Supernovae
A supernova is a catastrophic stellar explosion in which so much energy is
released that the supernova alone can outshine an entire galaxy of billions
of stars. In addition to the radiant energy produced, ten times as much
energy goes into the kinetic energy of the material blown out by the
explosion, and a hundred times as much is carried off by neutrinos.
Two distinct kinds of supernova are recognized, known as Type I and Type II.
They are distinguished by the presence of hydrogen features in the spectrum
of Type II supernovae, which are absent from Type I. Both types include
other subclasses.
Type Ia supernovae are thought to be white dwarfs in binary systems, where
mass transfer from the companion takes place. a wave of carbon burning
through the newly acquired material could account for the energy released.
The explosion may represent the total disintegration of the white dwarf.
Type II supernovae appear to be stars of eight solar masses or more that
have run the course of stellar evolution and totally exhausted the nuclear
fuel available in their cores. In the absence of energy generation, the
pressure balancing the weight of the overlying layers is removed. When the
crunch comes, the core collapses in less than a second and when the density
of nuclear matter is reached, there is a sudden strong resistance to further
pressure, the imploding material bounces back and an outward shock wave is
generated. The outer layers of the star are blown outwards at thousands of
kilometres per second, leaving the core exposed as a neutron star.
Description:Supernova SN 1994D in galaxy NGC 4526. The supernova is the star between the
star on the left and the galaxy. As it can be seen, the supernova is as bright as the whole galaxy which hosts
the progenitor. SN 1994D was a type Ia supernova.
Credit: Javier Méndez.
Technical information: Image acquired using a CCD camera on the Jacobus Kapteyn
Telescopes.
Available formats: GIF (39 K)
