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  • richardmitnick 11:12 am on November 23, 2018 Permalink | Reply
    Tags: , , , , Black holes: from absurd idea to fact of nature, , Sir Arthur Eddington publicly ridiculed Chandrasekhar in an infamous encounter at the Royal Astronomical Society in 1935, Subrahmanyan Chandrasekhar, , Yet history proved Eddington wrong   

    From COSMOS Magazine: “Black holes: from absurd idea to fact of nature” Subrahmanyan Chandrasekhar 

    Cosmos Magazine bloc

    From COSMOS Magazine

    22 November 2018
    Paul Davies

    1
    Subrahmanyan Chandrasekhar meets the press in 1983, shortly after winning the Nobel Prize.
    Bettmann / Contributor / Getty Images

    2
    Credit Mark Garlick / Science Photo Library

    In 1930 a 20-year-old Indian student named Subrahmanyan Chandrasekhar was sailing from Madras to England to pursue his studies in astrophysics. During the voyage he toyed with equations describing the stability of stars. And from a few lines of this mathematics, a momentous discovery emerged.

    Astronomers of the day had only a sketchy understanding of what makes stars tick. They knew that a star is a ball of hot gas engaging in a cosmic balancing act. The gas tries to expand out into the vacuum of the surrounding space but gravity holds it back. In stars like the sun, an equilibrium is achieved, but only as long as the gas burns fuel to generate heat, which we now know is produced by nuclear reactions in the core.

    However, uncertainty surrounded the question of what happens when the fuel runs out. It seemed that gravity would inevitably gain the upper hand, causing the star to contract, and the smaller the radius, the fiercer the gravitational force would become at the surface. Astronomers had long been familiar with tiny stars known as white dwarfs, which contain a mass comparable to the sun but squashed into a volume roughly the size of the Earth. These burned-out stellar remnants are so dense that their atoms are pressed cheek by jowl. Further compression would mean the atoms themselves would be crushed, which was initially assumed to be impossible due to the laws of quantum physics.

    From his nautical calculations Chandrasekhar discovered otherwise. The equations suggested that if a star has a big enough mass, the crushing effect of its immense gravity would cause the atomic electrons to approach the speed of light, rendering the stellar material more squishy and heralding the further gravitational collapse of the star. In the absence of any other factor, the ball of matter would implode totally and vanish down its own gravitational well, forming an object that today we call a black hole. But in the early 1930s such an object was considered too outlandish to take seriously.

    Chandrasekhar was able to calculate the critical mass above which this gravitational instability would set in. The answer he obtained was 1.44 solar masses, now known as the Chandrasekhar limit. On reaching England, he announced his result, only to find it was ignored or dismissed as nonsense from a young upstart. The most distinguished astronomer of the day, Sir Arthur Eddington, publicly ridiculed Chandrasekhar in an infamous encounter at the Royal Astronomical Society in 1935, declaring that there should be a law of nature “to prevent a star from behaving in this absurd way!”

    Yet history proved Eddington wrong. If a burned-out star has a mass exceeding Chandrasekhar’s limit, it does indeed collapse. One possible fate is to form a so-called neutron star, in which the atoms are crushed into neutrons and the object stabilises at a radius about the size of Sydney. Neutron stars were discovered in the 1960s and today form an important branch of astronomy. Most of them have masses not far from the Chandrasekhar limit. More massive stars end their days by totally collapsing. When they shrink to a few kilometres across, their gravity is so great that even light cannot escape, and a black hole results.

    Although it took decades for the concept of a black hole to be fully understood and accepted, the basic idea was hiding in plain sight since just after Albert Einstein first published his general theory of relativity in 1915. Chandrasekhar acknowledged this in his 1983 Nobel Prize address, where he wrote: “This important result is implicit in a fundamental paper by Karl Schwarzschild published in 1916”. Although the theoretical possibility of a black hole was inherent all along in Einstein’s theory, it took the youthful genius of Chandrasekhar to prove that such an object could result from the transformation of a dying star.

    By the time of the Prize, the existence of black holes had become firmly established, and Subrahmanyan Chandrasekhar’s calculations fully vindicated. Yet he was so stung by Eddington’s derision, he decided to leave the UK in 1937 and settle in the US, where he followed a distinguished career until his death in 1995.

    Chandrasekhar died leaving open a fascinating question. Might there exist an intermediate state between a neutron star and a black hole? This would be an object above 1.44 solar masses, too heavy to form a neutron star, but prevented from total collapse by an exotic form of ultra-dense matter such as a soup of quarks – the constituents of protons and neutrons. To date nobody has discovered a quark star, but the notion remains a theoretical possibility, perhaps awaiting the attention of another student genius with the insight to settle the matter.

    See the full article here .


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  • richardmitnick 12:20 pm on November 7, 2018 Permalink | Reply
    Tags: , , , , , Demonstrated that there is an upper limit – now called the Chandrasekhar limit – to the mass of a white dwarf star, , Subrahmanyan Chandrasekhar   

    From COSMOS Magazine: “Science history: The astrophysicist who defined how stars behave” Subrahmanyan Chandrasekhar 

    Cosmos Magazine bloc

    From COSMOS Magazine

    07 November 2018
    Jeff Glorfeld

    1
    Subrahmanyan Chandrasekhar meets the press in 1983, shortly after winning the Nobel Prize. Bettmann / Contributor / Getty Images

    Subrahmanyan Chandrasekhar was so influential, NASA honoured him by naming an orbiting observatory after him.

    NASA/Chandra X-ray Telescope

    The NASA webpage devoted to astrophysicist Subrahmanyan Chandrasekhar says he “was known to the world as Chandra. The word chandra means ‘moon’ or ‘luminous’ in Sanskrit.”

    Subrahmanyan Chandrasekhar was born on October 19, 1910, in Lahore, Pakistan, which at the time was part of British India. NASA says that he was “one of the foremost astrophysicists of the 20th century. He was one of the first scientists to couple the study of physics with the study of astronomy.”

    The Encyclopaedia Britannica adds that, with William A. Fowler, he won the 1983 Nobel Prize for physics, “for key discoveries that led to the currently accepted theory on the later evolutionary stages of massive stars”.

    According to an entry on the website of the Harvard-Smithsonian Centre for Astrophysics, early in his career, between 1931 and 1935, he demonstrated that there is an upper limit – now called the Chandrasekhar limit – to the mass of a white dwarf star.

    “This discovery is basic to much of modern astrophysics, since it shows that stars much more massive than the Sun must either explode or form black holes,” the article explains.

    When he first proposed his theory, however, it was opposed by many, including Albert Einstein, “who refused to believe that Chandrasekhar’s findings could result in a star collapsing down to a point”.

    Writing for the Nobel Prize committee, Chandra described how he approached a project.

    “My scientific work has followed a certain pattern, motivated, principally, by a quest after perspectives,” he wrote.

    “In practice, this quest has consisted in my choosing (after some trials and tribulations) a certain area which appears amenable to cultivation and compatible with my taste, abilities, and temperament. And when, after some years of study, I feel that I have accumulated a sufficient body of knowledge and achieved a view of my own, I have the urge to present my point of view, ab initio, in a coherent account with order, form, and structure.

    “There have been seven such periods in my life: stellar structure, including the theory of white dwarfs (1929-1939); stellar dynamics, including the theory of Brownian motion (1938-1943); the theory of radiative transfer, including the theory of stellar atmospheres and the quantum theory of the negative ion of hydrogen and the theory of planetary atmospheres, including the theory of the illumination and the polarisation of the sunlit sky (1943-1950); hydrodynamic and hydromagnetic stability, including the theory of the Rayleigh-Benard convection (1952-1961); the equilibrium and the stability of ellipsoidal figures of equilibrium, partly in collaboration with Norman R. Lebovitz (1961-1968); the general theory of relativity and relativistic astrophysics (1962-1971); and the mathematical theory of black holes (1974- 1983).”

    In 1999, four years after his death on August 21, 1995, NASA launched an x-ray observatory named Chandra, in his honour. The observatory studies the universe in the x-ray portion of the electromagnetic spectrum.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

     
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