200 most important Astronomy topics - Sykalo Eugen 2023

The Cosmic Accelerators

The universe is full of mysteries, and one of the most intriguing ones is the origin of high-energy cosmic rays. These are particles that travel through space at almost the speed of light, and they can have energies that exceed the highest energies that can be produced in any man-made particle accelerator. What kind of processes in the universe can generate such extreme energies?

What are cosmic rays?

Cosmic rays are high-energy particles that originate in space. They were first discovered in the early 20th century by Victor Hess, who found that the ionization rate in the atmosphere increased with altitude. He concluded that there must be a source of ionizing radiation outside the Earth's atmosphere. Later experiments showed that these particles are not electromagnetic radiation, but rather charged particles, such as protons, electrons, or atomic nuclei.

Cosmic rays are constantly bombarding the Earth from all directions, with an energy spectrum that spans many orders of magnitude. Most of the cosmic rays that reach the Earth are low-energy particles that are easily stopped by the atmosphere. However, there are also cosmic rays with much higher energies, which can penetrate the atmosphere and even reach the surface of the Earth. The origin of these high-energy cosmic rays is still a mystery, but it is believed that they are produced in cosmic accelerators, which are sources of high-energy particles in space. These accelerators can produce particles with energies that exceed the highest energies that can be achieved in any man-made particle accelerator, such as the Large Hadron Collider (LHC) at CERN.

What are cosmic accelerators?

Cosmic accelerators are sources of high-energy particles in space that are believed to be responsible for the production of cosmic rays. These accelerators can produce particles with energies that exceed the highest energies that can be achieved in any man-made particle accelerator, such as the Large Hadron Collider (LHC) at CERN.

The origin of cosmic rays is still a mystery, but it is believed that they are produced in cosmic accelerators. There are several types of cosmic accelerators, which can be classified into two broad categories: astrophysical and cosmological. Astrophysical accelerators are sources that are associated with astronomical objects, such as supernova remnants, pulsars, or black holes. Cosmological accelerators, on the other hand, are sources that are not associated with any known astronomical object, but are believed to be related to the large-scale structure of the universe, such as galaxy clusters or cosmic voids.

Supernova remnants (SNRs) are one of the most promising astrophysical sources of cosmic rays. A supernova is a catastrophic explosion that occurs when a massive star runs out of nuclear fuel and collapses under its own gravity. The explosion releases an enormous amount of energy, which can accelerate particles to very high energies. When the supernova explosion reaches the surrounding interstellar medium, it generates a shock wave that propagates through the medium, accelerating particles to high energies. These particles can include protons, electrons, and atomic nuclei, which can be detected as cosmic rays on Earth. The evidence for SNRs as cosmic accelerators comes from observations of the gamma-ray emission from these sources. Gamma rays are a type of high-energy electromagnetic radiation, which can be produced by the interaction of cosmic rays with the interstellar medium. The gamma-ray emission from SNRs is consistent with the emission expected from cosmic-ray interactions, providing strong evidence that SNRs are sources of cosmic rays.

Pulsars are another promising astrophysical source of cosmic rays. A pulsar is a highly magnetized, rotating neutron star that emits beams of electromagnetic radiation. The rotation of the pulsar generates a strong electric field, which can accelerate particles to high energies. The evidence for pulsars as cosmic accelerators comes from observations of the synchrotron emission from these sources. Synchrotron emission is a type of radiation that is produced by charged particles that are accelerated in a magnetic field. Pulsars are known to emit synchrotron radiation, which is consistent with the emission expected from high-energy particles.

Cosmological accelerators are sources of cosmic rays that are not associated with any known astronomical object. These sources are believed to be related to the large-scale structure of the universe, such as galaxy clusters or cosmic voids. The evidence for cosmological accelerators comes from observations of the cosmic microwave background (CMB). The CMB is a type of radiation that was emitted when the universe was only 380,000 years old, and it provides a snapshot of the universe at that time. The CMB contains small fluctuations that are believed to be the result of acoustic waves that propagated in the early universe. These fluctuations can be used to infer the large-scale structure of the universe. Recent observations of the CMB have revealed a pattern of anomalies that is consistent with the presence of cosmological accelerators. These accelerators could be the result of the interaction of cosmic rays with the large-scale structures of the universe, such as galaxy clusters or cosmic voids.

Supernova remnants

One of the most promising astrophysical sources of cosmic rays is supernova remnants (SNRs). A supernova is a catastrophic explosion that occurs when a massive star runs out of nuclear fuel and collapses under its own gravity. The explosion releases an enormous amount of energy, which can accelerate particles to very high energies.

When the supernova explosion reaches the surrounding interstellar medium, it generates a shock wave that propagates through the medium, accelerating particles to high energies. These particles can include protons, electrons, and atomic nuclei, which can be detected as cosmic rays on Earth.

SNRs are complex structures that contain various physical components, such as the forward shock, the reverse shock, and the contact discontinuity. The forward shock is the outward-moving shock wave that compresses and heats the interstellar medium. The reverse shock is the inward-moving shock wave that forms when the supernova ejecta collide with the interstellar medium. The contact discontinuity is the interface between the shocked interstellar medium and the supernova ejecta.

The acceleration of particles in SNRs is believed to occur primarily at the forward shock, where the shock wave interacts with the interstellar medium. The shock wave generates a magnetic field, which can trap charged particles and accelerate them to high energies through a process called diffusive shock acceleration. This process involves the repeated reflection of particles between the shock front and the magnetic field, which gradually increases their energy.

The particles that are accelerated at the forward shock can include protons, electrons, and atomic nuclei. The protons are believed to be the dominant component of the cosmic rays produced in SNRs, accounting for about 90% of the total energy. However, the electrons and atomic nuclei can also be significant, depending on the details of the acceleration process.

The evidence for SNRs as cosmic accelerators comes from observations of the gamma-ray emission from these sources. Gamma rays are a type of high-energy electromagnetic radiation, which can be produced by the interaction of cosmic rays with the interstellar medium. The gamma-ray emission from SNRs is consistent with the emission expected from cosmic-ray interactions, providing strong evidence that SNRs are sources of cosmic rays.

In addition to gamma rays, SNRs can also emit other types of radiation, such as synchrotron radiation and thermal X-rays. Synchrotron radiation is a type of radiation that is produced by charged particles that are accelerated in a magnetic field, while thermal X-rays are emitted by hot gas in the SNR.

Pulsars

Pulsars are highly magnetized, rotating neutron stars that emit beams of electromagnetic radiation. The rotation of the pulsar generates a strong electric field, which can accelerate particles to high energies. Pulsars are believed to be one of the most promising astrophysical sources of cosmic rays.

The study of pulsars as cosmic accelerators is an active area of research in astrophysics and particle physics. By studying the properties of pulsars and the cosmic rays they produce, scientists can learn about the processes that occur in the most extreme environments in the universe, such as strong magnetic fields and relativistic particles. Pulsars can also provide information about the composition and structure of cosmic rays, as well as the properties of fundamental particles, such as protons and electrons.

The evidence for pulsars as cosmic accelerators comes from observations of the synchrotron emission from these sources. Synchrotron emission is a type of radiation that is produced by charged particles that are accelerated in a magnetic field. Pulsars are known to emit synchrotron radiation, which is consistent with the emission expected from high-energy particles. In addition, pulsars are also known to emit gamma rays, which can be produced by the interaction of cosmic rays with the interstellar medium.

Pulsars are complex objects with a variety of physical components, such as the magnetosphere, the emission region, and the pulsar wind. The magnetosphere is the region around the pulsar where the magnetic field dominates the dynamics. The emission region is the region where the high-energy particles are accelerated and emit radiation, such as synchrotron radiation and gamma rays. The pulsar wind is the outflow of particles and magnetic fields that is generated by the pulsar.

The acceleration of particles in pulsars is believed to occur primarily in the emission region, where the strong magnetic fields can accelerate particles to high energies through a process called curvature radiation. This process involves the emission of radiation when charged particles move along curved trajectories in a magnetic field. The accelerated particles can include protons, electrons, and atomic nuclei, which can be detected as cosmic rays on Earth.

Cosmological accelerators

Cosmological accelerators are a relatively new field of study in cosmic ray research, but they have the potential to provide valuable insights into the origin and evolution of cosmic rays. The idea that cosmological structures such as galaxy clusters and cosmic voids could accelerate particles to cosmic-ray energies is not new, but it has only recently become feasible to test this hypothesis with observations.

Several mechanisms have been proposed for the acceleration of particles in cosmological accelerators. One possibility is that the particles are accelerated by shocks generated by the interaction of cosmic rays with the intergalactic medium. Another possibility is that the particles are accelerated by turbulence in the intergalactic medium, which can amplify magnetic fields and accelerate charged particles. Yet another possibility is that the particles are accelerated by jets emanating from active galactic nuclei.

Recent observations of the CMB have revealed a pattern of anomalies that is consistent with the presence of cosmological accelerators. These anomalies could be the result of the interaction of cosmic rays with the large-scale structures of the universe, such as galaxy clusters or cosmic voids. However, the interpretation of these anomalies is still the subject of debate, and further observations and experiments will be necessary to confirm the existence of cosmological accelerators.