Galaxies. Spring 2009. Announcements. Current moon phase: waxing crescent. Planetarium trip Monday , May 4th. Show starts at 7:30 sharp. Location: http://www.astro.umass.edu/~salberts/astro103/tuesday/ Any transportation issues? No class on Tuesday, May 5th.
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Galaxies Spring 2009
Announcements • Current moon phase: waxing crescent. • Planetarium trip Monday, May 4th. • Show starts at 7:30 sharp. • Location: http://www.astro.umass.edu/~salberts/astro103/tuesday/ • Any transportation issues? • No class on Tuesday, May 5th. • Last class is Tuesday, May 12th: • Moon Projects due • candy + snacks
Quiz! Format: 20 questions; identify const., short answer, and multiple choice • Topics • Constellations (no mythology) & Objects We’ve Seen • The Moon • Planets (Venus and Saturn) • Angles & Coordinates • Seasons & the Sun • HR Diagrams • Things We’ve Seen • Ursa Major • Ursa Minor • Cassiopeia • Cepheus • Taurus • Pleiades • Gemini • Orion • Orion’s Belt • Betelgeuse • Rigel • Leo • Canis Major • Sirius • Bootes
Types of Galaxies - Spiral NGC 4594: “Sombrero Galaxy” M51: “Whirlpool Galaxy” NGC 1300 NGC 4414
Spiral Galaxies • M81: Different features stand out at different wavelengths. • Blue: UV light - tracing high energies, star formation, and young stars • Red: red visible light - lower energy, and older star populations
Types of Galaxies - Elliptical M87 M89 NGC 1132
Types of Galaxies - Irregulars NGC 1569 Large Magellanic Cloud M82
Our Galaxy: The Milky Way • Barred spiral • Over 100 billion stars • The sun is about 25,000 light years from the center (near Orion Spiral Arm) • Something menacing lurking in the center…
Black Hole! • Object with such a strong gravitational pull that even light can’t escape • All large galaxies feature a super-massive black hole in the center • Singularity – place of infinite density (say what?!) in the middle • Event Horizon – point of no return. If you cross this boundary, you can never escape.
Black Hole! • Black holes can have any mass • Schwarzschild radius: • Size to which an object must be squeezed down to make it into a black hole. G = Grav. Constant = 6.67 x 10-11 m3 kg-1 s-2 m = mass (kg) c = speed of light = 3.0 x 108 m s-1 The Sun: 3 km (1.8 miles) Earth: 0.4 inches You: 1 x 10-25 meters (10 billion times smaller than an electron)
Will the LHC Destroy the Planet??? • Large Hadron Collider: • smash iron nuclei together at nearly the speed of light (why???) • Nothing to worry about because: • Odds of making black hole: 1 in 50 million • Microscopic black hole would be harmless (Hawking Radiation) Collision Energy: 1148 TeV = 1.84 x 10-4 Joules mBH = E/c^2 = 2.04 x 10-21 kg Black Hole Evaporation Timescale: tev = 8.41 x 10-17 [mBH (kg)]3 sec Black hole would evaporate in 1 x 10-78 sec!
More Surprises with Galaxies • Fritz Zwicky • Estimated masses of galaxies to calculate total cluster mass • Measured velocities of galaxies in Coma Supercluster (how?) • Result: • Galaxies are moving way too fast! • Cluster should be flying apart, but it’s not. • What does this mean? Either: • Physics is wrong. • There’s “missing mass” in this cluster. DARK MATTER
More Evidence for Dark Matter • Rotation Curve: how fast things are orbiting in a galaxy compared to their distance from the center • Stars are orbiting way too fast in our galaxy. • Galaxies should also be flying apart! • … unless there’s hidden mass.
What is Dark Matter? • MAssive Compact Halo Objects (MACHOs) • black holes • white dwarfs • neutron stars • brown dwarfs • Weakly Interacting Massive Particles (WIMPs) • neutrinos • some exotic particles we have yet to prove the existence of (LHC!) Not enough to account for most of the dark matter.