The evolution of a star depends on its size. If a star is sufficiently large, the gravity forces holding it together may be large enough to collapse it into a very dense object composed mostly of neutrons. The density of such a neutron star is about 1014 times that of the Earth. Suppose that a star initially had a radius of 7 x 108 km, and it rotated once every 26 days. What would be the period of rotation if the star collapsed to a radius of 15 km? (1.19 x 10-14 days)

A non-rotating black hole has an ‘edge’ at what’s called it’s Schwartzschildradius. For a black hole of mass M, the Schwartzschild radius isRSch = 2GM/(c^2) where G is the gravitational constant and c is the speed of light. Close to black holes, we really should use Einstein’s theory of gravity (General Relativity) instead of Newton’s, but Newton’s is still a good approximation.Using Newtonian Gravity, find the gravitational force on a mass m at theSchwartzschild radius of a black hole. (Your answer for this should look likeFgrav = an expression in terms of G, M, m, c and numbers.) Is the forcesmaller or larger for a more massive black hole?

As a star ages, it is believed to undergo a variety of changes. One of the last phases of a star's life is to gravitationally collapse into a black hole. If suppose our Sun would end up a Black hole, what will happen to the orbit of the planets of the solar system? (Assuming that the planets are not affected by the evolving stages of the Sun prior to becoming a black hole and noting that for calculation of gravitational force of attraction, the distance being considered is from center to center of the two bodies). Justify your answer.

Neptune has a mass of 1.0 × 1026 kg and is 4.5 × 10⁹ km from the Sun with an orbital period of 177.5 years. Planetesimals in the outer primordial solar system 4.5 billion years ago coalesced into Neptune over hundreds of millions of years. If the primordial disk that evolved into our present day solar system had a radius of 10¹1 km and if the matter that made up these planetesimals that later became Neptune was spread out evenly on the edges of it, what was the orbital period of the outer edges of the primordial disk? Express your answer rounded to the nearest year, and be sure not to do any rounding before expressing your final answer. P = years

The Oort Cloud extends out to (possibly) one light-year from the sun.  Objects in the Oort Cloud are still gravitationally bound to the sun.  Suppose one such iceball orbits the sun in a circle.  I'm going to alter some numbers, such as the mass of the sun and even G.  The gravitational force is directed toward the sun and has the following magnitude: Calculate the force on the object if these are the numbers: G = 6.1*10-11 N*m2/kg2 M = 2.7*1030 kg m = 1.5*108 kg r = 19*1015 m Calculate your answer in microNewtons (10-6 N).

A neutron star is an astrophysical object having a mass of roughly 2.8 × 1030 kg (about 1.4 times the mass of the sun) but a radius of only about 12 km. If you were in a circular orbit of radius 320 km (about 200 mi), how long would it take you to go once around the star?   It would take about _______ s to go once around the star.

In 1999, scientists discovered a new class of black holes with masses 100 to 10,000 times the mass of our sun that occupy less space than our moon. Suppose that one of these black holes has a mass of 1x10^3 suns and a radius equal to one-half the radius of our moon. What is the density of the black hole in g/cm^3? The radius of our sun is 7.0x10^5 km, and it has an average density of 1.4x10^3 kg/m^3. The diameter of the moon is 2.16x10^3 miles.

The star HD 69830's mass is 1.7 ✕ 1030 kg, its radius is 6.3 ✕ 105 km, and it has a rotational period of approximately 35 days. If HD 69830 should collapse into a white dwarf of radius 7.8 ✕ 103 km, what would its period (in s) be if no mass were ejected and a sphere of uniform density can model HD 69830 both before and after?

The supermassive black hole at the center or our galaxy (Sagittarius A*) has a mass equal to 4.3 million Suns (the mass of the Sun is 1.99 × 1030 kg). The distance from Sgr A* to Earth is 7,940 parsecs, where one parsec is equal to 3.09 × 1016 m. (a) What is the gravitational force that Sgr A* exerts on a 75 kg person on Earth, in units of Newtons? Hint: use Newton's law of universal gravitation. (b) Suppose the same person is sitting 1.0 meter away from a paperclip with a mass of 1.0 grams. What is the gravitational force that the paperclip exerts on the person? (c) Compare the forces from parts (a) and (b). Which is greater?

Plaskett's binary system consists of two stars that revolve in a circular orbit about a center of mass midway between them. This statement implies that the masses of the two stars are equal (see figure below). Assume the orbital speed of each star is |v| 190 km/s and the orbital period of each is 12.9 days. Find the mass M of each star. (For comparison, the mass of our Sun is 1.99 x 1030 kg.) solar masses M XCM M