Through ERC Advanced Grant SNDUST 694520, plus earlier STFC grants, we have been investigating observationally how much dust can be formed in the high-velocity ejecta of core-collapse supernovae (CCSNe) fom massive stars and, via numerical hydrodynamical modelling, how much of this dust can survive passage through supernova reverse shocks and later impacts with interstellar material. This work has included observations made with NASA's Spitzer Space Telescope, ESA's Herschel Space Observatory, the Atacama Large Millimeter Array (ALMA), the Gemini 8-m telescopes and ESO's 8‑m Very Large Telescope. The overall goal is to determine whether CCSNe can make a major contribution to the dust reservoirs of galaxies observed at both high and low redshifts. This page gives details of some of our projects.
Due to its location in the Perseus arm of the Milky Way, Cassiopeia A (Cas A) is embedded in dense clouds of interstellar material which made the explosion of its massive progenitor star 330 years ago hardly visible to the naked eye. Studying the condensation of dust in Cas A thus requires infrared and submillimetre observations of the thermal dust emission, but at the same time the contamination by dust emission from foreground and background interstellar dust and the remnant's synchrotron radiation in those wavebands should be corrected for.
Supernovae are very rare, and the closest one recorded in the last 300 years was detected in 1987, in a small galaxy close to the Milky Way. Using the European Space Agency's Herschel Space Observatory, UCL astronomers detected about 200,000 Earth masses of dust which has condensed out of the remains of the star which exploded. The dust grains contain the heavy elements which are so important for life, and the observations show that supernovae can be efficient dust-forming factories.
![Modelled fits to the SN 1993J [OIII] λ5007,4959 Å doublet at 16 years and the SN 1980K Hα line at 30 years. The intrinsic dust-free modelled line profile is given in yellow, the dust-affected modelled line profile in red and the observed line profile in blue.](images/damocles_fits.png "Modelled fits to the SN 1993J [OIII] λ5007,4959 Å doublet at 16 years and the SN 1980K Hα line at 30 years. The intrinsic dust-free modelled line profile is given in yellow, the dust-affected modelled line profile in red and the observed line profile in blue.")
Blue-shifted line emission can be a common and long-lasting feature of the optical spectra of some core-collapse supernovae, with emission lines of oxygen and hydrogen often exhibiting red-blue asymmetries and significant substructure at both early times (e.g. SN 2006jc (Smith et al. 2008), SN 2005ip, SN 2006jd (Stritzinger et al. 2012) and SN 2010jl (Smith et al. 2012; Gall et al. 2014)) and at late times (e.g. Milisavljevic et al. 2012). If these lines can be modelled then it may be possible to determine the masses of dust in supernova ejecta and supernova remnants (SNRs). This is particularly useful at late-time epochs (~5 years) where core-collapse supernovae are not currently accessible at mid-infrared and longer wavelengths.
One of the most surprising discoveries made by the Herschel Space Observatory during its mission was the detection in the Crab Nebula of the noble gas molecule ArH+. This molecular ion, also known as argonium, had previously only been studied in the laboratory.
It is well established that (sub-)micron sized dust grains can form in over-dense gas clumps in the expanding ejecta of supernova remnants. However, highly energetic shock waves occur in the ejecta which can potentially destroy a large fraction of the newly formed dust grains. The gas in the ejecta can be heated up to billions of Kelvins and is accelerated to a few hundred kilometere per second, which causes thermal and kinematic sputtering of the dust grains. Moreover, dust grains can collide with each other at high velocities and get fragmented or even vaporized. Previous predictions for dust survival rates depend strongly on initial parameters and range from less than 0.1% to 99%. The net dust survival rate is crucial for determining whether or not supernovae significantly contribute to the dust budget in the interstellar medium.
last updated 06 July 2022
