Astronomers ID earliest recorded supernova

Astronomers think they have identified the remains of the first ever supernova recorded by people on Earth.

The remnant, RCW 86, was thought to be around 10,000 years old, but new data is forcing the stargazing community to revise this figure quite considerably downwards. They now believe it is around 2,000 years old, and that it could be the remains of the supernova recorded in 185 AD by Chinese astronomers.

The Chinese noted that it sparkled like a star and did not appear to move in the sky, arguing against it being a comet. Also, the observers noticed that the star took about eight months to fade, consistent with modern observations of supernovas.

"There have been previous suggestions that RCW 86 is the remains of the supernova from 185 AD," said Jacco Vink of University of Utrecht, and lead author of the study. "These new X-ray data greatly strengthen the case."

The data comes from the European Space Agency's XMM Newton and Chandra orbital observatories.

The researchers worked out the age of the remnant by studying how fast the outer layers of material were moving away from the centre of the explosion. They tracked one section of the shell to work out an expansion velocity. In combination information about the size of the remnant and a basic understanding of how supernovas expand they were able to estimate how long since the star had gone boom.

The expansion velocity was much faster than previous studies of the remnant had indicated, and the team says this is likely due to the nature of the space it is expanding into.

Before the star exploded, it would have sent out a massive shock wave, effectively creating a bubble of stellar wind in the area around the star. Some of the exploded material is still within this irregularly shaped area, but some has hit denser material beyond it and slowed down.

The faster moving material in the bubble gives a better indication of the supernova's age, and it is this material the team has now measured. ®