Liverpool Telescope captures the earliest spectra of a Type Ia supernova

Quick response observations by the Liverpool Telescope (LT) have led to the earliest spectra of a Type Ia supernova, and have helped astronomers to refine their theories on what causes these types of stellar explosions. The supernovae, known as SN2011fe, was first spotted in the Pinwheel Galaxy (M101 or NGC5457) on the 24th August 2011 by the Palomar Transient Factory (PTF) telescope - just 11 hours after it first erupted - but within an hour of the alert going out, the LT had taken a spectra of the event and confirmed that the supernova was indeed a Type Ia. The results of this, and subsequent investigations have just been published in the journal Nature.

Image of SN2011fe in the Pinwheel Galaxy
Before and after images of the Type Ia supernova SN2011fe
Credit: B J Fulton / LCOGT

Type Ia supernovae (SN Ia’s) are incredibly bright, but are so similar to each other that astronomers use them as standard candles with which to measure the distance of galaxies. It was thought that they occur in close-orbiting binary star systems, where a dense, compact white dwarf star made of carbon and oxygen is sweeping up material from a bloated companion star. As it acquires more material, it grows towards the limit of how massive a white dwarf can be - thought to be around 1.4 times the mass of the Sun. When it reaches that limit, nuclear reactions restart on the surface of the white dwarf and causes it to undergo a massive supernova event that ejects material back into the cosmos. The mass of the white dwarf drops again and once the supernova has died down, it resumes its previous existence. However, as long as material is being transferred onto the white dwarf, the pattern will repeat.

The recent observations, and the LT spectra in particular, confirmed that the star from which the supernova originated was made of carbon and oxygen, and that it was indeed around 1.4 solar masses. This is the strongest evidence yet that the previous view of what causes Type Ia supernova was indeed correct.