Galaxies are said to build up very slowly and take billions of years to reach their great mass. But a newly discovered galaxy that appeared in the universe when it was only 1.8 billion years old tells a different story. It formed stars at speeds hundreds of times faster than the Milky Way, and grew to 200 billion stars in less than 500 million years – perhaps the fastest speed in the universe.
Galaxies are slowly building up. They start with very small nuggets and merge together over hundreds of millions and even billions of years, growing steadily until they reach their present size in today's universe.
This is known as the hierarchical model and is the prevailing theory used to explain the growth of galaxies over cosmic time.
But astronomers using the University of Arizona large binoculars telescope discovered a strange ball (there always has to be a strange ball, right?). This galaxy called C1-23152 is billions of light years away from us. Its light has been moving for over 12 billion years, making it a relatively young galaxy on the cosmic scene that appears when our universe was only 1.8 billion years old.
C1-23152 grew to 200 billion suns in just 500 million years. Image via INAF / HST / NASA / ESA.
By measuring the age, metal content, and speed of the stars in C1-23152, the study's astronomers discovered something amazing. As far as you can tell, this galaxy grew out of nowhere and took only 500 million years to do so.
At the height of its star formation, C1-23152 spawned hundreds of stars each year, with an average of a few stars being awarded each day. To give you some perspective, the Milky Way currently only produces a handful of stars per year.
In less than half a billion years, C1-23152 managed to move from a cosmic nobody to a massive superstar galaxy.
But if C1-23152 didn't grow up in the usual hierarchical way, then how did it get so big so quickly? Astronomers believe that C1-23152 is the result of a massive cosmic accident in which two giant gas clouds collided in the early universe, triggering a round of rapid star formation that could last hundreds of millions of years and form a galaxy in the process.
By studying more galaxies like C1-23152, astronomers can better understand all of the complicated ways galaxies build up in our universe.