Much faster than one would anticipate for a collapsing star, millisecond pulsars spin. Finding a black widow system where the pulsar has vaporised and consumed much of its companion star offers the finest chance to investigate these neutron stars. Astronomers were only able to weigh the pulsar of one of these companions thanks to the Keck I telescope’s ability to catch its spectrum. It is the heaviest known object and may be getting close to the maximum limit for neutron stars.
One of the fastest spinning neutron stars in the Milky Way galaxy, a compact, collapsed star has virtually absorbed the whole mass of its stellar companion and grown into the heaviest neutron star yet seen. It spins 707 times per second. This record-breaking neutron star, which weighs 2.35 times as much as the sun, allows scientists to better comprehend the peculiar quantum state of matter that exists inside these dense objects, which, if they are much heavier, collapse completely and vanish as black holes.
In the nucleus of a uranium atom, for example, “we know basically how matter behaves at nuclear concentrations,” said Alex Filippenko, Distinguished Professor of Astronomy at the University of California, Berkeley. “A neutron star is like one huge nucleus, but it’s not at all apparent how they would behave when you have one and a half solar masses of this stuff, which is around 500,000 Earth masses of nuclei all clinging together.”
According to Roger W. Romani, a professor of astrophysics at Stanford University, neutron stars are the densest objects in the universe aside from black holes, which are impossible to study because their event horizons are hidden from view. One cubic inch of a neutron star weighs over 10 billion tonnes. Thus, the neutron star, also known as pulsar PSR J0952-0607, is the densest object visible from Earth. The 10-meter Keck I telescope on Maunakea in Hawaii, which was only able to record a spectrum of visible light from the furiously blazing companion star, now shrunk to the size of a big gaseous planet, made it possible to measure the neutron star’s mass. The stars are located in the direction of the constellation Sextans, some 3,000 light years away from Earth.
PSR J0952-0607, discovered in 2017, is known as a “black widow” pulsar, a reference to the female black widow spiders’ propensity to eat the much smaller male after mating. For more than a decade, Filippenko and Romani have been researching black widow systems in an effort to determine the maximum size that can be reached by neutron stars and pulsars.
We demonstrate that neutron stars must attain at least this mass, 2.35 plus or minus 0.17 solar masses, by combining this measurement with those of several other black widows, said Romani, a professor of physics in Stanford’s School of Humanities and Sciences and a member of the Kavli Institute for Particle Astrophysics and Cosmology. “This in turn offers some of the strongest limitations on the characteristics of matter at densities several times greater than those seen in atomic nuclei. In fact, this discovery excludes a large number of dense-matter physics models that were previously well-liked.”
The interior is likely to be a soup of neutrons and up and down quarks, the building blocks of regular protons and neutrons, but not exotic matter like “strange” quarks or kaons, which are particles that contain a strange quark, if 2.35 solar masses is close to the upper limit of neutron stars, the researchers claim. According to Romani, neutron stars with high maximum masses are made up of a mixture of nuclei and their dissolved up and down quarks all the way to the core. This rule disqualifies a number of suggested states of matter, particularly those having unusual internal compositions.
How big would they become?
In general, astronomers concur that when a star with a core mass greater than 1.4 solar masses collapses at the end of its life, it creates a dense, compact object whose interior is under such intense pressure that all atoms are crushed together to create a sea of neutrons and their subnuclear byproducts, quarks. These neutron stars are born spinning and, despite being too faint to be seen in visible light, expose themselves as pulsars by generating light beams that flash Earth as they rotate, much like the rotating beam of a lighthouse. These light beams include radio waves, X-rays, and even gamma rays.
The typical speed of “ordinary” pulsars is roughly once per second, which is easily explained given the star’s usual rotation before it collapses. It is difficult to explain why some pulsars repeat hundreds or even 1,000 times per second unless stuff has dropped onto the neutron star and spun it up. However, no companion may be seen for some millisecond pulsars. Each single millisecond pulsar may have once had a companion, but it has been stripped away, which is one explanation for their isolation.
“The process of evolution is utterly fascinating. two exclamation marks, “said Filippenko. “Material leaks over to the neutron star as it develops and begins to turn into a red giant, spinning it up in the process. A jet of particles begins to emanate from the neutron star as it starts to spin up and become extremely energetic. The donor star is subsequently struck by that wind, which begins removing material from it. Eventually, the donor star’s mass falls to that of a planet, and if additional time passes, it vanishes completely. That explains how single millisecond pulsars could develop. They had to be in a binary pair, so they weren’t all alone at first, but over time, their partners slowly vanished, leaving them alone.”
This origin theory for millisecond pulsars is supported by the pulsar PSR J0952-0607 and its dim companion star. The remnants of regular stars that have contributed mass and angular momentum to their pulsar companions, spinning them up to millisecond periods and increasing their mass in the process, according to Romani, are what are known as these planet-like objects. In a display of cosmic resentment, the black widow pulsar, which has already swallowed a sizable portion of its mate, is now heating and evaporating the companion to planetary masses, and possibly causing complete extinction, according to Filippenko.
