Nature: Astronomers have identified two new supernovae that occurred more than 10 billion years ago, one of which is the oldest known supernova. Both supernovae were originally identified in deep-sky images from the 3.6-m Canada-France-Hawaii telescope. Jeff Cooke of the Swinburne University of Technology in Australia and his colleagues then used the 10-m Keck I telescope to take spectral measurements of the supernovae. The spectra obtained had redshifts of 2.05 and 3.9, setting the ages of the supernovae at 10.4 billion and 12 billion years, respectively. The universe itself is only 13.7 billion years old. The observational data from the younger of the two suggests that the star that exploded had a mass of about 250 suns. The explosion appears to have been a pair-instability supernova, where gamma rays produced internally become matter and antimatter particles that annihilate each other. The data from the older supernova aren’t clear enough to determine the type of supernova or the exact mass of the star, though it had to have been more than 100 solar masses.