Massive early galaxies discovered

The earliest massive galaxies ever observed have been discovered by a team using data from a five-year survey of the Universe by ESO's VISTA telescope.

The red marks in this image of the UltraVISTA field show where the newly discovered massive galaxies lie.
Credit: ESO/UltraVISTA team. Acknowledgement: TERAPIX/CNRS/INSU/CASU

Astronomers have pinpointed previously hidden giant galaxies that existed when the Universe was just 0.75 to 2.1 billion years old.

Studying more of these galaxies than any previous observation has enabled the team to find out for the first time exactly when such massive galaxies formed.

Astronomers observe galaxies to learn more about their formation and evolution, but this task becomes trickier when they attempt to peer deeper into space, seeking out the fainter, earlier galaxies that existed when the Universe was just forming. Not only are they difficult to spot; older galaxies are also much more rare and difficult to find, as most of their galactic counterparts have died out.

Using ESO’s VISTA survey telescope, Karina Caputi of the Kapteyn Astronomical Institute at the University of Groningen led a team that have discovered previously unseen, distant galaxies. They used images from the UltraVISTA survey, a five-year project to image the Universe, and were able to make a record of faint galaxies that existed when the Universe was in its infancy.

UltraVISTA observations were combined with data from NASA’s Spitzer Space Telescope to enable the team to uncover 574 new massive galaxies. The near-infrared properties of the observations meant the team could peer through space dust to see galaxies that would otherwise be obscured.

“We found no evidence of these massive galaxies earlier than around one billion years after the Big Bang, so we’re confident that this is when the first massive galaxies must have formed,” says Henry Joy McCracken, a co-author on the paper.

The team found that these massive, early galaxies are more common than previously thought and actually constitute half of the total number of massive galaxies that existed when the Universe was between 1.1 and 1.5 billion years old. The results contradict current models of galactic evolution, which do not at present theorise any massive galaxies existing during this early period.

There could also be even dustier massive galaxies that UltraVISTA cannot see. If this is the case, and they are eventually discovered, it could completely change the current view of how galaxies formed in the early Universe.


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