It was 30 Years Ago Today ...
On February 24th 1987, two astronomers, Ian Shelton and Oscar Duhalde spotted a new ‘star’ in the night sky over the Las Campanas Observatory in Chile. Confirmed independently by Albert Jones in New Zealand, this star was to become a subject of study and fascination for many years to come.
It was in fact a supernova (known as SN1987A; denoting it was the first to be discovered in 1987) and it was soon identified as an explosion of the blue supergiant star, Sanduleak -69° 202. In itself, this was something of a surprise as blue supergiants were not believed to be the progenitor stars of supernovae. SN1987A was classified as a Type II supernova; one that does show spectral lines of hydrogen (Type I supernovae arise from hydrogen-less environments such as more evolved stars and more exotic white dwarfs).
Supernovae are rare events – they generally only occur in more massive stars, those that are more than ten times the mass of our Sun and it’s believed that there is on average one supernova per galaxy per century. In fact, the last recorded supernova in our Milky Way Galaxy was in 1604. The supernova occurred in the Large Magellanic Cloud, a nearby neighbour to our Milky Way.
One feature that made SN1987A so unique was that its optical light as seen from Earth was preceded by a burst of neutrinos, a particle associated with supernovae but never previously detected. Only 25 neutrinos were ever detected, the majority by the Kamiokande II experiment, based in Japan but these detections paved the way for a new type of astronomy based on the detection of neutrinos (as opposed to traditional astronomy which detects electromagnetic radiation). This research has led to detectors such as IceCube at the South Pole and KM3NeT in the Mediterranean Sea.
Since SN1987A occurred 30 years ago, we might expect to have seen by now a compact stellar remnant known as a neutron star. That we haven’t confounds astronomers who suggest that perhaps a neutron star is present but shielded by dust and gas as the shells of material continue to expand. A second explanation is that this particular supernova has created a black hole; an object even trickier to detect since it emits no light at all.
You can read more about this object here where an article was produced to celebrate its tenth anniversary showing expanding rings of material associated with the supernova but probably created ahead of its final explosion. Here is an article which shows time-lapse images of the volume of space around SN1987A.
In the hydrogen alpha image below, the area around SN1987A is circled. If you think supernovae are interesting, why not have a go at looking at some real data? Our Spotting a Supernova activity allows you to analyse images of a supernova target and use your results to plot a light curve that shows how the object initially brightens and then fades over time. You can find the activity here.