The PSR J1023+0038 neutron star | ESA website
The PSR J1023+0038 neutron star | ESA website
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New Delhi: A physicist at Tata Institute of Fundamental Research (TIFR) has measured a tiny deformation the size of a bacterium in a neutron star located over 4,500 light years away — a feat that opens up a new window into the world of physics.

Neutron stars are extremely dense objects. Stars the size of a city pack a mass equivalent of 10 Suns. Some of these stars spin several hundred times per second, and are called millisecond pulsars.

The discovery was made in a binary system consisting of a neutron star, named PSR J1023+0038, and an ordinary star that revolve around each other.

In a new study, published in the journal Monthly Notices of the Royal Astronomical Society, Sudip Bhattacharyya, an associate professor at TIFR, described how he inferred a microscopic change in a millisecond pulsars located thousands of light years away.

The measurement is an important step in the world of physics, considering that one requires a microscope to make measurements of that order on Earth. But Bhattacharyya managed to detect this in a star located so far away that it would take a ray of light 4,500 years to travel the distance.

A tiny change in the cosmos has far reaching implications. Even a small deformation in millisecond pulsars would send out continuous gravitational waves across the universe.

Gravitational waves are ripples in the fabric of space and time that were first detected by an international collaboration of researchers in 2015. The ability to detect these distortions in space and time have allowed scientists to spot mergers of black holes and neutron stars taking place far away from the solar system.

Such mergers emit transient waves, lasting for just a fraction of a second or a few seconds.

However, continuous gravitational waves from a slightly deformed and spinning neutron star, have so far eluded research teams.

This is because current instruments do not have the capability to detect these waves, if the deformation is too small.

These measurements can now inform how accurate detectors need to be in order to directly observe continuous gravitational waves, Bhattacharyya told ThePrint.


Also read: NASA discovers 240-year-old ‘newborn’ neutron star that’s twice the sun’s mass


How was the deformation discovered

A small deformation in the neutron star, which causes it to emit continuous gravitational waves, slows down the spin rate of the star.

In binary systems such as the one with PSR J1023+0038, some amount of matter can get transferred from one body to another — a phenomenon known as mass transfer.

PSR J1023+0038 is a unique cosmic source, because it is the only millisecond pulsar for which two spin rates have been measured, Bhattacharyya said.

“In one state, the neutron star has some mass transferred from the companion star and another state, there is no mass transfer,” he said.

Using these two sets of measurements and basic fundamentals of physics, Bhattacharyya was able to pinpoint how much of this slow down in the spin of the star can be attributed to the emission of gravitational waves.

Since the emission of gravitational waves is attributed to a deformation in the star, the data helped indirectly estimate the neutron star’s microscopic deformation.

“Neutron star is one of the densest objects in the universe. Most of the physics around these stars is not well understood,” Bhattacharyya said.

Moreover, neutron stars have extremely strong magnetic fields.

“How matter interacts in this magnetic field is also not understood because such fields can not be recreated in the laboratory,” he said.

The deformation in the star can tell us a lot about how the stars are formed and how they evolve, he added.


Also read: Scientists at LIGO detect heaviest binary neutron star merger ever known


 

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