The Astronomy Book

236

IT HAS TO BE

SOME NEW

KIND OF STAR

QUASARS AND PULSARS

I

n the late 1950s, astronomers

across the world started to find

mysterious, compact sources

of radio signals in the sky without

any corresponding visible objects.

Eventually a source of these radio

waves was identified—a faint point

of light, which became known as a

quasar. In 1963, Dutch astronomer

Maarten Schmidt discovered a

quasar that was hugely distant (2.5

billion light-years away). The fact

that it was so easily detected meant

it must be pouring out energy.

Searching for quasars

By the mid 1960s, many radio

astronomers were searching for

new quasars. One such figure

IN CONTEXT

KEY ASTRONOMERS

Antony Hewish (1924 –)

Jocelyn Bell Burnell (1943–)

BEFORE

1932 English physicist

James Chadwick discovers

the neutron.

1934 Walter Baade and Fritz

Zwicky propose that stars

that explode as supernovae

leave behind collapsed

remnants made of closely

packed neutrons, which

they name neutron stars.

AFTER

1974 American astrophysicists

Joseph Taylor and Russell

Hulse discover two neutron

stars, one of them a pulsar,

orbiting each other.

1982 American astrophysicist

Donald Backer and colleagues

discover the first millisecond

pulsar, which spins 642 times

per second.