The first ever direct observations of a type1a supernova – the ‘standard candle’ for astronomers to measure distance – have been made.
Exploding stars called Type 1a supernovas are ideal for measuring cosmic distance because they have consistent luminosity and are bright enough to spot across the Universe. While many theories exist about the types of star systems involved in these explosions, until now, no one has ever directly observed one.
In Science, a team from the Palomar Transient Factory (PTF) presents the first-ever direct observations of a Type1a supernova progenitor system. The astronomers found evidence that suggested that the explosion of a Type 1a supernova, called PTF 11kx, contains a red giant star. They also discovered that the system previously underwent at least one much smaller nova eruption before it ended its life in a destructive supernova. The system is located 600 million light years away in the constellation Lynx.
Ben Dilday, lead author of the study said: “This was the most exciting supernova I’ve ever studied. For several months, almost every new observation showed something we’d never seen before.”
Conversely, indirect observations of another Type 1a supernova explosion – conducted last year by the PTF team – showed no evidence of a red giant star. Taken together, these observations suggest that type 1a supernovae are not all born the same way, despite appearing indistinguishable.
The PTF survey in southern California was crucial to finding PTF11kx and uses a robotic telescope to scan the sky nightly. Data travels more than 400 miles via high-speed networks to supercomputers that sift through it to identify events.
In January, the pipeline detected the supernova. Peter Nugant- a senior scientist at the Lawrence Berkeley National Laboratory (Berkeley Lab) – and his postdoctoral researcher Jeffrey Silverman immediately followed up on the event, using telescopes at various observatories.
Unusually strong calcium signals in the gas and dust surrounding the supernova were observed until the signal dropped and eventually disappeared. Then, 58 days after the supernova went off, a sudden, strong burst of calcium reappeared. The observations suggested that the new supernova material had collided with the old material. The phenomenon is known as a recurrent nova.
Type 1a supernovas occur in systems where a white dwarf accretes mass from a nearby star until it cannot grow any bigger and explodes. Many astrophysicists concluded that it would not be possible to produce Type 1a supernova from recurrent nova systems. PTF 11kx represents the first observational evidence to refute this.