The 8-Millisecond Pulsar That Could Redefine Physics

A dead star the size of a small city spinning seven hundred times per second has an almost ridiculous quality. The mind rejects your attempts to visualize it. However, that is precisely what one of these objects is doing as it sits about 8,000 light-years away inside a densely populated cluster of stars known as NGC 6624. It was dubbed PSR J1823-3021G by astronomers. The participating scientists frequently refer to it as “the interesting one.”

MeerKAT, a radio telescope located in the Karoo, a semi-desert region of South Africa where the night skies are so dark you can practically feel them pressing down, made the discovery. Out of MeerKAT’s sixty-four dishes, only about forty had been pointed at nine globular clusters by the team. In six, they discovered new pulsars. A total of eight. That would be considered a strong haul by most surveys. One signal, however, stood out in that batch; it was a little off, a little obstinate, and in an orbit that resembled a swerve rather than a circle.

The researchers were troubled by that in the constructive way that science is troubled. Unusually for a millisecond pulsar, PSR J1823-3021G has a highly elliptical orbit and seems to be paired with a very heavy companion. The most likely explanation is that this pulsar had a previous partner, lost it in a violent close encounter in the cluster’s crowded center, and then found a new one. In essence, stellar partner-swapping. It’s physics, but it sounds like gossip.

One of the co-authors, Tasha Gautam, of Bonn, described it cautiously, as scientists do when they have serious suspicions but are reluctant to express them. The mass of the pulsar may be more than twice that of the Sun. Alternatively, it could be the first verified pairing of a millisecond pulsar with another neutron star, which is even more uncommon. A door is opened by either scenario. The first focuses on the maximum strength of neutron-star matter before it collapses into a black hole. The second provides a clean laboratory where general relativity can be tested under circumstances that Einstein was not alive to witness.

It’s difficult to ignore how frequently the word “laboratory” keeps coming up in these discussions. As though the universe created these things expressly for human experimentation. You could drive across a sphere containing hundreds of thousands of Earth-masses in twenty minutes. Magnetic fields unimaginable. Like a lighthouse spinning at industrial speed, beams of radio light swept past us.

Naturally, pulsars have previously done this. They have repeatedly, sometimes uncomfortably, pushed physics forward. Long before LIGO directly confirmed gravitational waves, we had indirect evidence of them thanks to the discovery of the first binary pulsar decades ago. If the follow-up data hold up, there is a feeling among those involved that PSR J1823-3021G might be another one of those nudges. That disclaimer is important. Promising signals have burned astronomers in the past.

The hardware feels different now. MeerKAT is a forerunner of the Square Kilometre Array, which is being constructed throughout Australia and South Africa and will eventually dwarf all radio observatories ever used by humans. Eight pulsars in a few cluster centers were identified by even a partial array. The more comprehensive survey is already in progress, utilizing all sixty-four dishes and extending into the periphery of additional clusters. We anticipate dozens more discoveries. Compared to this one, some of them might be stranger.

For the time being, however, the focus is on a rapidly rotating object in Sagittarius, swinging through an orbit that alludes to a violent past and may be heavy enough to distort our existing models. The numbers are still being verified to see if it truly redefines physics. However, the questions it poses are legitimate, and the people posing them sound more like detectives who think they’ve discovered something worthwhile than like reporters.