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# Stars Test 3

### 3rd Test for Stars the Galaxy and the Universe.

The laws of physics are identical in any inertial frame of reference.
Special relativity All observers will see that light moves at a speed c, regardless of the frame of reference.
Space-time Events occur in a four-dimensional "space-time" What is perceived as space and what is perceived as time depends on the frame of reference.
Consequences of Special Relativity Moving clocks run slowly. An object in motion is shorter than an object at rest. Different observers disagree on what things happen at the same time.
Lorentz Factor How much time is dilated or length shortened by high velocity. gamma=sqrt(1/(1-(nu^2/c^2))).
General Relativity Mass warps space-time much as a bowling ball warps in a rubber sheet. Light rays are curved by gravity. Mass distorts the geometry of space time.
geodesic curved lines or obits that are caused by mass/gravity
Gravitational lensing Light travels on the geometry of spacetime, so gravity can deflect the path of light
Gravitational redshift Stretches the wavelength of light leaving a large mass.
Gravitational waves. Travel through the fabric of spacetime at the speed of light.
Free fall the same as free float.
Equivalence Principle Free fall is the same as free float. When you are falling freely in a gravitational field, you are in an inertial frame of reference!
Black holes Singularities in spacetime.
Event horizon Boundary of the black hole. The point of no return. 1M. black hole = 3 km.
Hawking radiation Black hole lose more mass than they gain through other means, are expected to shrink and ultimately vanish.
Galaxy Self-gravitating "collection of stars". Vary widely in size and shape and can contain from about 1 million to >400 billion stars.
How galaxies are classified? Appearence
Spiral Galaxies Flattened and thin. Can look round if face-on, flat if edge-on. Mostly cold gas in spiral. Where new stars form.
Elliptical Galaxies Some galaxies are oval-shaped from any angle. Mostly hot gas, no star formation in elliptical galaxies.
Irregular Galaxies. Neither Spiral nor Ellipitcal.
Types of spiral galaxies plain and barred. classified by how bright the center is and how tightly wound the arms are.
Sa/SBa bright center, tight arms.
Sc/SBc dim center, loose arms.
S0 elliptical
Sizes of galaxys Size does not determine a galaxy's appearance. An elliptical galaxy can be a dwarf galaxy or a giant galaxy. BUT! All spirals are large.
What the different light waves show about a spiral galaxy ultraviolet light will show massive, young, hot stars concentrated in the spiral arms, in red light we see less concentrated older stars in the arms, and from hydrogen emissions, see massive stars forming in spiral arms.
Gas and dust are concentrated along the spiral arms. Clouds are compressed in the arms. Hot, young O and B stars produce UV/blue light, that ionizes HII regions
Luminous Matter Normal Matter
Proof of Darkmatter Rotation speed should decrease with larger radius, when in fact, it does not.
How much dark matter is in a spiral galaxy? 95%. Located in a large, dark matter halo around the galaxy
Active Galactic Nuclei (AGN) Many galaxies have bright AGN. Quasars are extremely luminous. Luminosity of the AGN can eqaul that of the rest of the galaxy.
Quasar Closest one is 1 billion light years away. A center of violent activity in the hearts of large galaxies. Stand for "quasi-stellar radio source"
Seyfert galaxies and radio galaxies Low-luminosity cousins of quasars
percentage of galaxies that contain AGN 3%
What powers AGN? Light ranges from radio to gamma rays. Synchrotron radiation means large magnetic fields.
Supermassive masses of thousands to tens of billions of solar masses.
Unified model a central supermassive black hole with an accretion disk.
Supermassive Black Holes Jets of material shoot out from the poles of the system. A dense ring (torus) of dust blocks the central regions. What we see depends on the viewing angle.
How to determine the mass of a black hole By measuring the orbital speeds of gas near the black hole.
Supermassive black holes probably exist at the centers of all galaxies.
Normal galactic nuclei do not contain accretion disks.
AGN's source of fuel Material in the accretion disk. Without it, the black hole can only be found by gravitational effects.
Why don't all galaxies have AGN? They used to, but need interactions and mergers in order to perturb gas into the centers to feed the AGN. Once the gas is used up, accretion shuts off and the AGN goes quiet.
Hubble tuning fork
What kind of galaxy is the milky way? a barred spiral galaxy. Two major spiral arms. Middle-of-the-road giant barred spiral: SBbc galaxy.
The roll of dust in viewing the Milky Way. Dust blocks light, making things fainter. They look farther away. There is a lot of dust in our galaxy. infrared light view of the milky way is much smoother because dust absorption does not affect infrared light as much.
Three groups of Milky Way stars A large flat disk with spiral arms. The Sun is a disk star. A bright central bulge. A diffuse, extended halo of stars.
Distance of the center of the Milky Way from the Sun. The center of the Milky Way is 27,000 light years from the Sun.
Wavelength a neutral hydrogen gas emits lamda = 21 cm.
How do we know the milky way is rotating? Doppler shifts. When gas moves toward us, emission is blue shifted. When gas moves away from us, emission is red-shifted.
Rotation curve orbit speed is constant at all distances (a flat rotation curve.) Rotation yields mass of the milky way.
How to determine the age of the Milky Way? Difference in the ages of globular clusters. Open clusters are much younger. Hot, massive stars are found in disk. In milky way, we see no young globular clusters.
Determining the age of a star. The more massive elements found in a star, the more prior star formation took place.
How heavy elements are created. Elements heavier than boron must have been produced in stars then spread by supernovae and other processes.
Where do newly formed stars lie? close to the mid-plane. Younger stars appear close to the thin disk but will gradually diffuse away from the mid-plane. Older stars form a thicker disk about 12000 lightyears thick.
Massive stars emit UV light and strong winds which heat interstellar medium and ionize it. Hot gas and the UV light then escapes into the halo.
high velocity stars have large radial velocities (motions measured by the doppler shift), or proper motions (transverse motions on the plane fo the sky calculated by measuring stellar positions at different times. Members of the halo.
Cosmic rays charged particles moving at near the speed of light. (many are accelerated in supernova remnants.) have high energies, are trapped by the milky way's magnetic field.
Milky Way's black hole. there is a black hole at the milky way's center, which is revealed by it's gravity. about 4*10^6 M. Relatively quiescent and not classified as an AGN.
Emissions of falling gas onto the milky way's black hole. x-rays and gamma-rays.
Formaton of halo stars in the milky way. all halo stars have some heavy elements, so at least one prior generation of stars must have existed. halo objects were formed before interstellar gas was concentrated into the disk. Later star formation was all in the disk.
How to find distances in out galaxy/to other galaxies. Globular clusters which are bound collection of up to a million stars. luminous and can be seen at great distances.
Created by: 29pachyderm