Why in the News?

Researchers have reported the detection of an exceptionally massive black hole merger, labelled GW231123.

About Black Holes and Black Hole Merger:

• Overview: Black holes are extremely dense celestial objects whose gravitational pull is so strong that even light cannot escape.
• Types of Black Holes:

1. 1. Stellar-mass: Around 20 times the mass of the Sun or more.
   2. Intermediate-mass: Between 100 and 100,000 times the mass of the Sun.
   3. Supermassive: From 100,000 to several billion times the mass of the Sun.

• Black Hole Merger:
  • Occurs when two black holes orbit each other, lose energy via gravitational waves, and merge into a larger black hole.
  • The GW231123 event involved black holes of approximately 140 and 100 solar masses, forming a final black hole of 225 solar masses — the largest detected through gravitational waves.
  • Scientists suggest such massive black holes may form via hierarchical mergers (successive black hole mergers).
  • Supports theories on the formation of supermassive black holes, often found at galactic centers.

Recent Observations:

• Event Timing: The GW231123 event was detected on November 23, 2023, though it occurred billions of years ago.
• Signal Characteristics:
  • Lasted only a tenth of a second but matched Einstein’s predictions under General Relativity.
  • Both black holes were rapidly spinning, hinting at a complex formation history.
• Scientific Significance:
  • Involved intermediate-mass black holes, rarely observed in nature.
  • Challenges existing models of black hole formation via stellar collapse.
  • Indicates the presence of black holes in the so-called “forbidden mass gap”.
• Conference Presentation:
  • Findings to be presented at the 24th International Conference on General Relativity and Gravitation (GR24) and the 16th Edoardo Amaldi Conference on Gravitational Waves, held in Glasgow, UK (July 14–18, 2025).
• Broader Implications:
  • Opens new questions about the origin of massive black holes.
  • Offers insights into gravitational physics, cosmology, astrophysics, and potentially particle physics or cosmic string theory.
  • Model refinements are ongoing to better understand such extreme cosmic phenomena.

Gravitational Wave Detection Network:

• Nature of Gravitational Waves: Invisible ripples in spacetime caused by cataclysmic cosmic events like black hole collisions; predicted by Einstein in 1916.
• Global Detection Network (LIGO–Virgo–KAGRA):
  • Laser Interferometer Gravitational-Wave Observatory (LIGO):
    • Operates two detectors in the United States (in the states of Louisiana and Washington).
    • First detected gravitational waves in 2015, leading to a Nobel Prize in Physics in 2017.
  • Virgo Observatory: Located near Pisa, Italy and operated by the European Gravitational Observatory.
  • Kamioka Gravitational Wave Detector (KAGRA): Located underground in the Kamioka mine, Japan, and notable for its cryogenic mirror technology.
• LIGO-India:
  • Under construction in Hingoli, Maharashtra in partnership with the US National Science Foundation.
  • Involves scientists from 17 Indian institutions.

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