Discovery of a neutron star that breaks all records!

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[EN VIDÉO] A “black widow” pulsar consumes its companion
Speaking of spiders, black widow spiders are the ones that devour their mates after mating. And astronomers have observed similar behavior in the sky. When a pulsar and a low-mass star form a binary system. Faced with the radiation emitted by the pulsar, the star has little chance of surviving for long. (in English) © NASA Goddard

She is a part of “black widows”, the dead stars that have consumed most of their companion star. A nickname that refers to these spiders which devours the male after itclutch. Named PSR J0952-0607, it was first discovered in 2017 as a millisecond pulsar potential, ie. rotation period between 1 and 10 milliseconds. And for good reason: it spins velocity a wonderful 707 revolutions on itself per second, which actually according to a study published in the journal The Astrophysical Journal Letters and freely available, “the fastest rotating pulsar on the disk of The Milky Way » ! Several observing campaigns followed these first measurements, which made it possible to study the properties of this astonishing star.

It spins at the enormous speed of 707 revolutions per second

In practice, black widow spiders correspond to neutron stars which spin at astronomical speeds so that they can attract enough fabric of their companion binary so that only a small fraction of lot solar power. Only two dozen are currently known, as they are particularly difficult to detect.

“As the companion star evolves and begins to become one red giantthe material spreads overneutron star, and that makes the neutron star spin. As she purrs, she becomes incredibly energetic, and a wind of particles start to come out of the neutron. This wind then hits the donor star and begins to remove material, and over time the donor star’s mass drops to that of a planet, and if more time passes, it disappears completely. Black Widows weren’t solitary to begin with—they must have been in a binary pair—but they gradually evaporated their companions, and now they’re solitary.” explains Alex Filippenko, co-author of the study and professor emeritus of astronomy at the University of California at Berkeley.

Its companion star has shrunk to the size of a giant planet

Thus, characterizing PSR J0952-0607 was not an easy task. As the researchers explain, if it could be detected thanks to the pulsating signal emitted by its rapid rotation, however, this signal is not sufficient to characterize it. You must be able to observe your companion in visible light. But that’s the problem: she was almost completely consumed! Its mass has decreased to 20 times its mass Jupiterbarely 2% of the mass of Sun !

“These planet-like objects are debris from normal stars that contributed mass and cinematic momentspin their pulsar companions at times of milliseconds, increasing their mass in the process”said Roger W. Romani, first author of the study and astronomer at Stanford University. It then undergoes a lock-off tide : since its part closest to the black widow is much more attracted than the farthest part, it rotates synchronous and simultaneously performs a trip on itself and a trip around the other star in 6.4 hours. It is this phenomenon that occurs in the case of the Pluto-Charon system, but also the Earth-Moon system!

And it is ultimately this locking that allowed its observation. Because the temperature on its face, on the neutron star side, rises to 6,200 Kelvinslightly more than the temperature of The surface of the sunjust allowing it to be observed with great telescope. Thus it is Keck I, a telescope from the eponymous observatory located on the island of Hawaii and possessing a mirror primary 10 meters in diameter, which was facing PSR J0952-0607, located about 3,000 light-years in the direction of constellation from Sextant. A total of six 15-minute observations have taken place over the past four years to capture the system in a specific position oforbit doing brightness acceptable for measurements.

The most massive neutron star observed to date

After these observations, the researchers compared the spectrum obtained with that of known stars to derive the velocity orbital of the star, in order to finally be able to calculate the mass of the neutron star which accompanies it. They found a mass of 2.35 ± 0.17 solar masses, making it theneutron star the most massive ever observed! Above this mass, these stars at the extreme density could well change to black hole. “We can continue to search for black widows and similar neutron stars that skate even closer to the edge of the black hole. But if we don’t find any, it strengthens the argument that 2.3 solar masses is the true limit, out above which they become black holes.”says A.Filippenko.

But even for such a mass, scientists wonder about the nature of the star. It corresponds to a heart ofmassive star which contracted in on itself while the outer layers of this same star were blown away by a violent explosion called a supernova. The heart has contracted so much that there is no longer any questionatoms this time, but of the particles that make them up, hence the term neutron star. The average density is 1017 kg/m3which is the same as that of the atomic nucleus! “We know roughly how matter behaves at nuclear densities, such as in the nucleus of a uranium atom.comments Alex Filippenko. A neutron star is like a giant core, but when you have a solar mass and a half of that stuff, or about 500,000 Earth masses of cores all hooked together, there’s no telling how they’re going to behave. »

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