Astronomy Chapter 15

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Hubbel classified galaxies into what categories?: Spiral
Barred spiral
Elliptical
Irrecular
How are spiral galaxies named?: "S" means the galaxy is a spiral galaxy. and in lower case letters a-d (a=largest bulge, c=smallest bulge)
Barred spiral galaxies: look just like spiral galaxies but they have a bar along the bulge. these are named as "SB" with the same lowercase a-c designation for its size of bulge.
How are eliptical galaxies named?: "E" and then they are given a number from 0 to 7 depending upon the magnitude of their elongation (0= completely circular while 7= eliptical)
What are teh two classes of eliptical galaxies?: Giant elipticals= more than 1 trillion stars

Dwark ellipticals= more than 1 million stars
Eliptical galaxies -gas -star formation -age -color -similar to what portion of the milky way: little or no gas

no star formation

older

redder

Halo
What are S0 galaxies?: Galaxies that are between elipticals and spiral galaxies
what if the galaxy has a bar, how is it denoted: SB0.
Irregular galaxies are further divided into what two categories...: Irr I- irregular spirals

Irr II- irregular others
In general, irregulars are...: smaller than most spirals but larger than dwarf ellipticals
What are the Megallanic clouds?: Two irregular galaxies that can be seen with the naked eye in the Southern hemisphere.
What two things are important to note about Hubble's galaxy tunning fork diagram: 1.) it is NOT an evolutionary sequence

2.) S0 (between elliptical and spiral) sits in the middle.
Because of Cepheid variable stars, we can now extend our distance ladder to...: 15 Mpc
Type I supernovae are also called "standard candles". because of their brightness we are able to see out to...: 200 Mpcs
What is the tully-fisher relation?: the relationship that exists between luminosity and rotational speed.
The distance ladder: Radar ranging, stellar paralax, spectroscopic paralax, variable stars, tully-fisher, standard candles, Hubble's law
What is the "local group"?: A group of about 20 galaxies including our own that is about 1 Mpc large
Most galaxies in the world are traveling around: with other galaxies in clusters of varying richness.
EVERY GALAXY (WITH A FEW EXCEPTIONS) IS...: RECEDNING AWAY FROM US (red-shiftted spectral lines)
What is the equation for calculating red shift?: z = delta lambda/lambda = v / c
Hubble later found not only that galaxies are receding from us but that...: those that are further from us are receding faster according to his equation.
What is hubbel's law?: V= Ho x D (Ho= 65km/sec Mpc)
What is the difference between Active galaxies and normal galaxies?: higher luminosities and a different spectra than normal galaxies.
What are three types of active galaxies?: Seyferts
Quasars
Radio Galaxies
Characteristics of Seyfert Galaxies: almost all LUMINOSITY from the center

BROAD emission line spectrum= high velocity in the center

VERY VARIABLE
What are radio galaxies?: Galaxies that unlike stars can emit most of their energy in the radio wavelength. Must be absolutely massive (millions of Pcs.)
How are radio galaxies further classified? what are the classes?: Depending on their "radio morphology"

Core-halo or Lobe
Core-halo radio galaxies: Most of the energy comes from a small nucleus in the middle surrounded by a weaker halo.
Lobe radio galaxies: The majority of the emission comes from the lobes.

Lobes occur where jets from the nucleus collide with intracluster gas.
What do some believe about core-halo and lobe radio galaxies?: they may be the same galaxies seen from different angles.
How do quasars appear in the sky?: appear stellar in the naked eye.

They are blue, with broad, strong and unfamiliar spectral patterns.
THE SPECTRUM OF A QUASAR IS ACTUALLY JUST ___________ BUT...: Hydrogen emission line spectrum but seen at much higher red shifts than any of Hubble's galaxies.
Quasars are -distance -size -luminosity -: Very far away

point-like (very small)

THE MOST LUMINOUS ACTIVE GALAXIES!
power source of an active galaxy?: central gravitational forces (black hole)

Infalling gas forms accretion disk

as gas spirals in friction heats the matter and creates high luminosities.

some of the gas is driven out through jets.

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