Every time, looking at the stars, a person involuntarily asks the question: “What is there in heaven?” All this beauty seems to be magic because it is beyond our reach. Perhaps, on one of the planets of another solar system, very far from us, an unknown creature looks at the Sun and asks itself the same question: “What secrets does this star hide?” No matter how hard we try, we will never solve all the mysteries of space, but this does not stop us from making new attempts. This list contains ten incredible types of stars.
10. Hypergiant star
The hypergiant star took place in this list only because of its size. Indeed, it is difficult for us to imagine how massive these stars are, but the largest NML Cygni has a radius of 1650 times the Sun’s radius, which is 7.67 astronomical units. For comparison, the orbit of Jupiter is at a distance of 5.23 astronomical units from the Sun, and Saturn is at a distance of 9.53 astronomical units. Due to their enormous size, these stars live no more than several tens of millions of years. The hypergiant Betelgeuse, a star in the constellation Orion, is expected to go supernova over several hundred thousand years. When this happens, it will eclipse the moon by more than a year, and it will be visible even during the day.
9. Hypervelocity star
Unlike other stars on this list, the hyperspeed star is no different from others, except it zooms through space at incredible speed. Trapped in the center of the galaxy and thrown from there by the forces of gravity, these stars have a rate of one to two million miles per hour. All known hyperspeed stars of our galaxy are doomed to fly out of it and wander in the dark for the rest of their lives.
8. Cepheid variable
Cepheids (or variable stars) usually include stars that have a mass of 5-10 times the mass of our Sun, which grows and decrease at regular intervals, which gives the impression that they are pulsating. Cepheids expand due to the incredibly high pressure inside the core, but as soon as they increase in size, the pressure drops, and they contract again. This cycle of enlargement and contraction continues throughout the entire existence of the Cepheids.
7. Black dwarf
If a star is too small to become a neutron star or at least explode into a supernova, then it will eventually turn into a white dwarf – a faint star that has expended all its energy and is not under pressure from within its core. Often not more significant than Earth, white dwarfs are slowly cooled by electromagnetic radiation. Over an unimaginably long period, white dwarfs cool enough to stop emitting light and heat, thus becoming so-called black dwarfs, almost invisible to the observer. The black dwarf is the final stage of evolution for many stars. It is believed that not a single black dwarf currently exists in the universe, as it takes too long for a star to reach this stage. For example, the Sun is not threatened by this for at least another 14.5 billion years.
6. Shell star
When people think of a star, they tend to imagine a vast, flaming ball floating in space. In fact, due to centrifugal force, the stars acquire a slightly flattened shape. For most celebrities, the degree of deformation is negligible, but some of the stars spinning at high speed take the form of a rugby ball. Due to rotation, these stars eject large volumes of matter, creating a shell of gas that surrounds them in the equatorial region. This is where the shell stars get their name. The image shows the shell star Alpha Eridan (Achernar), surrounded by a translucent white shell mass.
5. Neutron star
The neutron star is the next stage in the evolution of a supernova. It is a tiny and highly dense ball – you guessed it – of neutrons. Many times thicker than the nucleus of an atom and not exceeding 12 kilometers in diameter, neutron stars are indeed a curious phenomenon in physics. Due to the high density of neutron stars, any atoms in contact with the surface of these stars are instantly torn apart. Subatomic particles disintegrate into particles before they can be rearranged into neutrons. The release of tremendous energy accompanies this process. For example, suppose a neutron star collides with a medium-sized asteroid. In that case, the amount of energy produced by gamma radiation during the collision will exceed the volume that the Sun can generate during its entire existence. Therefore, neutron stars near our solar system pose a severe threat to planet Earth.
4. Dark-energy star
Due to the many problems with our understanding of black holes, especially concerning quantum mechanics, other theories have been put forward to explain our observations. The dark energy star is just one of them. The essence of the idea is that a massive star does not become a black hole as a result of the collapse. Soon the space-time that exists within its limits is mutated into dark matter. According to the laws of quantum mechanics, this star has a unique property: it attracts matter and energy outside its event horizon, but inside it, there is an opposing gravity force, due to which part of the matter and energy is thrown back. Also, the theory states that once an electron passes through the event horizon of a dark energy star, it will be converted into a positron – also known as an antielectron – and ejected. When this antiparticle collides with an electron, a small explosion of energy occurs. It is believed that this could explain the massive amount of radiation in the center of the galaxy, where a supermassive black hole is believed to exist.
3. Iron star
Stars create heavier nuclei, combining lighter ones into one whole (nuclear fusion) to further release energy. The heavier the element, the less energy is generated when combined. The path of transformation of a star is as follows: first, hydrogen turns into helium, then helium – into carbon, carbon – into oxygen, oxygen – into neon, neon – into silicon, and, finally, silicon – into iron. For the synthesis of iron, more energy is needed than is formed in this case. Therefore this stage is the last. Most stars die before they reach the stage of carbon conversion, and those that succeed are doomed to soon explode into supernovae. The Iron Star is an all-iron star that generates energy. How is this possible? Quantum tunneling is a phenomenon in which a particle crosses a barrier that, presumably, it would not be able to pass. For example, if you throw a ball at a wall, it will fall, hitting it. But according to quantum mechanics, there is a chance that the ball will go through the wall. This is called quantum tunneling.
It takes a lot of energy to convert iron, and there is an obstacle that prevents the conversion – more energy is needed than the star can release. And with quantum tunneling, iron can be transformed without using power at all.
The synthesis of iron through quantum tunneling is very unlikely; also, the star must have a considerable mass for the reaction to occur. Finally, iron is a relatively rare substance in space. For these reasons, it is assumed that the first iron stars will appear in about one quingentilion (1 with 1503 zeros).
Hypergiants – the largest of the stars – usually collapse into black holes ten times the mass of the Sun. The question is obvious: what could have contributed to the development of supermassive black holes in the centers of galaxies? No star could be big enough to turn into such a monster. Of course, one can assume that black holes grow and enlarge, absorbing matter, but contrary to popular belief, this is a rather lengthy process. Also, most supermassive black holes formed in the first two billion years of the universe; this is too short a time; not a single black hole is capable of developing into a monster like those we see today over such a period. One theory states that the first stars (Population III), composed only of helium and hydrogen, were more prominent than today’s hypergiants, quickly collapsed and transformed into black holes, which later merged into supermassive black holes.
Another theory, which is considered more likely, suggests that quasi-stars are involved in forming supermassive black holes. In the first billion years of the universe, large clouds of helium and hydrogen floated all over the place. If the matter contained in these clouds disintegrated quickly enough, then it could form a star with a small black hole in the center – a quasi-star that is a billion times brighter than the Sun. Usually, at this stage, the star goes supernova, causing the shell of the lead to fly apart in space. But if the material surrounding the star is large enough and dense enough, it will resist the explosion and slowly go into the black hole. Thus, the black hole will absorb the shell of the material surrounding the star, and over time it will become unimaginably large and very quickly.
1. Boson star
There are two main types of elementary particles: bosons and fermions. The most apparent difference between them is that particles with integer spin values are called bosons, and particles with half-integer spin values are called fermions. All elementary and complex particles such as electrons, neutrons, and quarks are fermions. Particles with energy – photons, gluons – are called bosons. Unlike fermions, countless bosons can be in the same quantum state at the same time. An intricate analogy can be drawn to understand better the difference between these particles: fermions are like buildings, and bosons are like ghosts. Only one structure can exist at a certain point in space because two buildings can’t stand in the same place. But in one place, there can be thousands of ghosts simultaneously since they do not live (by the way, bosons have mass, but you probably get the idea).
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