If you had asked this question before September 2005, most astronomers would have said that quasars are, by far, the most distant objects in the Universe. This has changed with the detection of a gamma-ray burst originating at the edge of the visible Universe.
A quasar is a distant galaxy with a supermassive black hole at its core. The black hole is pulling in interstellar gas at a furious rate. This releases energy—that is, light. The quasar, short for quasi-stellar object, is so far that this brilliant light looks like a pinpoint, or a star. There were other objects in the early Universe, to be sure. But the quasars are so bright that these are all we can see from this era… until now.
On September 4, 2005, NASA’s Swift satellite detected a very distant gamma-ray burst. These bursts are the most powerful explosions known. They occur from our perspective at a rate of about one per day. They are random and only last for a few seconds, though, so they are hard to detect. Scientists say they arise from the explosion of very massive stars, more massive than a supernova. Gamma-ray bursts signal the birth of a black hole, created as massive stars explode. They temporarily outshine quasars