|
|
Normal Stars
Normal stars such as the Sun are hot balls of gas millions of kilometers in
diameter. The visible surfaces of stars are called the photospheres, and
have temperatures ranging from a few thousand to a few tens of thousand degrees
Celsius. The outermost layer of a star's atmosphere is called the "corona", which means "crown". The gas in the coronas of
stars has been heated to temperatures of millions of degrees Celsius.
Most radiation emitted by stellar coronas is in X-rays because of its high temperature. Studies of X-ray
emission from the Sun and other stars are therefore primarily studies of the
coronas of these stars. Although the X-radiation from the coronas accounts for
only a fraction of a percent of the total energy radiated by the stars, stellar
coronas provide us with a cosmic laboratory for investigating how hot gases are
produced in nature and how magnetic fields interact with hot gases to produce
flares, spectacular explosions that release as much energy as a million hydrogen
bombs.
|
