BLACK HOLE

BLACK HOLE

Subject : Science & tech

Context : Until now, the number of black hole mergers detected by LIGO, VIRGO and KAGRA detectors is minuscule compared with the number of mergers actually taking place in the sky.

Concept :

• A black hole is formed when stars collapse and can be defined as a space in the universe with an escape velocity so strong that even light cannot escape it.
• Escape velocity is the speed at which an object must travel to override a planet or an object’s gravitational force.
• Since light cannot get out, black holes are invisible and can only be tracked with the help of a space telescope or other special tools.
• And the reason light cannot escape is mainly that the gravity inside a black hole is very strong as a result of a lot of matter being squeezed into a small space.
• It acts like an ideal black body reflecting no light. It continues to grow, by absorbing mass from its surroundings.

Black hole merger

• Gravitational waves, postulated by Albert Einstein 100 years ago but discovered only in 2015 do not produce any sound on their own.
• These are just ripples created in the fabric of space-time by moving celestial objects just like a moving boat produces ripples in water.
• But when converted into audio signals, these can produce signature sounds that can reveal the origin of the gravitational waves.
• The gravitational wave detected on September 14, 2015, is now known to have been produced by the merger of two black holes about 1.3 billion years ago.
• Scientists already knew the kind of sound that gravitational waves emanating from such events were likely to produce.
• As two such dense and massive objects, black holes or neutron stars, are about to merge, they start rotating around each other at almost the speed of light. The merger takes place within a fraction of a second.
• The gravitational waves released in this last bit, when converted into audio signals, produce sound that is within audible range of human beings.

LIGO

• The LIGO Scientific Collaboration (LSC) is a group of scientists focused on the direct detection of gravitational waves, using them to explore the fundamental physics of gravity, and developing the emerging field of gravitational wave science as a tool of astronomical discovery.
• The LSC works toward this goal through research on, and development of techniques for, gravitational wave detection; and the development, commissioning and exploitation of gravitational wave detectors.
• The project operates three gravitational-wave (GW) detectors. Two are at Hanford, Washington, north-western US, and one is at Livingston in Louisiana, south-eastern US.
• The proposed LIGO India project aims to move one advanced LIGO detector from Hanford to India.

VIRGO

• Virgo is a giant laser interferometer designed to detect gravitational waves.
• Virgo has been designed and built by a collaboration of the French Centre National de la RechercheScientifique (CNRS) and the Italian IstitutoNazionale di FisicaNucleare (INFN)
• It is now operated and improved in Cascina, a small town near Pisa on the site of the European Gravitational Observatory (EGO), by an international collaboration of scientists from France, Italy, the Netherlands, Poland, and Hungary.

KAGRA

• The Kamioka Gravitational Wave Detector (KAGRA), formerly the Large Scale Cryogenic Gravitational Wave Telescope (LCGT), is a project of the gravitational wave studies group at the Institute for Cosmic Ray Research (ICRR) of the University of Tokyo.
• It is Asia’s first gravitational wave observatory, the first in the world built underground, and the first whose detector uses cryogenic mirrors.