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Most stars die quietly by cooling down and "turning off" when they have exhausted their nuclear fuel. However, a few stars end in a gigantic thermonuclear explosion known as a supernova. These objects remain extremely luminous for a few weeks, sometimes outshining the galaxies in which they reside. Their extreme brightness at maximum makes them potentially powerful "standard candles" for probing the geometry and expansion of the universe. Type Ia supernovae are especially attractive candidates. Thought to be the complete thermonuclear disruption of a small, very dense stellar remnant called a white dwarf, they are highly homogeneous. And because of their immense luminosity at maximum light (up to 10 billion times that of the Sun), they can be observed at great distances. Mark Phillips, associate director of the Las Campanas Observatory, specializes in supernovae to understand the role they have in the evolution of the universe, and to determine how they can be used as baselines, or standard candles, for measuring distance.
Phillips has shown that type Ia supernovae can be used as standard candles because of a tight correlation between the rate of decline from maximum light and peak luminosity. Phillips and collaborators have extended their supernovae observations to the infrared. They have shown that type Ia supernovae exhibit a much smaller range of luminosities at these wavelengths, making them nearly perfect standard candles. Moreover, in infrared the absorption of the supernova light due to dust is negligible.
Phillips has joined with Wendy Freedman, Mario Hamuy, and Eric Persson in a new two-part, 5-year project called the Carnegie Supernova Program (CSP). They are obtaining light curves of approximately 100 nearby type Ia supernovae in the optical and infrared. This sample will provide a comparison for the second component of the CSP—near-infrared observations of about 50 high-redshift (0.3 < z < 0.7), or very distant, type Ia supernovae. The goal is to measure the expansion history of the universe from low to high redshift for a new measurement of the acceleration of the universe without as much dust absorption and luminosity corrections. The program should provide further clues to the nature of the mysterious dark energy that is driving the acceleration.
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