c) The star may be assumed to evolve with effective temperature, Teff, remaining constant. Show that the time, t₁, taken by sucha star to evolve from a large radius to some smaller radius, R₁, is given bywhere L₁ is the luminosity when the star has radius R₁.t₁=GM²7L₁R₁' d) Estimate the time scale for a protostar of one solar mass to contract down to a radius R = 2R while maintaining an effectivetemperature of 3300 K. Express your answer in years. Based on your answer, estimate the number of solar mass protostars onewould expect to detect in a volume limited survey of solar-type stars in the Galaxy that results in the detection of 106 stars intotal.

To start, we'll use the equation for the luminosity of a star: where L is the luminosity, R is the…

Answered: c) The star may be assumed to evolve…

Similar questions

What is the rate of thermal radiation emitted from a star with a radius of 2.310x 109mand a surface temperatureof8,420K?Assume that the spherical surface behaves as a blackbody radiator.[Surface Area of a sphere = 4πr2; Area of a circle = πr2or (π/4)d2]
The sun has a radius of 6.959 × 108 m and a surface temperature of 5.81 x 10° K. When the sun radiates at a rate of 3.91 x 1026 W and is a perfect emitter. What is the rate of energy emitted per square meter? Stefan-Boltzmann constant is 5.67 x 10-8 J/s-m2 K4 a) 5.6 x 107 W/m2 b) 12.8 x 107 W/m2 c) 6.4 x 107 W/m2 25.6 x 107 W/m2 5.6 x 1017 W/m2
a)Define the term “standard candle” as used in cosmology. b)The flux is defined asf(Dlum) = L/4πD^2lumwhere L is the absolute luminosity and Dlum is the distance to the radiation source (youmay assume z ≪ 1).Assume that we have measured the flux to be f = 7.234 10^−23 Wm^−2 and the absoluteluminosity is given by L = 3.828 x10^26W. Calculate the luminosity distance D lum to the objectin Mpc.
7) Calculate the luminosity of a star that has a radius of 4.2Rsumn and a temperature of 5T su Sun
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.
Compute the life expectancy of a 1.5M⊙ star.
2 of 7 Question A2 a) Calculate the mass loss rate of the Sun M due to the solar wind flow. Assume average properties of the solar wind of number density 6 protons cm³, and a flow speed of 450 km s-1. Express your answer in units of both kg per year, and solar masses per year. b) Suppose the solar wind flow is perfectly radial. Calculate the expected rate of change of solar rotation frequency dw at the present time, based on conservation of angular momen- tum. Give your answer in units of rad s-1 y-1 (i.e., radians per second per year) and also in terms of fractional change per year, i.e., 1 du. w dt' Use a current solar rotation period of P = 25.38 days to calculate the current angular frequency of rotation w. The moment of inertia of a uniform sphere is MR². You can assume that the radius of the Sun is approximately constant, and the change in its moment of inertia due to the solar wind is only due to the mass loss. Page 3 c) By observing the rotation period of stars similar to the…
a.Calculate the mass loss rate of the Sun M˙ due to the solar wind flow. Assume averageproperties of the solar wind of number density 6 protons cm−3, and a flow speed of 450 kms−1. Express your answer in units of both kg per year, and solar masses per year. b.Suppose the solar wind flow is perfectly radial. Calculate the expected rate of change ofsolar rotation frequency dω/dt at the present time, based on conservation of angular momentum. Give your answer in units of rad s−1 y−1(i.e., radians per second per year) and alsoin terms of fractional change per year, i.e., 1/ωdω/dt .Use a current solar rotation period of P = 25.38 days to calculate the current angularfrequency of rotation ω. The moment of inertia of a uniform sphere is 2/5 MR2. You canassume that the radius of the Sun is approximately constant, and the change in its momentof inertia due to the solar wind is only due to the mass loss. c.By observing the rotation period of stars similar to the Sun, it is inferred that their…
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)
c) Derive the Schwarzschild criterion for the onset of convection in an ideal gas, namely d ln T d ln P 7-1 Y Explain all steps in your derivation, and justify any assumptions that you make. d) In a region of convective instability near the surface of a solar-type star of total mass M, the temperature and pressure are related approximately by the expression P KT5/2. Show that the temperature gradient for an ideal gas in hydrostatic = equilibrium in this convection zone is given by dT dr 2Gm(r)μ 5Rr² Further, assuming that the mass in the convection zone is small compared to M, show that at a depth h measured from the top of the convection zone, the temperature is approximately given by T = Ts + 2GMμ -h₂ 5RR² when his small compared to R, and Ts is the temperature at the top of the convection zone.

c) The star may be assumed to evolve with effective temperature, Teff, remaining constant. Show that the time, t₁, taken by such a star to evolve from a large radius to some smaller radius, R₁, is given by where L₁ is the luminosity when the star has radius R₁. t₁ = GM2 7L₁R₁'