The Light House of the Universe

PULSARS

WHAT ARE PULSARS?• “Lighthouses of the Universe”

• Special kind of neutron star

• Emits beam of gamma rays, x rays, or radio waves which sweeps through Earth’s line of sight; pulsating effect

• Spins up to several 100 times a second

• Have highly intense magnetic and electric field (several trillion Gauss and Volts)

DISCOVERY• First one discovered by Cambridge

University Researchers Jocelyn Bell and Antony Hewish in 1967

• Detected pulses separated by 1.33 seconds from same position in the sky

• Second pulsar was discovered in the Crab Nebula with a period of 33 milliseconds; confirmed it was a rotating a neutron star

• Around 1600 pulsars found

FORMATION

• Stars having 8 to 25 times mass of sun initially

• At end of life undergoes supernova explosion (outer layers burst out)

• Electrons and protons are crushed together to form neutron core

• collapses into neutron star without collapsing into black hole

• 1.4 to 3.2 times mass of sun

• About 20 kilometres in diameter and extremely high density

STRUCTURE AND MECHANISM• When star collapses into a neutron

star radius is dramatically decreased to fraction of original star; very high speed

• As mass moves closer to centre of mass rotational speed increases

• Produces strong magnetic field

• Magnetic axis and rotational axis not aligned

• Combination of strong magnetic field and rapid rotation produces powerful electric field

• Electric field accelerates electrons

• High energy electrons produce radiations By acting as plasma to produce radiation

By interacting with photons or magnetic field

• Point of emission of radiation is somewhere around magnetic poles

• When beam around magnetic poles is in earth’s line of sight, radiation is detected

• Lighthouse effect

STRUCTURE AND MECHANISM

• rotation slows down over time as electromagnetic power is emitted

• When a pulsar's spin period slows down sufficiently, the radio pulsar mechanism turns off

HOW WE DETECT PULSARS• When rotating pulse is pointed towards earth, signal is detected

(mainly as x ray, gamma or radiowaves by spectroscopic methods)

• When pointed away signal fades

• Appear as pulses at very regular intervals

ACCRETION POWERED PULSARS• Binary System of pulsar and

companion star

• Gas from companion gets pulled in or “accreted” to magnetic polar caps (gravity)

• Mass transfer increases speed of rotation tremendously

• Converts them into millisecond pulsars

• CRAB PULSAR

Situated in Crab Nebula

Second Pulsar discovered

Has period 33 milliseconds

Forms major portion of emissions from the Crab Nebula

IMPORTANT PULSARS

A slow-motion movie of the Crab Pulsar taken at 800 nm wavelength (near-infrared) using a Lucky Imaging camera from Cambridge University, showing the bright pulse and fainter interpulse

• VELA PULSAR

Spins 11.195 times per second

Emits radio, optical and gamma rays

Brightest known object in gamma ray sky

Cycle of pulsed gamma rays from Vela Pulsar

• PSR J0108-1431

Oldest Pulsar known (200 million years old)

Only 770 LY from earth

• PSR J1823−3021A

Youngest millisecond pulsar yet observed (25 million years old)

Fastest pulsar yet observed 183.8 times per second

Detected in NGC 6624 (spherical cluster of ancient stars)

APPLICATIONS• Maps and Navigation – pulsar position to create a spacecraft navigation

system; eg. Sun’s position relative to 14 pulsars mapped out; identified by unique periods

• Precise Clocks – very regular period, more accurate than atomic clocks

• To Test theories of Gravity – strong gravitational force

THANK YOU