On April 23, 2009, NASA’s Swift satellite captured a glimpse of the most distant astronomical object ever seen—the fading afterglow of a massive stellar explosion called a gamma-ray burst. Astronomers calculated that the light from this burst took 13 billion years to reach Earth. This means the star exploded 13 billion years ago, just 630 million years after the Big Bang.
Astronomers hoped that this event would offer the first observational evidence of an elusive class of stars called Population III. These are the Universe’s earliest stars, which contain a mixture of hydrogen, helium, and a bit of lithium created in the Big Bang. As Population III stars exploded and died, they combined these lighter elements into heavier ones that seeded subsequent generations of stars, including our own Sun, a Population I star. “Population III stars are very likely to look quite different from stars that we are used to,” says University of Leicester astronomer Nial Tanvir, whose team closely studied the April 23 gamma-ray burst. “They also likely undergo rather different evolutionary histories. One would be rather surprised if any gamma-ray bursts they produced didn't also look different.”