Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 19, Problem 5Q
To determine
The reason main-sequence stars with masses less than
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For a main sequence star with luminosity L, how many kilograms of hydrogen is being converted into helium per second? Use the formula that you derive to estimate the mass of hydrogen atoms that are converted into helium in the interior of the sun (LSun = 3.9 x 1026 W).
(Note: the mass of a hydrogen atom is 1 mproton and the mass of a helium atom is 3.97 mproton. You need four hydrogen nuclei to form one helium nucleus.)
Place the following events in the formation of stars in the proper chronological
sequence, with the oldest first and the youngest last.
w. the gas and dust in the nebula flatten to a disk shape due to gravity
and a steadily increasing rate of angular rotation
x. a star emerges when the mass is great enough and the temperature is
high enough to trigger thermonuclear fusion in the core
y. the rotation of the nebular cloud increases as gas and dust
concentrates by gravity within the growing protostar in the center
z. some force, perhaps from a nearby supernova, imparts a rotation to a
nebular cloud
y, then z, then w, then x
z, then y, then w, then x
w, then y, then z, then x
z, then x, then w, then y
x, then z, then y, then w
MacBook Air
on
.H.
O O O O
Star A and Star B are both on the main sequence. Star A is 63 times more luminous than Star B. What is the ratio of their main-sequence lifetimes?
Hint: Refer to the stellar life expectancies equation,
t* =
M*
L*
=
M*
M*3.5
=
1
M*2.5
.
Chapter 19 Solutions
Universe: Stars And Galaxies
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- According to the text, a star must be hotter than about 25,000 K to produce an H II region. Both the hottest white dwarfs and main-sequence O stars have temperatures hotter than 25,000 K. Which type of star can ionize more hydrogen? Why?arrow_forwardTrue or False 8. Almost all stars are in binary systems. The book says: "So far you have been considering the deaths of stars as if they were all single objects that never interact, but more than half of all stars are members of binary star systems."From this, I would not necessarily say that almost all stars are in binary systems based on this alone, but some other information I am finding says up to 85%. However, the numbers seem to be all over the map outside the course material, and I can not find a solid figure in it from what I have looked at. If it helps, Stars and Galaxies, 10th Edition by Seeds and Beckman is my reference material.arrow_forwardA 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.arrow_forward
- Question 41 .Suppose you are looking at H-R diagrams of two similar star clusters. The most luminous main sequence stars in the Porcini cluster are much more luminous than the most luminous main sequence stars in the Morel cluster. What can you conclude? O the Porcini cluster is younger than the Morel cluster O the Porcini cluster is farther away than the Morel cluster O the Porcini cluster is lower in metallicity than the Morel cluster O the Porcini cluster is larger in diameter than the Morel clusterarrow_forwardObservations show that stellar luminosity, L, and mass, M, are related by L x M3.5 for main sequence stars. Obtain an expression that relates the main sequence life time and the mass of a star. You should assume that the luminosity is constant throughout a star's main sequence life time, and that the amount of mass converted into energy by a star while it is on the main sequence is given by AM main sequence life time of a 20 Solar mass star given that the Sun is expected to spend 1010 years on the main sequence. Comment on the significance of your answer. fM, where f is a constant. Estimate thearrow_forwardMost stars (Main sequence) generate light through the same mechanism. Because of this, there is an empirical relation between their mass, M, and their Luminosity, L. This relation could be written in the form L/Lsun = (M/Msun, This relation is shown in the log-log diagram below. Find the value of a and round it to the nearest integer. 10 104 102 10-2 10-4 0.1 1.0 2.0 0.2 0.5 5.0 10.0 20.0 Mam (solar masses) Luminosty (solar units)arrow_forward
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