American astronomers have discovered a whole class of space objects about which scientists previously had no idea. We are talking about dwarf black holes, which occupy an intermediate position between the most massive neutron stars and black holes of small mass, whose existence was not in doubt.
However, in recent years, more and more reports have appeared about unusual cosmic phenomena that can be caused by completely exotic objects. Lenta.ru talks about hypothetical stars whose existence may never be proved.
One of the cosmic phenomena, whose nature has not been fully discovered, is a gamma-ray burst – the release of a large amount of energy in the form of a huge explosion, which is observed in distant galaxies, a billion light-years from Earth. Despite the extreme rarity of these light signals, astronomers constantly record them due to the fact that gamma-ray bursts are one of the most striking events in the Universe. There is a smaller counterpart, called repeating soft gamma-ray bursts, and neutron stars with extremely strong magnetic fields can be the cause.
Gravastar looks like a black hole that absorbs matter, generates high-energy radiation, as well as Hawking radiation. However, inside it has a completely different metric called the de Sitter space, and, in fact, an ordinary vacuum with a positive cosmological constant. Dark energy is contained in the center of the gravastar, which prevents the outer shell from being compressed into a singularity.
A typical event horizon does not exist in a gravastar; its appearance is prevented by an ultrathin dark shell of practically indestructible matter, which behaves like an ideal fluid. According to physicist Emil Mottola (Emil Mottola), who suggested the existence of gravastars in 2002, anybody that fell on the gravastar will be destroyed and assimilated into the shell. At the same time, gravastar can reemit matter, which makes it an even brighter source of energy than black holes.
Other hypothetical objects – stars of dark energy – look a bit like gravastar. They are also born when a massive star dies, but a collapsing substance never reaches a singular state. Instead, matter breaks up into light particles and droplets of dark energy, which creates enough pressure to hold back the collapse. When particles decay, cosmic rays are formed – streams of high-energy particles, including positrons, which are also fixed by scientists. Dark energy stars were invented in 2005 by George Chapline, a physicist at Lawrence Livermore National Laboratory (USA). He believes that real black holes do not exist – there are only stars of dark energy.
As in the case of Gravastar, the behavior of a dark-energy star can be described using a quantum-mechanical fluid generated by a Bose-Einstein condensate (Bose condensate). The Bose-Einstein condensate is a phase state of matter formed by bosons – particles that can be in the same quantum state (roughly speaking, they cannot be fundamentally distinguished from one another even by their position in space). This distinguishes bosons from fermions (for example, electrons), for which the famous Pauli prohibition principle, which takes place at school, applies.
Physicists use the quantum-mechanical properties of a Bose-Einstein condensate (for example, super fluidity) to describe the properties of curved space-time. In the Chapline model, at the event horizon of a dark matter star, a phase transition of space time into a certain analogue of the Bose condensate occurs, as a result of which objects falling on the event horizon cease to decelerate infinitely for an external observer. Together with the lack of singularity in the center of the star, dark energy allowed reconciling the theory of relativity with quantum mechanics.
Between Light and Dark
Another object, consisting of hypothetical particles, is a preon star. Preons are particles of which quarks can consist. Preon stars have a higher density than neutron stars, but are still unable to collapse into a black hole. In diameter, they can reach one meter (if they contain the mass of a hundred planets of the Earth) or be the size of a pea (they contain the mass of the moon).
Also, an intermediate place between neutron stars and black holes is occupied by quark stars formed during the collapse of such a massive star that neutrons are not able to contain compression and decay into quarks. A quark star is a giant nucleon particle. If it contains quarks with aroma s (strange quarks), then such a star is called strange.
The existence of such stars is usually called into question by the scientific community. Careful observation of various objects eliminates the properties inherent to Gravastara and other exotic. A new article published in the journal Nature reports on the discovery of an object that is more massive than a neutron star, but smaller than ordinary black holes in the mass range of 5-15 Suns. This object revolves around a giant red star, and its mass is comparable to 3.3 Suns. However, astronomers are inclined to believe that they found exactly a black hole, albeit belonging to an unprecedented class of dwarf black holes.