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244 ad (Black Holes) : 3934.... જેન વિદ્વાનો મને સહાય કરશે એવી આશા સાથે આ લેખ પૂર્ણ કરું છું.'
Ml. 16-11-1996
ભાવનગર
1. Each new advance poses still more questions, sometimes making the universe more puzzling, not less. ('Black Holes, Quasars And The Universe' by Harry L. Shipman, Houghton
Mifflin Company, Boston, U.S.A. P. 14) 2. If we cannot see a black hole, how do we tell what it looks like ? The pencil and paper calculations of the theoretical physicists help us here.
[Ibidem P. 14) 3. The radius is numerically equal to 2.95 kilometres times of the mass of the
hole in solar masses. Our ten-solar-mass hole is thus 30 kilometres in radius or 60 kilometres across.
[Ibidem. P. 71] On Phobos the force of gravity is so small that a man's arm would be strong enough to put a small stone into orbit around it or even send it into orbit about Mars itself, some 9000 kilometres away. The escape velocity is only 5 m/s for Phobos. (Black Holes, by Jean-Pierre Luminet, Cambridge University Press, U.K., P.
6, 7] 5. To put a satellite into orbit, the rocket launcher has to reach a certain altitude,
inclined itself to be parallel to the Earth's surface and then increase its velocity to at least 8 km/s. At this velocity the centrifugal force (directed into space) balances the gravitational force (directed towards the centre of the Earth.)
[Ibidem, P. 6) 6. This critical velocity-identical for a pebble or a rocket - is called the escape
velocity. On the Earth's surface it is 11.2 km/s, and it can easily be calculated for any planet, star or other celestial body.
[Ibidem, P. 7] 7. The escape velocity is only 5 m/s for Phobos and 2.4 km/s for the moon, but
620 km/s for the Sun. From a more dense star, such as a white dwarf, it reaches several thousands kilometres per second.
[Ibidem, P. 7) 8. The greater the mass, the greater the escape velocity, and for a given mass the escape velocity will increase as the radius of the star decreases.
[Ibidem P. 7] 9. The notion of a black hole ultimately derives from the simple concept of
escape velocity. The velocity of light has been known to be about 3,00,000
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