1 / 19

Expansion of the Universe

Expansion of the Universe. Lab 10. Some Facts of Our Milky Way Galaxy. Distance from Sun to galactic center = 8 kpc ± 1 kpc Disk of our galaxy = 50 kpc diameter, 0.6 kpc thick, with a central bar-shaped bulge Central bulge is 2 kpc in diameter(has both Pop I and Pop II stars)

kueng
Download Presentation

Expansion of the Universe

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Expansion of the Universe Lab 10

  2. Some Facts of Our Milky Way Galaxy • Distance from Sun to galactic center = 8 kpc ± 1 kpc • Disk of our galaxy = 50 kpc diameter, 0.6 kpc thick, with a central bar-shaped bulge • Central bulge is 2 kpc in diameter(has both Pop I and Pop II stars) • Sun orbits center of galaxy at 790,000 km/hr, takes 220 million years to complete 1 orbit

  3. Facts about H • Hydrogen most abundant element in the universe but cannot emit visible light in the depths of cold interstellar space • However, DOES emit radio waves • This H is neutral not ionized, so called H I

  4. Detection of Spin-flips • Protons and electrons have mass, charge • Also have angular momentum (spin) which creates tiny magnetic field • So energy of H atom is different depending on orientation of spins (if same ↓, if opposite directions ↑, but energy difference = 10-6 x electron orbits) • photon emitted in a spin-flip transition has λ = 21 cm (long, radio)

  5. Dark Matter!!!! • Most of mass of galaxy (90%) does not emit anything that we can detect, so it is called dark matter • 90 million solar masses of matter exists inside the solar orbit • But orbital speeds do NOT decrease with distance from galactic center • So a large amount of mass must exist OUTSIDE solar orbit • Therefore, total mass of our galaxy = 1012 Mסּ

  6. MACHOs and WIMPs • Half of dark matter halo is composed of MACHOs • Massive Compact Halo Objects are ~ 0.5 Mסּ • Some part of dark matter are neutrinos • Also, some other subatomic particles called WIMPs (weakly interacting massive particles) which have a mass of 10-10,000> proton

  7. Winding Dilemma • Stars, dust, gas all orbit the galactic center with ~ same speed • But this creates a winding dilemma • So density waves must sweep around galaxy, which move more slowly around the galaxy than the matter inside • This crowding promotes stellar birth and recycling of ISM

  8. Just so you know…… • At center of our galaxy is a black hole millions of times more massive than Sun • Starlight warms dust grains to 10-90˚K, which then emits radiation at λ = 30-300 μm (far infra red, Wien’s law) • At near infra red λ, see cool stars (red giants) deep within Milky Way

  9. Types of Galaxies • Galaxies can be • spiral (Sa fat central bulge, Sc tiny central bulge) • barred spiral (SB) • elliptical (E7 flattest, E0 roundest, old red Pop II) • irregular (both old and young stars, lots of ISM, Irr I have a hint of structure eg Large Magellanic Cloud, SMC; Irr II have distorted shapes resulting mostly from collisions with other galaxies) • Giant ellipticals are rare, dwarf ellipiticals are common, ellipticals have no overall rotation, do not rotate • Spirals have a lot of overall rotation

  10. Distance ladder – ways to measure distances

  11. Masers – molecular clouds • Technique independent of distance ladder • Luminosity of star stimulates water molecules in a maser to emit intensely at microwave λ • Maser – microwave amplification by stimulated emission of radiation, like lasers which are stimulated by electric current to emit an intense beam of visible light

  12. Hubble Law • Most galaxies show a redshift spectrum • That is, nearby galaxies are moving away from us slowly, but distant galaxies are rushing away from us • This recessional movement is called the Hubble flow

  13. redshift • Redshift (z) is found by subtracting observed wavelength (λ) of a spectral line from ordinary wavelength (λo) to get difference (Δλ); divide result by λo • z = λ- λo= Δλ λo λo

  14. Hubble Law • V = Hod where v = recessional velocity of galaxy, Ho= Hubble constant (slope of line), d = distance to galaxy • Ho = 71km/s/Mpc • Or a galaxy 100 million parsecs away from us is racing away from us at a speed of 7100 km/s

  15. Galaxies collide! • However, all galaxies are NOT moving away from us! • In fact, some are approaching us, like the Andromeda galaxy • Collision scheduled for 6 billion years from today • Not to worry, our solar system is only ~4.5 billion years old!

  16. Review of terms • Keplers 3rd law • Relates size of orbit and time taken to go around the sun • P2 = a3

  17. Review of terms • Newton’s form of Keplers 3rd law • P2 = [(4π2)/(G(m1+m2))]a3 • P = sidereal period (secs) • a = semi major axis (m) • m1 = mass of 1st object (kg) • m2 = mass of 2nd object (kg) • G = universal constant of gravitation or (6.67x10-11)

  18. Review of terms • Parsec = A parsec is defined as the distance from the Sun which would result in a parallax of 1 second of arc as seen from Earth or 3.26 ly or 3.086x1016 m • Ly = distance traveled by light in one year or 9.461x1015 m • Declination – analogous to latitude • Right ascension – analogous to longitude • Apparent magnitude - doesn't measure how bright objects actually are; it measures how bright they appear to us, which also depends on how close they are eg Sun has m = -26.74 • Absolute magnitude - measures how bright objects actually are -- it is defined as the apparent magnitude that an object would have if it were located at a distance of 10 parsecs from us or Sun has abs m = 4.83

  19. Review of Terms • Nanometer – 10-9 m • Angstrom – 10-10 m, visible light ranges from 4000-8000 angstroms • Population I stars - young metal-rich, found in spiral galaxy arms • Population II stars – old, metal-poor, found in globular clusters in galactic nucleus • Semi major axis – ½ major axis • Cepheids – metal-rich more luminous shorter periods Type I or metal-poor dimmer Type II, apparent brightness and luminosity used with inverse square law to calculate distance to star • Universe – has billions of galaxies • Redshift – moving away • Blueshift – moving to

More Related