Supernovae and Supernova Remnants
What are Supernovae and Supernova Remnants?
A supernova is a massive stellar explosion that may briefly outshine its host galaxy, before fading from view over weeks or months.
It may mark the final stage in the relatively brief life of a massive star. As its nuclear fuel runs out, the star finally loses it battle with gravity and the core of the star collapses, and then rebounds outward and blasts much of the star's material into space. Alternatively, the victim may be a white dwarf star that accumulates matter from a companion star until it reaches the Chandrasekhar limit, causing runaway nuclear fusion in the interior that destroys the star.
The explosion sends a shock wave into the surrounding interstellar medium, sweeping up an expanding shell of gas and dust to create a supernova remnant. In the process, it enriches the interstellar medium with heavy elements, and possibly triggers the formation of a new generation of stars.
OH masers in Supernova Remnants
When massive stars explode in supernova events, they release colossal amounts of material and radiation which expands into the surrounding environment. When the shock wave from the supernova encounters dense molecular material, it can cause local collapse and lead to star-formation. A clear signpost of this activity is the hydroxyl maser at 1720 MHz, which signals the interaction of a shock with molecular material. The Astrophysical Maser Group carry out studies of OH masers in supernova remnants to gather important physical and kinematical information about the SNR environments.
The Radio Remnant of Supernova 1987A
SN 1987A in the Large Magellanic Cloud was the nearest supernova explosion observed in almost 400 years. Radio emission from SN 1987A was first detected with the MOST on 1987 February 25.23 UT (Turtle et al. 1987, Nature, 327, 38), two days after the detection of neutrinos. MOST continued to monitor the evolution of the radio emission through its decline, quiescence, recovery, and subsequent monotonic rise up to the present. The most recent data from the MOST light curve at 843 MHz show a clear steepening in the rate of increase of flux density, while on-going high-resolution imaging with the ATCA show that the corresponding shell of radio emission continues to expand.
For more information contact Dick Hunstead and Bryan Gaensler.
Supernova Remnants
The collapse of a massive star and the resulting supernova explosion are dramatic events which both complete the stellar life cycle and regulate the structure of the Galaxy's interstellar medium (ISM). However, we don't yet fully understand how stars explode; constraints on the many complicated processes which occur during core collapse are desperately needed. Since we rarely see a nearby star go supernova, our focus is on studying the aftermaths of supernova explosions, namely supernova remnants and young neutron stars, and in using these objects to infer the properties of the supernova, the progenitor star, and their surroundings. This work is providing new insights into the micro- and macro-physics of the core-collapse process, on the properties of supernova progenitors, and on the mechanisms which produce the diversity we see in the resulting compact objects.
For more information contact Bryan Gaensler , Shami Chatterjee
Stephen Ng
and
Lisa Harvey-Smith
Shocks and Particle Acceleration
On the basis of energetics alone, supernova remnants (SNRs) have long been considered a primary source of cosmic rays below "the knee" (i.e. with energies less than 10^15 electronvolts). First-order Fermi shock acceleration (also called diffusive shock acceleration), in which particles gain energy from scattering back and forth across the shock, has been suggested as the most probable acceleration mechanism in SNR shocks. However, it is only recently that observational evidence has emerged for acceleration in SNRs up to these energies, through the detection of non-thermal X-ray emission and TeV gamma-ray emission from a limited number of SNRs. We are studying those few SNRs which efficiently accelerate cosmic rays, with the aim of understanding what particular conditions and mechanisms are responsible for high-energy particle production.
For more information contact Bryan Gaensler , Shami Chatterjee
and Stephen Ng