astro 1030 - the milky way galaxy
What does the galactic center appear to have?
(1) a ring of molecular gas 400 pc across (2) a rotating ring or disk of matter a few parsecs across (3) a stellar density a million times higher than near Earth (4) strong magnetic fields• a strong X-ray source at the center
What does the galactic structure include?
(1) halo (2) disk & spiral arms (3) bulge (4) nucleus
What is the steps of the cosmic distance ladder?
(closest to Earth) radar ranging stellar parallax spectroscopic parallax variable stars (farther distance)
What did Herschel's findings look like?
(dust blocked a lot of the stars, leading to the irregular shape)
What does the galactic center look like in visible light?
(the two arrows in the inset indicate the location of the center, but it is entirely obscured by dust)
What is the abbreviation for 1 parsec?
1 pc
How many parsecs away is the nearest star to our solar system?
1.3 pc
How many light years away is the nearest star?
1.3 pc = 4 light years
How many parsecs are in 1 kiloparsec (1 kpc)?
1000 parsecs
What is 1 parsec (1 pc) equivalent to?
200,000 AU's
What is the distance to the Virgo Clusters?
25 million parsecs = 25 Mega-Parsecs (25 Mpc)
How far away is the moon?
250,000 miles away
What is the distance across the galaxy?
30 kpc (60 quadrillion miles; 6 x 10^17 miles)
How many light years is in a kiloparsec?
3260 light years
How many miles is 1 parsec?
6 trillion
What is the distance to the center of the galaxy from Earth?
8 kpc
How many miles across is Earth?
8,000 miles across
What is the distance to the Andromeda Galaxy?
800 kpc
How many miles across is the Sun?
800,000 miles across
How far away is the sun?
93,000,000 miles away
Who did one of the first attempts to measure the Milky Way?
Herschel
Why couldn't Herschel see the real structure of the Galaxy?
Interstellar dust blocks visible light from distant stars
What does our parent galaxy look somewhat similar to?
M81
The period-luminosity relationship is a crucial component of:
Measuring the distance with Cepheid variable stars
What does our galaxy look like?
Our galaxy consists of a disk of stars and gas, with a bulge of stars at the center of the disk, surrounded by a large spherical halo.
What all have about the same luminosity?
RR Lyrae stars
What have essentially the same luminosity curve, with periods from 0.5 to 1 day?
RR Lyrae stars
What are the two types of intrinsic variables that have been found?
RR Lyrae stars Cepheids
The location of the galactic center was identified using:
RR Lyrae stars in globular clusters
Where does variability of these stars (intrinsic variables) come from?
a dynamic balance between gravity and pressure
The spiral pattern of radio emission arising from Sagittarius A itself suggests what?
a rotating ring of matter only a few parsecs across
What kind of galaxy is our parent galaxy?
a spiral galaxy
The high speed motion of stars near the Galactic center is explained by:
a supermassive black hole
With RR Lyrae stars, knowing their what allows us to calculate the distance
apparent magnitude
Faster orbits =
bigger Doppler shifts
What has a luminosity that is strongly correlated with the period of their oscillations?
cepheids
What is the usefulness of RR Lyrae stars and Cepheids?
comes from their period-luminosity relationship
More gravity =
faster orbits
Where are globular clusters located in the galaxy structure?
halo
Where are old stars located in the galaxy structure?
halo
Where are random orbits located in the galaxy structure?
halo
Where are red stars located in the galaxy structure?
halo
Where is no gas located in the galaxy structure?
halo
How did Herschel attempt to measure the Milky Way?
he used the visible stars
What was Herschel unaware of when attempting to measure the Milky Way?
he was not aware that most of the galaxy, particularly the center, is blocked from view by vast clouds of gas and dust
How can you tell the difference between neutron stars and black holes?
if you can determine their mass
Stellar orbits in the disk are what?
in a plane and in the same direction
Where are many RR Lyrae stars found?
in globular clusters
Where would every star you've ever seen in the night sky be located on our galaxy?
inside a tiny circle compared to the overall galaxy
What has large oscillations around stability?
intrinsic variables (RR Lyrae stars Cepheids)
Whenever you have strong X-rays and gamma rays, what is the most likely cause?
is a neutron star or a black hole
With cepheids, once the period is measured, what is known and what happens?
luminosity; we then can proceed by calculating their distance by knowing their apparent brightness
The best way to determine the mass of a celestial object is to what?
measure orbit of the stars, planets, or moons orbiting around it
More mass =
more gravity
What are orbits in the halo and bulge?
much more random compared to the disk orbit
To measure the gravity from a celestial object, you need to measure what?
orbits of objects around the object being measured
What can we not get an actual picture of?
our galaxy, the milky way
What does the radio image of the galactic center show (and what does it look like)?
provides a view of the matter in the immediate vicinity of the Galaxy's center
What is the period of a cepheid variable?
ranges from about 1 day to 100 days
What does the infrared image of the region around the center of our Galaxy show (and what does it look like)?
shows many bright stars packed into a relatively small volume
What does the X-ray image of the galactic center show?
shows the relation of a hot supernova remnant (red) and Sgr A*, the suspected black hole at the very center of our Galaxy
Where is the halo located?
spherical region around whole galaxy
Where is the bulge located?
spherical region in center of disk
What are called intrinsic variables?
stars whose luminosity varies in a regular way, but much more subtly
What has little star formation?
the buldge
What has mostly random orbits in the galaxy structure?
the buldge
Where is there little gas located in the galaxy structure?
the buldge
Where are yellow/red stars located in the galaxy structure?
the bulge
With variable stars, what have we expanded?
the cosmic distance ladder
Where are blue colors located in the galaxy structure?
the disk
Where are forming star gas clouds located in the galaxy structure?
the disk
Where are most circular orbits found in the galaxy structure?
the disk
Where are most young stars located in the galaxy structure?
the disk
Where are open clusters located in the galaxy structure?
the disk
Where are spiral arms found?
the disk
Where is the nebula located in the galaxy structure?
the disk
What is 1 astronomical unit?
the distance between the earth and the sun (93,000,000 miles)
What are not all in the plane of the galaxy, so they are not obscured by dust and can be measured?
the globular clusters that have RR Lyrae stars
For two massive objects, what is proportional to the product of their masses divided by the square of the distance between them.
the gravitational force (Newton's Law)
To measure the mass of a celestial object, you need to measure what?
the gravity from the object
What is our parent galaxy?
the milky way galaxy
What emits x-rays?
the nucleus
What has some gas in the galaxy structure?
the nucleus
What has very rapid orbits of stars?
the nucleus
What shows gamma-rays (something weird)?
the nucleus
What/where is the galactic center?
the nucleus (the middle)
Gas needs to be traveling nearly at what for this strong x-rays and gamma rays to be created?
the speed of light
What allows us to measure the distance of RR Lyrae stars and Cepheids?
their period-luminosity relationship
Where does gas need to be at the speed of light for gamma rays and x-rays to be produced?
usually near compact objects
What are called cataclysmic?
variable stars (novae, supernovae, and related phenomena)
What happens when gas falls into black holes (and neutron stars)?
x-rays