8) A neutron star is found with a radius of 10 km and has a surface temperature of 1,000,000 K. Calculate its luminosity with respect to that of the Sun. nts)
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- Hypernovae are thought to be a. a star greater than 20 solar masses collapsing into a black hole. b. binary systems involving mass transferred to a neutron star. c. binary systems involving mass transferred to a white dwarf. d. two main-sequence stars colliding. e. binary systems involving mass transferred to a black hole.7) Calculate the luminosity of a star that has a radius of 4.2Rsumn and a temperature of 5T su SunA 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 white dwarf that remains when our Sun dies will be mostly made of A. helium. B. carbon. C. neutrons. D. hydrogen. Is the answer B? Thanks!3- Consider a binary star system in which the two stars are seen to be 1.50" apart. Determine the actual physical separation of those stars (in AU) if this binary system is located 9.50 1.y. from us.31) Star Sirius has an apparent magnitude of -1.47 and an absolute magnitude of 1.41. Estimate the distance to Sirius.
- 33) A star is observed to be having an absolute magnitude of -5.6 and is located at a distance of 159.96 pc. Estimate the apparent magnitudeIf a star is to eventually form a stellar black hole at any point in its life cycle what must happen? A. Gravity must be strong enough to compress all its material to be smaller than its schwartzchild radius B. it must pass by a supermassive black hole and tidal forces will do the rest C. Gravity must expand it so it can over power the nuclear forces that compress it and keep it from exploding by giving off all its heat D. A star will always have the same mass and radius and the only black holes that exist are ones that have existed shortly after the big bang12. A star with spectral type MO has a surface temperature of 3750 K and a radius of 0.63 Rsun: How many times more luminous is this star than the Sun? (if it is less luminous enter a number less than one) Answer: Submit All Answers Last Answer: 0.0923 Incorrect, tries 1/5. Hint: Use the Luminosity equation, which says that L is proportional to R^2 T^4. If you keep these as ratios compared to the sun, your L will also come out as a ratio compared to the Sun. This star has a mass of 0.4 Msun- Using the simple approximation that we made in class, what is the main sequence lifetime of this star? You may assume that the lifetime of the sun is 1010 yr. Answer: Submit All Answers Compare this to the lifetime of a MO star listed in Table 22.1 (computed using a more sophisticated approach). Is the value you calculated in the previous problem longer or shorter than what is reported in the table? (L for longer, S for shorter) (You only get one try at this problem.) Answer: Submit All Answers