Scialog: Collaborative Teams - 2015
Astronomy, University of California, Berkeley
Bringing Novae into the 21st Century
At least some areas of shock physics – the study of matter under extreme conditions – could use an update when it comes to modeling and understanding the titanic forces unleashed when certain types of stars explode.
Astrophysicist Raffaella Margutti, New York University, physicist Brian Metzger, Columbia University, and astrophysicist Ken Shen, University of California, Berkeley, are attempting to bring the astronomical community’s knowledge of several types of these immense explosions into the 21st century.
The trio is particularly interested in updating our knowledge about novae, which are massive nuclear explosions occurring on white dwarf stars. A white dwarf, also called a degenerate dwarf, is basically a burned-out star that has gone through its red giant phase and then shrunk to a small – about the size of earth -- extremely dense mass because all the electrons in its atoms are compressed, giving rise to even more intense gravitational forces. A typical white dwarf is about 200,000 times as dense as the earth, and theorists speculate a crystalline lattice of carbon and oxygen composes its core. In other words, it’s very nearly an immense diamond.
A nova occurs in a two-star – binary – system when the white dwarf’s immense gravity allows it to steal – or “accrete” – hydrogen from its neighboring, normal, star. Eventually, the powerful gravitational force of the white dwarf ignites a runaway nuclear fusion reaction in the pilfered hydrogen, resulting in a cataclysmic explosion on the surface of the white dwarf.
Astronomers and astrophysicists love novae because they are basically laboratories for studying shock physics in general, including the physical processes at work in supernovae, which are even larger and more spectacular explosions.
Novae and supernovae put out unimaginable blasts of energy that excite nearby atoms in gases and other matter drifting in space, which in turn generate other forms of electromagnetic radiation, including light and radio waves. All of these secondary phenomena provide useful clues about the nature of the cosmos. These spectacular explosions also produce extremely high-energy gamma rays, the most intense – and deadly -- form of electromagnetic radiation.
The trio hopes to mine novae observation data currently available, but relatively untouched, from the Swift and Chandra space-based observatories to make comparisons with what are called type-Ia supernovae progenitors. A type-Ia supernova is theorized to occur in a white dwarf binary system when so much matter has been accreted –perhaps from a neighboring white dwarf, rather than a normal star -- that a process called “carbon fusion” occurs, instantaneously converting much of the white dwarf’s matter into pure energy.
Needless to say, there are very few more spectacularly powerful explosions occurring in the cosmos than type-la supernovae. Margutti, Metzger and Shen hope to provide new insights into nova and supernova mechanisms and to develop new avenues of study for shock physics.