181
See also: The Tychonic model 44–47 ■ Quasars and pulsars 236–39 ■
Dark matter 268–71 ■ Dark energy 298–303
ATOMS, STARS, AND GALAXIES
The collapse was so powerful that it
annihilated matter, releasing a huge
amount of energy in accordance
with Einstein’s equation E=mc^2
(p.149). What was left was a neutron
star—a body composed of only
neutrons that were packed together
like the particles in an atomic
nucleus, only on a much larger
scale. A neutron star is only about
7 miles (11 km) across, but has
huge density and gravitational
pull. Neutrons can be packed more
closely than atomic nuclei, meaning
that a teaspoon of neutron star
weighs 10 million tons. The star’s
escape velocity (the velocity
required to escape its gravitational
pull) is nearly half the speed of light.
First detection
The concept of a neutron star
remained purely hypothetical
until 1967, when pulsars were
discovered. Pulsars were shown
to be rapidly spinning neutron
stars. In 1979, a powerful burst of
gamma rays was detected. This
has since been attributed to a
“magnetar”—a kind of neutron
star with a magnetic field billions
of times greater than Earth’s.
Many mysteries remain
regarding collapsing stars. Only
stars above the Chandrasekhar
Limit of 1.4 solar masses (p.178)
will become supernovae and form
neutron stars. A star above 3 solar
masses goes further and becomes
a black hole. There may be a halfway
stage in which neutron matter
degenerates even more into quark
particles—the particles from which
neutrons and protons are made.
Quark stars remain hypothetical,
but the search for them is on. ■A supernova in the Large Magellanic
Cloud blew out this cloud of shrapnel,
captured by the Chandra X-ray Space
Observatory. The explosion was caused
by the collapse of a massive star.Fritz Zwicky
Born in Bulgaria to a Swiss
father and Czech mother,
Fritz Zwicky emigrated to
the United States in 1925 to
work at Caltech with Robert
Millikan, a leading particle
physicist. In 1931, he began
a collaboration at the Mount
Wilson Observatory near Los
Angeles with Walter Baade,
a German astronomer, who
had just arrived from Europe.
It was this partnership
that led to the discovery of
supernovae and neutron stars,
but Zwicky’s work around this
time was also instrumental
in another great discovery.
Zwicky calculated that the
mass of galaxies, as indicated
by their gravitational effects,
was much greater than the
matter that could be measured
through observations. He
named the missing material
dunkle Materie, now better
known as dark matter. In
addition to his theoretical
work, Zwicky worked on the
development of jet engines
and took out more than 50
patents on his inventions.Key works1934 On Supernovae
(with Walter Baade)
1957 Morphological Astronomy