{"id":124789,"date":"2013-07-18T16:15:37","date_gmt":"2013-07-18T19:15:37","guid":{"rendered":"http:\/\/revistapesquisa.fapesp.br\/?p=124789"},"modified":"2015-08-06T15:12:00","modified_gmt":"2015-08-06T18:12:00","slug":"star-archeology","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/star-archeology\/","title":{"rendered":"Star archeology"},"content":{"rendered":"

\"045-047_CensoGalaxias_208_1\"<\/a><\/em><\/p>\n

A pioneering study has begun to trace the evolutionary\u00a0history of galaxies. Under the leadership\u00a0of Spaniard Enrique P\u00e9rez of the Institute of Astrophysics\u00a0of Andaluc\u00eda, the study has identified\u00a0where and when the stars were formed in approximately one hundred galaxies that have emerged in the last 10 billion\u00a0years and are relatively close to the Milky Way, which\u00a0is home to our Sun and the Earth. The study, published in\u00a0the journal Astrophysical Journal Letters in January of this year, compared different types of galaxies and enabled\u00a0scientists to understand how their stellar masses affect\u00a0the rate of star formation within them. The research team\u00a0included Brazilian astrophysicists Roberto Cid Fernandes\u00a0of the Federal University of Santa Catarina\u2014who, in 2005,\u00a0developed Starlight, a software code that analyzes light\u00a0emitted by galaxies to reconstruct the history of their stellar\u00a0populations and conduct a kind of star archeology\u2014and his\u00a0doctoral student, Andr\u00e9 Luiz de Amorim.<\/p>\n

The research confirmed that galaxies with hundreds of\u00a0billions of stars and very high masses formed most of their\u00a0stars more than five billion years ago from the inside out, and\u00a0today, these galaxies are true star sanctuaries. Smaller galaxies with only a few billion stars are old, but they continue to\u00a0form stars in all their regions.<\/p>\n

The study was based on data from the CALIFA survey (Calar\u00a0Alto Legacy Integral Field Area Survey), a collaboration of\u00a080 researchers from 13 countries whose mission is to observe\u00a0details of star formation in approximately 600 galaxies. The project, begun in 2010, uses a telescope at the Calar Alto Observatory\u00a0in Andaluc\u00eda, Spain.<\/p>\n

The sample of 105 galaxies, as described\u00a0in Astrophysical Journal Letters,\u00a0is insignificant when compared with the\u00a0billions of galaxies in the visible Universe.\u00a0It is small, too, when compared\u00a0with the total number of galaxies\u2014approximately one million\u2014already observed\u00a0by the largest astronomical survey\u00a0ever conducted, the Sloan Digital Sky\u00a0Survey (SDSS), which was accomplished\u00a0through the efforts of another international\u00a0consortium using a telescope in\u00a0the United States. However, while the\u00a0SDSS analyzed light from galaxies as\u00a0if each one were a point in the sky, the\u00a0CALIFA survey uses a more costly and\u00a0complex technique that divides each galaxy\u00a0into a thousand pieces and analyzes\u00a0the light from each piece separately. The\u00a0result is a map that reveals the differences\u00a0in the physical and chemical properties\u00a0of the various parts of the galaxy.<\/p>\n

The CALIFA survey observes galaxies\u00a0that are at relatively close distances\u201470\u00a0million to 400 million light-years away\u2014in the Milky Way. These galaxies are neither\u00a0distant enough to observe what they\u00a0were like in the remote history of the Universe nor close enough to identify\u00a0their stars individually.<\/p>\n

\"045-047_CensoGalaxias_208_2\"<\/a>Critical mass<\/strong>
\nThe most important selection criterion\u00a0was to observe galaxies with the\u00a0greatest variety of colors and luminosities.\u00a0When seen from more or less the\u00a0same distance, young galaxies are bluish,\u00a0while older ones are reddish. Luminosity\u00a0serves as an indicator of a galaxy\u2019s\u00a0mass: the brighter it is, the more stars\u00a0it contains. \u201cThe idea was to ensure a\u00a0diversity of galaxies in order to have an\u00a0overall view,\u201d Fernandes says.\u00a0By analyzing the CALIFA data using\u00a0Starlight, the researchers determined\u00a0what combination of young and old stars\u00a0contributed to the light from each piece\u00a0of the galaxies. Following this method,\u00a0the astrophysicists identified when and\u00a0with what frequency the stars formed in\u00a0various galactic regions.<\/p>\n

The first difference confirmed by the\u00a0study concerns the rate of star formation.\u00a0Galaxies with a mass of more than 70\u00a0billion suns condensed all their gas into\u00a0stars rapidly when they were young and\u00a0formed most of their stars five billion\u00a0years ago. Galaxies of the same age but\u00a0less than 10 billion solar masses expel\u00a0their gas sparingly. \u201cThe lower-mass galaxies\u00a0continue to form stars at a respectable\u00a0rate, while for the higher-mass galaxies,\u00a0the party\u2019s over,\u201d Fernandes says.<\/p>\n

Another difference lies in the order\u00a0of star formation. The low-mass galaxies\u00a0formed their stars more or less at the\u00a0same time throughout, starting slightly\u00a0earlier in their outer regions. In the highmass\u00a0galaxies, however, the opposite occurred: star formation began earlier in the\u00a0center and moved outward. This pattern,\u00a0in fact, appears to have occurred in the\u00a0Milky Way itself, a galaxy of approximately\u00a060 billion solar masses. \u201cThe regions\u00a0farther from the center of the Milky Way have fewer heavy chemical elements than\u00a0the inner regions,\u201d explains astrophysicist\u00a0H\u00e9lio J. Rocha-Pinto of the Federal\u00a0University of Rio de Janeiro, who studies\u00a0remnants of collisions between the Milky\u00a0Way and dwarf galaxies. \u201cThis is indirect evidence that the stars in the inner region\u00a0formed first and chemically enriched that\u00a0part of the galaxy more rapidly.\u201d<\/p>\n

This difference between the center\u00a0and the periphery, however, does not\u00a0increase with galaxy mass. It reaches its\u00a0maximum in galaxies of approximately\u00a070 billion solar masses, in which the\u00a0stars in the center were formed twice as\u00a0quickly as those on the periphery.<\/p>\n

\u201cThere is something special about that\u00a0critical mass,\u201d Fernandes says. However,\u00a0no one knows exactly what that something\u00a0special is. Rocha-Pinto suggests\u00a0that the critical mass is the mass beyond\u00a0which galaxies do not grow in isolation. Scientists believe that the larger galaxies\u00a0were formed out of mergers of smaller\u00a0galaxies\u2014events in which star formation\u00a0increases in the centers of the recently\u00a0formed galaxies.<\/p>\n

Fernandes, however, calls attention to\u00a0another possibility. Large galaxies have\u00a0black holes at their centers that are so\u00a0large that they would interfere with star\u00a0formation. In small galaxies, fewer stars\u00a0are formed because some of the gas is expelled from the galaxy during supernova\u00a0explosions. Both of these effects could be\u00a0less operant in galaxies of critical mass\u00a0and could increase star formation. \u201cThe\u00a0question,\u201d according to Rocha-Pinto, \u201cis\u00a0whether we can prove the effects we are proposing are of the magnitude to explain\u00a0what we are observing.\u201d<\/p>\n

Next year, the astronomers working\u00a0on the SDSS hope to begin a similar\u00a0study, called MaNGA, that will map\u00a010,000 galaxies. \u201cIncreasing the sample\u00a0by a factor of 100 will be transformational,\u201d\u00a0says astrophysicist Kevin Bundy of\u00a0the University of Tokyo, Japan, who is\u00a0coordinating the MaNGA study. \u201cWe\u2019re\u00a0going to test the CALIFA conclusions\u00a0and much more.\u201d<\/p>\n

Scientific article<\/em>
\nP\u00c9REZ, E. et al<\/em>. The evolution of galaxies resolved in space\u00a0and time: an inside-out growth view<\/a>. The Astrophysical\u00a0Journal Letters<\/strong>. v. 763. Jan. 2013.<\/p>\n","protected":false},"excerpt":{"rendered":"Survey identifies three patterns of galaxy evolution","protected":false},"author":14,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[159],"tags":[205,206,207],"coauthors":[103],"class_list":["post-124789","post","type-post","status-publish","format-standard","hentry","category-science","tag-astronomy","tag-biodiversity","tag-bioenergy"],"acf":[],"_links":{"self":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/124789","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/users\/14"}],"replies":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/comments?post=124789"}],"version-history":[{"count":0,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/124789\/revisions"}],"wp:attachment":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media?parent=124789"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/categories?post=124789"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/tags?post=124789"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/coauthors?post=124789"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}