Taking the distance to the Crab pulsar to be 2000 pc and the bolometric magnitude at maximum brightness of the respective type Il supernovae explosion to be Mbol=-17, estimate the peak apparent magnitude. Compare this to the maximum brightness of Venus (m- -4), which can sometimes be seen during daytime.

A main sequence star of mass 25 M⊙has a luminosity of approximately 80,000 L⊙. a. At what rate DOES MASS VANISH as H is fused to He in the star’s core? Note: When we say “mass vanish '' what we really mean is “gets converted into energy and leaves the star as light”. Note: approximate answer: 3.55 E14 kg/s b. At what rate is H converted into He? To do this you need to take into account that for every kg of hydrogen burned, only 0.7% gets converted into energy while the rest turns into helium. Approximate answer = 5E16 kg/s c. Assuming that only the 10% of the star’s mass in the central regions will get hot enough for fusion, calculate the main sequence lifetime of the star. Put your answer in years, and compare it to the lifetime of the Sun. It should be much, much shorter. Approximate answer: 30 million years.

Use t =  1 M2.5 to compute the life expectancy of a 0.8-solar-mass star. (A solar lifetime is approximately 10 billion years.)

A supernova’s energy is often compared to the total energy output of the Sun over its lifetime. Using the Sun’s current luminosity, calculate the total solar energy output, assuming a 1010 year main-sequence lifetime. Using Einstein’s formula E=mc2 calculate the equivalent amount of mass, expressed in Earth masses. [Hint: The total energy output of the Sun over its lifetime is given by its current luminosity times the number of seconds in a year times its ten billion-year lifetime; ; mass of earth = 6×1024kg; c = 3×108m/s. Your answer should be 200-300 Earth masses.]

If Bν ~ 10-5 Jy Ω-1, what is the brightness temperature (TB) at 1 GHz?

Consider a Schechter luminosity function of the form where a = 0.9, ΦΣ = -0 (L)dL = D(+) L e-(L/Lx)dL, L 0.012h3 Mpc3 and L - 1010h Lo. Calculate the total number density. Express the final answer in terms of h where h = Ho/(100 km s−¹Mpc¯¹) (Ho is the Hubble constant).

A protostar evolves from a temperature T = 3500 K and a luminosity L = 5000 times that of the Sun to T = 5000 K and L = 3 solar units. What is its radius (a) at the start, and (b) at the end of the evolution? (need full step)

Suppose a protostar has a luminosity of 39,473 L⊙ and a surface temperature of 4,130 K (Kelvins). What is the radius of this protostar? [Enter your answer as a multiple of the Sun's radius. I.e., if you find R = 20 R⊙ , enter 20. This problem is easier if you start with the relevant equation and create a ratio using the Sun's values. Recall that the Sun has a surface temperature of 5778 K. ]

What is the escape velocity (in km/s) from the surface of a 1.1 M neutron star? From a 3.0 M neutron star?

If a circular accretion disk around a 1.4 M, neutron star has a radius of 1.00 x 105 km as measured from the center of the neutron star to the edge of the disk, what is the orbital velocity (in km/s) of a gas particle located at its outer edge? (The mass of the Sun is GM 1.99 x 1030 kg. Hint: Use the circular orbit velocity formula, V, = ; make sure to express quantities in units of meters, kilograms, and seconds.) km/s