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- 2. WHAT DO YOU THINK? Do all galaxies have spiral arms? Are galaxies isolated objects? Are all other galaxies moving away from the Milky Way?
- 3. You will discover…You will discover… How galaxies are categorized by their shapes. That galaxies contain huge amounts of dark matter. That galaxies are found in clusters. How some galaxies merge while others devour their neighbors. That the universe is expanding.
- 4. Types of GalaxiesTypes of Galaxies 1.1. SpiralSpiral 2.2. Barred SpiralBarred Spiral 3.3. EllipticalElliptical 4.4. IrregularIrregular
- 5. Hubble’s Diagram of Galaxy TypesHubble’s Diagram of Galaxy Types
- 6. 1. Spiral Galaxies1. Spiral Galaxies Type Sa Type Sb Type Sc
- 8. Spiral Galaxies Seen Edge-onSpiral Galaxies Seen Edge-on M104: Sa galaxy NGC 891: Sb galaxy NGC 4631: Sc galaxy
- 9. Variety in Spiral ArmsVariety in Spiral Arms M33: A Spiral Galaxy with Flocculent Spiral Arms – created by explosions. M74: a Grand Design Spiral Galaxy – created by waves, like ripples in water.
- 10. 2. Barred Spiral Galaxies2. Barred Spiral Galaxies M58: SBa galaxy M83: SBb galaxy NGC 1365: SBc galaxy
- 11. 3. Elliptical Galaxies3. Elliptical Galaxies M105: E0 galaxy M49: E4 galaxy NGC 4526: E7 galaxy
- 12. 4. Irregular Galaxies4. Irregular Galaxies Large Magellanic Cloud, Irr 1 galaxy NGC 4485 (Irr 2) and NGC 4490 (Sc) galaxies
- 13. Galaxies are Clumped in SpaceGalaxies are Clumped in Space Galaxies occur in groups calledGalaxies occur in groups called ClustersClusters. The. The galaxies in a Cluster are bound by gravity togalaxies in a Cluster are bound by gravity to each other, and can collide.each other, and can collide. Our Galaxy belongs to a Cluster called “TheOur Galaxy belongs to a Cluster called “The Local Group.”Local Group.” Clusters of galaxies occur in bigger groupsClusters of galaxies occur in bigger groups calledcalled SuperclustersSuperclusters. Most Superclusters are. Most Superclusters are not gravitationally bound units like Clusters are.not gravitationally bound units like Clusters are. All the Clusters are moving away from eachAll the Clusters are moving away from each other as the Universe expandsother as the Universe expands..
- 14. A Cluster of GalaxiesA Cluster of Galaxies The Fornax Cluster of Galaxies
- 15. The Local Group – Our ClusterThe Local Group – Our Cluster Our Galaxy belongs to a poor, irregular (wimpy) cluster – consisting of about 40 galaxies (including M31 Andromeda) – called the Local Group.
- 16. Colliding GalaxiesColliding Galaxies Galaxies that belong to the same ClusterGalaxies that belong to the same Cluster can collide.can collide. Sometimes these galaxies pass throughSometimes these galaxies pass through each other, and sometimes they combine.each other, and sometimes they combine. TheThe individual starsindividual stars in the collidingin the colliding galaxiesgalaxies do not hit each otherdo not hit each other, but the, but the huge clouds of gas and dust do collidehuge clouds of gas and dust do collide..
- 17. Colliding GalaxiesColliding Galaxies Pairs of colliding galaxies often exhibit long “antennae” of stars ejected by the collision.
- 18. Colliding Galaxies “Mano a Mano”Colliding Galaxies “Mano a Mano” NGC 2207 (right) and IC 2163 are orbiting and gravitationally distorting each other.
- 19. Our Local SuperclusterOur Local Supercluster and Other Superclustersand Other Superclusters Our Local Group (cluster) is at the center of the diagram. Our Local Supercluster extends out to the Virgo Cluster.
- 20. Beyond Superclusters –Beyond Superclusters – Filamentary Structure in the UniverseFilamentary Structure in the Universe 2-Micron All Sky Survey (Infrared) – 1.6 million galaxies shown.
- 21. Beyond Superclusters –Beyond Superclusters – Filamentary Structure in the UniverseFilamentary Structure in the Universe Distribution map of 62,559 galaxies in two wedges extending out in opposite directions from the Earth (done with galaxy redshifts).
- 22. The Universe is ExpandingThe Universe is Expanding The Redshift of Superclusters shows us thatThe Redshift of Superclusters shows us that the Universe is expanding. This Redshift isthe Universe is expanding. This Redshift is called the “called the “Cosmological RedshiftCosmological Redshift,” because,” because it isit is caused by the expansion of spacecaused by the expansion of space.. TheThe farther awayfarther away a galaxy is from us, thea galaxy is from us, the faster it movesfaster it moves away from us:away from us: GALAXY SPEED = GALAXY DISTANCE xGALAXY SPEED = GALAXY DISTANCE x HUBBLE’S CONSTANT (HHUBBLE’S CONSTANT (H00).). This is called “Hubble’s Law,” after EdwinThis is called “Hubble’s Law,” after Edwin Hubble, who discovered it.Hubble, who discovered it.
- 23. Hubble’s LawHubble’s Law TheThe farther awayfarther away a galaxy is from us, thea galaxy is from us, the faster it movesfaster it moves away from us:away from us: GALAXY SPEED = GALAXY DISTANCE x HUBBLE’S CONSTANT (HGALAXY SPEED = GALAXY DISTANCE x HUBBLE’S CONSTANT (H00).).
- 24. The Hubble Telescope looks back to when theThe Hubble Telescope looks back to when the Universe was very young.Universe was very young.
- 25. HST – Galaxies 12.5 Billion LY AwayHST – Galaxies 12.5 Billion LY Away
- 26. HST – Galaxies >13 Billion LY AwayHST – Galaxies >13 Billion LY Away
- 27. WHAT DID YOU THINK? Do all galaxies have spiral arms? No. Galaxies may be either spiral, barred spiral, elliptical, or irregular. Only spirals and barred spirals have arms. Are galaxies isolated objects? No. Galaxies are grouped in clusters, and clusters are grouped in superclusters. Are all other galaxies moving away from the Milky Way? All galaxies except those in our Local Group (cluster) are receding from us. Some local galaxies are actually moving toward us.
Editor's Notes
- Edwin Hubble is one of Time magazine’s most important people of the 20th Century: www.time.com/time/time100/scientist/profile/hubble.html . Hubble was also on the cover of the February 9, 1948 issue of Time. A web site devoted to Hubble’s life and work is at www.edwinhubble.com . SEDS maintains an excellent database of Messier objects: www.seds.org/messier/ .
- FIGURE 16-12 Hubble’s Tuning Fork Diagram Hubble summarized his classification scheme for galaxies with this tuning fork diagram. Elliptical galaxies are classified by how oval they appear, while spirals and barred spirals are classified by the sizes of their central bulges and the correlated winding of their spiral arms. An S0 or SB0 galaxy, also called a lenticular galaxy, is an intermediate type between ellipticals and spirals. It has a disk but no spiral arms.
- FIGURE 16-1 Spiral Galaxies (Nearly Face-on Views) Edwin Hubble classified spiral galaxies according to the tightness of the spiral arms and the size of the nuclear bulge. Sa galaxies have the largest nuclear bulges and the most tightly wound spiral arms, while Sc galaxies have the smallest nuclear bulges and the least tightly wound arms. The images are different colors because they were taken through filters passing different colors. (left: NASA/Hubble Space Institute; middle: Robert Gendler; right: Anglo-Australian Observatory)
- FIGURE 16-2 Andromeda (M32) Andromeda is a beautiful spiral galaxy and is the only galaxy visible to the naked eye from the Earth’s northern hemisphere. Without a telescope, it appears to be a fuzzy blob in the constellation of Andromeda. Located only 0.9 Mpc (2.9 Mly) from us, Andromeda is gravitationally bound to the Milky Way, and it covers an area in the sky roughly 5 times as large as the full Moon. Two other galaxies, M32 and M110), are also labeled on this photograph. The points of light peppering the image are stars in our Galaxy. (Bill and Sally Fletcher/Tom Stack and Associates)
- FIGURE 16-3 Spiral Galaxies Seen Nearly Edge-on from the Milky Way (a) Because of its large nuclear bulge, this galaxy is classified as an Sa. If we could see it face-on, the spiral arms would be tightly wound around a voluminous bulge. (b) Note the smaller nuclear bulge in this Sb galaxy. (c) At visible wavelengths, interstellar dust obscures the relatively insignificant nuclear bulge of this Sc galaxy. (a: European Southern Observatory; b: Anglo-Australian Observatory/David Malin Images; c: Dr. Rudy Schild, Smithsonian Astrophysical Observatory)
- FIGURE 16-4 Variety in Spiral Arms The differences in spiral galaxies suggest that at least two mechanisms create spiral arms. (a) This flocculent spiral galaxy has fuzzy, poorly defined spiral arms.
- FIGURE 16-8 Barred Spiral Galaxies As with spiral galaxies, Edwin Hubble classified barred spirals according to the tightness of their spiral arms (which correlates with the sizes of their nuclear bulges). SBa galaxies have the most tightly wound spirals and largest nuclear bulges, SBb have moderately tight spirals and medium-sized nuclear bulges, while SBc galaxies have the least tightly wound spirals and the smallest nuclear bulges. (a: Johan H. Knapen and N. K. Szymanek, University of Hertfordshire; b: ESO, European Southern Observatory; c: Jean-Charles Cuillandre/CFHT/ Photo Researchers, Inc.)
- FIGURE 16-11 Elliptical Galaxies Hubble classified elliptical galaxies according to how round or elongated they appear. An E0 galaxy is round; a very elongated elliptical galaxy is an E7. Three examples are shown here. (a: J. D. Wray, McDonald Observatory; b & c: © 1999 Princeton University Press/Zsolt Frei and James E. Gunn)
- FIGURE 16-13 Irregular Galaxies (a) At a distance of only 179,000 ly, the Large Magellanic Cloud (LMC), an Irr I irregular galaxy, is the third closest known companion of our Milky Way Galaxy. (The Milky Way’s closest known companion, the Canis Major Dwarf, is shown in Figure 15- 16.) About 62,000 ly across, the LMC spans 22% across the sky, about 44 times the angular size of the full Moon. Note the huge a Large Magellanic Cloud, an Irr 1 galaxy b NGC 4485 (Irr 2) and NGC 4490 (Sc) galaxies H II region (called the Tarantula Nebula or 30 Doradus) toward the left side of this image. Its diameter of 800 ly and mass of 5 million Suns makes it the largest known H II region. (b) The small irregular (Irr II) galaxy NGC 4485 (bottom galaxy) interacts with the highly distorted Sc galaxy NGC 4490, also called the Cocoon Galaxy. This pair is located in the constellation Canes Venatici. (a: Anglo-Australian Observatory; b: Hoher Observatory)
- FIGURE 16-14 A Cluster of Galaxies This group of galaxies, called the Fornax cluster, is about 60 million light-years from Earth. Both elliptical and spiral galaxies are easily identified. The barred spiral galaxy at the lower left is NGC 1365, the largest and most impressive member of the cluster. For a closer view of NGC 1365, see Figure 16-8. (Anglo-Australian Observatory, photos by David Malin, © 1984 Royal Observatory, Edinburgh)
- FIGURE 16-18 The Local Group Our Galaxy belongs to a poor, irregular cluster consisting of about 40 galaxies called the Local Group. This map shows the distribution of about threequarters of the galaxies. The Andromeda Galaxy (M31) is the largest and most massive galaxy in the Local Group. The second largest is the Milky Way itself. M31 and the Milky Way are each surrounded by a dozen satellite galaxies. The recently discovered Canis Major Dwarf Galaxy is the Milky Way’s nearest known neighbor.
- FIGURE 16-25 Interacting and Colliding Galaxies (a) Pairs of colliding galaxies often exhibit long “antennae” of stars ejected by the collision. This particular system is known as NGC 4676 or “the Mice” (because of its tails of stars and gas). It is 300 million ly from Earth in the constellation Coma Berenices. The collision has stimulated a firestorm of new star formation, as can be seen in the bright blue regions. Mass can also be seen flowing between the two galaxies, which will eventually merge. (a: NASA, H. Ford/JHU, G. Illingworth/ UCSC/Lick, M. Clampin/STScI, G. Hartig/STScI, The ACS Science Team, and ESA; b: NASA)
- FIGURE 16-25 Interacting and Colliding Galaxies. (b) These two galaxies, NGC 2207 (right) and IC 2163, are orbiting and tidally distorting each other. Their most recent close encounter occurred 40 Myr ago when the two were perpendicular to each other and about one galactic diameter apart. Computer simulations indicate that they should eventually coalesce. (a: NASA, H. Ford/JHU, G. Illingworth/ UCSC/Lick, M. Clampin/STScI, G. Hartig/STScI, The ACS Science Team, and ESA; b: NASA)
- FIGURE 16-15 Clusters of Galaxies in Our Neighborhood This is a drawing of a sphere of space 250 Mpc (800 Mly) across centered on the Earth in the Local Cluster. The spherical dots represent the locations of the nearby clusters of galaxies, while the flat circles represent the projection of the cluster locations onto the plane of the Milky Way. To better see the three-dimensionality of this figure, yellow arcs are drawn from each cluster down to the green projection of the Milky Way’s plane extended out through the universe. The Great Attractor is an as-yet-unseen mass toward which the Local Group and other nearby clusters of galaxies are flowing.
- FIGURE 16-16 Structure in the Universe (a) This infrared map called 2MASS, for 2-Micron All Sky Survey, shows the light from 1.6 million galaxies. The entire sky is projected onto an oval; the blue band running vertically across the center of the image is light from the plane of the Milky Way. Note the filamentary structure with regions almost devoid of galaxies, surrounded by thin regions full of them.
- FIGURE 16-16 Structure in the Universe (b) This map shows the distribution of 62,559 galaxies in two wedges extending out in opposite directions from the Earth. For an explanation of right ascension, see Section 1-3. Note the prominent voids surrounded by thin areas full of galaxies. (a: 2MASS; IPAC/Caltech; and the University of Massachusetts; b: Courtesy of the 2dF Galaxy Redshift Survey Team/Anglo-Australian Observatory)
- FIGURE 16-30 The Hubble Law The distances and recessional velocities of distant galaxies are plotted on this graph. The straight line is the “best fit” for the data. This linear relationship between distance and speed is called the Hubble law.
- FIGURE 16-32 Distant Galaxies (a) The young cluster of galaxies MS1054-03, shown on the left, contains many orbiting pairs of galaxies, as well as remnants of recent galaxy collisions. Several of these systems are shown at the right. This cluster is located 8 billion light-years away from Earth. (b) This image of more than 300 spiral, elliptical, and irregular galaxies contains several that are an estimated 12 billion light-years from Earth. Two of the most distant galaxies are shown in the images on the right, colored in red at the centers of the pictures. (a, b: P. Van Dokkum, Uner of Granengen, ESA and NASA)
- FIGURE 16-32 Distant Galaxies (a) The young cluster of galaxies MS1054-03, shown on the left, contains many orbiting pairs of galaxies, as well as remnants of recent galaxy collisions. Several of these systems are shown at the right. This cluster is located 8 billion light-years away from Earth. (b) This image of more than 300 spiral, elliptical, and irregular galaxies contains several that are an estimated 12 billion light-years from Earth. Two of the most distant galaxies are shown in the images on the right, colored in red at the centers of the pictures. (a, b: P. Van Dokkum, Uner of Granengen, ESA and NASA)