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Hydrogen Line: A Unique Signal


From UPSC perspective, the following things are important :

Prelims level: Hydrogen Line and its significance in interstellar studies

Why in the News?

The hydrogen line stands as a pivotal tool in contemporary astronomy, serving various purposes from studying distant stars to questing for extraterrestrial intelligence, should it exist.

What is a Hydrogen Line?

  • The hydrogen line is a special type of light that hydrogen atoms emit.
  • It happens when an electron, a tiny particle that orbits the nucleus of the hydrogen atom, jumps from a higher energy level to a lower one.
  • This jump releases energy in the form of light, specifically with a wavelength of about 21 centimetres. This wavelength is what scientists call the hydrogen line.

Why is it Important?

  • Hydrogen is everywhere in the universe. It’s the simplest and most abundant element, making up about 75% of the universe’s elemental mass.
    • So, studying the hydrogen line allows us to understand a lot about the composition and distribution of matter in the universe.
  • By observing the hydrogen line’s emission from different regions of space, astronomers can create maps showing where hydrogen gas is located.
  • Secrets about the early Universe: The hydrogen line also holds secrets about the early universe. Shortly after the Big Bang, the universe was filled with hydrogen gas.
    • By studying the hydrogen line from distant parts of the universe, astronomers can learn about its conditions and evolution billions of years ago.

How Do We Interpret Hydrogen Line?

  • Radio telescope data enables mapping of hydrogen distribution, revealing locations of hydrogen clouds crucial for understanding galaxy and galaxy cluster formation and evolution.
  • Observing hydrogen line emission from different galaxy parts enables studying internal structures and dynamics, like rotation curves, offering insights into mass distribution within galaxies.
  • Observing hydrogen lines from distant galaxies unveils early universe conditions, aiding in understanding cosmic evolution’s initial stages.

What’s Next?

  • New Discoveries: Scientists are continually developing new technologies and techniques to improve the sensitivity and resolution of radio telescopes.
    • This enables them to detect fainter signals and uncover new insights into the universe’s hydrogen content.
  • Exploring Dark Matter: The hydrogen line observations could also contribute to understanding dark matter, an invisible substance that makes up about 27% of the universe’s total mass-energy content.
    • By studying the hydrogen distribution in relation to the gravitational effects observed in galaxies, scientists hope to shed light on the nature of dark matter.


[2012] A team of scientists at Brookhaven National Laboratory including those from India created the heaviest anti-matter (anti-helium nucleus). What is/are the implication/implications of the creation of anti-matter?

  1. It will make mineral prospecting and oil exploration easier and cheaper.
  2. It will help prove the possibility of the existence of stars and galaxies made of anti-matter.
  3. It will help us understand the evolution of the universe.

Select the correct answer using the codes given below:

(a) 1 only

(b) 2 and 3 only

(c) 3 only

(d) 1, 2 and 3

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