GN-z11 is 25 percent smaller than the Milky Way and contains barely one percent of its star mass. That makes sense, given that we're looking at an infant galaxy. However, the number of new stars being formed there outpaces the Milky Way's by 20 times. It's these bright new stars that illuminate the galaxy enough to be seen by the Hubble.
"It's amazing that a galaxy so massive existed only 200 million to 300 million years after the very first stars started to form. It takes really fast growth, producing stars at a huge rate, to have formed a galaxy that is a billion solar masses so soon," Garth Illingworth of UC Santa Cruz said in a statement. If these measurements are correct, and NASA is confident they are, that would mean GN-z11 formed near the start of the epoch of reionization, the period of time in which the first galaxies coalesced.
The team's finding will be published in the Astrophysical Journal. "We've taken a major step back in time, beyond what we'd ever expected to be able to do with Hubble. We managed to look back in time to measure the distance to a galaxy when the Universe was only three percent of its current age," the paper's lead author, Yale's Pascal Oesch, said.