Using the James Webb Space Telescope, astronomers discovered the oldest known galaxy – GLASS-z13. It is 13.5 billion years old, and it was formed about 300 million years after the Big Bang.
GLASS-z13 is 1,600 light-years in diameter (as compared to our Milky Way, which is 105,000 light years in diameter). Its mass is about a billion times that of the sun. On a cosmic scale, that's not much, but scientists have yet to understand how it grew to this size in just hundreds of millions of years when the universe was producing its first stars.
Before GLASS-z13, GN-z11 was considered to be the oldest galaxy.