Astronomers study supernovae because the maximum luminosity of a stellar catastrophe can equal that of a billion suns, which is an awesome spectacle to see. By studying which stars become supernovae, we gain new insights into the course of the stellar life cycle. The explosion causes the star to expand and thin out, and this allows us to see ever deeper into the exploding matter. Matter is thrown into space at a few percent of the speed of light. When this happens, astronomers can read the signals from the outer layers of the stars and probe the nature of the star both before and after it exploded. Through these observations, we gain new insight into the formation of compact objects, such as neutron stars and black holes. The ejected matter is enriched in new elements, and thus, Supernovae are principal drivers of the nuclear evolution of the Universe.
Supernovae are also an important factor in the physical structure and composition of galaxies. The energy released by supernovae may stimulate or inhibit the formation of stars. Supernovae may also eject matter from galaxies in supernova-heated galactic winds. Additionally, Supernovae serve as exquisite indicators of extragalactic distances. Through the study of Supernovae, we can determine the history of the cosmic expansion.
A major issue in supernova research is determining how stars shed mass prior to explosion. The investigators will study the interaction of the exploding star, when the explosion collides with matter that was expelled before the explosion. Deeper understanding of these issues will expand our knowledge of how and when stars eject matter. The investigators seek to determine whether stars have multiple episodes of mass loss. They also want to know how the loss of mass alters the distribution of matter around the star. To better understand these questions, the investigators will study select stars that contain no hydrogen by the time they explode as supernovae because this means either the stars have expelled all their hydrogen-rich material into space or a companion star has accreted it. The investigators will also determine how the strength of the collision varies in time because the collision properties are related to the nature of the underlying supernova.
This research project will help further our understanding of our place in the Universe. It will serve to train young scientists in the STEM fields. It will promote deeper understanding of science in the public. It will be accompanied by broad outreach in appropriate venues for writing and speaking.
The investigators use the 2.7m Harlan J. Smith telescope at McDonald Observatory, in Texas, to search for the collision of supernovae. Narrow-band filters permit a rapid search for emission of hydrogen features that signify the presence of the collision of the supernova with previously-expelled hydrogen-rich material. The narrow-band filter observations also indicate variations in the strength of the hydrogen emission, which is a further clue to the nature of the interaction. The investigators will continue studies of collisions with the Hobby-Eberly Telescope to confirm that the hydrogen emission is from shocked material and not from ambient concentrations of hydrogen in the interstellar medium. They perform observations at other wavelengths, including the use of the NSF's Very Large Array radio observatory, to further constrain the properties - temperature and density - of the shocked material.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
