This Record-Breaking 'Black Widow' Pulsar Is The Biggest Neutron Star Ever

One of the most extreme stars in the Milky Way has just gotten even weirder.

Scientists have measured the mass of a neutron star named PSR J0952-0607, and found that it is the most massive neutron star ever discovered, registering 2.35 times the mass of the Sun.

If true, this is very close to the theorized upper mass limit of about 2.3 solar masses for neutron stars, which is an excellent laboratory for studying these ultra-dense stars at what we think are on the verge of collapse, in hopes of better understanding. strange quantum states of the matter they are made of.

“We know roughly how matter behaves at nuclear densities, such as in the nuclei of uranium atoms,” said astrophysicist Alex Filippenko of the University of California, Berkeley.

“A neutron star is like one giant core, but when you have one and a half solar masses of this material, which is about 500,000 Earth masses of cores all stuck together, it’s not at all clear how they’re going to behave.”

Neutron stars are the collapsing cores of massive stars whose masses are between about 8 and 30 times the mass of the Sun, before they become supernovae and blow most of their mass into space.

These cores, which tend to be about 1.5 times the mass of the Sun, are among the densest objects in the Universe; the only ones that are denser are black holes.

Their mass packed into a ball is only 20 kilometers (12 miles) or so; at that density, protons and electrons can combine to form neutrons. The only thing keeping these balls of neutrons from collapsing into a black hole is the force it takes for them to occupy the same quantum state, which is described as degenerating pressure.

In some ways this means that neutron stars behave like massive atomic nuclei. But what happens at this tipping point, where the neutrons form exotic structures or blur into smaller particles, is hard to say.

PSR J0952-0607 is already one of the most interesting neutron stars in the Milky Way. These are known as pulsars – neutron stars that spin very fast, with a beam of radiation emanating from the poles. As the star rotates, these poles pass through the observer (us) like a cosmic beacon so that the star appears to be pulsating.

These stars can be very fast, their rotation speed on the millisecond scale. PSR J0952-0607 is the second fastest pulsar in the Milky Way, rotating at 707 times per second. (The fastest is only slightly faster, with a rotation rate of 716 times per second.)

It is also known as the “black widow” pulsar. The star is in close orbit with the companion binary – so close that its large gravitational field pulls material away from the companion star. This material forms an accretion disk that spins and enters the neutron star, like water swirling around a drain. The angular momentum of the accretion disk is transferred to the star, causing its rotational rate to increase.

A team led by astrophysicist Roger Romani of Stanford University wanted to better understand how PSR J0952-0607 fits into the timeline of this process. The binary companion star is small, less than 10 percent the mass of the Sun. The research team conducted a careful study of the system and its orbit and used that information to derive new, precise measurements for the pulsar.

Their calculations returned a result of 2.35 solar masses, giving or taking 0.17 solar masses. Assuming a standard neutron star starts at about 1.4 times the mass of the Sun, that means PSR J0952-0607 has sucked out one Sun’s worth of matter from its binary partner. This, the team says, is very important information to have about neutron stars.

“This provides some of the strongest constraints on the properties of matter at several times the density seen in atomic nuclei. Indeed, many popular models of solid matter physics are excluded by these results,” explains Romani.

“The high mass maximum for a neutron star indicates that it is a mixture of core and upper and lower quarks dissolved all the way to the core. This excludes many proposed states of matter, particularly those with exotic interior compositions.”

Binary also demonstrates a mechanism by which isolated pulsars, without binary companions, can have millisecond rotation rates. Companion J0952-0607 is almost gone; once completely devoured, the pulsar (if it does not exceed the upper mass limit and collapses further into the black hole) will maintain its extremely fast rotational speed for some time.

And it will be alone, just like all the other isolated millisecond pulsars.

“When the companion star evolves and starts to become a red giant, the material spills over onto the neutron star, and it spins the neutron star. As it spins, it now becomes highly energized, and a wind of particles starts to escape the neutron star. The wind then hits the donor star and begins to disarm. matter, and over time, the mass of the donor star decreases to that of a planet, and as more time passes, it disappears altogether,” Filippenko said.

“So that’s how single millisecond pulsars can form. They weren’t alone to begin with – they had to be in a binary pair – but they gradually evaporated their companions, and now they’re solitary.”

This research has been published in Astrophysics Journal Letter.

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