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Gravitational Wave Observations

Clearest Black Hole Merger signal allows probe of Hawking’s Law

Prelims Only | Science Tech | Mains Paper 3: Awareness in various sc and tech fields

Why in the News?

Researchers have detected the clearest gravitational wave signal, GW250114, from merging black holes, confirming Stephen Hawking’s 1971 Black Hole Area Theorem.

Clearest Black Hole Merger signal allows probe of Hawking’s Law

About GW250114:

  • Overview: GW250114 is the clearest gravitational wave signal ever detected, observed on January 14, 2025, by LIGO (US), Virgo (Italy), and KAGRA (Japan).
  • What Happened: It came from the collision of two black holes, each about 30 times the Sun’s mass, located 1.3 billion light-years away.
  • Importance: Published in Physical Review Letters (Sept 2025), it gave the strongest proof of Stephen Hawking’s Black Hole Area Theorem (1971) and confirmed Einstein’s General Theory of Relativity.

Back2Bascis: Black Holes

  • Overview: A black hole is a region in space where gravity is so strong that even light cannot escape.
  • Formation: Created when a massive star collapses after using up its fuel.
  • Types:
  1. Stellar Black Holes – formed from dead stars.
  2. Supermassive Black Holes – at the centre of galaxies.
  3. Intermediate or Primordial – smaller or early-universe types.
  • Properties: Defined by mass, spin, and charge; grow by absorbing matter or merging with other black holes.

What is a Black Hole Merger?

  • Process: Two black holes orbit each other, come closer, and finally collide to form a bigger black hole.
  • Phases:
  1. Inspiral – they lose energy and move inward.
  2. Merger – they collide, sending out gravitational waves.
  3. Ringdown – the new black hole settles down.
  • Observation: These mergers create powerful ripples in spacetime called gravitational waves, first detected by LIGO in 2015.

What is the Hawking’s Black Hole Area Theorem (1971)?

  • Idea: The total surface area of black holes never decreases — it can only stay the same or increase.
  • Analogy: Similar to the Second Law of Thermodynamics, where disorder (entropy) always increases.
  • Meaning: When two black holes merge, the new black hole’s surface area is greater than or equal to the combined areas of the originals.
  • Proof: The GW250114 event (2025) confirmed this by showing that the total area increased, just as Hawking predicted.
[UPSC 2019] Recently, scientists observed the merger of giant ‘blackholes’ billions of light-years away from the Earth. What is the significance of this observation?

Options: (a) Higgs boson particles’ were detected.

(b) Gravitational waves’ were detected. *

(c) Possibility of inter-galactic space travel through ‘wormhole’ was confirmed.

(d) It enabled the scientists to understand ‘singularity’.

 

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