logging in or signing up The Milky Way joverba Download Post to : URL : Related Presentations : Let's Connect Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Copy embed code: Embed: Flash iPad Dynamic Copy Does not support media & animations Automatically changes to Flash or non-Flash embed WordPress Embed Customize Embed URL: Copy Thumbnail: Copy The presentation is successfully added In Your Favorites. Views: 222 Category: Education License: All Rights Reserved Like it (0) Dislike it (0) Added: May 09, 2012 This Presentation is Public Favorites: 0 Presentation Description No description available. Comments Posting comment... Premium member Presentation Transcript PowerPoint Presentation: The Milky Way GalaxyPowerPoint Presentation: Our Parent Galaxy From Earth, see few stars when looking out of galaxy (red arrows), many when looking in (blue arrows). Milky Way is how our Galaxy appears in the night sky (b).PowerPoint Presentation: Our Parent Galaxy Our Galaxy is a barred spiral galaxy. Here are two spiral galaxies, which are thought to resemble the Milky Way:PowerPoint Presentation: Measuring the Milky Way Unfortunately, he was not aware that most of the Galaxy, particularly the center, is blocked from view by vast clouds of gas and dust . One of the first attempts to measure the Milky Way was done by William Herschel using visible stars.PowerPoint Presentation: Measuring the Milky Way We have already encountered variable stars –novae, supernovae, and related phenomena – these are called cataclysmic variables . There are other stars whose luminosity varies in a regular way, but much more subtly. These are called intrinsic variables . Two types of intrinsic variables have been found: RR Lyrae stars, and Cepheids .PowerPoint Presentation: Measuring the Milky Way The upper plot is an RR Lyrae star. All such stars have essentially the same luminosity curve, with periods from 0.5 to 1 day. The lower plot is a Cepheid variable; Cepheid periods range from about 1 to 100 days.PowerPoint Presentation: Measuring the Milky Way The variability of these stars comes from a dynamic balance between gravity and pressure – they have large oscillations around stability.PowerPoint Presentation: Measuring the Milky Way The usefulness of these stars comes from their period–luminosity relation :PowerPoint Presentation: Measuring the Milky Way This allows us to measure the distances to these stars. RR Lyrae stars all have about the same luminosity ; knowing their apparent magnitude allows us to calculate the distance . Cepheids have a luminosity that is strongly correlated with the period of their oscillations; once the period is measured, the luminosity is known and we can proceed as above.PowerPoint Presentation: Measuring the Milky Way Many RR Lyrae stars are found in globular clusters . These clusters are not all in the plane of the Galaxy, so they are not obscured by dust and can be measured. This yields a much more accurate picture of the extent of our Galaxy and our place within it.PowerPoint Presentation: Measuring the Milky Way We have now expanded our cosmic distance ladder one more step:PowerPoint Presentation: Galactic Structure This artist’s conception shows the various parts of our Galaxy , and the position of our Sun :PowerPoint Presentation: Galactic Structure The Galactic halo and globular clusters formed very early; the halo is essentially spherical. All the stars in the halo are very old , and there is no gas and dust.PowerPoint Presentation: Galactic Structure The Galactic disk is where the youngest stars are, as well as star formation regions – emission nebulae, large clouds of gas and dust.PowerPoint Presentation: Galactic Structure Surrounding the Galactic center is the Galactic bulge , which contains a mix of older and younger stars.PowerPoint Presentation: Galactic Structure This infrared view of our Galaxy shows much more detail of the Galactic center than the visible-light view does, as infrared is not as much absorbed by gas and dust.PowerPoint Presentation: Galactic Structure Stellar orbits in the disk are in a plane and in the same direction; orbits in the halo and bulge are much more random.PowerPoint Presentation: The Formation of the Milky Way Any theory of galaxy formation should be able to account for all the properties below:PowerPoint Presentation: The Formation of the Milky Way The formation of the Galaxy is believed to be similar to the formation of the solar system, but on a much larger scale:PowerPoint Presentation: Galactic Spiral Arms Measurement of the position and motion of gas clouds shows that the Milky Way has a barred spiral form:PowerPoint Presentation: Galactic Spiral Arms The spiral arms cannot rotate along with the Galaxy; they would “curl up”:PowerPoint Presentation: Galactic Spiral Arms Rather, they appear to be density waves , with stars moving in and out of them much as cars move in and out of a traffic jam:PowerPoint Presentation: Galactic Spiral Arms As clouds of gas and dust move through the spiral arms, the increased density triggers star formation . This may contribute to propagation of the arms. The origin of the spiral arms is not yet understood.PowerPoint Presentation: The Mass of the Milky Way Galaxy The orbital speed of an object depends only on the amount of mass between it and the Galactic center:PowerPoint Presentation: The Mass of the Milky Way Galaxy Once all the Galaxy is within an orbit, the velocity should diminish with distance, as the dashed curve shows. It doesn’t; more than twice the mass of the Galaxy would have to be outside the visible part to reproduce the observed curve. Yes! Wut?PowerPoint Presentation: The Mass of the Milky Way Galaxy What could this “ dark matter ” be? It is dark at all wavelengths, not just the visible. Stellar-mass black holes ? Probably no way enough could have been created Brown dwarfs , faint white dwarfs , and red dwarfs ? Currently the best star-like option Weird subatomic particles ? Could be, although no evidence so farPowerPoint Presentation: The Mass of the Milky Way Galaxy A Hubble search for red dwarfs turned up very few; any that existed should have been detected:PowerPoint Presentation: The Mass of the Milky Way Galaxy The bending of spacetime can allow a large mass to act as a gravitational lens : Observation of such events suggests that low-mass white dwarfs could account for about half of the mass needed. The rest is still a mystery.PowerPoint Presentation: The Galactic Center This is a view towards the Galactic center , in visible light. The two arrows in the inset indicate the location of the center; it is entirely obscured by dust.PowerPoint Presentation: The Galactic Center These images, in infrared , radio , and X-ray , offer a different view of the Galactic center.PowerPoint Presentation: The Galactic Center The Galactic center appears to have a stellar density a million times higher than near Earth; a ring of molecular gas 400 pc across; strong magnetic fields ; a rotating ring or disk of matter a few parsecs across; and a strong X-ray source at the centerPowerPoint Presentation: The Galactic Center Apparently, there is an enormous black hole at the center of the Galaxy, which is the source of these phenomena. An accretion disk surrounding the black hole emits enormous amounts of radiation.PowerPoint Presentation: The Galactic Center These objects are very close to the Galactic center . The orbit on the right is the best fit; it assumes a central black hole of 3.7 million solar masses.PowerPoint Presentation: Summary Galaxy is stellar and interstellar matter bound by its own gravity Our Galaxy is spiral Variable stars can be used for distance measurement, through period–luminosity relationship True extent of our Galaxy can be mapped out using globular clusters Star formation occurs in disk, but not in halo or bulgePowerPoint Presentation: Summary cont. Spiral arms may be density waves Galactic rotation curve shows large amounts of undetectable mass at large radii; called dark matter Activity near Galactic center suggests presence of a 2–3 million solar-mass black hole You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.