Topic PULSAR
Course name : Astronomy and Cosmology
Course code : PH-402

Group Members
1. Md.. Jahir Alam(202)
2. Sudipto Das(203)
3. Utpal Chandra Barman(204)
4. Mehedi Hassan(206)
5. Md. Atikul Islam(207)
6. Md. Sohel Rana(208)
7. Md Motiur Rahman Shamim(210)

Pulsars
We will discuss about the following points in this
presentation.
1. Introduction to Pulsar.
2. Properties of pulsar.
3. Discovery of pulsar.
4. Formation of pulsar from neutron star.
5. Crab pulsar & Binary pulsar.
6. Mechanism & radiating process of pulsar.
7. Application & Milestone.

Where we are ??
Definitely in the universe.
The Universe is all
of space and time (spacetime)
and its contents, which
includes planets, moons, mino
r planets, stars, galaxies, the
contents of intergalactic
space and
all matter and energy.
The size of the entire Universe
is still unknown.
Images Of Universe
Inception

A star is a luminous sphere
of plasma held together by
its own gravity.
Star
The Sun emits electromagnetic radiation

ALL ABOUT MASS OF CORE REMNANT
< 1.4 Solar Masses
> 3 Solar Masses
1.4 - ~3 Solar Masses
= White dwarf
= Neutron star
= Black hole

Neutron stars are created when
giant stars die in supernovas and
their cores collapse, with the
protons and electrons essentially
melting into each other to form
degenerate neutron gas.
Electrons & Protons
Combine
Degenerate Neutron Gas
NEUTRON STAR
Neutron stars

VERY, VERY DENSE!

It is predicted that supernovae triggered by stars
that do not have enough mass for their cores to
form black holes will result in neutron stars.
• “Quiet” neutron stars, non emitting
• Binary pair
• Pulsars
• Magnetars
• What is pulsar?
• **Pulsars are the rapidly rotating neutron stars
that emit periodic pulse of electromagnetic
radiation as like lighthouse does.
• **The strong magnetic field of the neutron star
concentrates charged particles in two regions and
the radiation is emitted in two directional beams.

Properties of pulsar
• Density of 1017 Kg/m-3.
• Thimbleful has a mass of 109
tonnes.
• Rotates once to several hundred times per
second.
• Acceleration due to gravity at surface of
pulsar is ~ 1012
m.s-2
(10 m.s-2
at Earth).
• Escape velocity ~ 50% of the speed of
light.

Typical pulsar diameters are approximately 20 to 25 kilometres
with a mass roughly 1.4 times the mass of the Sun. The mean
density is approximately 6.7 x 1014 grams/cm3 which is
equivalent to a single sugar cube weighting as much as all of
humanity (approximately the weight of 7 billion people).

Classification:
• Three distinct classes of pulsars are
currently known to astronomers,
according to the source of the power
of the electromagnetic radiation:
• Rotation-powered pulsars, where the
loss of rotational energy of the star
provides the power.

• Accretion-powered pulsars (accounting
for most but not all X-ray pulsars), where
the gravitational potential
energy of accreted matter is the power
source (producing X-rays that are
observable from the Earth).
• Magnetars, where the decay of an
extremely strong magnetic field provides
the electromagnetic power.

The first PULSER : PSR
B1919+21
period of 1.3373 seconds
pulse width of 0.04 seconds

Born : 11 May
1924 (age 93)
Nationality : British
Jocelyn Bell Burnell
Born : 15 July
1943 (age 73)
Nationality : British
Antony Hewish

In 1967 , Jocelyn Bell Burnell was a P.hd student of
cambridge university. Antony Hewish was her supervisor. She
was doing thisis about “
The Measurement of radio source diameters using a diffraction method.
The first pulsar was observed on November 28, 1967 .
They observed pulses separated by 1.33 seconds that
originated from the same location on the sky,

 Bell observed that the unusual reading was regular (every
1.3373011 seconds)
It Might it be a message sent by intelligent beings from another
world? they half-kiddingly named the signal LGM1. But that left
them with a dilemma Who could they tell? And what would they
say?
Radio Observations of the Pulse Profiles and Dispersion Measures of Twelve Pulsars

 By 1968 most opinion settled on neutron stars as the
best solution. This came from a theory put forth
by Robert Oppenheimer and Fritz Zwicky in the
1930s, predicting that when a massive star died, it
would collapse into an incredibly dense, spinning body, a
neutron star.
 They announced the discovery, though they still hadn't
determined the nature of the source.
 Bell found another pulsing signal. Only this one was
slightly different -- it pulsed at 1.2 second intervals. And
it came from the other side of the sky. These two differences
made it extremely unlikely that the source was intelligent
beings.

 In 1968 Bell earned her PhD -- pulsars appeared in the
appendix of her dissertation.
 In 1974, Antony Hewish awarded the Nobel Prize in physics for
playing a decisive role in the discovery of pulsars
 They changed the name of the signal from LGM to CP1919,
for Cambridge pulsar. It emits radio waves.

Formation of Pulsar
• The formation of a pulsar is very similar to the creation of a neutron
star. When a massive star with 4 to 8 times the mass of our Sun dies,
it detonates as a supernova. The outer layers are blasted off into
space, and the inner core contracts down with its gravity. The
gravitational pressure is so strong that it overcomes the bonds that
keep atoms apart.
• Electrons and protons are crushed together by gravity to form
neutrons. The gravity on the surface of a neutron star is about 2 x
1011 the force of gravity on Earth. So, the most massive stars
detonate as supernovae, and can explode or collapse into black
holes. If they’re less massive, like our Sun, they blast away their
outer layers and then slowly cool down as white dwarfs.

• But for stars between 1.4 and 3.2 times the mass of the Sun,
they may still become supernovae, but they just don’t have
enough mass to make a black hole. These medium mass
objects end their lives as neutron stars, and some of these can
become pulsars or magnetars. When these stars collapse,
they maintain their angular momentum.
• But with a much smaller size, their rotational speed increases
dramatically, spinning many times a second. This relatively
tiny, super dense object, emits a powerful blast of radiation
along its magnetic field lines, although this beam of radiation
doesn’t necessarily line up with it’s axis of rotation. So, pulsars
are simply rotating neutron stars.

SMALLER STARS (LIKE OUR SUN)
( Don’t worry, we have around 5
billions years left yet … )

How is a pulsar formed

Simply pulsars mean pulsating stars. A pulsar is
from pulse and -ar as in quasar.
A pulsar is a highly magnetized, rotating neutron star that emits a beam
of electromagnetic radiation. This radiation can be observed only when the
beam of emission is pointing toward Earth as like lighthouse and is
responsible for the pulsed appearance of emission. This produces a very
precise interval between pulses that range from milliseconds to seconds for
an individual pulsar. Pulsars are believed to be one of the candidates of the
observed ultra-high-energy cosmic rays .
After Formation of Pulsar

• The Crab Pulsar (PSR B0531+21) is a
relatively young neutron star. The star is the
central star in the Crab Nebula, a remnant of
the supernova SN 1054, which was widely
observed on Earth in the year
1054 Discovered in 1968, the pulsar was the
first to be connected with a supernova
remnant.
Crab Pulsar

PROPERTIES
• The Crab Pulsar is one of very few pulsars to be identified
optically. The optica pulsar is roughly 20 km in diameter and
the pulsar "beams" rotate once every 33 milliseconds, or 30
times each second. The outflowing relativistic wind from the
neutron star generates synchrotron emission, which produces
the bulk of the emission from the nebula, seen from radio
waves through to gamma rays. The most dynamic feature in
the inner part of the nebula is the point where the pulsar's
equatorial wind slams into the surrounding nebula, forming
a termination shock .
• The termination shock is the boundary marking one of the
outer limits of the Sun's influence, and is one boundary of the
Solar System. It is where the bubble of solar wind particles
slows down so that the particles are traveling slower than the
speed of sound. The solar wind particles slow down when
they begin to press into the interstellar medium. The solar
wind is made of plasma.

CRAB NEBULA & PULSAR

DISCOVERY OF BINARY PULSAR
• The first binary pulsar, PSR
B1913+16 or the "Hulse-Taylor
binary pulsar" was discovered in
1974 at Arecibo by Joseph
Hooton Taylor, Jr. and Russell
Hulse

What Is Binary Pulsar?
• A binary pulsar is a pulsar with a binary companion, often a white
dwarf or neutron star. (In at least one case, the double pulsar PSR
J0737-3039, the companion neutron star is another pulsar as well.)
Binary pulsars are one of the few objects which allow physicists to
test general relativity because of the strong gravitational fields in
their vicinities. Although the binary companion to the pulsar is
usually difficult or impossible to observe directly, its presence can be
deduced from the timing of the pulses from the pulsar itself, which
can be measured with extraordinary accuracy by radio telescopes.
• It was concluded that the pulsar was orbiting another star very
closely at a high velocity, and that the pulse period was varying due
to the Doppler effect: As the pulsar was moving towards us, the
pulses would be more frequent; and conversely, as it moved away
from us fewer would be detected in a given time period. One can
think of the pulses like the ticks of a clock

How pulsars radiate electromagnetic radiation i.e.
radio waves & X-rays?
Now at a glance: Giant star Supernovae Neutron stars + rotation Pulsars
A great number of theories since have been proposed by
astronomers to explain the mechanism of radiation from
pulsars.
Most of them failed to describe the mechanism clearly .
One of the most reliable theory is Gold’s model of pulsars .
It was T. Gold who first suggested a plausible mechanism by
which the radiation that radiated from pulsating neutron
stars could be explained clearly.

In the intense magnetic field of pulsar ,any charged
Particle that may escape from its surface will constrained
to move along the magnetic lines of force .The aggregated
particles is thus whirled with angular velocity around the
neutron star .
In this manner, a co-rotating magnetospheres formed
around the neutron star . The tangential velocity of this
Whirling particles gradually increases as they move
further
and further from the stellar surface.
Gold(1969) first suggested that the magnetic field of a
rapidly rotating neutron star will force the plasma to co-
rotate at a large enough radius to bring the velocity of
particles close to c (velocity of light).
The circle described by particles is called velocity of
light circle of radius c=rw .where w=angular velocity

The relativistic plasma beam near this circle will radiate radio
waves perpendicular to the beam , but at the velocity of the
light circles where the particles attain the velocity of light will
break away the magnetosphere and out the surrounding regions
of space.
The observation of the crab nebula suggested that these high
energy particles when leave the influence of the parent neutron
star stream into the nebula to supply the perennial energy
source from nebula over the entire spectral range from X-ray to
radio waves as a narrow beam .
A narrow beam might be formed in many ways ,of which the
following seem to be typical :
(a) Synchroton radiation
(b) Cerenkov radiation
(c)A relavistics effect of a rapidly moving source.

Synchrotron mechanism: A synchrotron is a particular type of
cyclic particle accelerator, descended from the cyclotron, in
which the accelerating particle beam travels around a fixed
closed-loop path. The magnetic field which bends the particle
beam into its closed path increases with time during the
accelerating process, being synchronized to the
increasing kinetic energy of the particles.

:
Cherenkov radiation results when a charged
particle, most commonly an electron, travels
through a dielectric (electrically polarizable) medium
with a speed greater than that at which light
propagates in the same medium.
Moreover, the velocity that must be exceeded is
the phase velocity of light rather than the group
velocity of light . Then a cone of light emits
backwards direction as bow of water waves
generate in case of ship in water.
So many information we have
gathered during this time
Now we will turning back to the Gold
model and conclude the above
discussion:-
Cerenkov radiation

1.The radius of the velocity of light circle for crab pulsar NP 0532 is 1600 k.m. with
shortest time period 0.033 seconds.
2.And for companion pulsar NP 0527 is 160,000 k.m. with time period 3.7 seconds.
3.Since the pulsars rotate with very high velocities ,the radiation will be strongly
beamed in a narrow cone in a forward tangential direction sweeping a particular
region periodically ,as a result any distant observer will observe that the the
pulsar behaves like a light house.
4.The observed fluctuations in pulse amplitude may be due to the change in the
interstellar medium through which the pulses propagates to a great distances
before reaching the earth . It is sometimes found that the pulse structure remains
fairly constant over a period of several times . This statement mean interstellar
medium remains unchanged during this time .
According to Mr. Gold ,it is deduced that

Application of pulsar
Maps
Pulsar maps have been included on the two Pioneer Plaques as well as
the Voyager Golden Record.
--Pioneer Plaque is a plaque of golds analysed aluminium that connects
with the antenna of spacecraft of Pioneer-10 and Pioneer-11.When the
spacecraft contact with the surface of any interstellar objects then the Plaque
prevents yhe destruction.
--Voyager Golden Record is the record that connects with the Voyager
spacecraft.
They show the position of the Sun, relative to 14 pulsars, which are identified
by the unique timing of their electromagnetic pulses, so that our position
both in space and in time can be calculated by
potential extraterrestrial intelligences.

Precise clocks
Generally, the regularity of pulsar emission does
not rival the stability of atomic clocks. However,
for some millisecond pulsars, the regularity of
pulsation is even more precise than an atomic
clock. This stability allows millisecond pulsars to
be used in establishing ephemeris time[ or in
building pulsar
clocks.

Gravitational waves detectors
There are 3 consortia around the world which use pulsars
to search for gravitational waves. In Europe, there is
the European Pulsar Timing Array (EPTA); there is
the Parkes Pulsar Timing Array (PPTA) in Australia; and
there is the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav) in Canada and the US.
Together, the consortia form the International Pulsar
Timing Array (IPTA). The pulses from Millisecond
Pulsars (MSPs) are used as a system of Galactic clocks.
Disturbances in the clocks will be measurable at Earth. A
disturbance from a passing gravitational wave will have a
particular signature across the ensemble of pulsars, and
will be thus detected.

Milestone
• In 1993, the Nobel Prize in Physics was awarded
to Taylor and Hulse for the discovery of pulsar
that generate gravitational radiation. This pulsar
orbits another neutron star with an orbital period
of just eight hours. Einstein's theory of general
relativity predicts that this system should emit
strong gravitational radiation.

Reference;
Books:
1. Shu, F. H.; The Physical Universe; An Introduction to Astronomy.
2. Baidyanath Basu; An introduction to Astrophysics.
3. Hoyle, F.; Highlights in Astronomy.
Website:
1. www.universetoday.com/25376/pulsars/
2. www.space.com/32661-pulsars.html
3. www.nasa.gov/subject/8731/pulsars/
4. https://en.wikipedia.org/wiki/Pulsar