Ch. 17 The Milky Way Galaxy

An average star that is farther out from the galactic center than our sun would most likely be moving

at about the same speed as our sun

The closest star to our sun is about four light years away, in the center of our galaxy, a typical distance between neighboring stars would be

.04 light years

The closest star to our sun is about four light years away. In the center of our galaxy, a typical distance between neighboring stars would be

.04 light years

The distance from our sun to the center of the Milky Way Galaxy is roughly

30,000 light years

The constellation Sagittarius is where the Milky Way

Is thickest

The source that is called Sgr A* emits

both x-rays and radio waves

In our Milky Way, the Orion Spur is

closest arm to our sun

The velocities with which stars and gas clouds orbit the center of our galaxy is measured by observing their

doppler shifts

The Big Bang theory predicts that most of the dark matter in our galaxy and elsewhere must consist of something other than the known chemical elements. This prediction

has been tested by looking for rogue planets

Cepheid variable stars with the same luminosity usually

have similar periods

The stars of the Milky Way are mostly found

in a band of stars stretching across the sky

One indication that there is a lot of invisible matter in the outer halo of our galaxy is that the stars in that region orbit with velocities that

increase with increasing distance from the center

Extragalactic nebulae such as the Great Nebula in Andromeda were not immediately recognized as galaxies similar to our own Milky Way because they were thought to be

smaller, nearby objects

The mass of Sgr A* has been determined by observing

the motions of stars near it

The main evidence for the presence of invisible matter in our galaxy is

the velocities with which stars orbit

Our sun is roughly at the center of

the visible part of the Milky Way.

The theory that dark matter is not real and is just a a problem with our theory of gravity has been falsified by

an observation of what happens when clusters of galaxies collide

How many stars similar to our sun would need to be collected at once place to equal the power output of Sgr A*?

a million

The overall shape of our Milky Way Galaxy is thought to be

a spiral somewhat like the nearby Andromeda Galaxy

Observations of the collision of two galaxy clusters have shown that dark matter

is not the result of an incorrect theory of gravity

The motions of the stars near Sgr A* make it possible to determine its

mass

The mass that is distributed in different parts of our Milky Way Galaxy is estimated by

measuring how stars orbit the center of the galaxy

Near the center of the Milky Way there is an intense radio source whose mass is approximately three

million solar masses within several light days of the center.

In comparison to RR Lyra variables, Cepheid variable stars are

more luminous and less common

In a spiral galaxy, long-lived stars such as our Sun

move in and out of spiral arms

The observation that stars father from the center of our galaxy orbit faster is thought to mean that

much of the mass is outside the central bulge

Population I stars in our galaxy include

only younger stars such as our sun.

The population II stars of our Milky Way

orbit the central bulge in all directions.

The doppler shift of familiar spectral lines from gas clouds and stars in our galaxy measures their

orbital velocities within the galaxy.