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Science & Tech.
Mahesh

03/01/24 07:15 AM IST

Super-energetic particle

In News
  • Dr. Fujii, an astronomer at Japan’s Osaka Metropolitan University, discovered the cosmic ray when analysing data collected between May 2008 and November 2021 by the Telescope Array Project in the U.S.
Cosmic Rays
  • Cosmic rays are streams of energetic particles and clusters of particles coming from outer space and the sun.
  • They include protons and alpha particles (nuclei of helium atoms).
  • Only low-intensity cosmic rays reach the earth’s surface.
  • Their energy is mostly lost in the atmosphere itself, as they smash into atoms of the atmospheric gases and produce a shower of other particles.
  • Otherwise life wouldn’t have been possible on the earth.
Energy inside Amaterasu
  • Data collected by the Telescope Array Project indicated the Amaterasu cosmic ray had an energy of 240 exa-electron-volt (EeV).
  • The electron-volt (eV) is a unit of energy, like joules, used to measure the energy of subatomic particles.
  • The energy of 1 eV is approximately 1.6 × 10-19 joules. One joule is the energy required to light a one-watt bulb for one second.
  • It is easy to see how small this amount is when we realise a lamp we use at night uses about 15 J per second, or about 0.004 J/s.
  • The light-particles in sunlight have an energy of about 1.6-3.1 eV, for example.
  • When one deuterium nucleus and one tritium nucleus undergo fusion, they release one helium atom, one neutron, and 17.6 million eV of energy.
  • The mass-energy of a single Higgs boson particle, which is considered ‘heavy’, is 125.1 billion eV.
  • Cosmic rays typically range in energy from about one billion eV to about 100 billion billion eV.
  • The Amaterasu cosmic ray had an energy of 240 EeV – or 240 billion billion eV. This is extremely high.
  • The discovery of the Amaterasu cosmic ray could thus boost efforts to spot more such events as well as help make sense of their properties.
Significance
  • Ultra-high-energy cosmic rays (UHECRs) are subatomic particles from extragalactic sources with energies greater than 1 EeV.
  • Scientists have observed UHECRs more energetic than 100 EeV. But typically, cosmic rays with more energy than around 60 EeV don’t ‘survive’ beyond a certain distance in space.
  • This is because of the cosmic microwave background (CMB) – radiation in the microwave frequency leftover from the Big Bang and which today pervades the universe. This background radiation, as Dr. Fujii & co. wrote in their paper, “suppresses the flux of UHECRs above 60 EeV”.
  • The longer a UHECR passes through the CMB, the greater the suppression is.
  • As a result, any UHECRs we spot on the earth should have come from a distance across which this suppression wouldn’t have been complete. Scientists have estimated this to be 50-100 megaparsec, or 1,500-3,000 billion billion km.
  • An amazing feature of the Amaterasu particle is that if you look along the direction it came, towards its point of origin, there is nothing to be seen – meaning it appears to have come from an empty part of the universe.
Cosmic rays can be divided into two types:
  • Those originating from beyond our solar system, called galactic cosmic rays (GCR), and high-energy particles emitted by the sun, called solar cosmic rays, that are mainly protons.
  • Solar cosmic rays originate primarily in solar flares. In modernity, the particles in these rays have come to be called solar energetic particles.
  • By tracking these cosmic rays, scientists have found that the mass ratio of helium to hydrogen nuclei – that is, the ratio of the total masses of hydrogen and helium present – is about 28:100, meaning there are about 28 grams of alpha particles for every 100 grams of protons in cosmic rays.
  • This ratio is similar to the abundance of helium and hydrogen in the early universe.
  • GCRs are slowly changing streams of high-energy particles that constantly strike the earth. They are thought to originate outside the solar system in events such as supernovae. (A supernova is an explosion that occurs when a massive star nears the end of its life after running out of matter that it can fuse.)
  • When cosmic ray particles reach the earth’s atmosphere, they ionise air molecules that are at least about 3 km above the surface. Beyond that, they will have lost most of their energy.
Source- The Hindu

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