The smaller the mountains on the neutron star , the smaller the gravitational waves they produce.
The general trend is that the upper limit of mountains on neutron stars is getting smaller.
These "mountains" may be hundreds of times smaller than previous predictions.
3D visualization of a neutron star.
New research shows that neutron stars are covered with "mountains" just a fraction of a millimeter high, meaning these bulges are hundreds of times smaller than previously estimated.
Neutron stars are compact stellar objects, similar in size to a large city about 6.2 miles (10 kilometers) in diameter, and weighing at least 1.4 solar masses (1.4 times the weight of the Sun). They are born from the explosive death of stars weighing between 10 and 25 solar masses. As a result, they are among the densest objects in the universe and possess an extremely powerful gravitational field , approximately 2 billion times that of the Earth. This extreme gravity squeezes neutron stars into nearly perfect spheres, which are surrounded by a smooth but solid crust.
However, previous studies have found that deformation of the Earth's crust creates mountains on the surfaces of these stars.
Now, new findings presented at the 2021 National Astronomy Conference in the UK suggest that these mountains may be hundreds of times smaller than scientists previously thought.
Lead researcher Fabian Gittins, a PhD student at the University of Southampton in the United Kingdom, said, "They should probably be called 'bumps' or 'hills' rather than 'mountains.'
Imperfect spheres
Neutron stars have crusts that are external to the star The solid layer, similar to the Earth's crust, is composed of broken nuclei of heavy elements, which contains the ultra-dense neutron soup inside the star. It is about 0.6 miles (1 kilometer) thick and is the least dense region of the star.
Mountains form when the crust is under intense pressure and begins to fracture. "There are many ways these mountains can form." "All it takes is for the star to change its shape," Gittins said. "
An expert's impression of the strong electromagnetic fields surrounding neutron stars.
Possible explanations for the formation of the mountains include increased strain from their strong electromagnetic fields or the fact that they spin more slowly over time. But it could also be caused by a process called Caused by the glitch phenomenon in which a star suddenly starts spinning faster, Gittins says.
However, whatever causes the mountains to form, their size is limited by the amount of strain the crust can endure before breaking apart.
The stronger the crust, the larger the mountains it can support, Gittins said. Expect less Gittins and his team predicted the size of neutron star mountains by creating computer models that accurately simulated the neutron star's crust. "We subjected these models to various mathematical forces that create mountains," Gittins said. "We added strength. size until the crust cracks. "
This supports the team's prediction of the largest possible mountain range that a neutron star could sustain without breaking up. Their new prediction suggests that earlier estimates that placed these peaks at one centimeter high may have major flaws." While studying the issue, We found that previous studies had technical problems with their methods," Gittins Says
"One of the main problems is that previous predictions assumed that the shape of the neutron star's crust would stretch the crust to the maximum at every point, but this has proven to be physically impossible. "Our approach is not to pull the crust to the maximum at every point, but at a single point," he added. "Ripples in neutron stars are known to spin rapidly because they retain the angular momentum from their exploding parent stars," Gittins said. "When a neutron star spins out of shape in an asymmetric way, it spins around it." Causes ripples in the fabric of space-time," Gittins said. "These ripples are called gravitational waves. ”
Researchers first used the Laser Interferometer Gravitational Wave Observatory (LIGO) to detect gravitational waves from two rotating black holes in 2015. As previously reported by Live Science, LIGO has detected two separate gravitational wave events produced by the collision of neutron stars. , but isolated neutron stars remain elusive."Currently, we cannot detect gravitational waves from rotating neutron stars," Gittins said. However, he added, these modifications also tell scientists a lot about neutron stars. The smaller the mountains on a neutron star, the smaller the gravitational waves they produce. Therefore, their lack of detection may support Gittins' prediction.
"Given that we know the sensitivity of the detector, we can put an upper limit on how big the mountains on the neutron star must be," Gittins said. "The general trend is that the upper limit is getting smaller and smaller."
BY: Harry Baker
FY: Li Jinyang
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