The stars have fascinated people from time immemorial. Thanks to modern science, we know quite a lot about stars, about their different types and structures. The knowledge of this topic is constantly updated and refined; astrophysicists are speculating on a number of theoretical stars that may exist in our universe. Along with theoretical stars, there are also star-like objects, astronomical structures that look and behave like stars, but do not have the standard characteristics that we describe as stars. The objects on this list are on the verge of physics research and have not been directly observed … yet.
Quark star
At the end of its life, a star can collapse into a black hole, white dwarf, or neutron star. If the star is dense enough before it goes supernova, the stellar remains will form a neutron star. When this happens, the star becomes extremely hot and dense. With such matter and energy, the star tries to collapse into itself and form a singularity, but the fermionic particles in the center (in this case, neutrons) obey the Pauli principle. According to him, neutrons cannot be compressed to the same quantum state, so they are repelled from the collapsing matter, reaching equilibrium.
For decades, astronomers have assumed that the neutron star would remain in equilibrium. But as quantum theory developed, astrophysicists proposed a new type of star that could appear if the degenerative pressure of the neutron core ceased. It is called a quark star. As the pressure of the star's mass increases, neutrons decay into their constituents, up and down quarks, which, under high pressure and high energy, could exist in a free state, instead of producing hadrons like protons and neutrons. Dubbed "strange matter," this quark soup would be incredibly dense, denser than a regular neutron star.
Astrophysicists are still debating how exactly these stars might have formed. According to some theories, they occur when the mass of the collapsing star is between the mass required to form a black hole or neutron star. Others suggest more exotic mechanisms. The leading theory is that quark stars form when dense packets of pre-existing strange matter wrapped in weakly interacting particles (WIMPs) collide with a neutron star, seeding its core with strange matter and initiating a transformation. If this happens, the neutron star will maintain a "crust" of neutron star material, effectively continuing to look like a neutron star, but at the same time possessing a core of strange material. Although we haven't found any quark stars yet,many of the observed neutron stars might well be secretly.
Promotional video:
Electroweak stars
While a quark star may be the last stage in a star's life before it dies and becomes a black hole, physicists recently proposed another theoretical star that could exist between a quark star and a black hole. A so-called electroweak star could maintain equilibrium through a complex interaction between weak nuclear force and electromagnetic force known as electroweak force.
In an electroweak star, the pressure and energy from the star's mass would press on the quark star's strange matter core. As the energy increases, the electromagnetic and weak nuclear forces would mix so that there would be no difference between the two forces. At this energy level, the quarks in the nucleus dissolve into leptons, like electrons and neutrinos. Most of the strange matter will turn into neutrinos, and the released energy will provide enough force to prevent the star from collapsing.
Scientists are interested in finding an electroweak star because the characteristics of its core would be identical to those of the young universe one billionth of a second after the Big Bang. At that point in the history of our universe, there was no distinction between weak nuclear force and electromagnetic force. It turned out to be quite difficult to formulate theories about that time, so a find in the form of an electroweak star would significantly help cosmological research.
An electroweak star must also be one of the densest objects in the universe. The core of an electroweak star would be the size of an apple, but about two Earths in mass, making such a star, in theory, denser than any previously observed star.
Object Thorn - Zhitkova
In 1977, Kip Thorne and Anna Zhitkova published a paper detailing a new type of star called the Thorn-Zhitkova Object (OTZ). OTZ is a hybrid star formed by the collision of a red supergiant and a small, dense neutron star. Since the red supergiant is an incredibly large star, it will take hundreds of years for a neutron star to simply break through the inner atmosphere first. While it is burrowing into the star, the orbital center (barycenter) of the two stars will move towards the center of the supergiant. Eventually, the two stars will merge to form a large supernova and ultimately a black hole.
When observed, OTZ would initially resemble a typical red supergiant. Nevertheless, OTZ would have a number of unusual properties for a red supergiant. Not only will its chemical composition differ, but a neutron star burrowing into it will emit radio flares from the inside. It is rather difficult to find OTL, since it does not differ much from the ordinary red supergiant. In addition, OTZ is rather formed not in our galactic environs, but closer to the center of the Milky Way, where the stars are packed more closely.
However, this did not stop astronomers from searching for a cannibal star, and in 2014 it was announced that the supergiant HV 2112 could be a possible OTZ. Scientists have found that HV 2112 has an unusually high amount of metallic elements for red supergiants. The chemical composition of HV 2112 matches what Thorne and Zhitkova suggested in the 1970s, so astronomers consider this star a powerful candidate for the first observed OTG. Further research is needed, but it would be cool to think that humanity has discovered the first cannibal star.
Frozen star
An ordinary star burns hydrogen fuel, creating helium and supporting itself with the pressure from within, born in the process. But someday hydrogen runs out and eventually the star needs to burn heavier elements. Unfortunately, the energy escaping from these heavy elements is not as much as from hydrogen, and the star begins to cool down. When a star goes supernova, it seeds the universe with metallic elements, which then participate in the formation of new stars and planets. As the universe matures, more and more stars explode. Astrophysicists have shown that along with the aging of the Universe, its total metallic content also increases.
In the past, there was practically no metal in stars, but in the future, stars will have a significantly increased metal abundance. As the universe ages, new and unusual types of metallic stars will form, including hypothetical frozen stars. This type of star was proposed in the 1990s. With the abundance of metals in the universe, newly formed stars will need lower temperatures to become main sequence stars. The smallest stars with a mass of 0.04 stellar (on the order of the mass of Jupiter) can become main sequence stars, maintaining nuclear fusion at temperatures of 0 degrees Celsius. They will be frozen and surrounded by clouds of frozen ice. In the far, distant future, these frozen stars will displace most of the ordinary stars in the cold and bleak universe.
Magnetospherically eternally collapsing object
Everyone is already accustomed to the fact that a lot of incomprehensible properties and paradoxes are associated with black holes. In order to somehow cope with the problems inherent in black hole mathematics, theorists have hypothesized a whole host of star-shaped objects. In 2003, scientists stated that black holes are not actually singularities, as they are used to believe, but are an exotic type of star called "magnetospherically forever collapsing object" (MVCO, MECO). The MVCO model is an attempt to deal with a theoretical problem: the matter of the collapsing black hole appears to be moving faster than the speed of light.
MVCO forms like an ordinary black hole. Gravity surpasses matter, and matter begins to collapse into itself. But in MVCO, the radiation arising from the collision of particles creates an internal pressure similar to the pressure generated in the fusion process in the star's core. This allows MVCO to remain absolutely stable. It never forms an event horizon and never completely collapses. Black holes will eventually collapse into themselves and evaporate, but the collapse of the MVCO will take an infinite amount of time. Thus, it is in a state of perpetual collapse.
The MVCO theories solve many black hole problems, including the information problem. Since the MVCO never collapses, there is no problem of information destruction, as in the case of a black hole. However, no matter how wonderful the MVKO theories are, the physicist community welcomes them with great skepticism. Quasars are believed to be black holes surrounded by a luminous accretion disk. Astronomers hope to find a quasar with the exact magnetic properties of the MVCO. So far, none have been found, but perhaps new telescopes that will study black holes will shed light on this theory. In the meantime, MVKO remains an interesting solution to the problems of black holes, but far from a leading candidate.
Population Stars III
We have already discussed the frozen stars that will appear towards the end of the universe, when everything becomes too metallic for hot stars to form. But what about stars on the other end of the spectrum? These stars, formed from the primordial gases left over from the Big Bang, are called Population III stars. The stellar population diagram was introduced by Waltor Baade in the 1940s and described the metal content of a star. The older the population, the higher the metal content. For a long time, there were only two populations of stars (with the logical name population I and population II), but modern astrophysicists began a serious search for stars that should have existed immediately after the Big Bang.
There were no heavy elements in these stars. They consisted entirely of hydrogen and helium, interspersed with lithium. Population III stars were absurdly bright and huge, larger than many modern stars. Their yards not only synthesized common elements, but were fueled by dark matter annihilation reactions. They also lived very little, only a few million years. Ultimately, all the hydrogen and helium fuel of these stars burned out, they used heavy metal elements for fusion and exploded, scattering heavy elements throughout the universe. Nothing survived in the young universe.
But if nothing survived, why should we think about it? Astronomers are very interested in population III stars as they will enable us to better understand what happened in the Big Bang and how the young universe developed. And the speed of light will help astronomers in this. Given the constant magnitude of the speed of light, if astronomers can find an incredibly distant star, they will essentially look back in time. A group of astronomers from the Institute of Astrophysics and Space Sciences are trying to see the galaxies that are farthest from Earth that we have tried to see. The light of these galaxies should have appeared several million after the Big Bang and could contain light from the stars of Population III. Studying these stars will allow astronomers to look back in time. In addition, studying the stars of Population III will also show us where we came from. These stars were among the first to seed the Universe with elements that give life and are necessary for human existence.
Quasi star
Not to be confused with a quasar (an object that looks like a star, but is not), a quasi-star is a theoretical type of star that could only exist in a young universe. Like OTZ, which we spoke about above, the quasi-star was supposed to be a cannibal star, but instead of hiding another star in the center, it hides a black hole. The quasi stars should have formed from massive Population III stars. When ordinary stars collapse, they go supernova and leave a black hole. In quasi-stars, the dense outer layer of nuclear material would have absorbed all the energy escaping from the collapsing core, stayed in place and would not go supernova. The outer shell of the star would remain intact, while the inner shell would form a black hole.
Like a modern fusion star, a quasi-star would reach equilibrium, although it would be supported by more than just fusion energy. The energy radiated from the core, a black hole, would provide pressure to resist gravitational collapse. The quasi-star would feed on matter falling into the inner black hole and release energy. Because of this powerful emitted energy, the quasi-star would be incredibly bright and 7000 times more massive than the Sun.
Eventually, however, the quasi-star would have lost its outer shell after about a million years, leaving only a massive black hole. Astrophysicists have suggested that ancient quasi stars were the source of supermassive black holes at the centers of most galaxies, including ours. The Milky Way may have started with one of these exotic and unusual ancient stars.
Preon star
Philosophers have argued for centuries about the smallest possible division of matter. By observing protons, neutrons and electrons, scientists thought they had found the basic structure of the universe. But as science moved forward, particles were found less and less, and our concept of the universe had to be revised. Hypothetically, the division could go on forever, but some theorists consider preons to be the smallest particles of nature. Preon is a point particle that has no spatial expansion. Physicists often describe electrons as point particles, but this is the traditional model. Electrons actually have an expansion. In theory, preon doesn't have one. They can be the most basic subatomic particles.
While preon research is currently out of fashion, that doesn't stop scientists from discussing what preon stars might look like. The preon stars would be extremely small, the size between a pea and a soccer ball. The mass packed in this tiny volume would be equal to the mass of the Moon. Preon stars would be light by astronomical standards, but much denser than neutron stars, the densest objects observed.
These tiny stars would be very difficult to see, thanks to gravitational lensing and gamma rays. Due to their inconspicuous nature, some theorists consider the proposed preon stars to be candidates for dark matter. And yet scientists at particle accelerators are mostly concerned with the Higgs boson, rather than looking for preons, so their existence will or may not be confirmed very soon.
Planck star
One of the biggest questions about black holes is: what are they like from the inside? Countless books, films, and articles have been published on this topic, ranging from fantastic speculation to the hardest and most exact science. And there is no consensus yet. Often the center of a black hole is described as a singularity with infinite density and no spatial dimensions, but what does this really mean? Modern theorists are trying to get around this vague description and find out what actually happens in a black hole. Of all the theories, one of the most interesting is the assumption that there is a star in the center of the black hole called the Planck star.
The proposed Planck star was originally conceived to resolve the black hole information paradox. If we consider a black hole as a singularity point, it has an unpleasant side effect: information will be destroyed, penetrating into the black hole, violating the laws of conservation. However, if there is a star in the center of the black hole, it will solve the problem and help with questions of the black hole event horizon as well.
As you must have guessed, Planck's star is a strange thing, which, however, is supported by conventional nuclear fusion. Its name comes from the fact that such a star will have an energy density close to that of Planck. Energy density is a measure of the energy contained in a region of space, and Planck's density is a huge number: 5.15 x 10 ^ 96 kilograms per cubic meter. This is a lot of energy. Theoretically, that much energy could be in the Universe right after the Big Bang. Unfortunately, we will never see a Planck star if it is located inside a black hole, but this assumption allows us to solve a number of astronomical paradoxes.
Fluffy ball
Physicists love to come up with funny names for complex ideas. Fluffy Ball is the cutest name you could think of for a deadly region of space that could kill you instantly. The fluffy ball theory stems from an attempt to describe a black hole using string theory ideas. Essentially, the fluffy ball is not a real star in the sense that it is not a miasma of fiery plasma fueled by fusion. Rather, it is a region of entangled strings of energy supported by their own inner energy.
As mentioned above, the main problem with black holes was figuring out what was inside them. This deep problem is both an experimental and a theoretical enigma. Theories of standard black holes lead to a number of contradictions. Stephen Hawking showed that black holes evaporate, which means that any information in them will be lost forever. Black hole models show that their surface is a high-energy "firewall" that vaporizes incoming particles. Most importantly, theories of quantum mechanics don't work when applied to the singularity of a black hole.
A fluffy ball solves these problems. To understand what kind of fluffy ball is, imagine that we live in a two-dimensional world, like on a piece of paper. If someone places a cylinder on paper, we will perceive it as a two-dimensional circle, even if this object actually exists in three dimensions. We can imagine that arrogant structures exist in our universe; in string theory they are called branes. If multidimensional branes existed, we would only perceive them with our 4D senses and mathematics. String theorists have suggested that what we call a black hole is actually our low-dimensional perception of a multidimensional string structure crossing our four-dimensional spacetime. Then the black hole will not be a singularity; it will only be the intersection of our space-time with multidimensional strings. This intersection is the fluffy ball.
All of this seems esoteric and raises many questions. However, if black holes are actually fluffy tangles, they will solve a lot of paradoxes. They will also have slightly different characteristics than black holes. Instead of a one-dimensional singularity, a fluffy ball has a certain volume. But, despite a certain volume, it does not have an exact event horizon, its borders are "fluffy". It also allows physicists to describe a black hole using the principles of quantum mechanics. Anyway, a fluffy ball is a funny name that dilutes our strict scientific language.
Based on materials from listverse.com
Ilya Khel