outer layer and collapse around its carbon core, turning into a “white dwarf”
about the size of the Earth. It will move across the main sequence of the H-R
diagram toward the bottom left of the diagram. It will become smaller and
less bright but with a high surface temperature. Over billions of years, it will
cool until eventually any surviving astronomers will start calling it a “black
dwarf.” Smaller stars than the Sun will
burn much longer. When they run out of
fuel, they may simply collapse into a white
dwarf, or they may brieÀ y burn helium and
then collapse into a white dwarf.
The death of really large stars is much
more spectacular. When they run out of
hydrogen they, too, become unstable. They
start burning helium, and when that’s gone, temperatures will still be high
enough for them to burn their way through carbon and a number of other
elements including oxygen and silicon. Eventually, they start producing
iron (which has 26 protons in its nucleus), and the temperature at their core
reaches 4 billion degrees Celsius. Cesare Emiliani describes this dramatic
phase in the death of a large star:
A star 25 times more massive than the Sun will exhaust the
hydrogen in its core in a few million years, will burn helium for
half a million years, and—as the core continues to contract and
the temperature continues to rise—will burn carbon for 600 years,
oxygen for 6 months, and silicon for 1 day. (Emiliani, The Scienti¿ c
Companion, p. 61)When its iron core shuts down, the star will collapse catastrophically in just
a second, before exploding in a “supernova.” Most of its mass will be hurled
into space. Its core will collapse into a “neutron star,” a ball of matter so
dense that all its atoms are crushed into their nucleus. If the supernova is
large enough the collapse will go even further, to form a “black hole.” A
black hole is an object so dense that not even light can escape its gravitational
pull. In the extreme temperatures of a supernova, the remaining elements of
the periodic table can be manufactured in just a few seconds, all the way
If you’re wearing a gold
ring, it was forged in a
supernova and is on very
temporary loan to you!