Chapter Chapter 15: 15: The Milky Way Galaxy
Chapter 15:Chapter 15:The Milky
Way Galaxy
Lesson PlanLesson Plan Idea of GallaxiesIdea of Gallaxies
Parson’s observationsParson’s observations Hubble’s observationsHubble’s observations
Cerpheid VariablesCerpheid Variables Milky WayMilky Way
CenterCenter Hershel’s observationsHershel’s observations Interstellar gasInterstellar gas Shapley’s observations (pr #7, pg 400)Shapley’s observations (pr #7, pg 400)
Disk mappingDisk mapping 21sm – radiation (pr #9, pg 405)21sm – radiation (pr #9, pg 405)
NucleusNucleus Infrarred viewInfrarred view Synchrotron radiation (pr #11, pg 409)Synchrotron radiation (pr #11, pg 409) X-ray radiationX-ray radiation Suppermassive black hole (pr #13, pg 410)Suppermassive black hole (pr #13, pg 410)
RotationRotation Dark matter (pr #10, pg 412)Dark matter (pr #10, pg 412)
WHAT DO YOU THINK?
How many stars does the Milky Way Galaxy contain?
Where is our Solar System located in the Milky Way Galaxy?
Is the Sun moving through the Milky Way Galaxy and, if so, about how fast?
You will discover…You will discover…
the Milky Way Galaxy—billions of stars along with gas and dust bound together by mutual gravitational attraction
the properties of our Milky Way Galaxy Earth’s location in the Milky Way how interstellar gas and dust enable star formation to
continue in our Galaxy that observations reveal the presence of significant mass
in the Milky Way that astronomers have yet to identify that there is a black hole at the center of our Galaxy
Schematic Diagrams ofSchematic Diagrams ofthe Milky Waythe Milky Way
Edge-on view showing the Milky Way’s disk
Schematic Diagrams ofSchematic Diagrams ofthe Milky Waythe Milky Way
Two possible distributions of the spiral arms of our Galaxy. Our Galaxy has at least four major spiral arms and several shorter arm segments.
Telescope of the Mid-Telescope of the Mid-Nineteenth CenturyNineteenth Century
Built by the Earl of Rosse in 1845, a 1.8-m-diameter telescope.
Telescope of the Mid-Telescope of the Mid-Nineteenth CenturyNineteenth Century
Lord Rosse’s sketch of the spiral structure of the galaxy M51
A modern photograph of M51 (also called NGC 5194)
Messier 100 and CepheidsMessier 100 and Cepheids
Period-Luminosity RelationPeriod-Luminosity Relation
Our GalaxyOur Galaxy
Wide-angle photograph spanning half the Milky Way, as seen from the equatorial latitudes
View Toward the Galactic CenterView Toward the Galactic Center
More than a million stars in the disk of our Galaxy fill this view, which covers a relatively clear window just 4º south of the galactic nucleus in Sagittarius.
Electron Spin & the Hydrogen AtomElectron Spin & the Hydrogen Atom
Mapping the GalaxyMapping the Galaxy
Radio waves from various gas clouds exhibit slightly different Doppler shifts, permitting astronomers to sort out the gas clouds and map the Galaxy.
Map of the GalaxyMap of the Galaxy
This map (left), based on radio telescope surveys of 21-cm radiation, shows the distribution of hydrogen gas in the Milky Way.
Two Views of Spiral Galaxy M83Two Views of Spiral Galaxy M83
Our GalaxyOur Galaxy
Diameter is about 100,000 Diameter is about 100,000 lyly
Sun about 26,000 ly from Sun about 26,000 ly from the galactic centerthe galactic center
Disk contains gas, dust Disk contains gas, dust and Population I starsand Population I stars
Halo is composed mostly Halo is composed mostly of Population II stars.of Population II stars.
Infrared View of the Milky WayInfrared View of the Milky Way
Taken by the COBE satellite in 1997
The Galactic CenterThe Galactic Center
Two Views of the Galactic NucleusTwo Views of the Galactic Nucleus
Radio image taken at the VLA
Two Views of the Galactic NucleusTwo Views of the Galactic Nucleus
Infrared image showing the motion of six stars in the vicinity of the unseen massive object at the position of the radio source Sagittarius A* ().
Orbits of Stars in Our GalaxyOrbits of Stars in Our Galaxy
NGC 4144, very similar to the Milky Way
The Nearest GalaxyThe Nearest Galaxy
Canis Major dwarf elliptical galaxy
Differential Rotation of the GalaxyDifferential Rotation of the Galaxy
Stars closer to the Galaxy’s center than the Sun are overtaking the solar system, while stars farther from the center are lagging behind us.
The Galaxy’s Rotation CurveThe Galaxy’s Rotation Curve
Microlensing by Dark MatterMicrolensing by Dark Matterin the Galactic Haloin the Galactic Halo
Gravitational fields cause light to change direction.
Microlensing by Dark MatterMicrolensing by Dark Matterin the Galactic Haloin the Galactic Halo
The light curve of the gravitational microlensing of light from a star in the Galaxy’s nuclear bulge by an intervening object.
WHAT DID YOU THINK? How many stars does the Milky Way Galaxy contain? The Milky Way has about 200 billion stars. Where is our solar system located in the Milky Way
Galaxy? The solar system is between the Sagittarius and Perseus
spiral arms about 26,000 ly from the center of the Galaxy.
Is the Sun moving through the Milky Way Galaxy and, if so, how fast?
The Sun orbits the center of the Milky Way Galaxy at a speed of 828,000 km per hour.
Key TermsKey Terms
dark matter (missing mass)disk (of a galaxy)distance modulusgalactic cannibalismgalactic nucleusgalaxyhalo (of a galaxy)microlensingMilky Way Galaxymissing mass
nebula (plural nebulae)nuclear bulgerotation curve (of a galaxy)Sagittarius AShapley–Curtis debatespin (of an electron or proton)spiral armsynchrotron radiation21-cm radio radiation