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 22, Problem 8Q
To determine
The part of the galactic halo or the galactic diskin which star formation took place recently.
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Suppose that stars were born at random times over the last 10e10 years. The rate ofstar formation is simply the number of stars divided by 10e10 years. The fraction ofstars with detected extrasolar planets is at least 9 %. The rate of star formation can bemultiplied by this fraction to find the rate planet formation. How often (in years) doesa planetary system form in our galaxy? Assume the Milky Way contains 7 × 10e11 stars.
I've done this problem 3 different times from scratch and looked at similar problems here. Each time my answer is 1.587 (1.59 rounded to 2 significant figures), but when I submit, it says the answer is wrong. What do you think?
How are giant molecular clouds (GMCs), the loci of most star formation, themselves formed out of diffuse interstellar gas?
What processes determine the distribution of physical conditions within star-forming regions, and why does star formation occur in only a small fraction of the available gas?
How is the rate at which stars form determined by the properties of the natal GMC or, on a larger scale, of the interstellar medium (ISM) in a galaxy?
What determines the mass distribution of forming stars, the initial mass function (IMF)?
Most stars form in clusters (Lada & Lada 2003); how do stars form in such a dense environment and in the presence of enormous radiative and mechanical feedback from other YSOs?
An important part of the lifecycle of galaxies like the Milky Way is the self regulation of formation of future generations of stars. Which statement best describes this process?
A) Massive stars explode as Supernovae, heating nearby gas which then can't form stars, and even forcing the gas out of the galaxy in asuperbubble.
B) Low mass stars like our Sun explode as Supernovae, heating nearby gas which then can't form stars, and even forcing the gas out the galaxy in asuperbubble.
C) Stars fuse new elements in their cores which mix with nearby gas clouds, preventing the collapse of the clouds and hence stopping new starformation.
D) The stars lock up material in their cores (like White Dwarf and Neutron Stars) meaning they can act as gravitational seeds for future starformation.
Chapter 22 Solutions
Universe: Stars And Galaxies
Ch. 22 - Prob. 1QCh. 22 - Prob. 2QCh. 22 - Prob. 3QCh. 22 - Prob. 4QCh. 22 - Prob. 5QCh. 22 - Prob. 6QCh. 22 - Prob. 7QCh. 22 - Prob. 8QCh. 22 - Prob. 9QCh. 22 - Prob. 10Q
Ch. 22 - Prob. 11QCh. 22 - Prob. 12QCh. 22 - Prob. 13QCh. 22 - Prob. 14QCh. 22 - Prob. 15QCh. 22 - Prob. 16QCh. 22 - Prob. 17QCh. 22 - Prob. 18QCh. 22 - Prob. 19QCh. 22 - Prob. 20QCh. 22 - Prob. 21QCh. 22 - Prob. 22QCh. 22 - Prob. 23QCh. 22 - Prob. 24QCh. 22 - Prob. 25QCh. 22 - Prob. 26QCh. 22 - Prob. 27QCh. 22 - Prob. 28QCh. 22 - Prob. 29QCh. 22 - Prob. 30QCh. 22 - Prob. 31QCh. 22 - Prob. 32QCh. 22 - Prob. 33QCh. 22 - Prob. 34QCh. 22 - Prob. 35QCh. 22 - Prob. 36QCh. 22 - Prob. 37QCh. 22 - Prob. 38QCh. 22 - Prob. 39QCh. 22 - Prob. 40QCh. 22 - Prob. 41QCh. 22 - Prob. 42QCh. 22 - Prob. 43QCh. 22 - Prob. 44QCh. 22 - Prob. 45QCh. 22 - Prob. 46QCh. 22 - Prob. 47QCh. 22 - Prob. 48QCh. 22 - Prob. 49QCh. 22 - Prob. 50Q
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- Consider the following five kinds of objects: open cluster, giant molecular cloud, globular cluster, group of O and B stars, and planetary nebulae. A. Which occur only in spiral arms? B. Which occur only in the parts of the Galaxy other than the spiral arms? C. Which are thought to be very young? D. Which are thought to be very old? E. Which have the hottest stars?arrow_forwardWould you expect to observe every supernova in our own Galaxy? Why or why not?arrow_forwardA molecular cloud is about 1000 times denser than the average of the interstellar medium. Let’s compare this difference in densities to something more familiar. Air has a density of about 1 kg/m3, so something 1000 times denser than air would have a density of about 1000 kg/m3. How does this compare to the typical density of water? Of granite? (You can find figures for these densities on the internet.) Is the density difference between a molecular cloud and the interstellar medium larger or smaller than the density difference between air and water or granite?arrow_forward
- A planetary nebula expanded in radius 0.3 arc seconds in 30 years. Doppler measurements show the nebula is expanding at a rate of 35 km/s. How far away is the nebula in parsecs? First, determine what distance the nebular expanded in parsecs during the time mentioned. Δd = vpc/sTs So we first need to convert the rate into pc/s and the time into seconds: vpc/s = vkm/s (1 pc / 3.09 x 1013km) vpc/s = ? Ts = (Tyr)(365 days/yr)(24 hrs/day)(3600 s/hr) Ts = ? s Δd= vpc/sTs Therefore, Δd = ? pcarrow_forwardSuppose that stars were born at random times over the last 1010 years. The rate of star formation is simply the number of stars divided by 1010 years. The fraction of stars with detected extrasolar planets is at least 11 %. The rate of star formation can be multiplied by this fraction to find the rate planet formation. How often (in years) does a planetary system form in our galaxy? Assume the Milky Way contains 3 × 1011 stars.arrow_forwardConsider the Milky Way disk, which has a 50 kpc diameter and a total height of 600 pc. Suppose that the Sun orbits precisely at the mid-plane of the disk in a circular orbit. Supernovae explosions happen randomly throughout the disk at a rate of about 2 per 100 years. Consider a spherical region around the Sun with a radius of 300 pc. Ignore the Milky Way bulge and halo in this problem; assume the Milky Way disk is perfectly uniform and extends all the way through the region of the bulge. (I.e., the Milky Way is modeled *only* as a cylindrical disk--like a hockey puck-- with constant density throughout.) If a particular supernova goes off at a random location within the disk, what is the probability that it went off in the 300 pc radius spherical region near the Sun? Express your probability as a percentage (but without writing the percent sign). [Hint: there is a 100% probability that the supernova went off somewhere in the volume of the Milky Way disk; there is a 50% probability that…arrow_forward
- As a cluster of stars begins to age, which type of star in the cluster will move off the main sequence of the H-R diagram first? 1) all the stars in a cluster are born at the same time; so they will all move off the main sequence at the same time, as they evolve 2) G type stars, like our Sun 3) M type stars, which are the coolest 4) the lowest mass stars, which have the least amount of fuel for fusion 5) the O and B type starsarrow_forwardThe Milky Way galaxy has about 5 x 10⁹ solar masses of gas in total. If 13 solar masses of that gas is turned into stars each year, how many more years could the Milky Way keep up with such a star formation rate? years (Note for comparison that the age of the universe is about 13.5 billion years, which can be written 1.35e10 years. Also, the value given is in the ballpark of how much gas in the Milky Way is used to make new stars each year.)arrow_forwardSuppose you observe a star orbiting the galactic center at a speed of 1100 km/s in a circular orbit with a radius of 14 light-days. Calculate the mass of the object that the star is orbiting. Express your answer in solar masses to two significant figures.arrow_forward
- If a standard passenger aircraft can fly at 0.32 km/s (716 mph), how long (in yr) would it take to reach the sun? ______ yr How long (In yr) would it take to reach the galactic center? (Note: 1 pc = 3.1 x 10^13 km. The radius of the suns orbit around the galactic center is approximately 8,300 pc.) ______ yrarrow_forwardAt the average density of a star-forming molecular cloud, about 900 atoms per cm3, determine how large a sphere you would need to encompass mass equal to that of the Sun? Enter the radius of this sphere in light-years. (HINTS: 900 atoms per cm3 corresponds to a density of 1.51×10-18kg/m^3; the mass of the Sun is 2×1030kg) (The volume of a sphere is 4/3 * π * R3) (my previous answer of 6.812 X 1015 was incorrect)arrow_forwardHotter, more massive stars are virtually absent from globular clusters. What does this tell us? a) Only that for some reason, massive stars never formed in these clusters. b) Globular clusters are among the youngest objects in our galaxy. c) Globular clusters are among the oldest objects in the Galaxy.arrow_forward
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