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Black Hole

 

Source: From some website(searched by Google Inc….)

There are many popular myths concerning black holes, many of them perpetuated by Hollywood. Television and movies have portrayed them as time-traveling tunnels to another dimension, cosmic vacuum cleaners sucking up everything in sight, and so on. It can be said that black holes are really just the evolutionary end point of massive stars. But somehow, this simple explanation makes them no easier to understand or less mysterious.

Black Holes: What Are They?
 

Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun. If a star that massive or larger undergoes a supernovaexplosion, it may leave behind a fairly massive burned out stellar remnant. With no outward forces to oppose gravitational forces, the remnant will collapse in on itself. The star eventually collapses to the point of zero volume and infinitedensity, creating what is known as a " singularity ". Around the singularity is a region where the force of gravity is so strong that not even light can escape. Thus, no information can reach us from this region. It is therefore called a black hole, and its surface is called the " event horizon ".

But contrary to popular myth, a black hole is not a cosmic vacuum cleaner. If our Sun was suddenly replaced with a black hole of the same mass, the Earth's orbit around the Sun would be unchanged. (Of course the Earth's temperature would change, and there would be no solar wind or solar magnetic storms affecting us.) To be "sucked" into a black hole, one has to cross inside the Schwarzschild radius. At this radius, the escape speed is equal to the speed of light, and once light passes through, even it cannot escape.

The Schwarzschild radius can be calculated using the equation for escape speed:

v_esc = (2GM/R)^1/2

For photons, or objects with no mass, we can substitute c (the speed of light) for V_esc and find the Schwarzschild radius, R, to be

R = 2GM/c²

If the Sun was replaced with a black hole that had the same mass as the Sun, the Schwarzschild radius would be 3 km (compared to the Sun's radius of nearly 700,000 km). Hence the Earth would have to get very close to get sucked into a black hole at the center of our Solar System.

If We Can't See Them, How Do We Know They're There?
 

Since stellar black holes are small (only a few to a few tens of kilometers in size), and light that would allow us to see them cannot escape, a black hole floating alone in space would be hard, if not impossible, to see. For instance, the photograph above shows the optical companion star to the (invisible) black hole candidate Cyg X-1.

However, if a black hole passes through a cloud of interstellar matter, or is close to another "normal" star, the black hole can accrete matter into itself. As the matter falls or is pulled towards the black hole, it gains kinetic energy, heats up and is squeezed by tidal forces. The heating ionizes the atoms, and when the atoms reach a few million Kelvin, they emit X-rays. The X-rays are sent off into space before the matter crosses the Schwarzschild radius and crashes into thesingularity. Thus we can see this X-ray emission.

Binary X-ray sources are also places to find strong black hole candidates. A companion star is a perfect source of infalling material for a black hole. A binary system also allows the calculation of the black hole candidate's mass. Once the mass is found, it can be determined if the candidate is a neutron star or a black hole, since neutron stars always have masses of about 1.5 times the mass of the Sun. Another sign of the presence of a black hole is its random variation of emitted X-rays. The infalling matter that emits X-rays does not fall into the black hole at a steady rate, but rather more sporadically, which causes an observable variation in X-ray intensity. Additionally, if the X-ray source is in a binary system, and we see it from certain angles, the X-rays will be periodically cut off as the source is eclipsed by the companion star. When looking for black hole candidates, all these things are taken into account. Many X-ray satellites have scanned the skies for X-ray sources that might be black hole candidates.

Cygnus X-1 (Cyg X-1) is the longest known of the black hole candidates. It is a highly variable and irregular source, with X-ray emission that flickers in hundredths of a second. An object cannot flicker faster than the time required for light to travel across the object. In a hundredth of a second, light travels 3,000 kilometers. This is one fourth of Earth's diameter! So the region emitting the X-rays around Cyg X-1 is rather small. Its companion star, HDE 226868 is a B0 supergiant with a surface temperature of about 31,000 K. Spectroscopicobservations show that the spectral lines of HDE 226868 shift back and forth with a period of 5.6 days. From the mass-luminosity relation, the mass of this supergiant is calculated as 30 times the mass of the Sun. Cyg X-1 must have a mass of about 7 solar masses, or else it would not exert enough gravitational pull to cause the wobble in the spectral lines of HDE 226868. Since 7 solar massesis too large to be a white dwarf or neutron star, it must be a black hole.

However, there are arguments against Cyg X-1 being a black hole. HDE 226868 might be undermassive for its spectral type, which would make Cyg X-1 less massive than previously calculated. In addition, uncertainties in the distance to the binary system would also influence mass calculations. All of these uncertainties can make a case for Cyg X-1 having only 3 solar masses, thus allowing for the possibility that it is a neutron star.

Nonetheless, there are now about 20 binaries (as of early 2009) for which the evidence for a black hole is much stronger than in Cyg X-1. The first of these, an X-ray transient called A0620-00, was discovered in 1975, and the mass of the compact object was determined in the mid-1980's to be greater than 3.5 solar masses. This very clearly excludes a neutron star, which has a mass near 1.5 solar masses, even allowing for all known theoretical uncertainties. The best case for a black hole is probably V404 Cygni, whose compact star is at least 10 solar masses. With improved instrumentation, the pace of discovery has accelerated, and the list of dynamically confirmed black hole binaries is growing rapidly.

What About All the Wormhole Stuff?

Unfortunately, wormholes are more science fiction than they are science fact. A wormhole is a theoretical opening in space-time that one could use to travel to far away places very quickly. The wormhole itself is two copies of the black hole geometry connected by a throat. The throat, or passageway, is called an Einstein-Rosen bridge. It has never been proven that wormholes exist, and there is no experimental evidence for them, but it is fun to think about the possibilities their existence might create.

Note: Also refer from the Wikipedia, it has more information than this……

Site Reference: http://en.wikipedia.org/wiki/Black_hole

CHRONOLOGY OF THE MAIN EVENTS IN PHYSICS:

 

Source: Great Physicsts from Galileo to Hawking by William H Cropper

 

                           The major events took place in the physics field.

The events are,

 

1564 Galileo Galilei is born in Pisa, Italy.

1591 Galileo’s legendary demonstration on the Tower of Pisa.
1616 Robert Cardinal Bellarmine’s injunction to Galileo.
1622 Galileo publishes The Assayer.
1632 Galileo publishes Dialogue concerning the Two Chief World Systems.
The Inquisition orders Galileo’s publisher to cease publication of the
Dialogue.
1633 Galileo appears before the Inquisition.
Galileo in Arcetri.
1638 Galileo publishes Discourses on Two New Sciences.
1642 Galileo dies in Arcetri.
Isaac Newton is born in Woolsthorpe, England.
1661 Newton enters Trinity College, Cambridge University.
1665 Plague in England.
Newton, in Woolsthorpe, begins to think about calculus, gravity, and
optics.
1668 Newton is appointed Lucasian Professor of Mathematics at Cambridge.
1671 Newton’s reflecting telescope is demonstrated to the Royal Society.
1684 Newton publishes De Motu corporum in gyrum.
1687 Newton publishes the Principia.
1696 Newton moves from Cambridge to London.
1704 Newton publishes the Opticks.
1727 Newton dies in London.
1791 Michael Faraday is born in Newington, Surrey, now part of London.
1796 Sadi Carnot is born in Paris.
1801 Thomas Young discovers his principle of interference based on a wave
model of light.
1814 Robert Mayer is born in Heilbronn, Germany.
1818 James Joule is born in Manchester, England.
1820 Hans Christian Oersted’s experiment demonstrating a magnetic effect
produced by an electric effect.
1821 Hermann Helmholtz is born in Potsdam, Germany.
Faraday’s experiment demonstrating electromagnetic rotation.
Augustin Fresnel characterizes light as waves that vibrate perpendicularly
to their direction of motion.
1822 Rudolf Clausius is born in Ko¨ slin, Prussia.
1824 Carnot publishes Reflections on the Motive Power of Fire.
William Thomson is born in Belfast, Northern Ireland.
1831 Faraday discovers electromagnetic induction.
James Clerk Maxwell is born in Edinburgh, Scotland.
Chronology of the Main Events 465
1832 Carnot dies in Paris.
Faraday formulates the laws of electrochemistry.
1834 E´ mile Clapeyron publishes a mathematical version of Carnot’s theory.
1837 Faraday studies electrostatic induction.
1839 Willard Gibbs is born in New Haven, Connecticut.
1842 Mayer publishes his first paper.
1843 Joule publishes his first determinations of the mechanical equivalent
of heat.
1844 Ludwig Boltzmann is born in Vienna.
1845 Mayer publishes his second paper, including a calculation of the mechanical
equivalent of heat.
Thomson develops a mathematical theory of electrostatic lines of force.
Faraday observes the effect of a magnetic field on polarized light.
1847 Joule publishes results of his paddle-wheel experiments for determination
of the mechanical equivalent of heat.
Helmholtz publishes On the Conservation of Force.
1848 Thomson publishes his thermometry principle.
1850 Clausius publishes his first paper on heat theory, in which he introduces
the function U and derives the equation dQ dU PdV.
1851 Thomson publishes On the Dynamical Theory of Heat.
1852 Faraday defends the reality of lines of force.
1854 Thomson defines absolute temperature in terms of Carnot’s function.
Clausius publishes his second paper on heat theory and derives a state
function that would later represent entropy.
Maxwell publishes his first paper on electromagnetism, On Faraday’s
Lines of Force.
1855 Thomson joins the Atlantic Telegraph Company.
1857 Clausius publishes his first paper on the molecular theory of gases.
1858 Max Planck is born in Kiel, Germany.
1860 Maxwell publishes his first paper on the molecular theory of gases.
1861 Maxwell publishes his second paper on electromagnetism, On Physical
Lines of Force.
1864 Walther Nernst is born in Briesen, West Prussia.
1865 Clausius publishes his last paper on heat theory, in which he completes
his theories of energy and entropy, and states the two laws of
thermodynamics.
Maxwell publishes his third paper on electromagnetism, A Dynamical
Theory of the Electromagnetic Field.
1867 Faraday dies at Hampton Court, Middlesex, England.
Maria Sklodowska is born in Warsaw, Poland.
1871 Maxwell is appointed to the Chair of Experimental Physics at
Cambridge.
Helmholtz goes to Berlin.
Ernest Rutherford is born near Nelson, New Zealand.
1873 Maxwell publishes A Treatise on Electromagnetism.
Gibbs publishes a geometrical interpretation of thermodynamics, with
emphasis on the energy and entropy concepts.
1875–78 Gibbs publishes On the Equilibrium of Heterogeneous Substances.
1878 Mayer dies in Heilbronn, Germany.
Lise Meitner is born in Vienna.
466 Chronology of the Main Events
1879 Maxwell dies in Cambridge, England.
Albert Einstein is born in Ulm, Germany.
1885 Niels Bohr is born in Copenhagen, Denmark.
1887 Erwin Schro¨dinger is born in Vienna.
1888 Clausius dies in Bonn, Germany.
1889 Joule dies in Sale, England.
Edwin Hubble is born in Marshfield, Missouri.
1892 Louis de Broglie is born in Dieppe, France.
1893 Nernst publishes his textbook, Theoretische Chemie.
1894 Helmholtz dies in Berlin.
1896 Boltzmann publishes the first volume of Lectures on Gas Theory.
Henri Becquerel discovers the radioactivity of uranium.
1898 Boltzmann publishes the second volume of Lectures on Gas Theory.
Marie and Pierre Curie announce their discoveries of polonium and
radium.
1900 Planck publishes his paper on blackbody radiation, which, in a limited
way, introduces the concept of energy quantization.
Wolfgang Pauli is born in Vienna.
1901 Gibbs publishes Elementary Principles in Statistical Mechanics.
Werner Heisenberg is born in Wu¨ rzburg, Germany.
Enrico Fermi is born in Rome.
1902 Rutherford and Frederick Soddy publish a series of papers in which
their transmutation theory of radioactivity is developed.
Einstein is appointed technical expert third class in the Bern, Switzerland,
Patent Office.
Paul Dirac is born in Bristol, England.
1903 Gibbs dies in New Haven, Connecticut.
1905 Nernst goes to Berlin.
Einstein publishes his papers on relativity, the photoelectric effect,
and colloidal particles as molecules.
1906 Nernst publishes his heat theorem.
Rutherford discovers α-particle scattering.
Boltzmann dies in Duino, a village near Trieste, Italy.
Pierre Curie dies in Paris.
1907 Thomson dies near Largs, Scotland.
Rutherford goes to Manchester.
1909 Hans Geiger and Ernest Marsden publish their paper on α-particle
scattering by metallic foils.
1910 Subrahmanyan Chandrasekhar is born in Lahore, then in India, now
in Pakistan.
1911 Rutherford proposes the nuclear model of the atom.
1913 Einstein moves to Berlin.
Bohr publishes his first paper on the structure of atoms and molecules.
1913–14 Henry Moseley publishes his papers on the x-ray spectra of the
elements.
1915 Einstein publishes his paper on general relativity.
1918 Richard Feynman is born in Far Rockaway, New York.
1919 Rutherford becomes director of the Cavendish Laboratory in
Cambridge.
1921 The Bohr Institute is inaugurated in Copenhagen.
Chronology of the Main Events 467
1923 De Broglie presents his theory of wave-particle duality for matter.
1924 Hubble reports cosmic distance measurements beyond our galaxy.
1925 Heisenberg publishes his first paper on matrix mechanics.
Max Born, Heisenberg, and Pascual Jordan publish their comprehensive
paper on matrix mechanics.
Pauli introduces his exclusion principle.
1926 Schro¨dinger publishes his first paper on wave mechanics.
Born publishes his first paper on the probability interpretation of
quantum mechanics.
Fermi publishes his first paper on quantum statistics.
1927 Heisenberg proposes his uncertainty principle.
1928 Dirac introduces his relativistic electron equation.
1929 Murray Gell-Mann is born in New York.
Hubble publishes his first paper on the linear relation between recession
speeds of galaxies and their distances from Earth.
Dirac introduces his hole theory, identifying a hole as a proton.
1931 Dirac proposes the existence of the antielectron, later called the
positron.
John Cockcroft and Ernest Walton study nuclear reactions with proton
beams generated in a linear accelerator.
1933 Einstein moves to Princeton, New Jersey.
Fermi publishes his paper on the theory of β decay.
1934 Marie Curie dies in Sancellemoz, France.
Chandrasekhar publishes his first white-dwarf paper.
1937 The particle later identified as the μ lepton is discovered.
Rutherford dies in Cambridge, England.
1938 Meitner and Otto Frisch propose their theory of fission.
1939 Bohr and John Wheeler publish their paper on the mechanism of
fission.
Robert Oppenheimer, George Volkoff, and Richard Tolman propose a
theory of neutron stars.
Oppenheimer and Hartland Snyder show that an idealized imploding
star forms a black hole.
1941 Nernst dies at his country estate near Bad Muskau, Germany.
1942 Fermi and associates achieve the first sustained nuclear chain
reaction.
Stephen Hawking is born in Oxford, England.
1943 Los Alamos National Laboratory begins operation near Santa Fe, New
Mexico.
1945 Trinity test of a plutonium bomb near Alamogordo, New Mexico.
1946 The first two “V-particles” are discovered.
George Gamow proposes a preliminary big-bang theory.
1947 Planck dies in Go¨ ttingen, Germany.
The Shelter Island Conference meets.
1948 The Pocono Conference meets.
Ralph Alpher, Hans Bethe, and Gamow extend the big-bang theory.
1949 The Oldstone Conference meets.
1952 Chandrasekhar becomes managing editor of the Astrophysical Journal.
1953 Hubble dies in San Marino, California.
Gell-Mann proposes the strangeness scheme.
468 Chronology of the Main Events
1954 Fermi dies in Chicago.
1955 Einstein dies in Princeton.
1956 Conservation of parity in weak interactions is questioned by Tsung-
Dao Lee and Chen Nin Yang.
The electron neutrino is detected.
1958 Pauli dies in Zu¨ rich, Switzerland.
1961 Schro¨dinger dies in Alpbach, Austria.
Gell-Mann proposes SU(3) symmetry for hadronic structure: the eightfold
way.
1962 Bohr dies in Copenhagen.
The μ neutrino is detected.
1964 The particle is discovered.
Gell-Mann proposes the quark model, with three flavors of quarks.
A fourth quark flavor, called “charm,” is introduced.
Roger Penrose proves that black holes must contain singularities.
1965 The “color” concept is introduced in particle physics.
1967 Wheeler coins the term “black hole.”
1968 Meitner dies in Cambridge, England.
1969 Hawking and Penrose prove that the universe began in a singularity.
1972 Feynman proposes his parton model.
1973 The theory of asymptotic freedom and confinement of quarks is
proposed.
1974 Discovery of the J/ particle.
Experimental evidence for the charmed quark is reported.
Hawking shows that black holes are not quite black.
1975 The τ lepton is detected.
1976 Heisenberg dies in Munich, Germany.
1977 Experimental evidence for the bottom quark is reported.
1979 Experimental evidence for gluons is reported.
1984 Dirac dies in Miami, Florida.
1987 De Broglie dies in Paris.
1988 Feynman dies in Los Angeles, California.
1989 Experimental evidence for the existence of only three generations of
quarks and leptons is reported.
1995 Experimental evidence for the top quark is reported.
Chandrasekhar dies in Chicago.
2000 The τ neutrino is detected.