PULSARS : STARS WITH A PULSE

OVERVIEW What are neutron stars? A day on a neutron star. Pulsars. Why do pulsars have

intense magnetic field? To what good are pulsars

to us.

NEUTRON STARS

Pulsars are just a kind of neutron stars so it’s essential to get a grip of these first.

The stars that come into being at the end of a massive star’s lifetime are called neutron stars.

When these massive stars have finished burning their nuclear fuel, they undergo a supernova explosion.

The event of formation of neutron stars is called core-collapse supernova’.

The central region of the star collapses so much that even electron, proton combine to form neutron and hence the name neutron star.

A DAY ON NEUTRON STAR

The size of neutron star as compared to the Earth and a White Dwarf

+ Small diameter + High mass=Super

High Density. Density of an average neutron star

would be around 5 x 1017 kg/m3 . Rotates about 40,000 times a minute. Crust is about 1 km thick but 100 billion

times stronger than steel. Has a very tiny atmosphere(made

mostly of iron 56 and lighter elements) . The surface is about 1 million degrees

Celsius. They have an escape velocity of about

33% the speed of light.

PULSARS Discovered by Jocelyn Bell in 1967. She observed a pulsar whose pulsations lasted for

about 0.04 seconds and were 1.3373 seconds apart, called pulsar period.

It was initially named LGM-1, for Little Green Men . Bell and her instructor assumed it as a sign of

extraterrestrial life. Later Thomas Gold recognized that pulsars were

rotating neutron stars. So pulsar is a kind of neutron star that emits beams

of radiation that sweep through Earth’s line of sight. A special phenomenon called lighthouse effect is

observed. All pulsars are neutron stars, not all neutron stars

are pulsars!

A diagram of pulsar showing its rotation and magnetic axis

When normal stars collapse into pulsars(neutron stars) their magnetic fields also compress and become enormously intense as much as a trillion times Earth’s magnetic field.

Pulsars spin fast for the same reason ice skaters pull in their arms to spin, following conservation of angular momentum.

The Vela Pulsar

APPLICATIONS OF PULSARS

In Map reading.

As precise clocks.

As gravitational wave detectors.

Relative position of the Sun to the centre of the galaxy and 14

pulsars

REFERENCES For the Love of Physics… by

Walter Lewin. Einstein for Everyone… by

Robert L. Piccioni. http://www.fromquarkstoquasa

rs.com http://imagine.gfsc.nasa.gov/do

cs/science/know_|1/pulsars.html