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Context: Physicist Roger Penrose, has won the 2020 Nobel Prize in Physics - jointly, along with  Reinhard Genzel and Andrea Ghez - for the discovery that black hole formation is a robust prediction of the general theory of relativity.

More about news:

  • Andrea Ghez is only its fourth woman recipient. 
  • Ghez works at the Keck Observatory on Hawaii’s Mauna Kea, and Genzel at the Very Large Telescope facility on Paranal mountain in Chile.
    • The twin Keck Observatory telescopes are the world’s most scientifically productive optical and infrared telescopes. 
    • The Very Large Telescope (VLT) is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile.

Roger Penrose’s research

  • This year’s Nobel prize in physics awards is for for the discovery that “black hole formation is a robust prediction of the general theory of relativity”
  • Penrose, in collaboration with cosmologist Stephen Hawking Raychauduri equation, for a mathematical description of Black Holes in 1969.
  • Einstein proposed his General Theory of Relativity in 1915. The General Relativity had predicted the existence of black holes.
  • As per the scientists there were points where physical quantities grew infinitely large or vanished. 
  • They are called event horizon — the point of no return beyond which even light cannot escape the black hole’s gravitational attraction. 
  • Penrose identified the formation of trapped surfaces as the condition for the formation of black holes. 

Images of blackholes

  • Recently an image of the black hole at the centre of the Messier 87 galaxy, 55 light years from Earth, was released by scientists.
  • Black holes do not emit or radiate anything, even light. So their image cannot be captured. 
  • The black hole can be “seen” only because it is enclosed within a very bright, orange-red doughnut-shaped ring in the image. 
  • But the area just outside its boundary, called the event horizon, which has vast amounts of gas, clouds and plasma swirling violently, emit all kinds of radiations, including visible light.

Works by Reinhard Genzel  and Prof. Ghez

  • The other half of the prize is jointly awarded to Reinhard Genzel and Prof. Ghez for showing that the dense region in the centre of our galaxy — the Milky Way — is indeed a black hole. 
  • They showed that the slightly unusual trajectories and the speed of the stars could only be explained by the presence of a very massive but invisible, heavenly body. 
  • Sagittarius A*: This is now known to be the Sagittarius A* supermassive black hole, which has a mass four million times that of the Sun and is confined to an area roughly the size of our Solar System.
    • Sagittarius A* occupies the centre of the Milky Way, which is about 26,000 light years away. 
    • Around this, all stars in the galaxy orbit. 
    • Sagittarius A* is one of two black holes whose photographs have been captured by the Event Horizon Telescope project. 
  • The scientists tracked nearly 30 stars, particularly a star named S-2 (or S-O2). 
  • These stars followed elliptical, Keplerian, orbits, which can only imply a central concentrated massive object — a supermassive black hole. 

Indian contribution:

  • Indian physicist Amal Kumar Raychaudhuri had produced theoretical results while working on general relativity and came up with an equation that is named after him. 
  • Raychaudhuri Equation assumes that the “universe is represented by a time-dependent geometry but does not assume homogeneity or isotropy at the outset”. 
  • In fact, one of its aims is to see whether non-zero rotation (spin), anisotropy (shear) and/or a cosmological constant can succeed in avoiding the initial singularity.’

Black holes:

  • A black hole is a place in space where gravity pulls so much that even light can not get out. 
  • The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying. 
  • Because no light can get out, people can't see black holes.
  • Space telescopes with special tools can help find black holes.

How Do Black Holes Form?

  • Stellar black holes are made when the center of a very big star falls in upon itself, or collapses. When this happens, it causes a supernova. 
  • A supernova is an exploding star that blasts part of the star into space.

Stellar evolution: It is a description of the way that stars change with time.

The life of a star: 

  • Stars are born out of the gravitational collapse of cool, dense molecular clouds.
  • Death of star: Once the hydrogen in the core has all been burned to helium, energy generation stops and the core begins to contract.This causes the star to expand enormously and increase in luminosity – the star becomes a red giant.
  • Once the helium has all been converted, the inert carbon core begins to contract and increase in temperature.
  • What happens next depends on the mass of the star
    • Stars less than 8 solar masses
      • The carbon core continues to contract until it is supported by electron degeneracy pressure. Eventually, the outer layers of the star are ejected completely and ionised by the white dwarf to form a planetary nebula.
  • Stars greater than 8 solar masses
    • The contracting core will reach the temperature for carbon ignition, and begin to burn to neon. 
    • If the core has a mass less than about 3 times that of our Sun, the collapse of the core may be halted by the pressure of neutrons. In this case, the core becomes a neutron star. 
    • If the core has a mass greater than about 3 solar masses, even neutron pressure is not sufficient to withstand gravity, and it will collapse further into a stellar black hole.

Event Horizon Telescope project

  • The EHT is an international collaboration that has formed to continue the steady long-term progress on improving the capability of Very Long Baseline Interferometry (VLBI) at short wavelengths.  
  • This is the technique of linking radio dishes across the globe.
  • It creates an Earth-sized interferometer.
  • It has been used to measure the size of the emission regions of the two supermassive black holes with the largest apparent event horizons: SgrA* at the center of the Milky Way and M87 in the center of the Virgo A galaxy.

Interferometers 

  • They are investigative tools used in many fields of science and engineering. 
  • They are called interferometers because they work by merging two or more sources of light to create an interference pattern, which can be measured and analyzed.

Keplarian orbits

Johannes Kepler developed three laws which described the motion of the planets across the sky.

  • The Law of Orbits: All planets move in elliptical orbits, with the sun at one focus.
  • The Law of Areas: A line that connects a planet to the sun sweeps out equal areas in equal times.
  • The Law of Periods: The square of the period of any planet is proportional to the cube of the semimajor axis of its orbit.

Kepler's laws were derived for orbits around the sun, but they apply to satellite orbits as well.


Image source: The Hindu

After reading this article, answer the following question for Mains answer writing practice. Also you can get your answer checked free of cost by clicking on the following link.

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Q) In general relativity, the Raychaudhuri equation is a fundamental result describing the motion of nearby bits of matter. Discuss how the equation contributed to the discovery of black holes.