New supernova observation reveals details about massive dying stars

Before and after of supernova SN 2013cu in the galaxy UGC 9379, about 330 million light-years away. The left image is from the Sloan Digital Sky Survey; the right image is from the robotic telescope at the Palomar Observatory. [Credit: Avishay Gal-Yam, Weizmann Institute of Science]

For the first time, scientists have direct evidence that the biggest and brightest stars die in supernova explosions. The evidence comes in the form of SN 2013cu, a gigantic star that scientists were able to virtually catch in the act of going supernova last year. A new robotic sky survey, called the intermediate Palomar Transient Factory (iPTF) scans the sky for supernova events, alerting astronomers to possible supernovae so they can be observed very soon after they happen. The iPTF caught SN 2013cu soon after it detonated, allowing astronomers to make detailed observation of the dying star. Most of the time, astronomers are not aware of what type of star went supernova once they go off, since — for the last 400 years, anyway — all supernovae we’ve observed have gone off in other galaxies and we don’t tend to catalog the different types of stars in other galaxies.

Wolf-Rayet star

Wolf-Rayet star WR 124 [Credit: Yves Grosdidier (University of Montreal and Observatoire de Strasbourg), Anthony Moffat (Universitie de Montreal), Gilles Joncas (Universite Laval), Agnes Acker (Observatoire de Strasbourg), and NASA]

This is what makes this latest discovery so extraordinary. Astronomers were able to tell from the supernova spectrum, obtained very soon after the detonation, that this particular object was what is called a Wolf-Rayet star (see image above), a huge and hot type of star that is so massive, astronomers weren’t even sure if it would go supernova when it died. This particular star became what is called a Type IIb supernova. Astronomers will use this information to better understand the way massive stars change throughout their lifetimes.