CH. 15: Dark Matter

Label the parts of the Milky Way as shown here by identifying the galactic plane, an area far from the plane, and the area that is close but not on the galactic plane.

far from galactic plane: space away from the center
on the galactic plane: on the mainstream down the center
in between on and far from the galactic plane: the space between on the center and the top where far of the galactic plane is

What does the abundance of heavy elements tell you about the origin of a star?

 The more heavy elements a star has, the more recently it was formed.

How do astronomers know that dark matter is present in galactic halos

the speeds of orbiting stars remain about the same far from the center of the galaxy

How do astronomers detect dark matter?

by comparing luminous mass to gravitational mass

Based on hydrogen emission, where is star formation occurring? 

the right and left arm

Describe the Milky Way Galaxy

mostly dark matter
has globular clusters
has two major arms

What do the following images depict?

The different stages in evolution of a high-mass star’s life

Why are older stars found farther from the midplane of a galactic disk?

stars have lived long enough to move there

Why are most of the Milky Way’s satellite galaxies so difficult to detect?

They are very faint

What are cosmic rays?

high-energy particles

What can be deduced when looking at the galactic center and seeing that there is no redshift or blueshift?

The sun and the center are not moving toward or away from each other

How was dark matter first detected?

the rotation speed of galaxies was too high for the amount of gravity that could be present due to the luminous mass

Why is the Andromeda Galaxy now moving toward us?

This is due to the mutual gravitational attraction between the Milky Way and Andromeda galaxies.

The images depict the stellar “recycling” that takes place as the death of stars provide materials for the birth of new ones

label the stages starting from the top and follow the arrows

interstellar medium, star formation, supernovae and stellar mass loss, stellar nucleo-synthesis

Where is the Sun located in the Milky Way Galaxy?

What is the best evidence for dark matter in the Milky Way?

the observation that the rotational curve is quite flat at great distances from the center

Which technique/tool helped determine the size of the galaxy?

Globular clusters as standard candles

Which technique/tool helped determine the rotational curve of the galaxy?

Doppler shift of 21-cm line in H II clouds

Which technique/tool helped determine that there is a black hole in the center of the galaxy?

Kepler’s laws applied to star motions

Which technique/tool helped determine the age of the galaxy?

Main-sequence turnoff of globular clusters

Which technique/tool helped determine the high star formation of the galaxy?

Spectral analysis of star atmospheres

Why are spiral arms like traffic jams?

they only last a short time
are composed of objects that enter and leave constantly

Rank the slowest astronomical phenomena to the fastest

The following figure depicts the dense molecular clouds in the midplane of the galaxy. Identify key features of this region.

green part with arrows- Composed mostly of molecular hydrogen, and where many stars are born
green arrow at the top- Energy emitted when charged particles are accelerated in a curved path
blue at the bottom- Mostly fast-moving protons, but some are nuclei of helium and carbon
pink line- A field that helps describe the electromagnetic properties of various points in space