Astronomers discover rare pulsar using uGMRT near Pune

Using the upgraded Giant Metrewave Radio Telescope (uGMRT), the world’s largest radio telescope located at Khodad, Narayangaon, 80 km from Pune, the team led by Jyotirmoy Das discovered PSR J1617–2258A, a millisecond pulsar, spinning 232 times a second. It sits just three-quarters of a core radius from the crowded heart of the cluster.

“Its unusual orbit, combined with a low-mass companion, makes it a rare system and an important laboratory for testing Einstein’s theory of general relativity,” Das told The Indian Express.

This discovery and its scientific implications represent an important result and highlight the world-class capabilities of the uGMRT. “This is the first pulsar in the ancient star cluster Messier 80 (M80), also known as NGC 6093,” Das said.

It is the first discovery from the new Globular Clusters GMRT Pulsar Search (GCGPS) project. The GCGPS project is an international collaboration uniting scientists from NCRA–TIFR (India), the Max Planck Institute for Radio Astronomy (Germany), the National Radio Astronomy Observatory (USA), and the University of Oxford (UK).

On millisecond pulsars

Millisecond pulsars are tiny, city-sized stellar remnants that spin hundreds of times per second, sweeping radio beams across space like cosmic lighthouses. A newly discovered millisecond pulsar from the GCGPS project circles a small companion roughly every 19 hours. But instead of a neat circle, its path is stretched into a long oval, unusually ‘lopsided’ for such a tight system. “In the crowded bustle of a globular cluster, close gravitational fly-bys can kick orbits into odd shapes, forming a PSR J1617-2258A-like system (its orbital ‘eccentricity’ is about 0.54),” Das, the lead author, explained.

Because the compact orbit is so stretched, the team could actually watch the ellipse itself slowly turn in space, a drift called the advance of periastron, predicted by Einstein’s general relativity due to spacetime curvature. According to Das, this precision is about half a degree per year. “To put that in perspective, this pulsar’s orbit shifts in a single day by roughly as much as Mercury’s perihelion shifts in an entire decade,” he added.

‘Fresh tests of Einstein’s theory’

That precise measurement lets astronomers ‘weigh’ the system. Together, the pulsar and its companion have a mass of about 1.67 times that of the Sun. According to Jayanta Roy, a scientist from NCRA-TIFR and one of the authors of the paper, that mix, a tight orbit, a highly stretched path, and a lightweight companion makes this system a rarity.

“Among known binary millisecond pulsars, only a few are both more compact and more eccentric, and those all have heavier partners. PSR J1617–2258A sits in a nearly empty corner of the millisecond-pulsar family portrait, hinting at an unusual evolutionary history,” Roy said.

This system gives researchers a clean laboratory to test gravity with a brand-new object in a dense stellar environment.

Bhaswati Bhattacharyya, a member of the GCGPS collaboration and another scientist from NCRA-TIFR, indicated that continued monitoring using uGMRT can sharpen the mass estimates and may spot additional relativistic quirks, offering fresh tests of Einstein’s theory and new clues to how close stellar encounters shape pulsars in globular clusters.

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