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CNR: Alamanacco della Scienza

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N. 6 - 27 mar 2013
ISSN 2037-4801

International info   a cura di Cecilia Migali

Tecnologia

‘Alma‘ rewrites the history of Universe‘s stellar baby boom

Observations with the Atacama Large Millimeter/submillimeter Array (Alma) show that the most vigorous bursts of star birth in the cosmos took place much earlier than previously thought. The results are published in a set of papers of the journal 'Nature' and of the 'Astrophysical Journal'. The research is the most recent example of the discoveries coming from the new international Alma observatory, which celebrates its inauguration today.

The most intense bursts of star birth are thought to have occurred in the early Universe, in massive, bright galaxies. These starburst galaxies convert vast reservoirs of cosmic gas and dust into new stars at a furious pace - many hundreds of times faster than in stately spiral galaxies like our own galaxy, the Milky Way. By looking far into space, at galaxies so distant that their light has taken many billions of years to reach us, astronomers can observe this busy period in the Universe's youth.

"The more distant the galaxy, the further back in time one is looking, so by measuring their distances we can piece together a timeline of how vigorously the Universe was making new stars at different stages of its 13.7 billion year history", said Joaquin Vieira (California Institute of Technology, Usa), who led the team and is lead author of the paper in the journal Nature.

The international team of researchers first discovered these distant and enigmatic starburst galaxies with the US National Science Foundation's 10-metre South Pole Telescope (Spt) and then used Alma to zoom in on them to explore the stellar baby boom in the young Universe. They were surprised to find that many of these distant dusty star-forming galaxies are even further away than expected. This means that, on average, their bursts of star birth took place 12 billion years ago, when the Universe was just under 2 billion years old - a full billion years earlier than previously thought. Two of these galaxies are the most distant of their kind ever seen - so distant that their light began its journey when the Universe was only one billion years old. What's more, in one of these record-breakers, water is among the molecules detected, marking the most distant observations of water in the cosmos published to date.

The team used the unrivalled sensitivity of Alma to capture light from 26 of these galaxies at wavelengths of around three millimeters. Light at certain specific wavelengths can be produced by gas molecules in these galaxies, and the wavelengths are stretched by the expansion of the Universe over the billions of years that it takes the light to reach us. By measuring the stretched wavelengths, astronomers can calculate how long the light's journey has taken, and place each galaxy at the right point in cosmic history.

"Alma's sensitivity and wide wavelength range mean we could make our measurements in just a few minutes per galaxy - about one hundred times faster than before", said Axel Weiss (Max-Planck-Institut für Radioastronomie in Bonn, Germany), who led the work to measure the distances to the galaxies. "Previously, a measurement like this would have been a laborious process of combining data from both visible-light and radio telescopes".

For a few galaxies the team combined the Alma data with measurements from other telescopes, including the Atacama Pathfinder Experiment (Apex) and Eso's Very Large Telescope. The astronomers were using only a partial array of 16 of Alma's full complement of 66 giant antennas, as the observatory was still under construction at an altitude of 5000 meters on the remote Chajnantor Plateau in the Chilean Andes. When complete, Alma will be even more sensitive, and will be able to detect even fainter galaxies. For now, astronomers targeted the brighter ones. They took advantage of a helping hand from nature, too: using gravitational lensing, an effect predicted by Einstein's general theory of relativity, where light from a distant galaxy is distorted by the gravitational influence of a nearer foreground galaxy, which acts like a lens and makes the distant source appear brighter.

 

 

Per saperne di più: - www.eso.org/public/news/eso1313/