Astronomy | Astrophysics Answers

Using the virial theorem, explain why there is a need to postulate the existence of dark
matter.

What is a Seyfert galaxy? Explain how broad-line and narrow-line regions originate in a
Seyfert galaxy

Distinguish between spiral and barred spiral galaxies giving examples of each type of
galaxy.

Discuss Jeans criterion for the formation of stars and obtain an expression for Jeans mass
and Jeans length

What is the basis of classifying the planets inthe solar system as terrestrial and jovian?
State nebular hypothesis. Explain briefly (in not more that 150 words) the formation of
solar system as per the nebular model.

List different layers of the Sun’s atmosphere. Explain why the temperature in the
chromosphere increases with height. What gives riseto solar wind?

In fact, there is such a star (a-Centauri) except that its companion isn't a planet, but another Sun-like star. Does this fact make any difference in the forgoing calculation? Explain.

Consider a Sun-like star, which is orbited by a planet with a period of 80
years. If the separation of the star and the planet appears to be 20 arc
seconds, how far away is the star?

Neptune's moon Nereid has an orbital period of almost exactly one Earth year. If the mass of Neptune is around 1026 kilograms, what is the semimajor axis of Nereid's orbit?

the average temperature of the interior of a sun like star is of order 10^8k. estimate the mass of the star in terms of the solar mass if it has a radius of order 10^10cm