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The milky way galaxy

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Judy-ann Jardinan
Judy-ann Jardinan

The Milky Way Galaxy is a spiral galaxy that contains the solar system and Earth. It is estimated to be 100,000 light years in diameter and contains millions to billions of stars. The galaxy is composed of a disk, halo, and central bulge. Spiral arms in the disk contain dense clouds of gas and dust where new stars are forming. The sun orbits near the edge of the disk at a distance of about 8.2 kiloparsecs from the galactic center. All elements heavier than hydrogen and helium were produced through nuclear fusion in earlier generations of stars within the Milky Way over billions of years.

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The Universe of Galaxies Prepared by: Judy-ann P. Jardinan III-BEED
Chapter 17: The Milky Way Galaxy
Discovery of the Galaxy Overview Structure of galaxy The Spiral Arms and Star Formation Origin and History of the Milky Way Galaxy The Nucleus of the Galaxy
What is Galaxy ?
Galaxy •a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.
Discovery of the Galaxy
The Great Star System The ancient Greeks named that band galaxies kuklos, the “milky circle.” The Romans changed the name to via lactia,meaning “milky road” or “milky way.”
Galileo’s telescope revealed that the glowing Milky Way is made up of stars, and later astronomers realized that the sun must be located in a great wheel-shaped cloud of stars, which they called the star system.
In 1750 Thomas Wright Wright used the term universe because, so far as was known at the time, the Milky Way star system was the entire universe
In 18th Century Astronomers Sir William Herschel and Caroline Herschel (Sir William’s sister) set out to map the three- dimensional distribution of stars in the Milky Way.
….The sun is located near the center of this “grindstone” model universe
Variable Stars and Distance Estimates The variable stars Leavitt saw, Cepheids, are named after the first such star discovered, d Cephei. Many Cepheid variables are known today; they have pulsation periods from 1 to 60 days and lie in a region of the H–R diagram known as the instability strip
Cepheid's are clearly giant and supergiant stars. A related kind of variable, RR Lyrae stars, are named after the variable star RR in the constellation Lyra. They have a pulsation period of about half a day and lie at the low-luminosity end of the instability strip
Size of the Galaxy The Milky Way is only 100,000 light years in diameter.
Structure of galaxy
What are the components of Galaxy?
Disk Component It contains most of the galaxy’s stars and nearly all of its gas and dust. Because the disk is home to the giant molecular clouds within which stars form nearly all star formation in our galaxy takes place in the disk.
Halo a spherical cloud of stars and star clusters that contains almost no gas and dust. Because the halo contains no dense gas clouds, it cannot make new stars
Central Bulge a flattened cloud of billions of stars about 6 kpc in diameter. Like the halo, it contains little gas and dust. Astronomers often refer to the halo and the central bulge together as the spherical component of the galaxy.
What is the mass of the Galaxy ?
Current observations indicate that the sun orbits the center of our galaxy at about 240 km/s, moving in the direction of Cygnus. The evidence suggests the sun’s orbit is nearly circular, so given the current best estimate for the distance to the center of our galaxy, 8.2 kpc, you can find the circumference of the sun’s orbit by multiplying by 2p.
The Spiral Arms and Star Formation
Tracing the Spiral Arms Those spiral segments have been named for the prominent constellations through which they pass. Astronomers are now using infrared and radio telescopes to penetrate the interstellar dust, locate more distant OB associations, and trace the spiral arms even farther Objects used to map spiral arms are called spiral tracers
Radio Maps of Spiral Arms • Radio astronomers use the strong spectral line emission from carbon monoxide (CO) to map the location of giant molecular clouds in the plane of the galaxy
The Spiral Density Wave Theory In the spiral density wave theory, spiral arms are dynamically stable regions of compression that move slowly around the galaxy, just as the truck moves slowly down the highway. Gas clouds moving at orbital velocity around the galaxy overtake the slow-moving arms from behind and slam into the gas already in the arms.
The Nucleus of the Galaxy
Observations of the Galactic Nucleus 1.Observations at radio and infrared wavelengths reveal complex structures near Sgr A* caused by magnetic fields and by rapid star formation. Supernova remnants show that massive stars have formed there recently and exploded at the ends of their lives. 2.The center is crowded. Tremendous numbers of stars heat the dust, which emits strong infrared radiation 3. Finally, there is evidence that Sgr A* is a supermassive black hole into which gas is flowing. Observations of the motions of stars orbiting the central object indicate its mass is at least 4 million M}
Supermassive Black Hole
Origin and History of the Milky Way Galaxy
The Element-Building Process • The first stars that formed early in the universe’s history therefore had to be nearly pure hydrogen and helium. All of the other chemical elements have been produced by Nucleosynthesis -the process instars that fuses hydrogen and helium to make the heavier atom
Stellar Populations • They form and evolve in similar ways, but they differ, especially in their abundances of metals. >Population I stars are metal rich, containing 2 to 3 percent metals, whereas….. >Population II stars are metal poor, typically containing less than 0.1 percent metals.
The Age of Galaxy • The oldest open clusters are 9 to 10 billion years old. These ages come from the turnoff points in their H–R diagrams, but finding the age of an old cluster is difficult because old clusters change so slowly Studies of the Studies of the oldest globular clusters suggest that the halo of our galaxy is at least 13 billion years
Formation of the Galaxy • The monolithic collapse hypothesis (Top-down)says that the galaxy formed from a single large cloud of turbulent gas over 13 billion years ago. That cloud contracted to form our galaxy. As gravity pulled the gas inward, the cloud began to fragment into smaller clouds, and because the gas was turbulent, the smaller clouds had random velocities.
What are we? The Children of the milky
In a nutshell • The sun, with Earth in its clutch, is ripping along at about 240 km/sec (that’s 540,000 mph) as it orbits the center of the Milky Way Galaxy. We live on a wildly moving ball of rock in a large galaxy that humanity calls home, but the Milky Way is more than just our home. Perhaps “parent galaxy”would be a better name • Except for hydrogen atoms, which have survived unchanged since the universe began, you and Earth are made of metals—atoms heavier than helium. There is no helium in your body, but there is plenty of carbon, nitrogen, and oxygen. There is calcium in your bones and iron in your blood. All of those atoms and more were cooked up inside stars or in their supernova deaths
• Stars are born when clouds of gas orbiting the center of the galaxy collide with the gas in spiral arms and are compressed. That process has given birth to generations of stars, and each generation has produced elements heavier than helium and spread them back into the interstellar medium. The abundance of metals has grown slowly in the galaxy
References • Universe (Solar systems, Stars, and Galaxies) 7th Edition by Seeds and Backman • http://www.setterfield.org/Astronomy/Galaxies.html • http://astronomy.nju.edu.cn/~lixd/GA/AT4/AT425/HTML/AT42504.HT M
Mabalos!

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The milky way galaxy

  • 3. Discovery of the Galaxy Overview Structure of galaxy The Spiral Arms and Star Formation Origin and History of the Milky Way Galaxy The Nucleus of the Galaxy
  • 5. Galaxy •a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.
  • 7. The Great Star System The ancient Greeks named that band galaxies kuklos, the “milky circle.” The Romans changed the name to via lactia,meaning “milky road” or “milky way.”
  • 8. Galileo’s telescope revealed that the glowing Milky Way is made up of stars, and later astronomers realized that the sun must be located in a great wheel-shaped cloud of stars, which they called the star system.
  • 9. In 1750 Thomas Wright Wright used the term universe because, so far as was known at the time, the Milky Way star system was the entire universe
  • 10. In 18th Century Astronomers Sir William Herschel and Caroline Herschel (Sir William’s sister) set out to map the three- dimensional distribution of stars in the Milky Way.
  • 11. ….The sun is located near the center of this “grindstone” model universe
  • 12. Variable Stars and Distance Estimates The variable stars Leavitt saw, Cepheids, are named after the first such star discovered, d Cephei. Many Cepheid variables are known today; they have pulsation periods from 1 to 60 days and lie in a region of the H–R diagram known as the instability strip
  • 13. Cepheid's are clearly giant and supergiant stars. A related kind of variable, RR Lyrae stars, are named after the variable star RR in the constellation Lyra. They have a pulsation period of about half a day and lie at the low-luminosity end of the instability strip
  • 14. Size of the Galaxy The Milky Way is only 100,000 light years in diameter.
  • 16. What are the components of Galaxy?
  • 17. Disk Component It contains most of the galaxy’s stars and nearly all of its gas and dust. Because the disk is home to the giant molecular clouds within which stars form nearly all star formation in our galaxy takes place in the disk.
  • 18. Halo a spherical cloud of stars and star clusters that contains almost no gas and dust. Because the halo contains no dense gas clouds, it cannot make new stars
  • 19. Central Bulge a flattened cloud of billions of stars about 6 kpc in diameter. Like the halo, it contains little gas and dust. Astronomers often refer to the halo and the central bulge together as the spherical component of the galaxy.
  • 20. What is the mass of the Galaxy ?
  • 21. Current observations indicate that the sun orbits the center of our galaxy at about 240 km/s, moving in the direction of Cygnus. The evidence suggests the sun’s orbit is nearly circular, so given the current best estimate for the distance to the center of our galaxy, 8.2 kpc, you can find the circumference of the sun’s orbit by multiplying by 2p.
  • 22. The Spiral Arms and Star Formation
  • 23. Tracing the Spiral Arms Those spiral segments have been named for the prominent constellations through which they pass. Astronomers are now using infrared and radio telescopes to penetrate the interstellar dust, locate more distant OB associations, and trace the spiral arms even farther Objects used to map spiral arms are called spiral tracers
  • 24. Radio Maps of Spiral Arms • Radio astronomers use the strong spectral line emission from carbon monoxide (CO) to map the location of giant molecular clouds in the plane of the galaxy
  • 25. The Spiral Density Wave Theory In the spiral density wave theory, spiral arms are dynamically stable regions of compression that move slowly around the galaxy, just as the truck moves slowly down the highway. Gas clouds moving at orbital velocity around the galaxy overtake the slow-moving arms from behind and slam into the gas already in the arms.
  • 27. Observations of the Galactic Nucleus 1.Observations at radio and infrared wavelengths reveal complex structures near Sgr A* caused by magnetic fields and by rapid star formation. Supernova remnants show that massive stars have formed there recently and exploded at the ends of their lives. 2.The center is crowded. Tremendous numbers of stars heat the dust, which emits strong infrared radiation 3. Finally, there is evidence that Sgr A* is a supermassive black hole into which gas is flowing. Observations of the motions of stars orbiting the central object indicate its mass is at least 4 million M}
  • 29. Origin and History of the Milky Way Galaxy
  • 30. The Element-Building Process • The first stars that formed early in the universe’s history therefore had to be nearly pure hydrogen and helium. All of the other chemical elements have been produced by Nucleosynthesis -the process instars that fuses hydrogen and helium to make the heavier atom
  • 31. Stellar Populations • They form and evolve in similar ways, but they differ, especially in their abundances of metals. >Population I stars are metal rich, containing 2 to 3 percent metals, whereas….. >Population II stars are metal poor, typically containing less than 0.1 percent metals.
  • 32. The Age of Galaxy • The oldest open clusters are 9 to 10 billion years old. These ages come from the turnoff points in their H–R diagrams, but finding the age of an old cluster is difficult because old clusters change so slowly Studies of the Studies of the oldest globular clusters suggest that the halo of our galaxy is at least 13 billion years
  • 33. Formation of the Galaxy • The monolithic collapse hypothesis (Top-down)says that the galaxy formed from a single large cloud of turbulent gas over 13 billion years ago. That cloud contracted to form our galaxy. As gravity pulled the gas inward, the cloud began to fragment into smaller clouds, and because the gas was turbulent, the smaller clouds had random velocities.
  • 34. What are we? The Children of the milky
  • 35. In a nutshell • The sun, with Earth in its clutch, is ripping along at about 240 km/sec (that’s 540,000 mph) as it orbits the center of the Milky Way Galaxy. We live on a wildly moving ball of rock in a large galaxy that humanity calls home, but the Milky Way is more than just our home. Perhaps “parent galaxy”would be a better name • Except for hydrogen atoms, which have survived unchanged since the universe began, you and Earth are made of metals—atoms heavier than helium. There is no helium in your body, but there is plenty of carbon, nitrogen, and oxygen. There is calcium in your bones and iron in your blood. All of those atoms and more were cooked up inside stars or in their supernova deaths
  • 36. • Stars are born when clouds of gas orbiting the center of the galaxy collide with the gas in spiral arms and are compressed. That process has given birth to generations of stars, and each generation has produced elements heavier than helium and spread them back into the interstellar medium. The abundance of metals has grown slowly in the galaxy
  • 37. References • Universe (Solar systems, Stars, and Galaxies) 7th Edition by Seeds and Backman • http://www.setterfield.org/Astronomy/Galaxies.html • http://astronomy.nju.edu.cn/~lixd/GA/AT4/AT425/HTML/AT42504.HT M

Editor's Notes

  1. You will learn in this chapter how evidence reveals that you are inside a great wheel of stars, a galaxy. The Milky Way Galaxy is over 80,000 ly in diameter and contains more than 100 billion stars. It is your galaxy because you live in it, but you are also a product of it, because the stars in the Milky Way Galaxy made many of the atoms in your body. You begin this chapter by pondering the notion that the stars belong to you, but when you reach the end of the chapter, you may realize that you also belong to the stars
  2. The large group of stars outside of our own milky way Also may have gas and dust
  3. It was not until Galileo used his telescope in 1610 that anyone realized the Milky Way is made of a huge number of stars
  4. at star system appears from our location inside it as the band of the Milky Way encircling the sky.
  5. They assumed that they could see to the outer boundaries of the Milky Way in all directions and hypothesized that by counting the number of stars that were visible in different directions they could find the relative distances to the edges of the star distribution.
  6. In 1785, William Herschel published this diagram showing the shape of the star system as if it could be viewed edge-on from outside. The sun is located near the center of this “grindstone” model universe. >1785 - Herschel attempted to determine the shape and size of Galaxy Assumptions: All stars have same intrinsic brightness Star are arranged uniformly throughout the MW He could see to the edge of the MW
  7. >It is a Common Misconceptionthat the stars are eternal and unchanging, but astronomers have known for centuries that some stars change in brightness. ?In 1912, Henrietta Leavitt was studying a star cloud in the southern sky known as the Small Magellanic Cloud. On her photographic plates, she found many variable stars, and she noticed that the brightest had the longest periods.
  8. Most of the stars in the disk are middle- to lower-main-sequence stars like the sun, a few are red giants and white dwarfs, and fewer still are brilliant blue O and B stars. Th ose hot, massive stars are rare, but they are so luminous that they provide much of the light from the disk
  9. (intro) If you look “up” or “down,” out of the galaxy’s disk, you are looking away from the dust and gas, so you can see into the galaxy’s halo >Halo stars are old, cool, lower-main-sequence stars, red giants, and white dwarfs. It is difficult to judge the extent of the halo, but it could have as much as 10 times the diameter of the visible disk
  10. side from OB associations, spiral tracers include young open star clusters, clouds of hydrogen ionized by hot stars (emission nebulae), and certain higher-mass variable stars. Notice that all spiral tracers are young objects, formed recently, astronomically speaking. O stars, for example, live for only a few million years.
  11. . (The dust that blocks our view at visual wavelengths is transparent to radio waves because radio wavelengths are much larger than the diameter of the dust particles.)
  12. e sudden compression of the gas can trigger the collapse of the gas clouds and the formation of new Newly formed stars and the remaining gas eventually move on through the arm and emerge from the front of the slow-moving arm to resume their travels around the galaxy
  13. The most mysterious region of our galaxy is its very center, the nucleus. At visual wavelengths, this region is totally hidden by dust and gas that dim the light it emits by 30 magnitudes
  14. A supermassive black hole is an exciting idea, but scientists must always be aware of the difference between adequacy and necessity. A supermassive black hole is adequate to explain the observations
  15. As you already know, medium-mass stars like the sun cannot ignite carbon fusion, but during helium fusion the heat and
  16. >Population I stars belong to the disk component of the galaxy and are sometimes called disk population stars. Th ey have nearly circular orbits in the plane of the galaxy and formed within the last few billion years. The sun is a Population I star, as are the type I Cepheid variables discussed in this chapter. >Population II stars belong to the spherical component of the galaxy and are sometimes called the halo population stars. These stars have randomly tipped orbits ranging from circular to highly elliptical. They are old stars that formed when the galaxy was young. The metal-poor globular clusters are part of the halo population, as are the RR Lyrae and type II Cepheids.
  17. Because astronomers know how to find the age of star clusters, they can estimate the age of the oldest stars in the galaxy, giving a lower limit to the age of the entire galaxy. The process sounds straightforward, but uncertainties make the easy answer hard to interpret. Also, the exact location of the turn off point depends on chemical composition, which differs slightly among clusters. Finally, open clusters are not strongly bound by gravity, so older open clusters may have dissipated as their stars wandered away. It is reasonable to suppose that the galactic disk is somewhat older than the oldest remaining open clusters, which suggests that the disk is at least 10 billion years old.
  18. Th at caused the stars and star clusters that formed from these fragments to have orbits with a wide range of shapes; a few were circular, most were elliptical, and some were extremely elliptical. Th e orbits were also inclined at different angles, resulting in a spherical cloud of stars—the spherical component of the galaxy. Of course, these first stars were metal poor because no stars had existed earlier to enrich the gas with metals