Galaxies Flashcards Preview

My Astronomy Notes > Galaxies > Flashcards

Flashcards in Galaxies Deck (30):
1

In which constellation seen from Earth is the centre of the Milky Way located?

Sagittarius

2

What is a Galaxy?

A group of billions of stars bound together by gravity

3

What is in the centre of a galaxy called?

A bulge of stars, also called a galactic nucleus

4

Outside of the galactic nucleus where are the rest of the stars located?

On a narrow disc or disk

5

On the disc what is the dust in between stars called?

Interstellar medium

6

From above the disc is made up of different what of stars?

Spiral arms

7

What is the area called in the centre of a galaxy where lots stars are formed?

The galactic bar

8

Where is the best place to view the centre of the galaxy from Earth?

The Southern Hemisphere

9

How is our solar system Angled to the disc of the Galaxy?

It is slightly above the main disc and is really quite tilted

10

Which is w particularly useful wave length to use when observing the Milky Way? Why?

21cm wavelength, in the radio wave category. This is useful because hydrogen gives this wavelength off and most matter in the universe is hydrogen , these wavelengths tend to go straight through material that would absorb visible waves

11

How are hydrogen waves picked up?

By huge radio telescopes or arrays of many of them

12

Around how far away from the centre bulge / galactic nucleus is the Earth?

Around 2 thirds of the way out

13

What are groups of stars called?

Clusters

14

What are the 2 types of clusters?

Open clusters and globular clusters.

15

What are open clusters?

A group of stars which are loosely bound by each other’s gravity. All the stars are around the same age as they formed from the same nebula, they don’t live long from around a few 100 million to 1 billion years. They are located on the disc

16

What are globular clusters?

A roughly spherical group of old stars and have a stronger mutual gravitational attraction. They are larger than open clusters and orbit the centre of the galaxy above or below the disc in what is call d the galactic halo

17

The Milky Way has approximately how many globular clusters? Counted so far

158

18

What are all the ams of a galaxy doing?

Rotating around the middle of the galaxy

19

How long does it take a galaxy to rotate approximately?

225 - 250 Million years

20

What happens to the wavelength (21cm hydrogen)of an object is moving away from where you are observing it? What is this called?

We’ll measure longer than 21cm which will make it appear nearer red on the wavelength spectrum. This is redshift.

21

What happens to the wavelength (21cm hydrogen) of an object if it is moving towards where you are observing it? What is this called?

We’ll measure shorter than 21cm, making it nearer blue on the wavelength spectrum. This is called blueshift.

22

How do we know the galaxy is rotating?

By measuring blueshift and redshift

23

What are the 3 types of AGN?

Seyfert, Quasars and Blazars

24

What does AGN stand for? What is it?

Active Galactic Nuclei
They are galaxies which have a radiation emitting centre

25

What is a Seyfert galaxy?

An AGN that look like normal galaxies in visible wavelengths but have a brighter core, which is radiation emitting. It is aligned so it’s North and South galactic poles are not in the direction of us/ Earth, they have the same sort of plane/ poles as out galaxy

26

How many different types of Seyfert galaxies are there? How are they different?

Type I emits a lot of UV and X-ray radiation
Type II emits a lot of infrared radiation
There are 2 types in total

27

What is a quasar galaxy?

An AGN that doesn’t appear to have much of a galaxy around it but is bright across the whole of the EM spectrum, they are strong radio sources as they have been red shifted, meaning they are very far away and young

28

What are Blazars?

An AGN similar to a Seyfert but is aligned differently such that the galaxies galactic North or South is directed at us/ Earth. They vary massively in brightness over time and fire huge amounts of gamma rays towards us

29

What does radiation come out of galaxies in?

In jets of energy

30

What are the types of galaxies (there shape/ classification)?

Elliptical galaxies (nearly circular to very eccentric)
Lenticular , a central bulge surrounded by a disc but the disc isn’t broken down into spirals
Spiral galaxies barred and regular
Irregular (2 galaxies have crossed and messed them up)