Shulou(Shulou.com)11/24 Report--

In the last Millennium Nova issue, it was said that the massive star in the binary system might be sucked away by the companion star in the final red giant phase, but when it experienced a supernova explosion and became a neutron star, it began to absorb the matter of the companion star. Some people may wonder: isn't the mass of the neutron star smaller than that of the previous star? why is the gravity stronger?

The key is that "accretion" here refers to "accretion" rather than "attraction". "accretion" is the matter of the companion star, not the whole of the companion star. Stripping off the material from each other depends on the tidal forces, not the simple gravitation.

The name tidal force comes from the tidal phenomenon that the earth's oceans and rivers are affected by the gravity of the moon. But although the tidal force is caused by gravity, it does not refer to a certain force, but to a gravitational difference. Because the gravitational force on different parts of an object in the gravitational field is different, it will have a tearing effect on the object, and the object will be torn apart when the gravitational difference between the parts is large enough.

It is usually said that the Roche limit of tearing celestial bodies is related to tidal forces. Then why aren't the people standing on the earth torn apart? Mainly because people are too small, the gravitational gradient acting on the human body on the scale of the earth is not so large. On such a small scale, the intermolecular forces that make up the human body are much stronger.

In other words, whether it can be torn apart depends not only on the tidal forces but also on whose structure is stronger. The action of the force is mutual, just like a clod and a stone, it is obvious that the clod will disintegrate first in the face of the same force. By the same token, when a fluffy star faces a dense neutron star, no matter whose gravity is strong, it must be the star that is disintegrated.

So the scene of a pulsar accretion companion star is usually a pulsar circling around the star while sucking material from the star, just like a bug nibbling at an apple around the circle, the so-called "nibbling". Not to mention stars, white dwarfs, which are also dense stars, can only be eroded in the face of neutron stars.

Much like the law of the jungle in nature, they also follow this law for celestial bodies in the universe.

In front of stars, planets tend to act only according to the face of the stars. The closer the planet is to the star, the more influence the activity on the star's surface will have on the planet. As the saying goes, "companionship is like a tiger". Whenever a star has a flare or coronal mass ejection, it will have a direct impact on the atmosphere of the planets around it. If you encounter a grumpy master like a red dwarf, the entire planet's atmosphere may not be preserved. If the planet were closer, it would be possible for itself to be roasted and vaporized or even directly flattened and torn apart. Even if the star eventually becomes a small white dwarf, it still poses an undiminished threat to the surrounding celestial bodies.

In February 2022, in an article published in the journal Nature, researchers used the Chandra X-ray Telescope to find traces of heavy element pollution in the atmosphere of a white dwarf star (G29-38).

We know that the remains of white dwarfs as low-mass stars are mainly composed of carbon and oxygen, and their atmosphere is made up of thin hydrogen or helium. But in an atmosphere that is supposed to be made up of light elements, researchers have detected heavy elements such as oxygen, magnesium, silicon and iron, meaning that rocky bodies are likely to die here.

The researchers speculate that some planets may have been torn apart by the tidal forces of the white dwarf and eventually fell into the accretion range of the white dwarf, forming a debris disk around it. The surface temperature of this white dwarf is unusually high, close to 100,000 degrees, 10 times that of the average white dwarf. The fragments that fell into the white dwarf star were eventually captured by us as the hot atmosphere excited intense X-rays.

Coincidentally, another team of researchers later found a similar phenomenon on another white dwarf (G238-44). And from it, people seem to see the end of our solar system in 5 billion years.

The researchers analyzed the spectrum of the white dwarf through Hubble and other telescopes and found that the abundance and proportion of heavy elements in its atmosphere were similar to those of Earth. This means that it is devouring Earth-like planets or similar moons, asteroids and other debris.

When it was a red giant, it had swallowed up the planets that were closer to it. When it becomes a white dwarf, the original planetary system will become chaotic under severe disturbance, and the planets close to it will be torn into countless pieces and become fragments like asteroid belts. With the accumulation of the white dwarf, these asteroids or fragments continue to fall to the gas and dust disk around the white dwarf, and finally fall on the surface of the white dwarf. For distant planets and comets, they may be safe for a long time. But once the killing process begins, one day they will inevitably become a midday meal for white dwarfs.

It can be seen that in planetary systems such as the solar system, white dwarfs are almost at the top of the celestial food chain. Even if it is located in a binary system, as long as the companion star stays in the giant star stage, the white dwarf star can eat it recklessly.

However, due to the size of the other party is too large, overeating white dwarfs may face a problem, that is, can not eat. "can't eat" is a big problem for white dwarfs, because once the eating process starts and stops, you can't stop eating as much as you can until you exceed your limit.

If a white dwarf does not eat very fast, then at a certain point, the hydrogen it accumulates will fuse out of control on its surface, and the accumulated material will be re-erupted, just like eating too much and vomiting itself. This phenomenon is called a nova explosion.

But if a white dwarf eats very fast and suddenly exceeds 1.44 times the solar mass (that is, the Chandraseka limit), its core will continue to collapse inward, and the internal fusion will be reignited, eventually releasing huge amounts of energy out of control, like eating too much and bursting the belly. This kind of thermonuclear explosion from the inside out is devastating for the white dwarf, and eventually it will be blown to pieces, a phenomenon known as the Ia supernova.

Although the white dwarf is at the top of the food chain, it also has natural enemies, such as the neutron star mentioned earlier. When a white dwarf meets a neutron star, with a denser neutron degeneracy, the neutron star can peel off and accrete the white dwarf, directly demoting each other to a planet of its own. We have already talked about it in the previous issue of pulsar planets, so we will not repeat it here.

Does the neutron star have any natural enemies? Of course, it is the most terrifying super-invincible ultimate gravitational monster in the universe, the truly top predator that can devour everything-the black hole.

Although the process of black hole annexation of neutron stars has not been directly observed except gravitational waves, in July 2022, in an article published in Physics Review D, the researchers simulated the merging process of black holes and neutron stars through computer clusters.

To simulate how a neutron star is torn apart by the tidal forces of a black hole, the researchers set the mass of the black hole at 5.4 and 8.1 times the mass of the sun, and the neutron star at 1.35 times the mass of the sun.

The simulation shows that when the merger begins, the neutron star is instantly torn apart by the black hole within milliseconds (the white part of the picture), and 80% of the matter is immediately swallowed by the black hole. In the following 10 milliseconds, the rest of the matter formed an one-arm spiral structure, some of the matter was thrown out, and the remaining 0.2 to 0.3 solar mass formed an accretion disk around the black hole. As the material from the accretion disk falls toward the black hole, the poles of the black hole burst out strong electromagnetic radiation and material jets, which may lead to brief gamma-ray bursts. The whole process takes only 1-2 seconds from the neutron star is torn to the black hole engulfing it completely, which shows that the black hole is really a top predator.

To sum up, in the celestial food chain of the universe, planets, moons, asteroids and even stars, like plants, are at the bottom of the food chain, while white dwarfs are "herbivores" that feed on "plants". And neutron stars are omnivores. What do you think a black hole will look like?

This article comes from the official account of Wechat: Linvo says ID:linvo001, author: Linvo

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