Astronomers have just annouced a superluminous supernova at z = 3.90. Swinburne astrophysicist Jeff Cooke and collaborators (including SAOers Emma Ryan-Weber and Gonzalo Diaz) have detected the most distant supernovae in the universe. The super-luminous supernovae (SLSNe) is at z=3.90 (another was found at z=2.05) and was observed using dedicated Swinburne time on the Keck Observatory in Hawaii. Gamma-ray bursts at higher redshifts that might be associated with supernovae have been found before, but this is the most distant supernovae yet found.
Recent surveys of the nearby universe discovered a hitherto unknown group of supernovae that has been labelled as “superluminous” and “ultraluminous”. These are typically 10 times more luminous than type Ia supernovae and 100 times more luminous than normal core-collapse supernovae.
One theory for the origin of SLSNe, known as the pair-instability hypothesis, is that the progenitors were massive 100-300 solar mass stars. If such stars could retain much of their initial mass during their evolution, their cores could get big enough and hot enough to create electron-positron pairs. This process can reduce the internal pressure making their cores contract resulting in 60 solar masses of carbon and oxygen undergoing a thermonuclear explosion. This explosion produces unstable, radioactive nickel-56, which can decay releasing gamma-rays that heat the supernova to the superluminous intensities observed.
Current research, albeit it on a handful of SLSNe (with luminosities greater than 7 x 1043 ergs/sec) suggest they can be classified as radioactively powered (SLSN-R), hydrogen-rich (SLSN-II), and hydrogen-poor (SLSN-I, the most luminous class). The SLSN-II and SLSN-I classes are more common, whereas the SLSN-R class is better understood.
With a redshift of z=3.90, the newly detected SLSNe has an age of 1.6 Gyr after the Big Bang, and a light travel time of 12 Gyr.
“Finding the first generation of stars is the current Holy Grail for astronomers. The distances of our supernovae overlap with the distances where we expect to find the first stars. Our search technique provides the means to detect and study the deaths of the first generation of stars and understand the chemical enrichment process of the Universe from the beginning”, Dr Cooke said.
The physical origins of the extreme luminosity emitted by SLSNe are a focus of current research. As well as the pair-instability hypothesis some astronomers are suggesting SLSNe could come about via a normal core-collapse mechanism in a very massive star or a supernova enhanced by a magnetic neutron star.
With several ongoing surveys efficiently detecting additional examples, the amount of information about these objects will increase substantially in the next few years.
For more information, see
- Superluminous supernovae at redshifts of 2.05 and 3.90, Cooke et al. (2012), Nature (doi:10.1038/nature11521)
- Cosmic explosions in the young Universe, Nature News & Views, Stephen J. Smartt
- Distant super-luminous supernovae found, Swinburne press release