What is a bosonic star?
A boson star is a hypothetical astronomical object consisting of bosons
An artistic representation of the collision of bosonic stars.
Bosonic stars could have formed as a resultgravitational collapse at the initial stages of the development of the Universe after the Big Bang. A supermassive bosonic star could, at least in theory, be located in the center of a galaxy, and this could explain many of the observed properties of active galactic nuclei. Bosonic stars are also considered as possible constituents of dark matter.
Scientists have not previously found any compelling reasonassume that such stars exist, and that the only known stable boson is a photon, a massless particle that always travels at the speed of light. The researchers speculated that binary bosonic stars could possibly be detected by the gravitational radiation they emit.
Bosons, fermions, photons
Boson stars are made of bosons. But what are bosons?
Boson is a particle or a quasiparticle with a wholethe value of the spin (intrinsic angular momentum), expressed in units of the Dirac constant. Bosons, unlike fermions, obey Bose-Einstein statistics, which allows an unlimited number of identical particles to exist in one quantum state.
Bosons were named after the Indian physicist Sh. Bose. The term "boson" was coined by Paul Dirac.
Systems of two or more identical bosons are described by wave functions that are even with respect to particle rearrangements.
Symmetric wave function of two bosons in an infinite square potential well
Fermion - a particle or quasiparticle with a half-integerspin value. All particles can be divided into two groups depending on the value of their spin: particles with integer spin belong to bosons, and particles with half-integer spin belong to fermions.
Examples of fermions:quarks (they form protons and neutrons, which are also fermions), leptons (electrons, muons, tau leptons, neutrinos), holes (quasiparticles in a semiconductor). Fermions are also quantum mechanical systems consisting of an odd number of fermions (and an arbitrary number of bosons).
Fermions obey the Pauli principle.Let us remember that this principle is one of the fundamental ones in quantum mechanics. According to him, two or more identical fermions cannot simultaneously be in the same quantum state. The thermodynamically equilibrium state of such a system is described by Fermi-Dirac statistics, which is where their name comes from. Name "fermion"was introduced by the English theoretical physicist Paul Dirac from the name of the Italian physicist Enrico Fermi.
Previously, scientists had not found any compelling reasonsassume that similar stars exist, and the only known stable boson is the photon, a massless particle that always travels at the speed of light. It was assumed that double bosonic stars could possibly be detected by the gravitational radiation they emit.
Until recently.
What did the scientists find out?
In September 2020, the LIGO and Virgo collaborationannounced the detection of the gravitational wave signal GW190521. It corresponded to the collision of two black holes whose masses are 85 and 66 times the mass of the Sun. Thanks to this event, a black hole with a mass of 142 Suns was formed. Scientists theorized that these were actually bosonic stars, made up of ultralight bosons. By the way, their mass is billions of times less than the mass of electrons. An unlimited number of bosons can occupy the same quantum state. This distinguishes them from fermions, which are subject to the Pauli exclusion principle.
The simulated black holes that spawned the GW190521 event before the merger. Credit: Deborah Ferguson, Karan Jani, Deirdre Shoemaker, Pablo Laguna, Georgia Tech, MAYA Collaboration
Previously, since 2015, LIGO and Virgo detectorsdiscovered and interpreted about 50 gravitational wave signals. All of them are believed to have arisen from mergers of black holes and neutron stars, which has allowed physicists to deepen their knowledge of these objects.
An artistic representation of the black holes that gave rise to the GW190521 event. Credit: Deborah Ferguson, Karan Jani, Deirdre Shoemaker, Pablo Laguna, Georgia Tech, MAYA Collaboration
Bosonic stars are almost as compact asblack holes, but, unlike them, they do not have an event horizon. When they collide, these exotic objects emit gravitational waves. It is as a result of their merger that a large bosonic star is formed. Over time, it can become an unstable object and simply collapse into a black hole.
Gravitational waves are ripples in the fabric of spacetime moving at the speed of light. Their sources are the most violent events in the universe.
Such an unusual mass of participants in the collisionhas become a big problem. The reason is simple - according to the generally accepted model of stellar evolution, a black hole with a mass of 85 solar could not have formed as a result of the collapse of a star. This gave rise to a number of doubts about the correctness of the interpretation of the GW190521 source.
The evolution of the black holes that gave rise to the event GW190521. Credit: Deborah Ferguson, Karan Jani, Deirdre Shoemaker, Pablo Laguna, Georgia Tech, MAYA Collaboration
As a result, scientists proposed an alternativean explanation of the origin of the GW190521 signal, In-Space reports. Physicists have suggested that there was a collision between two exotic objects known as bosonic stars. During their analysis, they were also able to estimate the mass of a new particle that makes up these objects—an ultralight boson with a mass billions of times less than the mass of an electron.
What will the new discovery lead to?
The source of gravitational waves captured in 2019year, there may have been two colliding bosonic stars, rather than a pair of massive black holes, physicists said in a study presented in Physical Review Letters. Unlike ordinary stars, bosonic stars are composed of ultra-light bosons. By the way, they are one of the most attractive candidates for dark matter. The discovery will move the search for the mysterious substance forward. If the conclusions of scientists are confirmed, then this event will be the first evidence of the existence of mysterious hypothetical objects that are candidates for invisible dark matter, which makes up 27% of the mass of the Universe.
Image of the MACS J0717.5 + 3745 galaxy cluster and dark mass distribution (blue)
spacetelescope.org
Recall dark matter in astronomy andcosmology, as well as in theoretical physics - a form of matter that does not participate in electromagnetic interaction and therefore is inaccessible to direct observation. It is about a quarter of the mass-energy of the Universe and manifests itself only in gravitational interaction.
The team found that even thoughthe analysis tends to support the hypothesis of black hole mergers, the data actually prefer the merger of bosonic stars, although not convincing. Professor Jose A. Font of the University of Valencia said: “Our results show that these two scenarios are almost indistinguishable in the data. And yet the hypothesis of an exotic bosonic star fits better. This is very interesting as the boson-star model is currently very limited and subject to significant improvements. A more advanced model could lead to even more proof of this scenario, and will also allow the study of previous observations of gravitational waves, assuming the merging of bosons and stars. "
Read also
Physicists have created an analogue of a black hole and confirmed Hawking's theory. Where it leads?
Abortion and science: what will happen to the children who will give birth
Scientists have discovered the speed limit in the quantum world
Electronvolt - off-system unit of energy,used in atomic and nuclear physics, in the physics of elementary particles and in related and related fields of science. In the Russian Federation, the electronvolt is approved for use as an off-system unit for an unlimited period of time with the scope of "physics".
Quasiparticle is a concept in quantum mechanics, the introduction of which makes it possible to significantly simplify the description of complex quantum systems with interaction, such as solids and quantum liquids.
Dirac's constant, or Planck's constant -Dirac is a sometimes used name for the reduced (reduced) Planck constant - a coefficient relating the angular frequency of a photon (or other quantum) to its energy. Usually the Dirac constant is called the rationalized or reduced Planck constant.
A quantum state is any possible state that a quantum system can be in. A pure quantum state can be described:
- In wave mechanics, a wave function,
- In matrix mechanics -state vector, or a complete set of quantum numbers for a particular system.
These descriptions are mathematically equivalent.
A quark is a fundamental particle in the Standard Model that has an electrical charge that is a multiple ofe/ 3, and not observed in a free state, butpart of hadrons (strongly interacting particles such as protons and neutrons). Quarks are structureless, pointlike particles; this has been verified up to a scale of about 10-16 cm, which is about a thousand times smaller than the size of a proton.
Proton is one of three (together with neutron andelectron) elementary particles from which ordinary matter is built. Protons are part of atomic nuclei; The serial number of a chemical element in the periodic table is equal to the number of protons in its nucleus.
Neutron (from lat.neuter - neither one nor the other) is a heavy elementary particle that has no electric charge. The neutron is a fermion and belongs to the class of baryons. Neutrons and protons are the two main components of atomic nuclei; the common name for protons and neutrons is nucleons.
Leptons are fundamental particles with half-integer spin that do not participate in strong interactions. Along with quarks and gauge bosons, leptons form an integral part of the Standard Model.
A hole is a quasiparticle, a carrier of a positivecharge equal to the elementary charge in semiconductors. The concept of a quasiparticle with a positive charge and a positive effective mass is nothing more than a terminological replacement for the concept of a real particle with a negative charge and negative effective mass.