Dr. Alexei Filippenko and his students will undertake an extensive, multifaceted investigation to discover and characterize large numbers of supernovae, which are the explosive deaths of certain types of stars. Supernovae synthesize and expel heavy elements, thereby dictating much of the chemical evolution of galaxies. The ejecta of supernovae blast through the interstellar medium, heating it and giving rise to phenomena such as galactic fountains. Shock waves from supernovae may also trigger vigorous bursts of star formation through compression of dense molecular clouds. Supernovae are probably responsible for the production of some of the most energetic cosmic rays in the Universe. Certain types of supernovae are exceedingly useful for measuring distances of galaxies billions of light years away, and are playing a crucial role in determinations of the age, global structure, and evolution of the Universe.
This project will continue the efforts of Dr. Filippenko's group to improve the understanding of the progenitor stars, explosion mechanisms, nucleosynthetic products, and cosmological utility of different types of supernovae. The adopted approach is largely observational, coupled with theoretical modeling through several informal collaborations. A new major goal is to discover supernovae very shortly after the explosion. Current and new data will be assembled for the purpose of improving the use of supernovae for cosmology and for obtaining clues to the physical nature of supernova progenitors.
The results from this study will have broad implications for topics as diverse as the chemical evolution of galaxies, the masses of black holes, the nature of gamma-ray bursts, and the expansion of the Universe. Results will be disseminated to a broad audience, both to students and to the general public. Planned activities include student trips to Lick Observatory, and the production of a 12-episode video course on black holes.
My (Alex Filippenko’s) research group is continuing to improve our understanding of supernovae, the explosive deaths of certain rare types of stars. Supernovae create heavy elements through nuclear reactions and expel them into space, making them available as raw materials for the formation of new stars, planetary systems, and ultimately life. As Carl Sagan eloquently said, "We are made of star stuff" – quite literally, the heavy elements in our bodies (carbon, oxygen, calcium, iron) were created in stars and supernovae long before the Solar System formed. We are trying to improve our knowledge of this process by learning what kinds of stars explode and how they do so. Supernovae are also important in many other ways. For example, being so powerful and nearly uniform in their observed properties, some types of supernovae (Type Ia) are exceedingly useful tools for measuring distances of galaxies billions of light years away. In 1998, they provided the first evidence that the expansion of the Universe is currently accelerating, a discovery that was honored with the 2011 Nobel Prize in Physics to the leaders of the two teams. (I was the only person to have been a member of both teams.) Supernovae have continued to play a crucial role in determinations of the age, overall structure, and evolution of the Universe – major topics in cosmology. The approach adopted by my team is largely observational, coupled with theoretical modeling through several informal collaborations. We have used primarily our 0.76-m Katzman Automatic Imaging Telescope (KAIT; see Figure 1) at Lick Observatory, the 3-m Shane (Figure 2) and 1-m Nickel (Figure 3) reflectors at Lick, and the two 10-m Keck telescopes in Hawaii (Figure 4). Moreover, we have used the Hubble Space Telescope for some studies. The approved NSF funds were specifically for the following. (a) The continuation of our Lick Observatory Supernova Search (LOSS) with KAIT, with a new major goal of discovering supernovae very shortly after the explosion, when they are changing rapidly. (b) The acquisition, calibration, analysis, and interpretation of extensive new data (brightness measurements and spectra) for supernovae found by LOSS and the Palomar Transient Factory, with particular emphasis on improving the utility of supernovae for cosmology and on shedding clues to the physical nature of the stars that explode (progenitors). (c) The analysis of new and existing data concerning pre-supernova outbursts and the nature of supernovae whose massive progenitors had previously lost their outer envelopes of gas. (d) The acquisition and analysis of spectra taken with optical systems that can detect the polarization of light, providing constraints on theoretical models through information on their shapes and internal structure. All of the goals of the project were accomplished, resulting in the publication of 125 refereed papers, as well as more than 100 brief reports (abstracts, telegrams, etc.). (a) Many dozens of new supernovae were found (e.g., Figure 5); the overall total for LOSS is now approaching 1000. The results of the first decade of LOSS were published in a set of 5 extensive papers. We successfully developed a new search strategy that resulted in the discovery and immediate follow-up observations of several extremely young supernovae. (b) We published analyses of many individually interesting supernovae, as well as a detailed study of our accumulated data on a set of several hundred Type Ia supernovae (6 papers). We improved the cosmological utility of Type Ia supernovae and shed light on their progenitors. (c) We discovered that some massive stars undergo substantial outbursts shortly before their final explosions, providing clues to the evolution of massive stars. We also identified several new varieties of stellar explosions that are difficult to understand with the conventional explosion mechanisms. (d) We found significant asymmetries in the explosions of certain kinds of massive stars. Much additional data has been collected for this part of the project, and analysis will continue in the next two years. Many undergraduate students, graduate students, and postdoctoral scholars were trained to conduct astrophysical research as part of this grant. They learned the latest techniques of observations, data calibration, analysis, and interpretation (Figure 6). They also wrote papers and proposals, and presented their research orally. They worked independently and as part of a team, and they learned how to teach others. The new knowledge and skills they acquired should be useful for them in the future, regardless of their chosen careers. Our scientific results were disseminated not only in technical journals, but also widely to the general public through about 160 public lectures, many press releases, media interviews (television, radio, newspaper), and my highly popular (800 students) introductory astronomy course at UC Berkeley. I was also a major consultant and participant in The History Channel's "The Universe" series (spanning seven seasons). Figure credits: 1−4, 6: Laurie Hatch (lauriehatch.com). 5: Alex Filippenko and S. Bradley Cenko.
