Extragalactic record-breaker
The title for earliest and most distant galaxy tends to change hands a lot these days. For now, it belongs to a galaxy known as GN-z11, which existed some 13.4 billion years ago. First described in a 2016 study published in The Astrophysical Journal, this far-flung galaxy is a whopping 32 billion light-years away — an extreme distance made possible thanks to the ever-expanding universe.
By taking spectroscopic measurements of GN-z11 with the Hubble Space Telescope, astronomers including Garth Illingworth of the University of California, Santa Cruz, looked back to when the universe was just 400 million years old — or 3 percent its current age. Although the distant galaxy during this time was just a fraction of the size of the present-day Milky Way, Illingworth and his colleagues were surprised to find GN-z11 churning out heaps of hot, young, massive stars at roughly 20 times the rate of our galaxy.
“One of the fascinating things about GN-z11 is that it is unexpectedly bright and massive for a galaxy at such an early time,” Illingworth says. “We still are not sure why this is so, but there is little doubt that it is unexpectedly luminous.”
Although astronomers already thought infant galaxies were most likely crucibles for plenty of fiercely burning stars, they did not expect to see them quite so early or in such great numbers.
“I think this comes from a perfect storm of events,” Illingworth explains. Clouds of pristine gas (almost all of it hydrogen and helium) are falling inward and colliding with each other. Bright, massive stars are forming within the metal-poor gas. And powerful shock waves are rippling through the gas itself, he explains. “All these things beget the initiation of new stars in bursts that give us the dramatic, compact, blue agglomerations of stars that we see as ‘early galaxies.’ ”
But Illingworth is quick to note that even the extremely distant GN-z11 is not one of the first galaxies to exist. Those “will be similar to GN-z11 — very small, forming stars at a great rate — but less bright, less massive, [and] with fewer stars,” he says. The first galaxies, however, will likewise appear as “dramatically young blue objects from all the star formation that is going on in bursts.”
Although we can learn a great deal about the early universe by studying specific galaxies near the edge of the cosmos, such as GN-z11, there is only so much we can conclude from individual case studies. Investigating the record-breakers is worthwhile, but studying the galactic masses can be more valuable.