Charles Hakes Fort Lewis College1

Charles Hakes Fort Lewis College2

Charles Hakes Fort Lewis College3 Chapter The Milky Way Dark Matter Extending the Distance Scale

Charles Hakes Fort Lewis College4 Mapping the Milky Way

Charles Hakes Fort Lewis College5 Spiral Galaxies A view of spiral galaxies from face- on and edge-on.

Charles Hakes Fort Lewis College6 Figure 14.1 Galactic Plane

Charles Hakes Fort Lewis College7 Mapping the Milky Way Radio observations can determine much of the structure and rotation rates.

Charles Hakes Fort Lewis College8 Mapping the Milky Way Radio observations can determine much of the structure and rotation rates. Orderly rotation in the plane. Random orbits in the halo.

Charles Hakes Fort Lewis College9 Figure Stellar Orbits in Our Galaxy

Charles Hakes Fort Lewis College10 Figure Observations of the Galactic Disk

Charles Hakes Fort Lewis College11 Mass of the Milky Way Recall Newton’s modification to Kepler’s third law:

Charles Hakes Fort Lewis College12 Figure Galaxy Rotation Curve

Charles Hakes Fort Lewis College13 Mass of the Milky Way There is apparently more mass than can be seen. Unseen mass out to ~50 kpc. Recall radius of observable Milky Way is ~15 kpc. Dark Matter Can detect gravitational effects Cannot detect any other way.

Charles Hakes Fort Lewis College14 Dark Matter Is not atomic or molecular clouds - we would detect those using spectroscopy. Could be brown dwarfs or white dwarfs - very difficult to see. MACHOs - MAssive Compact Halo Objects Could be exotic subatomic particles WIMPs - Weakly Interacting Massive Particles

Charles Hakes Fort Lewis College15 Figure Gravitational Lensing

Charles Hakes Fort Lewis College16 What observations suggest the mass of the Galaxy goes much farther out than its visible disc? A) the orbits of the open clusters in the disc B) x-ray images of other galaxies' discs from Chandra C) the rotation curve beyond 15kpc D) 21 cm maps of the spiral arms E) infrared observations of distant brown dwarfs

Charles Hakes Fort Lewis College17 What observations suggest the mass of the Galaxy goes much farther out than its visible disc? A) the orbits of the open clusters in the disc B) x-ray images of other galaxies' discs from Chandra C) the rotation curve beyond 15kpc D) 21 cm maps of the spiral arms E) infrared observations of distant brown dwarfs

Charles Hakes Fort Lewis College18 Galaxy Masses

Charles Hakes Fort Lewis College19 Figure 16.4 Galaxy Rotation Curves

Charles Hakes Fort Lewis College20 Galaxy Masses Galaxy masses determined from Newton’s modification to Kepler’s third law. Within the visible spiral, radial velocities (and masses) can be measured directly. Outside the visible spiral, observe multiple galaxy systems. Only radial velocity determined with Doppler shift. Reliable statistical information from lots of observation.

Charles Hakes Fort Lewis College21 Figure 16.5 Galaxy Masses from Newton’s modification of Kepler’s law

Charles Hakes Fort Lewis College22 Galaxy Masses Galaxies apparently have invisible halos similar to the Milky Way. All contain 3-10 times the visible mass. Mass discrepancy is even greater for clusters of galaxies.

Charles Hakes Fort Lewis College23 Figure 16.6 Dark Galaxy?

Charles Hakes Fort Lewis College24 Figure 16.7ab Galaxy Cluster X-Ray Emission Intergalactic space is filled with superheated gas in this cluster.

Charles Hakes Fort Lewis College25 Figure 16.7c Galaxy Cluster X-Ray Emission

Charles Hakes Fort Lewis College26 Figure 16.8 Head–Tail Radio Galaxy - Could this be a “ wake ” through intergalactic clouds?

Charles Hakes Fort Lewis College27 Extending the Distance Scale Variable Stars Tully-Fisher Relationship Supernovae Cosmological Redshift

Charles Hakes Fort Lewis College28 Figure 14.7 Variable Stars on Distance Ladder Greater distances can be determined than typically available through spectroscopic parallax, because these variables are so bright.

Charles Hakes Fort Lewis College29 Figure Local Group

Charles Hakes Fort Lewis College30 Tully-Fisher Relationship

Charles Hakes Fort Lewis College31 Figure 15.9 Galactic “ Tuning Fork ” Galaxies are classified according to their shape (Hubble classification) Elliptical Spiral Irregular

Charles Hakes Fort Lewis College32 Figure Galaxy Rotation Rotation rates can be determined using Doppler shift measurements Blue shift indicates moving towards you Red shift indicates moving away from you

Charles Hakes Fort Lewis College33 Tully-Fisher Relationship Rotation speed can be used to determine a galaxy’s total mass. A close correlation between rotation speed and total luminosity has been observed. Comparing (true) luminosity to (observed) apparent brightness allows us to determine distance Distance scale can be extended to ~200 Mpc.

Charles Hakes Fort Lewis College34 Figure Extragalactic Distance Ladder

Charles Hakes Fort Lewis College35 Supernovae Type II Supernovae Are a result of a very massive star’s core collapse Can vary in brightness, since the cores can vary in size. Therefore, they are not a good distance indicator.

Charles Hakes Fort Lewis College36 Supernovae Type I Supernovae White dwarf, carbon detonation Are a result of a white dwarf exceeding its Chandrasekhar limit (1.4 M solar ). They are all about the same size. They are very good distance indicators (Standard Candles).

Charles Hakes Fort Lewis College37 Standard Candles Standard Candles are easily recognizable astronomical objects whose luminosities are confidently known. Term usually only refers to very luminous objects Type I supernovae Other objects might include Rotating spiral galaxies Cepheid variables Main sequence stars

Charles Hakes Fort Lewis College38 Figure Extragalactic Distance Ladder

Charles Hakes Fort Lewis College39 Review Questions

Charles Hakes Fort Lewis College40 Which of these does not exist? A) a.06 solar mass brown dwarf B) a 1.3 solar mass white dwarf C) a six solar mass black hole D) a million solar mass black hole E) a 3.3 solar mass neutron star

Charles Hakes Fort Lewis College41 Which of these does not exist? A) a.06 solar mass brown dwarf B) a 1.3 solar mass white dwarf C) a six solar mass black hole D) a million solar mass black hole E) a 3.3 solar mass neutron star

Charles Hakes Fort Lewis College42 A star has an apparent magnitude of +1.0 and an absolute magnitude of If the distance between Earth and the star increases, the apparent magnitude would _____, and the absolute magnitude would _____. A) increase; decrease B) decrease; increase C) increase; not change D) decrease; not change E) not change; increase

Charles Hakes Fort Lewis College43 A star has an apparent magnitude of +1.0 and an absolute magnitude of If the distance between Earth and the star increases, the apparent magnitude would _____, and the absolute magnitude would _____. A) increase; decrease B) decrease; increase C) increase; not change D) decrease; not change E) not change; increase

Charles Hakes Fort Lewis College44 A star has apparent magnitude of +8.0 before it goes nova and increases its luminosity by 10,000 times. Its apparent magnitude after it goes nova is. A) +8.0 B) C) -8.0 D) -2.0 E) +3.0

Charles Hakes Fort Lewis College45 A star has apparent magnitude of +8.0 before it goes nova and increases its luminosity by 10,000 times. Its apparent magnitude after it goes nova is. A) +8.0 B) C) -8.0 D) -2.0 E) +3.0

Charles Hakes Fort Lewis College46 Using spectroscopic parallax, you find a star’s distance to be 76 parsecs. You now find out that the star isn’t a main sequence star, but is a red giant. Your distance estimate is A) too large B) too small C) fine - no significant change in estimate is needed.

Charles Hakes Fort Lewis College47 Using spectroscopic parallax, you find a star’s distance to be 76 parsecs. You now find out that the star isn’t a main sequence star, but is a red giant. Your distance estimate is A) too large B) too small C) fine - no significant change in estimate is needed.

Charles Hakes Fort Lewis College48 Which is correct? 1 - The new moon rises at noon. 2 - The first quarter moon rises at noon. 3 - The full moon rises at noon. 4 - The third quarter moon rises at noon.

Charles Hakes Fort Lewis College49 Which is correct? 1 - The new moon rises at noon. 2 - The first quarter moon rises at noon. 3 - The full moon rises at noon. 4 - The third quarter moon rises at noon.

Charles Hakes Fort Lewis College50 In Paris, France (50 degrees north latitude), what is the longest day of the year? 1: March 21 2: June 21 3: September 21 4: December 21

Charles Hakes Fort Lewis College51 In Paris, France (50 degrees north latitude), what is the longest day of the year? 1: March 21 2: June 21 3: September 21 4: December 21

Charles Hakes Fort Lewis College52 Where along the horizon does the Sun rise on June 21 in Paris, France? 1: Due east 2: North of east 3: South of east 4: Can’t tell with information given

Charles Hakes Fort Lewis College53 Where along the horizon does the Sun rise on June 21 in Paris, France? 1: Due east 2: North of east 3: South of east 4: Can’t tell with information given

Charles Hakes Fort Lewis College54 Three Minute Paper Write 1-3 sentences. What was the most important thing you learned today? What questions do you still have about today’s topics?