Presentation on theme: "Chapter 16: Other Galaxies"— Presentation transcript:
1 Chapter 16: Other Galaxies Edwin Hubble is one of Time magazine’s most important people of the 20th Century:. 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 .SEDS maintains an excellent database of Messier objects: .
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… 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 GalaxiesSpiralBarred SpiralEllipticalIrregular
5 Hubble’s Diagram of Galaxy Types FIGURE Hubble’s Tuning Fork DiagramHubble summarized his classification scheme forgalaxies with this tuning fork diagram. Elliptical galaxiesare classified by how oval they appear, while spiralsand barred spirals are classified by the sizes of theircentral bulges and the correlated winding of theirspiral arms. An S0 or SB0 galaxy, also called alenticular galaxy, is an intermediate type betweenellipticals and spirals. It has a disk but no spiral arms.
6 1. Spiral Galaxies Type Sa Type Sb Type Sc FIGURE 16-1 Spiral Galaxies (Nearly Face-on Views) EdwinHubble classified spiral galaxies according to the tightness of thespiral arms and the size of the nuclear bulge. Sa galaxies havethe largest nuclear bulges and the most tightly wound spiralarms, while Sc galaxies have the smallest nuclear bulges and theleast tightly wound arms. The images are different colorsbecause they were taken through filters passing different colors.(left: NASA/Hubble Space Institute; middle: Robert Gendler; right:Anglo-Australian Observatory)Type SaType SbType Sc
7 Andromeda (M31) FIGURE 16-2 Andromeda (M32) Andromeda is a beautiful spiral galaxy and isthe only galaxy visible to the naked eye fromthe Earth’s northern hemisphere. Without atelescope, it appears to be a fuzzy blob in theconstellation of Andromeda. Located only 0.9Mpc (2.9 Mly) from us, Andromeda isgravitationally bound to the Milky Way, and itcovers an area in the sky roughly 5 times aslarge as the full Moon. Two other galaxies,M32 and M110), are also labeled on thisphotograph. The points of light peppering theimage are stars in our Galaxy. (Bill and SallyFletcher/Tom Stack and Associates)
8 Spiral Galaxies Seen Edge-on FIGURE 16-3Spiral Galaxies Seen Nearly Edge-on from theMilky Way (a) Because of its large nuclear bulge, this galaxy isclassified as an Sa. If we could see it face-on, the spiral armswould be tightly wound around a voluminous bulge. (b) Notethe smaller nuclear bulge in this Sb galaxy. (c) At visiblewavelengths, interstellar dust obscures the relatively insignificantnuclear bulge of this Sc galaxy. (a: European Southern Observatory;b: Anglo-Australian Observatory/David Malin Images; c: Dr. Rudy Schild,Smithsonian Astrophysical Observatory)M104: Sa galaxyNGC 891: Sb galaxyNGC 4631: Sc galaxy
9 Variety in Spiral ArmsFIGURE 16-4 Variety in Spiral Arms The differences in spiralgalaxies suggest that at least two mechanisms create spiral arms.(a) This flocculent spiral galaxy has fuzzy, poorly defined spiralarms.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 Galaxies FIGURE 16-8 Barred Spiral Galaxies As with spiral galaxies,Edwin Hubble classified barred spirals according to the tightnessof their spiral arms (which correlates with the sizes of theirnuclear bulges). SBa galaxies have the most tightly wound spiralsand largest nuclear bulges, SBb have moderately tight spirals andmedium-sized nuclear bulges, while SBc galaxies have the leasttightly 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.)M58: SBa galaxyM83: SBb galaxyNGC 1365: SBc galaxy
12 4. Irregular Galaxies Large Magellanic Cloud, Irr 1 galaxy FIGURE Irregular Galaxies (a) At a distanceof only 179,000 ly, the Large Magellanic Cloud (LMC),an Irr I irregular galaxy, is the third closest knowncompanion of our Milky Way Galaxy. (The Milky Way’s closestknown 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 hugea Large Magellanic Cloud, an Irr 1 galaxy b NGC 4485 (Irr 2) and NGC 4490 (Sc) galaxiesH II region (called the Tarantula Nebula or 30 Doradus) towardthe left side of this image. Its diameter of 800 ly and mass of 5million Suns makes it the largest known H II region. (b) Thesmall irregular (Irr II) galaxy NGC 4485 (bottom galaxy) interactswith the highly distorted Sc galaxy NGC 4490, also called theCocoon Galaxy. This pair is located in the constellation CanesVenatici. (a: Anglo-Australian Observatory; b: Hoher Observatory)Large Magellanic Cloud, Irr 1 galaxyNGC 4485 (Irr 2) and NGC 4490 (Sc) galaxies
13 Galaxies are Clumped in Space Galaxies occur in groups called Clusters. The galaxies in a Cluster are bound by gravity to each other, and can collide.Our Galaxy belongs to a Cluster called “The Local Group.”Clusters of galaxies occur in bigger groups called Superclusters. Most Superclusters are not gravitationally bound units like Clusters are.All the Clusters are moving away from each other as the Universe expands.
15 The Local Group – Our Cluster FIGURE The Local Group Our Galaxy belongs to apoor, irregular cluster consisting of about 40 galaxies called theLocal Group. This map shows the distribution of about threequartersof the galaxies. The Andromeda Galaxy (M31) is thelargest and most massive galaxy in the Local Group. The secondlargest is the Milky Way itself. M31 and the Milky Way are eachsurrounded by a dozen satellite galaxies. The recently discoveredCanis Major Dwarf Galaxy is the Milky Way’s nearest knownneighbor.Our Galaxy belongs to a poor, irregular (wimpy) cluster – consisting of about 40 galaxies (including M31 Andromeda) – called the Local Group.
16 Colliding GalaxiesGalaxies that belong to the same Cluster can collide.Sometimes these galaxies pass through each other, and sometimes they combine.The individual stars in the colliding galaxies do not hit each other, but the huge clouds of gas and dust do collide.
17 Colliding GalaxiesFIGURE Interacting and CollidingGalaxies (a) Pairs of colliding galaxies oftenexhibit long “antennae” of stars ejected by thecollision. This particular system is known asNGC 4676 or “the Mice” (because of its tails ofstars and gas). It is 300 million ly from Earth inthe constellation Coma Berenices. The collisionhas stimulated a firestorm of new starformation, as can be seen in the bright blueregions. Mass can also be seen flowingbetween the two galaxies, which will eventuallymerge. (a: NASA, H. Ford/JHU, G. Illingworth/UCSC/Lick, M. Clampin/STScI, G. Hartig/STScI,The ACS Science Team, and ESA; b: NASA)Pairs of colliding galaxies often exhibit long “antennae” of stars ejected by the collision.
18 Colliding Galaxies “Mano a Mano” FIGURE Interacting and CollidingGalaxies. (b) These two galaxies, NGC 2207(right) and IC 2163, are orbiting and tidallydistorting each other. Their most recent closeencounter occurred 40 Myr ago when the twowere perpendicular to each other and aboutone galactic diameter apart. Computersimulations indicate that they should eventuallycoalesce. (a: NASA, H. Ford/JHU, G. Illingworth/UCSC/Lick, M. Clampin/STScI, G. Hartig/STScI,The ACS Science Team, and ESA; b: NASA)NGC 2207 (right) and IC 2163 are orbiting and gravitationally distorting each other.
19 Our Local Supercluster and Other Superclusters Our Local Group (cluster) is at the center of the diagram. Our Local Supercluster extends out to the Virgo Cluster.FIGURE Clusters of Galaxies in Our NeighborhoodThis is a drawing of a sphere of space 250 Mpc (800 Mly) acrosscentered on the Earth in the Local Cluster. The spherical dotsrepresent the locations of the nearby clusters of galaxies,while the flat circles represent the projection of the clusterlocations onto the plane of the Milky Way. To better see thethree-dimensionality of this figure, yellow arcs are drawn fromeach cluster down to the green projection of the Milky Way’splane extended out through the universe. The Great Attractor isan as-yet-unseen mass toward which the Local Group and othernearby clusters of galaxies are flowing.
20 Beyond Superclusters – Filamentary Structure in the Universe FIGURE Structure in theUniverse (a) This infrared map called 2MASS,for 2-Micron All Sky Survey, shows the lightfrom 1.6 million galaxies. The entire sky isprojected onto an oval; the blue band runningvertically across the center of the image islight from the plane of the Milky Way. Notethe filamentary structure with regions almostdevoid of galaxies, surrounded by thin regionsfull of them.2-Micron All Sky Survey (Infrared) – 1.6 million galaxies shown.
21 Beyond Superclusters – Filamentary Structure in the Universe FIGURE Structure in theUniverse (b) This map shows thedistribution of 62,559 galaxies in two wedgesextending out in opposite directions from theEarth. For an explanation of right ascension,see Section 1-3. Note the prominent voidssurrounded by thin areas full of galaxies.(a: 2MASS; IPAC/Caltech; and the University ofMassachusetts; b: Courtesy of the 2dF GalaxyRedshift Survey Team/Anglo-AustralianObservatory)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 Expanding The Redshift of Superclusters shows us that the Universe is expanding. This Redshift is called the “Cosmological Redshift,” because it is caused by the expansion of space.The farther away a galaxy is from us, the faster it moves away from us: GALAXY SPEED = GALAXY DISTANCE x HUBBLE’S CONSTANT (H0).This is called “Hubble’s Law,” after Edwin Hubble, who discovered it.
23 Hubble’s LawFIGURE The Hubble Law The distances andrecessional velocities of distant galaxies are plotted onthis graph. The straight line is the “best fit” for thedata. This linear relationship between distance and speed iscalled the Hubble law.The farther away a galaxy is from us, the faster it moves away from us: GALAXY SPEED = GALAXY DISTANCE x HUBBLE’S CONSTANT (H0).
24 The Hubble Telescope looks back to when the Universe was very young.
25 HST – Galaxies 12.5 Billion LY Away FIGURE Distant Galaxies (a) The young cluster ofgalaxies MS , shown on the left, contains many orbitingpairs of galaxies, as well as remnants of recent galaxy collisions.Several of these systems are shown at the right. This cluster islocated 8 billion light-years away from Earth. (b) This image ofmore than 300 spiral, elliptical, and irregular galaxies containsseveral that are an estimated 12 billion light-years from Earth.Two of the most distant galaxies are shown in the images on theright, colored in red at the centers of the pictures. (a, b: P. VanDokkum, Uner of Granengen, ESA and NASA)
26 HST – Galaxies >13 Billion LY Away FIGURE Distant Galaxies (a) The young cluster ofgalaxies MS , shown on the left, contains many orbitingpairs of galaxies, as well as remnants of recent galaxy collisions.Several of these systems are shown at the right. This cluster islocated 8 billion light-years away from Earth. (b) This image ofmore than 300 spiral, elliptical, and irregular galaxies containsseveral that are an estimated 12 billion light-years from Earth.Two of the most distant galaxies are shown in the images on theright, colored in red at the centers of the pictures. (a, b: P. VanDokkum, Uner of Granengen, ESA and NASA)
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.