. The latest data revealed that most of the large galaxies had maintained their constant production of stars at their outer edges. Star formation stopped in the densely packed, bulging centres. Alvio Renzini of Padova Observatory said that the star formation had stopped in their bulging, densely packed centres. This should help to shed light on the mechanisms behind the phenomenon, which has been long debated by astronomers. Scientists believe that fresh gas is stopped flowing into galaxies, starving them of new material and turning them into dead spheres. Natascha Schreiber, co-author, of the Max-Planck-Institut fur extraterrestrische Physik, Garching, Germany said that fresh gas stops flowing into a galaxy, starving it of material for new stars and turning it into a red, dead spheroid. This is about 13.8billion years after the Big Bang. The galaxies Tacchella, and others studied by her are usually viewed as they were over 10 million years ago. Citation: “Evidence of mature bulges after an inside-out quenching phase three billion years following the Big Bang,” S. Tacchella and colleagues, C. M. Carollo. A. Renzini. N. M. Forster Schreiber. P. Lang. S. Wuyts. G. Cresci. A. Dekel. R. Genzel. S. J. Lilly. C. Mancini. S. Newman. M. Onodera. Shapley. Tacconi. Tacconi. Woo and G. Zamorani. Science. Published 17 April, 2015 DOI: 10.1126/science. 1261094.
