Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 21, Problem 18E
Observations suggest that it takes more than 3 million years for the dust to begin clearing out of the inner regions of the disks surrounding protostars. Suppose this is the minimum time required to form a planet. Would you expect to find a planet around a 10-MSunstar? (Refer to Figure 21.12.)
Figure 21.12 Evolutionary Tracks for Contracting Protostars. Tracks are plotted on the H−R diagram to show how stars of different masses change during the early parts of their lives. The number next to each dark point on a track is the rough number of years it takes an embryo star to reach that stage (the numbers are the result of computer models and are therefore not well known). Note that the surface temperature (K) on the horizontal axis increases toward the left. You can see that the more mass a star has, the shorter time it takes to go through each stage. Stars above the dashed line are typically still surrounded by infalling material and are hidden by it.
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Suppose two protostars form at the same time, one with a mass of 0.5MSunSun
[Select ALL answers that are true in alphabetical order]A) The 10MSun protostar will have a smaller change in surface temperature during this phase than the 0.5MSun protostar.B) The 10MSun protostar will reach the main sequence cooler and fainter than the 0.5MSun protostar.C) The 10MSun star will end its main-sequence life before the 0.5MSun star even completes its protostar stage.D) The 10MSun protostar will have a smaller change in luminosity during the sequence shown than the 0.5MSun protostar.E) The 10MSun protostar will be much more luminous than the 0.5MSun protostar.
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
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O O O O
Use the following formula (fitted to data)
M = -4x10-13n
gR
Mo/year
for the mass loss of asymptotic giant branch stars to:
a) explain why L, g (gravity on surface), and R enter the equation the way they do (nominator
or denominator).
b) show that the expression for M is equivalent to
LR
M = -4x10-13n
Mo/year
M
c) estimate the mass loss rate of a star with M = 1 Mo, L = 7000 Lo, T = 3000 K. Assume
n = 1 and use the Stefan-Boltzmann equation to calculate R (in Ro).
Chapter 21 Solutions
Astronomy
Ch. 21 - Give several reasons the Orion molecular cloud is...Ch. 21 - Why is star formation more likely to occur in cold...Ch. 21 - Why have we learned a lot about star formation...Ch. 21 - Describe what happens when a star forms. Begin...Ch. 21 - Describe how the T Tauri star stage in the life of...Ch. 21 - Look at the four stages shown in Figure 21.8. In...Ch. 21 - The evolutionary track for a star of 1 solar mass...Ch. 21 - Two protostars, one 10 times the mass of the Sun...Ch. 21 - Compare the scale (size) of a typical dusty disk...Ch. 21 - Why is it so hard to see planets around other...
Ch. 21 - Why did it take astronomers until 1995 to discover...Ch. 21 - Which types of planets are most easily detected by...Ch. 21 - List three ways in which the exoplanets we have...Ch. 21 - List any similarities between discovered...Ch. 21 - What revisions to the theory of planet formation...Ch. 21 - Why are young Jupiters easier to see with direct...Ch. 21 - A friend of yours who did not do well in her...Ch. 21 - Observations suggest that it takes more than 3...Ch. 21 - Suppose you wanted to observe a planet around...Ch. 21 - Why were giant planets close to their stars the...Ch. 21 - Exoplanets in eccentric orbits experience large...Ch. 21 - When astronomers found the first giant planets...Ch. 21 - An exoplanetary system has two known planets....Ch. 21 - Kepler’s third law says that the orbital period...Ch. 21 - Calculate the transit depth for an M dwarf star...Ch. 21 - If a transit depth of 0.00001 can be detected with...Ch. 21 - What fraction of gas giant planets seems to have...
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- Look at the four stages shown in Figure 21.8. In which stage(s) can we see the star in visible light? In infrared radiation? Figure 21.8 Formation of a Star. (a) Dense cores form within a molecular cloud. (b) A protostar with a surrounding disk of material forms at the center of a dense core, accumulating additional material from the molecular cloud through gravitational attraction. (c) A stellar wind breaks out but is confined by the disk to flow out along the two poles of the star. (d) Eventually, this wind sweeps away the cloud material and halts the accumulation of additional material, and a newly formed star, surrounded by a disk, becomes observable. These sketches are not drawn to the same scale. The diameter of a typical envelope that is supplying gas to the newly forming star is about 5000 AU. The typical diameter of the disk is about 100 AU or slightly larger than the diameter of the orbit of Pluto.arrow_forwardA 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_forwardYou can estimate the age of the planetary nebula in image (c) in Figure 22.18. The diameter of the nebula is 600 times the diameter of our own solar system, or about 0.8 light-year. The gas is expanding away from the star at a rate of about 25 mi/s. Considering that distance=velocitytime , calculate how long ago the gas left the star if its speed has been constant the whole time. Make sure you use consistent units for time, speed, and distance. Figure 22.18 Gallery of Planetary Nebulae. This series of beautiful images depicting some intriguing planetary nebulae highlights the capabilities of the Hubble Space Telescope. (a) Perhaps the best known planetary nebula is the Ring Nebula (M57), located about 2000 lightyears away in the constellation of Lyra. The ring is about 1 light-year in diameter, and the central star has a temperature of about 120,000 °C. Careful study of this image has shown scientists that, instead of looking at a spherical shell around this dying star, we may be looking down the barrel of a tube or cone. The blue region shows emission from very hot helium, which is located very close to the star; the red region isolates emission from ionized nitrogen, which is radiated by the coolest gas farthest from the star; and the green region represents oxygen emission, which is produced at intermediate temperatures and is at an intermediate distance from the star. (b) This planetary nebula, M2-9, is an example of a butterfly nebula. The central star (which is part of a binary system) has ejected mass preferentially in two opposite directions. In other images, a disk, perpendicular to the two long streams of gas, can be seen around the two stars in the middle. The stellar outburst that resulted in the expulsion of matter occurred about 1200 years ago. Neutral oxygen is shown in red, once-ionized nitrogen in green, and twice-ionized oxygen in blue. The planetary nebula is about 2100 light-years away in the constellation of Ophiuchus. (c) In this image of the planetary nebula NGC 6751, the blue regions mark the hottest gas, which forms a ring around the central star. The orange and red regions show the locations of cooler gas. The origin of these cool streamers is not known, but their shapes indicate that they are affected by radiation and stellar winds from the hot star at the center. The temperature of the star is about 140,000 °C. The diameter of the nebula is about 600 times larger than the diameter of our solar system. The nebula is about 6500 light-years away in the constellation of Aquila. (d) This image of the planetary nebula NGC 7027 shows several stages of mass loss. The faint blue concentric shells surrounding the central region identify the mass that was shed slowly from the surface of the star when it became a red giant. Somewhat later, the remaining outer layers were ejected but not in a spherically symmetric way. The dense clouds formed by this late ejection produce the bright inner regions. The hot central star can be seen faintly near the center of the nebulosity. NGC 7027 is about 3000 light-years away in the direction of the constellation of Cygnus. (credit a: modification of work by NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration; credit b: modification of work by Bruce Balick (University of Washington), Vincent Icke (Leiden University, The Netherlands), Garrelt Mellema (Stockholm University), and NASA; credit c: modification of work by NASA, The Hubble Heritage Team (STScI/AURA); credit d: modification of work by H. Bond (STScI) and NASA)arrow_forward
- Give several reasons the Orion molecular cloud is such a useful “laboratory” for studying the stages of star formation.arrow_forwardYou can use the equation in Exercise 22.34 to estimate the approximate ages of the clusters in Figure 22.10, Figure 22.12, and Figure 22.13. Use the information in the figures to determine the luminosity of the most massive star still on the main sequence. Now use the data in Table 18.3 to estimate the mass of this star. Then calculate the age of the cluster. This method is similar to the procedure used by astronomers to obtain the ages of clusters, except that they use actual data and model calculations rather than simply making estimates from a drawing. How do your ages compare with the ages in the text? Figure 22.10 NGC 2264 HR Diagram. Compare this HR diagram to that in Figure 22.8; although the points scatter a bit more here, the theoretical and observational diagrams are remarkably, and satisfyingly, similar. Figure 22.12 Cluster M41. (a) Cluster M41 is older than NGC 2264 (see Figure 22.10) and contains several red giants. Some of its more massive stars are no longer close to the zero-age main sequence (red line). (b) This ground-based photograph shows the open cluster M41. Note that it contains several orange-color stars. These are stars that have exhausted hydrogen in their centers, and have swelled up to become red giants. (credit b: modification of work by NOAO/AURA/NSF) Figure 22.13 HR Diagram for an Older Cluster. We see the HR diagram for a hypothetical older cluster at an age of 4.24 billion years. Note that most of the stars on the upper part of the main sequence have turned off toward the red-giant region. And the most massive stars in the cluster have already died and are no longer on the diagram. Characteristics of Main-Sequence Starsarrow_forwardDescribe the evolution of a star with a mass similar to that of the Sun, from the protostar stage to the time it first becomes a red giant. Give the description in words and then sketch the evolution on an HR diagram.arrow_forward
- Stars that have masses approximately 0.8 times the mass of the Sun take about 18 billion years to turn into red giants. How does this compare to the current age of the universe? Would you expect to find a globular cluster with a main-sequence turnoff for stars of 0.8 solar mass or less? Why or why not?arrow_forwardWhy is star formation more likely to occur in cold molecular clouds than in regions where the temperature of the interstellar medium is several hundred thousand degrees?arrow_forwardThe evolutionary track for a star of 1 solar mass remains nearly vertical in the HR diagram for a while (see Figure 21.12). How is its luminosity changing during this time? Its temperature? Its radius? Figure 21.12 Evolutionary Tracks for Contracting Protostars. Tracks are plotted on the HR diagram to show how stars of different masses change during the early parts of their lives. The number next to each dark point on a track is the rough number of years it takes an embryo star to reach that stage (the numbers are the result of computer models and are therefore not well known). Note that the surface temperature (K) on the horizontal axis increases toward the left. You can see that the more mass a star has, the shorter time it takes to go through each stage. Stars above the dashed line are typically still surrounded by infalling material and are hidden by it.arrow_forward
- The star cluster shown in this image contains a few red giants as well as main-sequence stars ranging from spectral type B to M. Discuss the likelihood that exoplanets orbiting any of these stars might be home to life. (Hint: Estimate the age of the cluster.)arrow_forwardAs 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_forwardsuppose a planetary nebula is 2.8 pc in diameter, and doppler shifts in its spectrum show that the planetary nebula is 33 km/s. how old is the planetary nebula? 1 pc= 3.1 ×10^13 km and 1 yr= 3.2 × 10^7sarrow_forward
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