19 Apr 2019

Black hole and its evolution

Manifest Pedagogy

The blackhole is a phenomenon which has amused the scientific community for years. Any space event or detection is of prime importance as far as Prelims is concerned. The questions on space and time fabric has come last year. So, one can expect a question on blackhole.

In news

Picture of the black hole has been released

Placing it in the syllabus

Awareness in the field of space

Static dimensions

  • What is the black hole?
  • History of the black hole
  • Formation of the black hole

Current dimensions

  • Identification of black hole
  • Event Horizon Telescope

Content

What is the black hole?

A black hole is a space where gravity pulls so much that even light is unable to come out. The gravity is so strong due to the squeezing of matter into a small space.

A black hole is an object with an escape velocity greater than the speed of light – escape velocity is the speed required to escape from its gravitational grip.

Because no light can escape, black holes are invisible.  Space telescopes, however, can help find black holes with special instruments. They can observe material and star behavior that is very close to black holes.

The black hole is at the center of the M87 galaxy (M87-Messier is a supergiant elliptical galaxy in the constellation Virgo. One of the most massive galaxies in the local Universe), as observed by the Event Horizon Telescope

 

 

 

 

 

Types of black holes

There are three main types of black holes based on its mass and size they are:

  • Primordial black holes: These are the smallest ones and  Scientists believe this type of black hole is as small as a single atom but with the mass of a large mountain.
  • Stellar black holes: These are the most common type of medium-sized black holes. The mass of a stellar black hole can be up to 20 times greater than the mass of the sun and can fit inside a ball with a diameter of about 10 miles. Dozens of stellar mass black holes may exist within the Milky Way galaxy.
  • Supermassive black holes: These are the largest black holes. They have masses greater than 1 million suns combined and would fit inside a ball with a diameter about the size of the solar system. Scientific evidence suggests that every large galaxy contains a supermassive black hole at its center. Sagittarius A is the supermassive black hole in the center of the galaxy of the Milky Way. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths.

Formation of the Black holes

  • Scientists are of the opinion that the smallest black holes formed when the universe began.
  • Stellar black holes are created when a very large star’s center falls or collapses on itself. It causes a supernova when this happens. A supernova is an explosive star that blows into space part of the star.
  • It is also believed by scientists that the supermassive black holes were made at the same time as the galaxy they are in.

History and timeline of  important events in the exploration of black hole physics

  • 1640 – Ismaël Bullialdus suggests an inverse-square gravitational force law.
  • 1686 – Sir Isaac Newton publishes his universal law of gravitation in a three-volume work known as the Principia. His calculations explain the orbital motions of the Moon, planets, and comets, and allow scientists to calculate the masses of astronomical objects. A century later, two scientists apply Newton’s laws of gravity to calculate that a star of sufficient size and density could prevent light from leaving its surface, creating a ‘dark star.’
  • 1783 – John Michell, a rector in the village of Thornhill and one of Britain’s leading scientists, suggests that the surface gravity of some stars could be so strong that not even light could escape from them. Using contemporary ideas about gravity and the nature of light, Michell even calculates that a ‘dark star’ the mass of the Sun would be just a few miles in diameter, which matches the modern calculations for the size of a solar-mass black hole.
  • 1796 – French mathematician and astronomer Pierre-Simon Laplace discovers the concept of ‘dark stars’ independent of Michell. He posits that the ‘largest luminous bodies in the Universe may be invisible.’ After a new discovery about the properties of light, however, the concept is abandoned.
  • 1915 – Albert Einstein expands his theory of relativity to include the effects of gravity. His equations show that gravity is a ‘warp’ in spacetime caused by matter. The more massive an object, the greater it warps the space around it. Known as General Relativity, it provides the theoretical basis for black holes.
  • 1916 – Before Albert Einstein can solve the equations in his own theory of gravity, German astronomer and military officer Karl Schwarzschild crafts a solution that includes a startling finding: Enough matter packed into a small-enough space would have such a powerful gravitational field that nothing could escape from it, including light.
  • 1931 – making (Stellar) Waves- Young Indian astronomer Subrahmanyan Chandrasekhar defies conventional wisdom by showing that ‘heavy’ stars will end their lives in a more exotic state than stars like the Sun.
  • 1939 – A paper by the man who would lead the effort to develop the atomic bomb concludes that the inevitable fate of a heavy star is to collapse, cutting it off from the outside universe.
  • 1963 – Down the (Gravitational) Drain- Mathematician Roy Kerr shows that massive stars will ‘drag’ the spacetime around them like water swirling around a drain. Others soon realize that Kerr’s equations apply only to black holes, but that they should describe every black hole in the universe.
  • 1963 – Maarten Schmidt discovers that 3c273, an odd star-like point of light known as a quasar, is one of the most powerful objects in the universe. His finding leads to the realization that it and all quasars are powered by a supermassive black hole at the center of a galaxy.
  • 1967 – A black hole by any other name- Physicist John A. Wheeler brings the concept of “collapsed stars” to the forefront by coining a new name for them: black holes
  • 1971 – Piecing together a black hole- By combining X-ray, radio, and optical observations from telescopes in space and on the ground, astronomers identify the first possible ‘stellar-mass’ black hole, Cygnus X-1.
  • 1974 – Stephen Hawking shows that black holes may not be black after all: They may emit a form of radiation that will eventually cause them to evaporate.
  • 2000 – Astronomers discover that the evolution of supermassive black holes in the hearts of galaxies appears to be linked to the evolution of the galaxies themselves. The galaxies may help give birth to stars, then prevent the birth of others.
  • 2002 – NASA’s Chandra X-ray Observatory identifies double galactic black holes system in merging galaxies NGC 6240
  • 2004 – Further observations by a team from UCLA present even stronger evidence supporting Sagittarius A* as a black hole.
  • 2006 – The Event Horizon Telescope begins capturing data.
  • 2012 – First visual evidence of black-holes: Suvi Gezari’s team in Johns Hopkins University, using the Hawaiian telescope Pan-STARRS 1, publish images of a supermassive black hole 2.7 million light-years away swallowing a red giant.
  • 2015 – LIGO Scientific Collaboration detects the distinctive gravitational waveforms from a binary black hole merging into a final black hole, yielding the basic parameters (e.g., distance, mass, and spin) of the three spinning black holes involved.
  • 2019 – Event Horizon Telescope Collaboration released the first direct photo of a black hole, the supermassive M87 at the core of the Messier 87 galaxy.

Identification of black holes

  • It is not possible to see a black hole because strong gravity pulls all the light into the black hole center. But scientists can see how the strong gravity around the black hole affects the stars and gas. Stars can be studied by scientists to find out if they are flying around,  or orbiting, a black hole.
  • High – energy light is made when a black hole and a star are close together. It is not possible to see this kind of light with human eyes. To see the high – energy light, scientists use satellites and telescopes in space.

About Event Horizon Telescope

  • 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 in pursuit of this goal.  This technique of linking radio dishes across the globe to create an Earth-sized interferometer has been used to measure the size of the emission regions of the two supermassive black holes with the largest apparent event horizons: Sagittarius A  at the center of the Milky Way and M87 in the center of the Virgo A galaxy
  • The EHT project includes theoretical and simulation studies that are framing questions rooted at the black hole boundary.