Detailed Explanation:

Answer: Option 2 — 'Gravitational waves' were detected.

The merger of black holes is expected to generate powerful gravitational waves, which are ripples in spacetime caused by accelerating massive objects. Detecting these waves with instruments like LIGO (Laser Interferometer Gravitational-Wave Observatory) allows scientists to study these cosmic events even when they are too far away or obscured to observe directly with traditional telescopes. This observation opened a revolutionary new window for astronomical observations and confirmed a major prediction of Einstein's General Theory of Relativity.

❌ Option 1 – Incorrect: Higgs boson particles are detected in particle accelerators like the Large Hadron Collider (LHC), not through astronomical observations of black hole mergers.

❌ Option 3 – Incorrect: While wormholes are theoretical concepts in physics, no observation of black hole mergers has confirmed the possibility of intergalactic space travel through wormholes.

❌ Option 4 – Incorrect: While black hole mergers provide insights into extreme gravity, understanding the singularity (the point of infinite density at the center of a black hole) remains beyond current observational capabilities.

📝 Short Notes: Gravitational Waves

• Definition: Gravitational waves are ripples in the fabric of spacetime caused by violent cosmic events involving massive accelerating objects.
• Prediction: First predicted by Albert Einstein in 1916 as part of his General Theory of Relativity.
• First Detection: Directly detected for the first time in 2015 by LIGO (Laser Interferometer Gravitational-Wave Observatory).
• Sources: Merging black holes, colliding neutron stars, supernovae, and rotating neutron stars with asymmetries.
• Speed: Travel at the speed of light through spacetime.
• Significance: Opens a new field of gravitational wave astronomy, allowing observation of events invisible to electromagnetic telescopes.
• Nobel Prize: The 2017 Nobel Prize in Physics was awarded to Rainer Weiss, Barry Barish, and Kip Thorne for the LIGO detector and observation of gravitational waves.