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. 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.
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. 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. Researchers say the newfound galaxies are probably being seen as they were when the universe was about two-thirds its present age. Afterwards, and until the present day, the star-forming rate decreased quickly.