237
See also: Radio astronomy 179 ■ Supernovae 180–81 ■ Quasars and black holes 218–21 ■
Discovering black holes 254 ■ Ryle (Directory) 338−39
was Antony Hewish, part of a
radio astronomy research group at
Cambridge University. Hewish had
been working on a new technique
in radio astronomy based on a
phenomenon called interplanetary
scintillation (IPS), which is a
“twinkling,” or fluctuation, in
the intensity of radio emissions
from compact radio sources. The
twinkling of sources of visible
light, such as stars, is caused by
disturbances in Earth’s atmosphere
that the light has to pass through
(p.189). The twinkling of radio
sources, however, is caused by
streams of charged particles
emanating from the sun. As radio
waves pass through this “solar
wind,” they are diffracted, meaning
that the waves spread out, making
the radio source appear to twinkle.
Hewish hoped that IPS could
be used to find quasars. Radio
waves coming from a compact
source, such as a quasar, twinkle
more than radiation from a less
compact source, such as a galaxy,
and so quasars should twinkle
more than other radio sources.
Hewish and his team built a
large radio telescope designed
specifically to detect IPS. It
covered an area of nearly 4.5
acres (2 hectares), took two years
to construct, and required more
than 120 miles (190 km) of cable
to carry all the signals.NEW WINDOWS ON THE UNIVERSE
This image of a pulsar in the
Crab nebula, a well-known supernova
remnant, was taken in space by the
Chandra X-ray Observatory. The white
dot at the center is the neutron star.The pulses are definitely
coming from beyond
the solar system.The pulses cannot
be coming from aliens
on a planet orbiting a star as
there is no Doppler shift.Regular pulses of radio waves are coming
from a particular patch of sky.The pulses are coming from a tiny, rapidly
rotating neutron star—a pulsar.It has to be some new kind of star.
Members of the Cambridge radio
astronomy group built the new
telescope themselves. Among them
was a Ph.D. student named Jocelyn
Bell. When the telescope started
operating in July 1967, Bell was
made responsible for operating it
and analyzing the data, under the
supervision of Hewish. Part of her
job was to monitor output data
from the telescope, made by
pen recorders on chart-recorder
printouts. Examining about 100 ft
(30 meters) of chart paper every
day, Bell quickly learned to
recognize scintillating sources.Little Green Man 1
About two months into the project,
Bell noticed an unusual pattern of
signals, which she described as
“scruff.” It looked far too regular
and had too high a frequency to be
coming from a quasar. Checking
back through her records, she
found it had appeared in the data
before and always came from the
same patch of sky. Intrigued, Bell
started making more regular chart
recordings of the same area of sky.
At the end of November 1967, she
found the signal again. It was a
series of pulses, equally spaced
and always 1.33 seconds apart. ❯❯