A faint gamma-ray burst (GRB) captured last Thursday by NASA’s Swift satellite has smashed the record for the earliest, most-distant known object in the universe.
The burst, named GRB 090423 for its discovery date, went off in Leo and was seen to last for 10 seconds. Several teams, including a group using the Gemini-North telescope in Hawaii and a European group using the Very Large Telescope in Chile, followed up the Swift detection by observing the burst’s fading infrared afterglow. Based on how much the afterglow’s light was stretched by cosmic expansion since the era when the burst happened, the group determined that it went off about 630 million years after the Big Bang.
This means that the GRB’s gamma rays traveled for a mind-boggling 13.1 billion years before reaching Earth. That’s so far back in time that it’s meaningless to assign a specific “distance,” since large distances in the universe have themselves expanded by a factor of 9.2 since that time. From the burst’s perspective, Earth’s formation lay 8.5 billion years in the future.
The discovery also proves massive stars capable of exploding as GRBs existed when the universe was only 630 million years old. This is not a surprise; cosmologists think the very first stars formed when the universe was between 200 and 400 million years old.
