In a nova, why is the shell of hydrogen on the white dwarf consumed explosively rather than steadily?

If a neutron star has a radius of 12 km and rotates 1,352 times a second, what is the speed at which a point on the surface at the neutron star's equator is moving? Express your answer as a fraction of the speed of light. (Note: The speed of light is 3 ✕ 105 km/s.)

A distant Nebula is now 2.35 pc in radius and is expanding at 1100 km/s. Approximately when did the supernova occur?

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.

. The radius of the nebula is about 0.401 light-years. The gas is expanding away from the star at a rate of about 37 kilometers/second . Considering that distance = velocity x time, calculate how long ago the gas left the star if its speed has been constant the whole time. Make sure you use consistent units for time, speed, and distance. Answer in years.

If an X-ray binary consists of a 16 solar mass star and a neutron Star orbiting each other every 15.4 days, what is their average separation? (Hint: Use the version of Keller's third law for binary stars, Ma + Mb = a^3 /p^2 ; make sure you express quantities in unites of AU, solar masses, and years. Assume the mass of a neutron Star is 1.6 solar masses.)  ___________ AU

Comment on the difference between a nova and supernova. [Note: There are two basic types of supernova.]

Why are Cepheid variables important? O Cepheids variables are pulsating stars whose pulsation periods are directly related to their true luminosities. Therefore they can be used as distance indicators. O Cepheids variables are supermassive stars that are on the verge of becoming supernovae. Therefore they allow us to choose candidates to watch if we hope to observe a supernova. O Cepheid variables are stars that vary in brightness because they harbor a black hole. Therefore, they provide direct evidence for black holes. O Cepheids variables are a type of irregular galaxy, much more common in the early universe. Therefore they help to understand how galaxies formed.

If the sun, which has a rotational period of 25 days, collapses from its current radius (700,000 km) to the radius of a neutron star (10 km) without losing any of its mass, what will its rotational speed be in seconds afer collapse?

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.]