Distant Supernova Search

The value of the density of the universe as a fraction of critical density remains unknown. The ratio is often called Omega. Depending on whether Omega is 0.1 or 1, dark matter represents 90% or 99% of the mass of the universe. The main activity of the Center on this question has been the search for supernova at high redshift, which can be used as probes of the density of the universe.

Figure 3 The upper plot is an image of a galaxy taken in 1992. The lower plot is the same galaxy taken at the INT on Dec 22. The new source to the right of the galaxy is one of our supernova candidates.

The recent attempts to determine Omega show that a precise measurement is best performed through the determination of the geometry of the universe. One of the most attractice possibilities is to measure the apparent magnitude of Type Ia supernovae as a function of their redshift, taking advantage of the empirical consistency of Type Ia absolute magnitudes. Since these objects are believed to be white dwarfs that have been accreting matter from a binary companion and ignite when their mass reaches the Chadrasekhar limit (about 1.4 times the mass of the sun) the models and best data indicate that they should be little affected by evolution and therefore make good standard candles. The ultimate goal of the present program is to identify some 50 supernovae at redshift of 0.3 or higher in order to measure Omega to a statistical accuracy of 0.3rms.

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