Indian astronomers reveal rare type of millisecond pulsar

Pulsars are like cosmic lighthouses, beaming out radio signals as they spin extremely fast, as much as several hundreds of rotations around their axis in a second. Some of these pulsars are rotating hundreds of times per second – those are millisecond pulsars

A group of astronomers from the National Centre of Radio Astrophysics (NCRA) – Tata Institute of Fundamental Research (TIFR) Pune, led by Ankita Ghosh, a Ph.D. student at NCRA and her supervisor, professor Bhaswati Bhattacharyya of NCRA, revealed a rare type of millisecond pulsar (MSP) named PSR J1242-4712 using the upgraded Giant Metrewave Radio Telescope (uGMRT). The team found that the millisecond pulsar revolves round a very low-mass companion star weighing one-tenth of the mass of our Sun. The study shows that this MSP is in the process of destroying its companion. The research mostly focuses on how this system orbits and moves around each other and also about the special nature of the system.

Spider pulsar (at the centre) destroying its companion. (SOURCED)

Ghosh said, “Pulsars are like cosmic lighthouses, beaming out radio signals as they spin extremely fast, as much as several hundreds of rotations around their axis in a second. Some of these pulsars are rotating hundreds of times per second – those are millisecond pulsars (MSPs). MSPs are considered to be older neutron stars that got a boost in the spin from a nearby star by accreting material and angular momentum from its companion, spinning faster and faster in the process, leaving a lightweight companion.”

“In some of the MSP systems, the pulsar and the companion star are in a very close orbit. The intense energy spewing from the MSP can strip away its companion’s material which can block the radio signals from the pulsar causing an eclipse. This interaction creates MSPs with super lightweight companions, dubbed ‘spider’ MSPs. As they are thought to destroy their companion, the two subcategories of spider MSPs are named: ‘black widows’ with tiny companions (having less than one-twentieth of the mass of our Sun) and ‘redbacks’ with slightly heavier companions,” Ghosh said.

Ghosh and the team from NCRA studied an MSP, J1242-4712, which was also discovered with GMRT in 2016 by professor Bhattacharyya and team. This particular MSP spins so fast that it completes a full rotation around its axis in just 5.31 milliseconds.

Professor Bhattacharyya said, “Using observations from the uGMRT at 400 MHz and 650 MHz, the team managed to nail down some precise timing details for this pulsar. Pulsar timing is like monitoring a celestial clock, tracking its regular pulses of radio waves. They might spin up or slow down slightly like a clock losing or gaining a few seconds over time. Pulsar timing involves carefully measuring these tiny changes. This can unveil mysteries, from extreme physics to the relationships between the pulsar and its companion.”

Ghosh and the team got an impressive timing accuracy of 2.4 microseconds for the PSR J1242-4712. They also figured out that PSR J1242-4712 is locked in with a companion star weighing 0.08 times the mass of our Sun, and the duo complete a full rotation around each other once every 7.7 hours. This MSP also briefly eclipses when it is nearest to its companion in orbit, confirming that PSR J1242-4712 is a ‘spider’ MSP with a sub-class of either ‘redback’ or ‘black widow’. However, unlike most ‘redbacks’, the J1242−4712 doesn’t have an optically visible companion star but has a more dynamic orbit and heavier companion which closely resembles ‘redbacks’ as compared to ‘black widows’. Its characteristic age has been estimated to be 4 billion years.

The research was published in the Astrophysics Journal. The other members of this project are: professor Andrew Lyne from the Jodrell Bank Centre for Astrophysics, University of Manchester; professor David Kaplan from the Centre for Gravitation, Cosmology and Astrophysics, University of Wisconsin-Milwaukee, USA; and professor Jayanta Roy from NCRA and others.