When a white dwarf explodes as a type Ia supernova, its death is so bright that its light can be detected across the Universe. A new observation using the Hubble Space Telescope identified the farthest type Ia supernova yet seen, at a distance of greater than 10 billion light-years. In the tradition of supernova surveys, this event was nicknamed for Woodrow Wilson, 28th President of the United States. The previous record-holder, Supernova Mingus, was about 350 million light-years closer to Earth.

White dwarfs are the remains of stars similar in mass to the Sun. Since such a star would have to live out its entire life to form a white dwarf, there are limits to how early in the Universe's history a type Ia supernova can explode. Only 8 white dwarf supernovas have been identified farther than 9 billion light-years away. (Some core-collapse supernovas, which are the explosions of very massive stars, have been seen farther than Supernova Wilson.) Since all such explosions happen in a similar way, cosmologists use them to measure the expansion rate of the Universe.

Astronomers found this violent event by comparing the light from several separate long exposures of the same patch of the sky, known as CANDELS (the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey). Bright as it was, the distance was so great that Supernova Wilson appeared as an enhancement of the luminosity of its host galaxy. The researchers subtracted the light of the galaxy without the supernova from the combined supernova-galaxy combination, then analyzed the residual light to identify it as type Ia.

The Universe was only a few billion years old when Supernova Wilson exploded, nearly as early as such an event could possibly occur. The early era of Supernova Wilson's explosion means it was likely the result of two white dwarfs merging rather than a single white dwarf exceeding its maximum mass. This is because the most massive white dwarfs require more time to form than the Universe's existence had provided.

The arXiv. Abstract number: 1304.0768 (About the arXiv). To be published in The Astrophysical Journal.