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What Leads To Pair Production Process In Pulsar’s Magnetospheres? (Cosmology)

Zaza Osmanov and his collaborators studied the possibility of efficient pair production in a pulsar’s magnetosphere. They showed that, the electrostatic field exponentially amplifies, by means of the relativistic centrifugal force. As a result, the field approaches to Schwinger limit¹, leading to pair creation process in the light cylinder (LC) area². Their study recently appeared in Arxiv.

In 1969, Thomas Gold suggested that, since pulsars are rotating neutron stars, centrifugal effects might be very important. This is because, these can energise the pulsar’s magnetospheric particles to energies enough for producing high energy electromagnetic radiation.

Later, it has been shown by Z. Osmanov and colleagues that the centrifugal force in the LC area is different for different species of particles (magnetospheric electrons and positrons). This in turn, might lead to charge separation creating the Langmuir waves. On the other hand, since the centrifugal force is time dependent, it acts as a parameter, amplifying the electrostatic field, and after it inevitably reach the Schwinger limit, it results in a pair production process.

Now, Z. Osmanov and his collaborators, studied this completely new mechanism of pair creation in the pulsar magnetosphere.

“We consider the normal period pulsars and study the possibility of pair production by means of the centrifugally driven electrostatic fields.”, told Z. Osmanov, professor at Free University of Tbilisi and lead author of the study.

Considering the typical pulsar parameters they showed that the electric field exponentially increases and gradually reaches the Schwinger limit, when efficient pair creation might occur.

They also analysed constraints imposed on the process and found that the process is so efficient that the number density of electron-positron pairs exceeds the Goldreich-Julian density by five orders of magnitude.

In addition, it has been shown that, this novel mechanism of pair production not only changes the number density of electron-positron plasmas in pulsar’s magnetospheres but also, it significantly influences the physical processes there. In particular, it is evident that the processes of particle acceleration strongly depends on the plasma density.

Finally, they showed that, the emission spectral pattern will be influenced as well by the efficient pair creation. This in turn, might give rise to coherent radio emission, which seems to be quite promising in the light of modern enigma – fast radio bursts.

“Since all these problems are beyond the intended scope of the paper we are going to consider them very soon.”, concluded authors of the study.


Note:
1) Schwinger limit is a scale above which the electrostatic field is expected to become nonlinear.
2) Light Cylinder area is a hypothetical area where the linear velocity of rotation coincides with the speed of light.


Reference: Z. Osmanov, G. Machabeli, N. Chkheidze, “The novel mechanism of pair creation in pulsar magnetospheres”, Arxiv, pp. 1-5, 2021. https://arxiv.org/abs/2105.09351


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