Cosmic Raw Material Fig 20-CO, P.438

Home , NGC 6520, Trapezium Cluster, Xi Cygni

Stars form in greatStars clouds form of gas in and great dust clouds of gas and dust

Slide 1 Cosmic raw material Fig 20-CO, p.438

Chapter Opener The Eagle Nebula (M16) Stars form in great clouds of gas and dust, and this image shows a large region of such cosmic raw material. The gas is visible because, about 2 million years ago, the cloud produced a cluster of bright stars, whose light ionizes the hydrogen gas nearby, causing it to glow. The cluster can be seen just above and to the left of the darker columns of dust at the center of the image. The dark columns or “elephant trunks” of material are seen in much more detail in Figures 20.1 and 20.2. This false-color image was created by combining images taken through filters that select lines of hydrogen alpha (green), oxygen (blue), and sulfur (red). (T.A. Rector, B.A. Wolpa, and OAO/NRAO/AURA/NSF)

1 The Central Region of the Orion Nebula

Slide 2 Fig 20-5a, p.443

Figure 20.5 The Central Region of the Orion Nebula The Orion Nebula harbors some of the youngest stars in the solar neighborhood. At the heart of the nebula is the Trapezium cluster, which includes four very bright stars that provide much of the energy that causes the nebula to glow so brightly. In these images, we see a section of the nebula in visible light (left) and infrared (right). The four bright stars in the center of the visible-light image are the Trapezium stars. Notice that most of the stars seen in the infrared are completely hidden by dust in the left image. (Left Image: Anglo-Australian Observatory; Right Image: 2MASS, IPAC & U. of Massachusetts)

2 The Trapezium cluster In Orion Nebula

The Orion Nebula harbors some of the youngest stars in the solar neighborhood

Slide 3 Fig 20-5b, p.443

3 The Rosette Nebula

A cluster of stars formed recently in the center of this nebula.

Stellar winds and pressure produced by the radiation from these hot stars have blown the gas and dust away from the cluster.

Slide 4 Fig 20-6, p.444

Figure 20.6 Stellar winds and pressure produced by the radiation from these hot stars have blown the gas and dust away from the cluster so that the newly formed stars are easily seen in visible light. The nebula still contains many globules of dust. This star formation region covers an area on the sky that is six times larger than the area covered by the full moon. The colors in this image are not what your eyes would see; our picture was produced by combining images taken in the emission lines of hydrogen alpha (red), oxygen (green), and sulfur (blue). (T.A. Rector, B.A.Wolpa, M. Hanna, and NOAO/AURA/NSF)

4 Star formation can move progressively through a molecular cloud Triggered star-formation

OB associations Groups of Different Ages, Sizes and Densities OB clusters

Slide 5 Fig 20-7, p.444

Figure 20.7 Propagating Star Formation This schematic diagram shows how star formation can move progressively through a molecular cloud. The oldest group of stars lies to the left of the diagram and has expanded because of the motions of individual stars. Eventually the stars in the group will disperse and no longer be recognizable as a cluster. The youngest group of stars lies to the right, next to the molecular cloud. This group of stars is only 1 to 2 million years old. The pressure of the hot, ionized gas surrounding these stars compresses the material in the nearby edge of the molecular cloud and initiates the gravitational collapse that will lead to the formation of more stars.

5 The 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 c) A stellar wind breaks out, confined by the disk to flow out along the two poles of the star. d) Stellar wind sweeps away the cloud material and halts the accumulation of additional material.

Slide 6 Fig 20-8, p.445

Figure 20.8 The 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 accreting envelope is about 5000 astronomical units. The typical diameter of the disk is about 100 AU or slightly larger than the diameter of the orbit of Pluto. (Based on drawings by F. Shu, F. Adams, and S. Lizano)

6 Hubble Images of a Gas Jets Flowing Away from a Protostar

•One million years old •Light from the star itself is blocked by a disk •Thinner material, above and below the central part of the disk reflect light toward us •The material in these disks is flowing outward at speeds up to 960,000 km per hour

Slide 7 Fig 20-9, p.447

Figure 20.9 Hubble Images of a Gas Jets Flowing Away from a Protostar Here we see a protostar, known to us as HH30, because it is a Herbig-Haro Object. The star is at a distance of about 450 LY and only about one million years old. Light from the star itself is blocked by a disk, which is over about 60 billion km in diameter and is seen almost edge-on. Thinner material, above and below the central part of the disk reflect light toward us. Jets are seen emerging in opposite directions and perpendicular to the disk. The material in these disks is flowing outward at speeds up to 960,000 km per hour. The series of three images show changes during a period of six years. Every few months a compact clump of gas is ejected, and its motion outward can be followed. The changes in the brightness in the disk may be due to motions of clouds within the disk that alternately block some of the light and then let it through. This image corresponds to the stage in the life of a protostar shown in Figure 20.8c. (A. Watson, K. Stapelfeldt, J. Krist, C. Burrows, & NASA)

7 Outflows from Protostars

Slide 8 Fig 20-10, p.448

Figure 20.10 Outflows from Protostars These images were taken with the Hubble Space Telescope and show jets flowing outward from newly formed stars. The top image shows HH 47, a protostar 1500 LY away (invisible inside a dusty disk at the left edge of the image), which produces a very complicated jet. The star may actually be wobbling, perhaps because it has a companion. Light from the star illuminates the white region at the left because light can emerge perpendicular to the disk (just as the jet does). At right the jet is plowing into existing clumps of interstellar gas, producing a shock wave that resembles an arrowhead. The white bar is the size of 1000 astronomical units (1000 times the distance between Earth and Sun). The bottom image (HH 1 and 2) shows a classic double-beam jet emanating from a protostar (hidden in a dust disk in the center) in the constellation of Orion. Tip to tip, these jets are more than 1 LY long. The bright regions (first identified by Herbig and Haro) are places where the jet is slamming into a clump of interstellar gas. (C. Burrows, J. Morse, J. Hester, and NASA)

8 Disks Around Protostars

Slide 9 Fig 20-11, p.449

Figure 20.11 Disks Around ProtostarsThese Hubble Space Telescope infrared images show disks around young stars in the constellation of Taurus, in a region about 450 LY away. In some cases we can see the central star (or stars—some are binaries). In other cases, the dark horizontal bands indicate regions where the dust disk is so thick that even infrared radiation from the star embedded within it cannot make its way through. The bright glowing regions are starlight reflected from the upper and lower surfaces of the disk, which are less dense that the central regions. (D. Padgett, W. Brandner, K. Stapelfeldt; IPAC/Caltech/JPL & NASA)

9 Evolutionary Tracks for Contracting Protostars

Stars that lie above the dashed line would typically still be surrounded by infalling material and would be hidden by it.

Slide 10 Fig 20-12, p.450

Figure 20.12 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 numbers next to each dark point on a track are the rough number of years it takes an embryo star to reach that stage. You can see that the more mass a star has, the shorter the time it takes to go through each stage. Stars that lie above the dashed line would typically still be surrounded by infalling material and would be hidden by it.

10 Disks Around Protostars

Range in size from two to eight times the orbit of Pluto

Slide 11 Fig 20-13, p.451

Figure 20.13 Disks Around Protostars These Hubble Space Telescope images show four disks around young stars in the Orion Nebula. The dark, dusty disks are seen silhouetted against the bright backdrop of the glowing gas in the nebula. The size of each image is about 30 times the diameter of our planetary system; this means the disks we see here range in size from two to eight times the orbit of Pluto. The red glow at the center of each disk is a young star, no more than a million years old. These images correspond to a stage in the life of a protostar shown in Figure 20.8d. (M. McCaughrean, C. R. O’Dell, and NASA)

11 Dust Ring Around a Young Star

The image was taken with a coronagraph, a device that covers the bright star itself and allows faint structures around it to be recorded.

Slide 12 Fig 20-14, p.452

Figure 20.14 Dust Ring Around a Young Star This near infrared image from the Hubble Space Telescope shows a narrow ring of dust around the very young star HR 4796A, which lies about 220 LY away in the constellation of Centaurus. The ring is very narrow, spanning the same distance as that which separates Mars from Uranus in our solar system. (The ring, however, is much further from its star, lying at what would be about twice the distance of Pluto from our Sun.) The image was taken with a coronagraph, a device that covers the bright star itself and allows faint structures around it to be recorded. (B. Smith, U. of Hawaii; G. Schneider, U. of Arizona; and NASA)

12 Stellar Evolution Life of Stars – battle between gravitational compression and internal gas pressure

The HR Diagram in General Slide 13

13 Evolutionary Tracks for Stars of Different Masses

from the main sequence through the red-giant or supergiant stage on the H–R diagram

Slide 14 Fig 21-4, p.469

Figure 21.4 Evolutionary Tracks for Stars of Different Masses The solid black lines show the predicted evolution from the main sequence through the red-giant or supergiant stage on the H–R diagram. Each track is labeled with the mass of the star that it is describing. The numbers show how many years each star takes to become a giant after leaving the main sequence. The red line is the zero-age main sequence. (Based on calculations by I. Iben)

14 Stellar Evolution

• Cause of Stellar Evolution • Stellar models • The Evolution of A One Solar Mass Star • Red Giants • Electron Degeneracy • The Helium Flash • Selection Effect • Thermal Pulses • White Dwarfs • Planetary Nebula • The Effect of Mass on Stellar Evolution

Slide 15

15 Cause of Stellar Evolution

• A star evolves because it uses itself for fuel. • Physical characteristics of the star changes depending on how much fuel it has used – Luminosity and color (radius and surface temperature) – The energy production mechanism and energy transport mechanisms – Goal: Hydrostatic equilibrium (balance) at each depth inside the star. • Source of energy – thermonuclear reactions Hydrogen - Helium - Carbon and Oxygen - Magnesium and Neon - Silicon, finally forming Iron • Iron will not fuse, it is not a source of energy

Slide 16

16 The Evolution of A One Solar Mass Star • When the central part of the protostar reaches about 8 million K fusion begins and the protostar becomes a star • Hydrogen into Helium via the proton-proton chain • 80% of star’s total lifetime spent on MS • Eventually the nuclear reactions inside the core stop • core collapses and heats up; the region just outside the core also heats up, the stars expands slightly

Slide 17

17 Stars Evolve, even •Fusion is occurring in the cores of stars on the Main- •H is being converted into He •Since 4 particles are Sequence converted to 1, the pressure drops •The core collapses and heats up. •This heats the outer layers which expand outward • fusion begins in a relatively thin shell surrounding the original core

Slide 18

18 Hydrogen shell source

The core is contracting and heating, H shell is burning, the envelope is expanding and cooling. SlideRadius 19 increases, T decreases – Red Giant

19 Evolution of a Star like the Sun on an H-R Diagram

A – MS to RG

B - a helium flash - readjustment of the star’s internal structure

C - brief period of stability during which helium is fused to carbon and oxygen in the core

D - the central helium is exhausted, the star becomes a giant again

the star has exhausted its inner resources and will soon begin to die

Slide 20 Fig 21-15, p.476

Figure 21.15 Evolution of a Star like the Sun on an H-R Diagram Each stage in the star’s life is labeled with a letter: (A) the star evolves from the main sequence to be a red giant, decreasing in surface temperature and increasing in luminosity; (B) a helium flash occurs at this point, leading to a readjustment of the star’s internal structure and to (C) a brief period of stability during which helium is fused to carbon and oxygen in the core (in the process the star becomes hotter and less luminous than it was as a red giant). (D) After the central helium is exhausted, the star becomes a giant again and moves to higher luminosity and lower temperature. By this time, however, the star has exhausted its inner resources and will soon begin to die. Where the evolutionary track becomes a dashed line, the changes are so rapid, they are difficult to model. (After calculations by Sackmann, Boothroyd, and Kraemer)

20 He fusion in the core

• He core contracting and heating up • T= 100 million K, density = 100 g/cm3 • Core become "electron degenerate“ • does not respond to temperature the way that normal (ideal) gasses do • Electron degenerate gases are rigid, they do not expand when heated • "thermal runaway“ -- EXPLOSION • In the case of a one solar mass star - "Helium Flash“ • The entire He core is quickly involved in fusion forming Carbon and releasing lots of energy. The temperature soars in the core region to about 300 million degrees. At this point the gas reverts back to a normal gas (the degeneracy "lifts") -- a 300 million degree gas. expands...... and cools off until it is quietly fusing helium to Carbon (and Oxygen) at around 100 million degrees • helium main sequence - it is burning He in its core

Slide 21

21 Helium in core of the star runs out

• core resumes its collapse/contraction. • heats as it contracts. • To fuse C and O to Mg and Ne the core temperature must reach 600 million degrees. • For a star the size of the sun this will never happen -does not have the mass needed to cause these kinds of temperatures. • It can be shown that the core mass needed for the fusion of C and O is 1.44 solar masses. This is called the Chandrasekar Limit • The core has again become electron degenerate; the degeneracy pressure is sufficient to stop the collapse of the core. • Outside the central core region two shell sources have become active. A He shell source is present just outside the C/O core, and a H shell source is active beyond that. The H/He envelope is beyond this shell source. • the shell source become very energetic as the inner core heats up. The envelope reacts to this by again expanding and cooling. The star once again becomes brighter and cooler; entering a second giant phase

Slide 22

22 Slide 23

23 Slide 24

24 Slide 25 p.480

Making Connections Relationship Between the Diameter of the Sun and its Age This diagram shows what our best models predict about how the diameter of the Sun will change over long periods of time. Shown on the same scale are the sizes of the orbits of the terrestrial planets. Note that the time-scale along the bottom changes as we move from section to section of the diagram. The planet orbits grow larger as the Sun loses mass. The Earth remains outside the Sun, while Mercury and Venus swallowed up. (Based on calculations by I-J. Sackman & K. Kramer)

25 Evolutionary Track for a Star Like the Sun

Mass loss, the hot inner core is exposed – planetary nebula

White dwarf - will continue to cool slowly for billions of years until all of its remaining store of energy is radiated away

Slide 26 Fig 22-2, p.492

Figure 22.2 Evolutionary Track for a Star Like the Sun This diagram shows the changes in luminosity and temperature for a star with a mass like the Sun’s as it nears the end of its life. After the star becomes a giant again (point A on the diagram), it will lose more and more mass as its core begins to collapse. The mass loss will expose the hot inner core, which will appear at the center of a planetary nebula. In this stage the star moves across the diagram to the left as it becomes hotter and hotter during its collapse (point B on the diagram). At first the luminosity remains nearly constant, but as the star begins to cool off, it becomes less and less bright (point C). It is now a white dwarf and will continue to cool slowly for billions of years until all of its remaining store of energy is radiated away. (This model assumes the Sun will lose about 46 percent of its mass during the giant stages; based on calculations by Sackmann, Boothroyd, and Kraemer.)

26 Slide 27 Fig 22-3, p.493

Figure 22.3 White Dwarf in a Young Cluster The cluster of stars shown in this Hubble image is in a neighboring galaxy called the Large Magellanic Cloud, at a distance of about 160,000 LY. The cluster is about 40 million years old. When astronomers construct its H–R diagram, they find that stars with masses of about 7.5 MSun are just beginning to evolve away from the main sequence. Yet the circled star is a white dwarf that is a member of the cluster. Since a star can only become a white dwarf if it has less than 1.4 MSun, this star must have lost more than six solar masses between the time it left the main sequence and the time it completed the giant phases of its evolution. (R. Elson and R. Sword, NASA)

27 Current models indicate that stars with initial masses of less than 8 solar Slide 28masses end their lives as WD's of various masses

28 Observational Evidence Low-mass stars A – MS (main sequence turn off ), fusing hydrogen into helium in the core of the star

B – RG branch - star runs out of hydrogen in the core, fusion moves away from the core, and into an expanding shell around the core

C – tip of RGB - helium created in the shell around the core, drops onto the core, causing it to heat up. When that core gets hot enough ( 100,000,000 K), it begins to fuse helium into carbon, helium flash , source of energy moves into the core, pushes the hydrogen fusing shell outwards, which cools and shuts off.

Slide 29

29 D – HB - fusing helium into carbon, in the core of the star

E - The Schwarzschild space Low mass stars

The asymptotic giant branch (AGB) - Stars on the HB will run out of helium in their cores eventually, begins to fuse helium into carbon in a shell, and the star expands once again

Thermal Pulses - The star is gently blowing its envelope into space - very hot, exposed, central core of electron degenerate carbon and oxygen surrounded by a nebula that consists of the old stellar envelope

F - white dwarf stars – stars that have finished all the nuclear fusion they can do Slide 30

30 Slide 31 Table 22-1, p.495

31 Evolution of Massive Stars

• If M> 8 Solar Masses - SN and Black Holes • Fuse C&O, forming Mg &Ne, than to silicon, and iron • Iron will not fuse, it is not a source of energy. • The core continues to collapse and heat until the iron nuclei photodisintigrate. (The iron nuclei separate into neutrons and protons). • The core continues to collapse until the protons and electron in the core combine, forming neutrons. • At this point the core is almost entirely neutrons and neutron degeneracy pressure arises. • If the core has a mass greater than about 3 solar masses the neutron degeneracy pressure is insufficient to stop the collapse and the core becomes a black hole. • If the mass is less than 3 solar masses the neutron core "firms up" and the rest of the in falling material runs into it and bounces off in an event called a Type II Supernova

Slide 32

32 Structure of an Old Massive Star

Slide 33 Fig 22-4, p.494

Figure 22.4 Structure of an Old Massive Star Just before its final gravitational collapse, a massive star resembles an onion. The iron core is surrounded by layers of silicon and sulfur, oxygen, neon, carbon mixed with some oxygen, helium, and finally hydrogen. (Note that this diagram is not precisely to scale, but is meant to convey the general idea of what such a star would be like.)

33 Slide 34

34 A Star Explodes

Supernova 1987A in the Large Magellanic Cloud

Slide 35 Fig 22-5, p.495

Figure 22.5 A Star Explodes We see before-and-after pictures of the field around Supernova 1987A in the Large Magellanic Cloud. An arrow points to the star that exploded. It’s easy to put such an arrow there after the explosion; astronomers can only wish such arrows appeared ahead of time so we could know which star was next. The difference in image quality between these pictures is an effect of the Earth’s atmosphere, which was steadier when the plates used to make the pre-supernova picture were taken. (Anglo-Australian Telescope Board)

35 The Change in the Brightness of SN 1987A with Time

Slide 36 Fig 22-8, p.500

Figure 22.8 The Change in the Brightness of SN 1987A with Time Note how the rate of decline of the supernova’s light slowed between days 40 and 500. During this time the brightness was mainly due to the energy emitted by newly formed (and fast-decaying) radioactive elements. (Courtesy N. Suntzeff/CTIO)

36 Slide 37 Table 22-3, p.502

37 The Ant Nebula – star losing mass

During the later phases of stellar evolution, stars expel some of their mass, which returns to the interstellar medium to form new stars

Slide 38 Fig 21-CO, p.464

Opening Figure. Here is a beautiful image of a star losing mass taken with the Hubble Space Telescope. This planetary nebula is known as Mz 3 or the Ant Nebula and is located at a distance of about 3000 light years from the Sun. We see a central star that has ejected mass preferentially in two opposite directions. The object is about 1.6 LY long. The image is color coded so that red corresponds to an emission line of sulfur; green to nitrogen; blue to hydrogen; and blue/violet to oxygen. (NASA, ESA, and The Hubble Heritage Team)

38 Stars in the Constellation of Sagittarius

This snapshot shows a yellowish population of older stars with a small cluster of younger bluish stars

Slide 39 Fig 21-1, p.466

Figure 21.1 Stars in the Constellation of Sagittarius This snapshot shows a yellowish population of older stars with a small cluster of younger bluish stars (NGC 6520), as well as a dark cloud (Barnard 86) that blocks the light from stars behind it. (© Anglo-Australian Telescope Board)

39 Slide 40 Table 21-1, p.467

40 Relative Sizes of Stars

Xi Cygni

Delta Boötis Sun

Slide 41 Fig 21-2, p.468

Figure 21.2 Relative Sizes of Stars This computer-generated graphic shows the size of the Sun (yellow), compared to the size of Delta Boötis, a giant star (orange) and Xi Cygni, a supergiant (red). The sizes of the other stars were measured using the Palomar Testbed Interferometer, an instrument that allows astronomers to make out much finer detail (greater resolution) by connecting together two telescopes 110 meters apart.(G. van Belle, JPL)

41 Slide 42 Table 21-2, p.468

42 The Supergiant Betelgeuse

Extremely extended atmosphere

Image taken in ultraviolet light with the Hubble Space Telescope—the first direct image ever made of the surface of another star

Slide 43 Fig 21-3, p.468

Figure 21.3 The Supergiant Betelgeuse This star is located in the constellation of Orion (see Figure 20.3). Here we see an image taken in ultraviolet light with the Hubble Space Telescope—the first direct image ever made of the surface of another star. As shown by the bars at the bottom, Betelgeuse has an extended atmosphere so large that, if it were at the center of our solar system, it would stretch past the orbit of Jupiter. (A. Dupree, R. Gilliland, and NASA)

43 Slide 44 Omega Centauri - several million stars Fig 21-5, p.470

Figure 21.5 Omega Centauri Located about 17,000 LY away, the globular cluster Omega Centauri is the most massive globular cluster in our Galaxy. It contains several million stars. (Photo by David Malin; © Anglo- Australian Observatory)

44 The Jewel Box

bright yellow supergiant and hot blue main-sequence stars

Slide 45 Fig 21-7, p.471

Figure 21.7 The Jewel Box (NGC 4755) This open cluster of young, bright stars is at a distance of about 8000 LY from the Sun. Note the contrast in color between the bright yellow supergiant and the hot blue main-sequence stars. The name comes from its 19th century description by John Herschel as “a casket of variously colored precious stones.” (Photo by David Malin; © Anglo-Australian Observatory)

45 From the theory:

Young Cluster H-R Diagram

Slide 46 Fig 21-8, p.472

Figure 21.8 Young Cluster H-R Diagram We see an H–R diagram for a hypothetical cluster at an age of 3 million years. Note that the high-mass (high-luminosity) stars have already arrived at the main-sequence stage of their lives, while the lower-mass (lower-luminosity) stars are still to the right of the zero-age main sequence, not yet hot enough to begin fusion of hydrogen.

46 The Young Cluster NGC 2264

Slide 47 Fig 21-9, p.472

Figure 21.9 The Young Cluster NGC 2264 Located about 2500 LY from us, this region of newly formed stars is a complex mixture of red hydrogen gas ionized by hot embedded stars, dark obscuring dust lanes, and brilliant young stars. (Photo by David Malin; © Anglo-Australian Telescope Board)

47 From observations:

H-R diagram for Cluster NGC 2264

Slide 48 Fig 21-10, p.472

Figure 21.10 H-R diagram for Cluster NGC 2264 Compare to Figure 21.8; although the points scatter a bit more here, the theoretical and observational diagrams are remarkably—and satisfyingly—similar. (Data by M. Walker)

48 The Open Star Cluster NGC 3293

Slide 49 Fig 21-11, p.473

Figure 21.11 The Open Star Cluster NGC 3293 All the stars in such clusters form at about the same time. The most massive stars, however, exhaust their nuclear fuel more rapidly and hence evolve more quickly than stars of low mass. As stars evolve, they become redder. The bright orange star in NGC 3293 is the member of the cluster that has evolved most rapidly. (Photo by David Malin; © Anglo-Australian Telescope Board)

49 H-R Diagram for Cluster M41

Slide 50 Fig 21-12, p.473

Figure 21.12 H-R Diagram for Cluster M41 This cluster is older than NGC 2264 (see Figure 21.10) and contains several red giants. Some of its more massive stars are no longer close to the zero-age main sequence (blue line).

50 H–R diagram for a hypothetical cluster at an age of 4.24 billion years

Slide 51 Fig 21-13, p.474

Figure 21.13 H-R Diagram for an Older Cluster We see the H–R diagram for a hypothetical cluster at an age of 4.24 billion years. Note that most of the stars on the upper part of the main sequence have now turned off toward the red-giant region.

51 H-R Diagram for Cluster 47 Tucanae

Only the lower portion of the main sequence, still remains in this old cluster

Slide 52 Fig 21-14, p.474

Figure 21.14 H-R Diagram for Cluster 47 Tucanae This H–R diagram is for the globular cluster 47 Tucanae (which you can see in Figure 28.3). Note that the scale of luminosity is different from those of the other H–R diagrams in this chapter. We are focusing on the lower portion of the main sequence, the only part where stars still remain in this old cluster.(Data by J. Hesser and collaborators)

52 Slide 53 Fig 21-16, p.478

Figure 21.16 A Gallery of Planetary Nebulae We show off the capabilities of the Hubble Space Telescope (HST) with a series of beautiful images depicting some intriguing planetary nebulae: (a) Perhaps the best known planetary is the Ring Nebula (M57), located about 2000 LY away in the constellation of Draco. The ring is about a 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. Blue isolates emission from very hot helium, which is located very close to the star; red shows emission from ionized nitrogen, which is radiated by the coolest gas farthest from the star; and green represents oxygen emission, which is produced at intermediate temperatures and is at an intermediate distance from the star. (H. Bond & Hubble Heritage Team) (b) In this planetary nebula, we see that 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 at a distance of about 2100 LY in the constellation Ophiuchus. (B. Balick, V. Icke, G. Mellema, and NASA) (c) In this image of the planetary nebula NGC 6751, blue regions mark the hottest gas, which forms a ring around the central star. Orange and red show the locations of cooler gas. The origin of these cool streamers is not known, but their shape indicates that they are affected by radiation and 53 stellar winds from the hot star at the center The temperature of the star is Slide 54 Fig 21-17, p.479

Figure 21.17 A Model to Explain the Many Different Shapes of Planetary Nebulae It may be that the many different shapes that we see in a gallery of planetary nebulae can be explained by a single model, viewed from different directions. In this model, the hot central star is surrounded by a thick torus (or donut) of gas. The star’s wind cannot flow out into space in the direction of the torus but can escape freely in directions perpendicular it. If we look along the direction of the flow, we will see a spherical shell of gas (like looking directly down into an empty ice cream cone). If we look along the equator of the torus, we will see both outflows. At in-between angles, we may see a very complex shape. (Based on a diagram by Sun Kwok, U. of Calgary, and the staff of Sky & Telescope magazine.)

54 Slide 55 Fig 21-16a, p.478

55 Slide 56 Fig 21-16b, p.478

Figure 21.16 A Gallery of Planetary Nebulae We show off the capabilities of the Hubble Space Telescope (HST) with a series of beautiful images depicting some intriguing planetary nebulae: (b) In this planetary nebula, we see that 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 at a distance of about 2100 LY in the constellation Ophiuchus. (B. Balick, V. Icke, G. Mellema, and NASA)

56 Slide 57 Fig 21-16c, p.478

Figure 21.16 A Gallery of Planetary Nebulae We show off the capabilities of the Hubble Space Telescope (HST) with a series of beautiful images depicting some intriguing planetary nebulae: (c) In this image of the planetary nebula NGC 6751, blue regions mark the hottest gas, which forms a ring around the central star. Orange and red show the locations of cooler gas. The origin of these cool streamers is not known, but their shape indicates 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 own solar system. The nebula is about 6500 LY from us and is located in the constellation of Aquila. (NASA, The Hubble Heritage Team and STScI/AURA)

57 Slide 58 Fig 21-16d, p.478

Figure 21.16 A Gallery of Planetary Nebulae We show off the capabilities of the Hubble Space Telescope (HST) with a series of beautiful images depicting some intriguing planetary nebulae: (d) This image of the planetary nebula NGC 7027 shows several stages of mass loss. Faint blue concentric shells surrounding the central region identify 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 at a distance of about 3000 LY in the direction of the constellation Cygnus. (H. Bond/STSci and NASA)

58 Slide 59 Fig 21-18, p.482

Figure 21.18 Eta Carinae With a mass at least 100 times that of the Sun, the hot supergiant Eta Carinae is one of the most massive stars known. This highly computer-processed image from the Hubble Space Telescope records the two giant lobes and equatorial disk of material it has ejected in the course of its evolution. The pink outer region is material ejected in an outburst seen in 1843, the largest such mass-loss event that any star is known to have survived. Moving away from the star at a speed of about 1000 km/s, it is rich in nitrogen and other elements formed in the interior of the star. The inner blue-white region is material ejected at lower speeds and thus still closer to the star. It appears blue-white because it contains dust and reflects the light of Eta Carinae, whose luminosity is four million times that of our Sun. (J. Morse, U. of Colorado, and NASA)