What is a type 1A supernova

1  Two main sequence stars orbit one another.


2  The larger star has a shorter life and becomes a red giant.


3  Gas spills onto the smaller star.


4  Both stars are engulfed in the gas cloud.


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.


7  The white dwarf gradually gains mass, until at a critical mass of about 1.4 solar masses it explodes.


Images drawn from Wikipedia

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