What is a type 1A supernova
5 The two stars spiral towards each other and so orbit at a much smaller distance. The larger star completes the red giant stage and becomes a white dwarf and the remaining gas cloud is blown away.
6 The smaller of the two stars eventually reaches the red giant stage. Gas from the red giant spills onto the white dwarf attracted by the strong gravitational field of the small dense body.
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Why are type 1A supernova important for distance measurement
9 This type 1a supernova can be recognised by characteristic radiation patterns. Because of the way they are created, with the supernova occurring at the critical mass of 1.4 solar masses, they all have the same brightness. By comparing the known real brightness with the observed brightness their distance from us can be calculated and so the distance of their parent galaxy is estimated.
One of the functions of the NASA Swift satellite is to search for these special supernova. It can make a complete recording of the event within a very short time of the start.
Other pages of notes and video on astronomy which may be useful are:
Units of distance notes and video Measuring distance by parallax/triangulation notes and video Life cycle of stars Geostationary and polar satellites notes and video Big Bang theory and evidence Development of the Universe after the Big Bang Real and apparent magnitude Hubble's Law and measuring distance notes and video The age of the universe notes and video Using Hertzsprung Russell diagrams notes and video Cepheid variable stars