The best parallaxes obtained with Hipparcos have an accuracy of 0.001 arcsec. If you want to measure the distance to a star with an accuracy of 10%, its parallax must be 10 times larger than the typical error. How far away can you obtain a distance that is accurate to 10% with Hipparcos data? The disk of our Galaxy is 100,000 light-years in diameter. What fraction of the diameter of the Galaxy’s disk is the distance for which we can measure accurate parallaxes?

Rapid variability in quasars indicates that the region in which the energy is generated must be small. You can show why this is true. Suppose, for example, that the region in which the energy is generated is a transparent sphere 1 light-year in diameter. Suppose that in 1 s this region brightens by a factor of 10 and remains bright for two years, after which it returns to its original luminosity. Draw its light curve (a graph of its brightness over time) as viewed from Earth.

As a person approaches the Schwarzschild radius fo a black hole, outside observers see all the processes of that person (their clocks, their heart rate, etc.) slowing down, and coming to a halst as they reach the Schwarzschild radius. (The person falling into the black hole sees their own processes unaffected.) But the speed of light is the same everywhere for all observers. What does this say about space as you approach the black hole?

Which is likely to be more common in our Galaxy: white dwarfs or black holes? Why?

Once again in this chapter, we see the use of Kepler’s third law to estimate the mass of supermassive black holes. In the case of NGC 4261, this chapter supplied the result of the calculation of the mass of the black hole in NGC 4261. In order to get this answer, astronomers had to measure the velocity of particles in the ring of dust and gas that surrounds the black hole. How high were these velocities? Turn Kepler’s third law around and use the information given in this chapter about the galaxy NGC 4261-the mass of the black hole at its center and the diameter of the surrounding ring of dust and gas-to calculate how long it would take a dust particle in the ring to complete a single orbit around the black hole. Assume that the only force acting on the dust particle is the gravitational force exerted by the black hole. Calculate the velocity of the dust particle in km/s.

It is believed that there is a black hole with a mass of approximately four million times the mass of the Sun near the centre of the Milky Way galaxy. Some stars are relatively close to this black hole. Assume that the semi-major axis of the orbit of one of these stars is 3.5 light days (ie. The distance that light would travel in 3.5 days).a) Find the orbital period of the star. (In years)b) Find the orbital speed of the star (in km/s), assuming that it is in a circular orbit.

The Schwarzschild radius RBH for an object of mass M is defined as (See image.) where c is the speed of light and G is the universal gravitational constant. RBH gives the radius of the event horizon of a black hole with mass M. In other words, it gives the radius to which some amount of mass M would need to be compressed in order to form a black hole.   1. The mass of the Sun is about 1.99 × 1030 kg. What would be the radius of a black hole with this mass?   2. The mass of Mars is about 6.42 × 1023 kg. What would be the radius of a black hole with this mass?   3. Suppose you want to make a black hole that is roughly the size of an atom (take RBH = 1.10 x 10-10 m). What would be the mass M of such a black hole?

Imagine that a space colony living in a large vessel is in a circular orbit at a distance of 55 km from the centre of a neutron star. The neutron star has a radius of 10.0 km and a mass of 4.4 X 1030 kg. (a) Find the velocity of the vessel in its orbit. (b) Find the period of the orbit.

What is the CMB? Group of answer choices A dense region of 4.5 million stars. A large star of 4.5 million solar masses. The cosmic microwave background of photons left over and cooled down from when the universe became transparent 300,000 years after the Big Bang. The space curvature of the universe