180
AN EXPLOSIVE
TRANSITION TO
A NEUTRON STAR
SUPERNOVAE
IN CONTEXT
KEY ASTRONOMERS
Walter Baade (1893–1960)
Fritz Zwicky (1898–1974)BEFORE
1914 American astronomer
Walter Adams first describes
white dwarf stars, which are
now known to be involved
in common novae.1931 Subrahmanyan
Chandrasekhar calculates
the greatest mass a white
dwarf can have.AFTER
1967 Antony Hewish and
Jocelyn Bell Burnell discover
pulsars, which are found to be
fast-spinning neutron stars.1999 A survey of the light
from type 1a supernovae
shows that the universe’s
expansion is accelerating
due to an unknown quantity
known as dark energy.I
n 185 ce, Chinese astronomers
recorded a phenomenon they
called a “guest star.” The star
had appeared in the direction of
Alpha Centauri, the closest star
system to Earth, and had shone
brightly for eight months before
vanishing. This is probably the
first recording of a supernova.
Mysterious new stars have
appeared several times across
the centuries. In 1572, Danish
astronomer Tycho Brahe named
one a nova, meaning “new.” With
the development of telescopes,
novae became subject to closer
scrutiny and were found to be
faint stars that lit up with a greatThe core of the collapsed
star is crushed into a
neutron star, made
of material containing
only neutrons.Faint stars can become
much brighter for short
periods, forming novae.Some novae release
vastly more energy
than others.Some of these
supernovae are formed
by the collapse of a
star that annihilates
its own matter.intensity for short periods. It was not
until the 1930s that two astronomers
at Caltech in California, Walter Baade
and Fritz Zwicky, calculated that
some novae released much more
energy than others. For example, they
calculated that S Andromedae, a
nova seen in 1885, had released the
equivalent of 10 million years of the
sun’s output all at once. Baade and
Zwicky dubbed these incredibly
energetic events “super-novae.”Core collapse
In 1934, Baade and Zwicky suggested
that a supernova was the core of a
large star, collapsing under its own
gravity after running out of fuel.