Sources of Cosmic Rays

Cosmic rays are high-energy particles that originate from various sources outside our solar system. These energetic particles continuously bombard the Earth and have been a subject of fascination and study for scientists for many decades. Despite their name, cosmic rays are not rays or electromagnetic radiation but instead consist of charged particles, such as protons, electrons, and heavier atomic nuclei.

Supernovae: Stellar Explosions

One of the primary sources of cosmic rays in the universe is supernovae, which are powerful explosions that occur at the end of a massive star’s life cycle. When a star many times more massive than our sun exhausts its nuclear fuel, it undergoes a catastrophic gravitational collapse. The ensuing explosion releases an enormous amount of energy, propelling high-energy particles into space.

These accelerated particles include protons, electrons, and heavier ions, and they can reach near the speed of light. Some of these particles eventually make their way to Earth, forming a significant component of the cosmic rays detected by our planet’s detectors.

• Example: The Crab Nebula

The Crab Nebula, a famous supernova remnant, is an excellent example of a cosmic ray source. It is the remnant of a supernova observed in the year 1054 and is located in the constellation Taurus. Scientists have observed the Crab Nebula to be a source of high-energy gamma rays and cosmic rays.

Active Galactic Nuclei (AGN)

Active Galactic Nuclei are the centers of galaxies where supermassive black holes reside. As matter falls into these black holes, vast amounts of energy are released in the form of electromagnetic radiation and powerful jets of particles. These jets can contain highly energetic protons and other particles that become cosmic rays.

• Example: M87 Galaxy

The M87 galaxy, located in the Virgo cluster, is home to one of the most massive black holes known. Its active galactic nucleus is known to produce cosmic rays that are detected here on Earth.

Solar Flares

Our own star, the Sun, also contributes to the cosmic ray population, albeit to a lesser extent than other cosmic ray sources. During solar flares, which are explosions on the Sun’s surface, particles get accelerated to high energies. Protons and electrons from these solar flares can become cosmic rays that affect space weather and can pose risks to astronauts and satellites.

• Example: Carrington Event

One of the most famous solar flares in history is the Carrington Event, which occurred in 1859. The solar storm associated with this flare was so intense that it caused widespread telegraph system disruptions and auroras visible as far south as the Caribbean.

Galactic Cosmic Rays (GCRs)

Galactic cosmic rays, as the name suggests, originate from within our Milky Way galaxy. While the exact sources of GCRs remain a subject of research, they are believed to be accelerated by the shockwaves generated by supernova explosions and the turbulent magnetic fields in the interstellar medium.

• Example: Voyager Spacecraft

The Voyager 1 and 2 spacecraft, launched by NASA in 1977, have provided valuable data on cosmic rays in the outer regions of the heliosphere and have helped scientists study galactic cosmic ray intensities beyond our solar system.

Extragalactic Cosmic Rays

Apart from the sources mentioned above, cosmic rays can also come from sources outside our galaxy. These extragalactic cosmic rays are the most energetic particles ever observed and likely originate from some of the most extreme environments in the universe, such as active galactic nuclei in distant galaxies or even from other cosmic phenomena like gamma-ray bursts.

• Example: Auger Observatory

The Pierre Auger Observatory, located in Argentina, is a state-of-the-art facility designed to detect and study ultra-high-energy cosmic rays. This observatory has provided crucial insights into the origin and nature of extragalactic cosmic rays.

Cosmic Ray Energies and Composition

Cosmic rays cover a wide range of energies, spanning from relatively low-energy particles to ultra-high-energy cosmic rays (UHECRs) with energies far exceeding anything we can produce in particle accelerators on Earth. The composition of cosmic rays varies, with the majority being protons and helium nuclei, but heavier elements like carbon, oxygen, and iron are also present in smaller quantities.

The following table illustrates composition of cosmic rays

Cosmic rays, with their incredible energies and mysterious origins, continue to be a subject of intense research in astrophysics. Supernovae, active galactic nuclei, solar flares, and other cosmic phenomena contribute to the cosmic ray population that constantly showers our planet.