Hubble snaps 'Christmas tree bauble'
New images from the Hubble Space Telescope show an appropriately festive-looking bubble of gas in our neighbouring galaxy, the Large Magellanic Cloud.
After a supernova explosion that took place four hundred years earlier, the expanding blast wave and ejected material have created a gaseous envelope which is expanding outwards into the interstellar medium.
Called SNR B0509-67.5, the bubble is about 160,000 light-years from Earth. It's about 23 light-years across and is expanding at more than 18 million kmh, says the Hubble team.
The ripples in its surface may be caused either by variations in the density of the ambient interstellar gas, or could possibly be driven from the interior by fragments from the initial explosion, they say.
The explosion itself was probably an example of a Type Ia supernova, thought to occur when a white dwarf star in a binary system robs its partner of material. It takes on more mass than it's able to handle - and eventually explodes.
Hubble’s Advanced Camera for Surveys observed the supernova remnant back in 2006 with a filter that isolates light from the glowing hydrogen seen in the expanding shell. These observations were then combined with visible-light images of the surrounding star field that were taken with the Wide Field Camera 3 this November.
The supernova might have been visible to southern hemisphere observers around the year 1600 - although there don't seem to be any records of a 'new star' in the right direction at that time.