Free Astronomy Magazine January-February 2021

JANUARY-FEBRUARY 2021 year-old universe. When the uni- verse was only ten percent of its current age (1-1.5 billion years after the Big Bang), most of the galaxies experienced a “growth spurt”. Dur- ing this time, they built up most of their stellar mass and other proper- ties, such as dust, heavy element content, and spiral-disk shapes, that we see in today’s galaxies. There- fore, if we want to learn how galax- ies like our Milky Way formed, it is important to study this epoch. Galaxies in the infant Universe were surprisingly mature M assive galaxies were al- ready much more mature in the early universe than previously expected. This was shown by an international team of astronomers who studied 118 distant galaxies with the Atacama Large Millimeter/submillimeter Ar- ray (ALMA). Most galaxies formed when the universe was still very young. Our own galaxy, for exam- ple, likely started forming 13.6 bil- lion years ago, in our 13.8 billion- by ALMA Observatory A rtist’s illustration of a galaxy in the early universe that is very dusty and shows the first signs of a rotationally supported disk. In this image, the red color represents gas, and blue/brown represents dust as seen in radio waves with ALMA. Many other galaxies are visi- ble in the background, based on optical data from VLT and Subaru. [B. Saxton NRAO/AUI/ NSF, ESO, NASA/STScI; NAOJ/Subaru]