Pulsar planets are the exoplanets that are revolving around millisecond pulsars (pulsars are fast rotating neutron stars. neutron stars are formed when a star of mass nearly 10 to 13 times the mass of the sun collapses under its own gravity and undergoes a supernova. After the supernova explosion, the remaining core is called the neutron star). Now, a millisecond pulsar is a pulsar that is present in a binary system. And is fed up by the matter of companion star.

These millisecond pulsars are generally formed in the binary systems because a millisecond pulsar need a companion to make it rotate at such high speeds (millisecond pulsar rotates at a hundred thousand times a second)

While searching for exoplanets the most impossible place where planets can be detected are around pulsars.

An artist’s impression of the binary star system PSR J1023+0038. The extremely dense, rapidly-spinning neutron star, just 10-15 kilometres in size, is in a close orbit with a more normal companion star. The strong gravity of the neutron star pulls gas from its companion, which spirals in towards the neutron star, forming a disc. Some fraction of that gas gets accelerated outwards in energetic, oppositely-directed jets, which give off the radio waves that can be seen by Earth’s radio telescopes. Image credit: ICRAR.

Astronomers thought there is no possibility of detecting planets around pulsars since any planets present would have been evaporated by the supernova explosion.

Surprisingly first exoplanets (planets that are beyond our solar system) were discovered around the pulsars.

The first two pulsar planets were detected by Aleksander wolszczan and dale frail around the pulsar PSR 1257+12

These planets are the first exoplanets and first pulsar planets and the first multi-planet planetary system.

These planets are very close to the pulsars and orbiting in closely circular orbits.

Millisecond pulsar needs a companion star but, in this system, the star is not detected so, there is a theory which explains the formation of these planets: After the supernova explosion the debris leftover forms the accretion disk/debris disk (the dust and gas revolving around the pulsar due to strong gravitational force and the magnetic forces) around the pulsar and planets are formed from the accretion disk just like the formation of the planets in our solar system.

This theory was confirmed when a debris disk is discovered around the magnetar 4U 0142+61 (neutron star which is having strong magnetic fields) that is located in the northern constellation of Cassiopeia at a distance of 13000 light-years. which was discovered by the team led by Deepto Chakrabarty of MIT by using the spitzer space telescope.

 This artist’s concept depicts a type of dead star called a pulsar and the surrounding disk of rubble discovered by NASA’s Spitzer Space Telescope. Image credit: NASA/JPL-Caltech

Pulsar planets were discovered with the pulsar timing measurements

Generally, pulsars have constant pulsar timing until anything around them disturbs the pulsar timing. Millisecond pulsars have constant pulse and constant speed.

Soon many pulsar planets were detected.

In 2000, a pulsar planet was discovered which is orbiting the millisecond pulsar (PSR B1620-26) as well as the companion white dwarf (WD B1620-26) this pulsar planet is present in the binary system.

 This planetary system was detected in the globular cluster. This planet is orbiting the pulsar due to the capture process. previously this planet was orbiting a main sequence star (sun like star) but in the globular cluster the density is high and the stars are too close to each other and by the strong gravitational force of the pulsar the planet got captured to the pulsar and started orbiting the pulsar.

capture process by neutron star

Another pulsar planet was discovered around the millisecond pulsar (PSR J1719-1438)

Which is thought to be the leftover core of the companion star. This pulsar planet is called a diamond planet because the core contains the end product of the nuclear reaction in the core of the stars which is the carbon. The compressed and highly dense carbon is diamond it is thought to have (10^31 carats)

Artist’s illustration of the pulsar and its orbiting planet. The blue line represents radio waves, and the gold circle represents the circumference of our sun. Image Credit: Swinburne Astronomy Productions

Despite the discovery of the exoplanets these pulsar planets are impossible for habitation. These are unhabitable due to the strong radiation from the pulsars and very close distance from the pulsars.

After the discovery of pulsar planets. astronomers went in search for exoplanets that are orbiting normal stars like the sun.

This is to be left for the next blog.

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Naga Navya Reddy

Naga Navya Reddy

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