A year after astronomers revealed that ancient galaxies were responsible for filling the universe with background infrared radiation, the same scientists now say there were more of these galaxies than the 200 initially reported.
This news, to be presented this week at a workshop in Germany organized by the Max Planck Institute of Astronomy, confirms previous studies indicating that star formation was much more rampant in the early universe than suspected.
Some cosmic background
Researchers believe that all galaxies, at some time in their distant past, emitted the radiation that now makes up what researchers call the Cosmic Infrared Background -- a faint infrared glow that permeates the entire universe. But the easiest galaxies to see are the nearby ones, which have long since stopped creating the emissions.
So, as astronomers love to do, they looked into the most distant recesses of the universe, thereby also looking back in time and seeing what our galaxy might have looked like billions of years ago. The newly spotted galaxies hide behind thick curtains of cosmic dust and have only recently been detectable by advanced, more sensitive infrared telescopes.
Lots of birth
The first results of the European Space Agency's Infrared Space Observatory (ISO) study, presented a year ago, told of 200 ancient galaxies in which far more stars were being born than astronomers had previously calculated based on optical observations. Optical investigations are limited because many distant galaxies are hidden behind curtains of dust. The galaxies found via infrared methods were also discovered to be more actively evolving than modern-day galaxies.
Having fully digested the initial results, five dozen astronomers are reporting this week on their more detailed conclusions, which include the newly-found galaxies and confirmation of the presence of lots of dust -- the stuff of which stars are made.
"We can fully confirm our estimates of last year about star formation, and we can also be much more specific about the galaxies we have observed", Italian astronomer Dario Fadda said. "We have detected more than a thousand distant young galaxies, seen for the first time in the infrared. Many of them had been observed with optical telescopes, but the fact that they are bright in the infrared means that they are dusty, and hence, that a lot of new stars are being born there. We are seeing galaxies evolving very quickly".
Researchers say the newfound galaxies are probably being seen as they were when the universe was about two-thirds its present age.
"The ISO results not only test the models of galaxy evolution, but also give new observational constraints on this process," said Hervé Dole, from the Institut d'Astrophysique Spatiale in France. "Now we can be sure that there was much more star formation than previously thought, and that the maximum for that star formation happened when the universe was between three- and one-thousand million years old -- assuming that the present universe is fifteen thousand million years old. Afterwards, and until the present day, the star-forming rate decreased quickly."
The latest results from the study will be published soon in the scientific journal Astronomy and Astrophysics.
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