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What is Hubble Constant?

Context:

Recently, a group of researchers from India and the United States has introduced an innovative technique for estimating the Hubble constant and the rate at which the universe is expanding.

Relevance:

GS III: Science and Technology

Dimensions of the Article:

  1. What is Hubble Constant?
  2. Measuring the Hubble Constant
  3. Discrepancies in Measurement
  4. A Novel Approach to Estimate the Hubble Constant

What is Hubble Constant?

  • Edwin Hubble’s law, from 1929, marked the first description of the universe’s expansion.
  • The Hubble constant is the measure of this expansion, but its precise value remains a cosmological debate.
Measuring the Hubble Constant

Calculating the Hubble constant requires two key pieces of information:

  • The distance between observers and celestial objects
  • The velocity at which these objects recede due to the universe’s expansion.
Measurement methods:
  • By comparing the observed brightness of a supernova to its expected brightness, scientists estimate its distance. They also measure the redshift, the stretching of light’s wavelength caused by the universe’s expansion, to gauge its velocity.
  • Researchers use variations in the Cosmic Microwave Background (CMB), the residual radiation from the Big Bang, to make Hubble constant estimates.
  • Gravitational waves, produced during massive celestial collisions like neutron stars or black holes, offer another approach. By analyzing the gravitational wave data’s shape, astronomers calculate the energy released in the collision and, hence, the distance to the objects.

Discrepancies in Measurement

  • Current measurements show a divergence in the Hubble constant values. The supernova-based method reports a value roughly two units higher than the CMB-based approach. The gravitational wave method is still evolving and lacks precision.
  • The discrepancy might stem from methodological errors or indicate that the Hubble constant itself changes over time.
  • This discrepancy arises because the three methods estimate the Hubble constant based on information from different cosmic eras. The CMB method relies on a younger universe, while the other two are anchored in an older cosmic epoch closer to the present day.

A Novel Approach to Estimate the Hubble Constant

  • Researchers have proposed a novel method for estimating the Hubble constant.
  • This method involves analyzing a set of lensed gravitational waves and their associated time delays.
  • Gravitational lensing occurs when a massive object, like a galaxy or galaxy cluster, bends and distorts the light from objects situated behind it.

Why is it Unique?

  • This approach provides an independent means of calculating the Hubble constant.
  • It has the potential to yield insights into other crucial cosmological parameters, including the density of matter in the universe.

Expert Insights

  • Experts in the field view this study as highly intriguing and a significant cosmological application of gravitational waves.
  • It introduces a fresh perspective on Hubble constant estimation, potentially contributing to a more precise understanding of the universe’s expansion rate and its fundamental properties.

-Source: The Hindu


 

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