Yong-Zhong Qian


Our Solar System: What Triggered Its Formation?

Courtesy NASA/JPL-Caltech

About 4.6 billion years ago, some event disturbed a cloud of gas and dust, triggering the gravitational collapse that led to the formation of the solar system. One hypothesis is that a nearby supernova—a star exploding at the end of its life cycle—initiated this event. My collaborators and I have examined why earlier forensic evidence based on studies of extinct radioactive nuclei in meteorites have been inconclusive, and shown how recent results from modeling supernovae and their impact on star formation have opened up new directions in researching the formation of our solar system.

Flavor Oscillations of Astrophysical Neutrinos

Using neutrinos produced by nuclear reactions in the sun, by interaction of cosmic rays with earth's atmosphere, and by accelerators and nuclear reactors on earth, a number of experiments showed that neutrinos oscillate among different flavors and therefore have mass. Yet some key parameters characterizing neutrino oscillations are unknown. New experiments such as MINOS and NOvA, in which the University of Minnesota plays a prominent role, are being carried out to probe these unknown parameters. Interestingly, supernovae that signify the explosive death of massive stars are prodigious sources of neutrinos and provide another venue to study neutrino oscillations. In fact, the number density of neutrinos near the core of a supernova is so large that new phenomena of neutrino oscillations arise. In particular, the flavor evolution for neutrinos of different energies traveling in different directions may be coupled together to produce collective oscillations. This new phenomenon is extremely sensitive to the unknown neutrino oscillation parameters, thereby allowing possible extraction of these parameters from the detection of neutrinos from a future supernova.

Diverse Supernova Sources for Neutrinos and Elements

A lecture on Neutrinos & Supernova Nucleosynthesis

r-Process Nucleosynthesis

A lecture on The r-Process: Status & Challenges

Chemical Evolution of Galaxies

A lecture on Hierarchical Structure Formation & Chemical Evolution of Galaxies