Research

OVERVIEW

I work in nuclear astrophysics. The most important questions that we address are: (1) How do stars evolve? (2) Why do some stars explode? (3) What is the origin of the elements in the universe?

Most elements are created in stars via nuclear fusion reactions. For example, stars like our sun fuse hydrogen into helium over a period of billions of years. Many different kinds of stars exist in the universe. Very old objects, like red giant stars in globular clusters, burn their nuclear fuel at low temperatures. Other stars, for example supernovae, novae and x-ray bursts, release their energy in stellar explosions. Many of the complex nuclear physics processes that occur during various stages of stellar burning are poorly understood.

Our group performs research in experimental, computational, and theoretical physics:

First, we measure these nuclear fusion reactions with our facilities based at the Triangle Universities Nuclear Laboratory (TUNL). Direct measurements of the nuclear fusion reactions at low bombarding energies below 1 MeV are performed using the ion accelerators at the Laboratory for Experimental Nuclear Astrophysics (LENA). Indirect measurements are performed using incident gamma-rays from the High-Intensity gamma-ray Source (HIgS) facility. Both of these facilities are world-record holders in terms of their ion beam or gamma-ray beam intensities.

Second, the data need to be modeled numerically. We have recently developed new techniques based on Monte Carlo simulations and on Bayesian inference to reliably extract the information of interest (i.e., thermonuclear reaction rates). We built and maintain a state-of-the-art nuclear physics numerical library for stellar computer models, called STARLIB.

Third, we use STARLIB to study theoretically the nucleosynthesis and nuclear energy production in many different stars, including red giants, AGB stars, massive stars, classical novae, and supernova shocks.

At the top of the page, from left to right, are shown: (i) a textbook that I wrote on the subject (“Nuclear Physics of Stars”); (ii) a review article on nuclear astrophysics (“Nuclear Astrophysics: the Unfinished Quest for the Origin of the Elements”) that I co-authored; (iii) a book chapter on classical novae that I co-authored; and (iv) a special issue of a research journal containing our 2010 evaluation of thermonuclear reaction rates that is used for computer simulations of stars. For an introduction to nuclear astrophysics on an undergraduate level, see Introduction to Nuclear Astrophysics. More detailed information on current projects for interested graduate students and postdocs is given below. My research is mainly funded by the U.S. Department of Energy.

The origin of the elements, based on latest research (up to 2018), is indicated in this Periodic Table of Elements.

RECENT RESEARCH