Galaxies and Dark Matter

active galaxy

A galaxy that emits an exceptional amount of energy over a wide range of wavelengths, from radio waves to X-Rays.

Quasars

An enormously bright, distant galaxy with a giant black hole at its center

Which of the following statements about the different types (shapes) of galaxies is correct?

Collisions and mergers between galaxies can sometimes change a galaxy's type.

spirals merging:

Elliptical

Which type(s) of galaxies don't currently have much star formation?

Ellipticals

What is the period-luminosity relation and who came up with it?

Henrietta Swan Levitt came up with it, the longer the period the greater the absolute magnitude

Which of the following statements about the implications of Hubble's Law is FALSE?

If you were observing the universe from a distant galaxy, you would NOT see all of the galaxies (except those in your own group) moving away from YOU

Describe the role and scale of dark matter.

It holds galaxies together, and is the dominant thing in galaxies. We can only see dark matter on the scale of galaxies

Which of the following objects is NOT considered useful to astronomers as a "standard bulb" for determining distances?

K-type stars

What is Hubble's law?

Knowing the distant tells how fast a galaxy is receding away

What is redshift and how do we calculate it?

Light trying to leave the galaxy gets redder as it recedes. We calculate it with ((Ho)/C)d = z

What is the difference between RR Lyrae and Cepheid variables?

RR Lyrae are about a day, Cepheid variables last for months (Both are standard candles so we can measure their galaxies)

Virgo Cluster

The cluster of galaxies of which our local group is a member. Contains roughly 2000 galaxies

Why are supermassive galaxies often found at the cores of rich galaxy clusters?

They have more stuff to eat (merge)

Sombrero Galaxy

Type Sa, large central bulge (lenticular)

starburst galaxy

a galaxy undergoing a rapid burst of star formation due to merging of galaxies

How did Hubble show that there are other galaxies?

by observing a Cepheid variable in a nearby galaxy and using it to get the distance

Antennae Galaxies

collided recently, sparking stellar formation

What was done by Edwin Hubble?

discovering the law about the motion of the galaxies away from us;classifying the galaxies by their shapes;establishing the expansion of the universe;. measuring the distance to the Andromeda "nebula"

What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?

finding the red shift and using Hubble's Law

The Tully-Fisher method for measuring the distance to galaxies relies on the observed relationship between the luminosity of a spiral galaxy and

its rotational velocity (as determined from the width of the 21-cm line)

The type of galaxy that sometimes has a distinct bar of stars running across the central region is

spiral

gravitational lensing

the distortion of the appearance of an object by a source of gravity between it and the observer

The Andromeda Galaxy (our nearest spiral neighbor) has spectral lines that show a blue shift. From this we may conclude that

this particular galaxy is moving towards us

local group of galaxies

a cluster of 28 or so galaxies that includes our own Milky Way Galaxy. the surrounding galaxies are gravitationally bound

Supercluster

a gigantic region of space in which many groups and clusters of galaxies are packed more closely together than elsewhere in the universe

One of the main projects being carried out by the Hubble Space Telescope is to measure the distances of galaxies located in groups dozens of millions of lightyears away. What method do astronomers use with the Hubble to find such distances?

finding Cepheid variables and measuring their periods

The reason type I supernovae are useful to astronomers for determining distances to other galaxies is that

they are very bright, and generally reach the same peak luminosity

Hydrogen gas

used as radio light source to image dark matter, represents cold gas and if it's moving; combines with x-ray to make hot gas

Baryonic Matter

"ordinary" matter consisting of protons and neutrons that comprises atoms, planets, stars, galaxies, and other bodies; gives off light

Implications of Hubble's law?

1. The law does NOT require us to be at the center of the expanding universe. 3. The law implies that the whole universe must be expanding. 4. The law can be used to measure distances to remote galaxies for which we can measure a Doppler Shift. 5. Although galaxies move away from each other, they themselves are not expanding in size

What is the age of the universe and how does that relate to the Hubble constant?

14 billion, its 1/Ho = To

What is the value of H0?

72 km/s/megaparsec

In a distant galaxy, whose light is just arriving from 9 billion light years away, our spectroscope should reveal that the most common element is

hydrogen

Hubble Deep Field

is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope.

If a galaxy contains a great deal of dark matter, then, compared to the mass-to-light ratio of the inner part, the mass-to-light ratio of the whole galaxy will be

more

According to Hubble's Law, if two galaxies are not part of our Local Group, and galaxy B is three times farther away from us as galaxy A, then galaxy B will

move away from us three times faster than A

A graduate student in astronomy needs to measure the mass of a spiral galaxy she is studying for her PhD thesis. Which of the following observations would be important for her to make?

obtain the rotation speed of stars or gas near the outer regions of the galaxy

Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the

the faster it is moving away from us

What type of galaxy is the milky way? Andromeda? Large and small Magellanic clouds?

Milky: Barred Spiral Andromeda: Normal Spiral Magellanic Clouds: Irregular

What does "red and dead" mean in terms of galaxies?

Not making any stars. The gas is heated, and the galaxies are very old

What are "rich' vs "poor" galaxy clusters?

Rich galaxy clusters have a lot of galaxies, poor galaxy clusters do not, ex of poor: local group

What results from irregular/dwarf galaxies merging?

Spiral

irregular and a spiral merging:

Spiral

What are lenticular galaxies?

Spiral galaxies that don't have gas (S0)

The type of galaxy that consists almost entirely of old stars and is thus less blue (more yellow and reddish) than the other types is

elliptical

Which type of galaxy has the highest massto-light ratio?

elliptical