Introduction

• On September 14, 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) made the Nobel Prize winning detection of gravitational waves.
• These observations are again in news due to some controversy among scientists over noise in detection.

What are Gravitational waves?

• Gravitational waves are ‘ripples’ in the fabric of space-time caused by some of the most violent and energetic processes in the Universe.
• Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity.

What causes Gravitational Waves?

The most powerful gravitational waves are created when objects move at very high speeds. Some examples of events that could cause a gravitational wave are:

• When a star explodes asymmetrically, for example, supernovas
• When two big stars orbit each other
• When two black holes orbit each other and merge

Why it is difficult to detect gravitational waves?

• The objects that create gravitational waves are far away. And sometimes, these events only cause small, weak gravitational waves.
• The waves are then very weak by the time they reach Earth. This makes gravitational waves hard to detect.

How are Gravitational Waves detected?

• When a gravitational wave passes by Earth, it squeezes and stretches space. LIGO can detect this squeezing and stretching.
• Each LIGO observatory has two “arms” that are each more than 2 miles (4 kilometers) long.
• A passing gravitational wave causes the length of the arms to change slightly.
• The observatory uses lasers, mirrors, and extremely sensitive instruments to detect these tiny changes.

Role of LIGO

• This is where LIGO’S detection of such waves in the universe gains significance in understanding the nature of black hole and its effect on space and time.
• LIGO has made six of such detection of these waves. Five of these were mergers of black holes in very different locations in space. One was the detection of a merger of two neutron stars.
• Each of these mergers of black holes had different characteristics with respect to their mass.
• Physicists had earlier modeled such mergers of black holes. LIGO provided them with actual data of the event. The last few detections of such merger have been done by another detector VIRGO.

The Controversy

• A group of scientists questioned the validity of the data collected by LIGO after first detection.
• The scientists argued that weeding out noise from such experiments was important which was not done properly by LIGO Scientific Collaboration (LSC).
• On this, LIGO has put up a clarification regarding the claim on noise and LSC plans to come out with a research paper that carries detailed explanations on the disputed issue of noise.