Page 30 - Ultimate Visual Dictionary (DK)

THE UNIVERSE

Neutron stars

and black holes

NEUTRON STARS AND BLACK HOLES form from the stellar cores that remain after
stars have exploded as supernovae (see pp. 26-27). If the remaining core is
between about one and a half and three solar masses, it contracts to form a
neutron star. If the remaining core is greater than about three solar masses,
it contracts to form a black hole. Neutron stars are typically only about
6 miles (10 km) in diameter and consist almost entirely of subatomic
particles called neutrons. Such stars are so dense that a teaspoonful
would weigh about a billion tons. Neutron stars are observed as Nebula of gas
pulsars, so-called because they rotate rapidly and emit two beams and dust
surrounds pulsar
of radio waves, which sweep across the sky and are detected as
short pulses. Black holes are characterized by their extremely Rapidly
strong gravity, which is so powerful that not even light can escape; rotating pulsar
as a result, black holes are invisible. However, they can be
detected if they have a close companion star. The gravity of the Beam of
radiation X-RAY IMAGE OF PULSAR
black hole pulls gas from the other star, forming an accretion from pulsar AND CENTRAL REGION
disk that spirals around the black hole at high speed, heating up OF CRAB NEBULA
and emitting radiation. Eventually, the matter spirals in to cross (SUPERNOVA REMNANT)
the event horizon (the boundary of the black hole),
thereby disappearing from the visible universe.
Rotational axis
of neutron star
PULSAR (ROTATING NEUTRON STAR)

Beam of radio waves Path of beam
possibly produced by of radio waves
rapid rotation of
magnetic field
Magnetic axis
North Pole
North magnetic
polar region
Solid, crystalline
external crust Magnetic
field line
Solid, neutron-rich
internal crust

Layer of
superfluid neutrons
Magnetic axis
Solid core
Beam of radio waves
possibly produced by
rapid rotation of
magnetic field
South Pole South magnetic
polar region

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