Select the correct options for the most critical factor to determining in every phase of a star’s life.

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Chapter 14, Problem 2TY

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Select the correct options for the most critical factor to determining in every phase of a star’s life.

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3. If a star converted every bit of its mass into energy the conversion efficiency would be 100%. However, no star is this efficient in its energy production. Stars with less than 1.3 solar masses (most stars are less than 1.3 solar masses) convert hydrogen into helium with an efficiency of only 0.7%. Bearing in mind that Nunki has a mass of 15.6 x 1030 kg, how long will it live if it converts all of its hydrogen into helium with an efficiency 0.7%? Please note that it won't actually convert all of its hydrogen into helium so this is a rather optimistic upper limit for the lifetime of Nunki. Also, 1 year = 365.25 days. Lifetime = 2.47167e1 X years

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.

A star is formed when the gravitational attraction overcomes the pressure due to the gases inside.Thus we can write(in-picture) .... Assuming the ideal gas equation, we can write P = nkT, where n is the number of atoms/volume. Let M and m denote the total mass and the mass of each gas atom. Using the above equation, show that the condition for star formation is that the mass of the star obeys M > MJ, where : (in-picture)