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What is a black hole ? Derive an expression for Schwarzs child radius of a black hole on the basis of Newtonian mechanics and explain its significance.
What is a white dwarf star ? Explain, on physical basis the existence of an upper limit on the mass of a white dwarf star. What is this limiting value called ?
What is interstellar extinction ? How does it help in determining the composition of ISM ?
Draw a labelled H-R diagram. How does it help into estimating the size and mass of a star.
What is solar wind ? Explain, briefly, the reasons for its occurrence. How are the Van-Allen radiation belts formed ?
Assume that sun radiates like a black body of temperature T. Calculate T using Stefan-Boltzmann law. Take Q=5.67 x 10^-8 Wm^-2K^-4 and Lo=4 x 10^26 W.
Estimate the radius of a star in thermal equilibrium of mass 10^30 kg and average internal temperature 10^7 K. It is given that
kB =1.38 x 10^-23 JK^-1, mH - 1.67 x 10^-27 kg and G=6.7 x 10^-11 m³ kg^-1s^-2.
Explain the horizon coordinate system used in astronomy. Show the horizon coordinates of a star on a celestial sphere for an observer at latitude 30°N.
The apparent magnitude of the sun is - 26.8. Determine its absolute magnitude. It is given that the distance between the sun and the earth is 1.5 x 10^11m.
A galaxy of absolute magnitude M= - 20 is at a distance of 700 kpc. Would it be visible to the unaided eye.
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