It looks like a cosmic pizza. But this colourful dish measures 25 light-years – that’s 150 trillion miles – from crust to crust. Lying 7,500 light-years away from Earth, it is really the remains of a star that blew itself to bits in a supernova suicide.
It became visible in daylight when it was first spotted in the 16th Century as a brilliant new star in the constellation of Cassiopeia.
The famous Danish astronomer Tycho Brahe spotted it shining brighter than Venus on 11 November, 1572, in the days before telescopes were invented.
Today, astronomers reveal that they have finally identified the type of supernova that caused the blast. They did so by measuring faint echoes of light bouncing back from dust clouds in interstellar space.
They used the Faint Object Camera and Spectrograph instrument on the Subaru telescope in Japan to break the light echoes down. This revealed the signatures of atoms present when the supernova exploded and identified the blast as a Type 1a supernova.
They conclude that gas from one star in a double-star system poured onto its white dwarf companion. It eventuallly set off a runaway nuclear reaction that blew it to bits.
Dr Tomonori Usuda, leader of the team which used the Subaru telescope in Japan, said: “Using light echoes in supernova remnants is time-travelling in a way, in that it allows us to go back hundreds of years to observe the first light from a supernova event.”
The breakthrough, which was made in September, is published in the journal Nature. Earlier this year, the explosion of a supernova in another galaxy was caught live. An earlier blast in our galaxy, around 150 years ago, was missed because it was hidden by a cloud of dust. Other stars are lined up to explode in the future.
Picture: The image was built up from photos taken by two observatories in space – Spitzer and Chandra – plus the 3.5 metre telescope at Calar Alto in Spain.