Galaxies

Question 1

Who is Magellan?

Answer 1

Portuguese Explorer Magellan gave his name to the Magellanic Cloud (only visible from the Southern Hemisphere).

Question 2

Who is Charles Messier?

Answer 2

Spent most of his life building the catalogue of stars. 110 nebulae and star clusters became known as “Messier objects” e.g. M13

In 1784 published a catalogue of 110 nebulae. (Nebulae is latin for ‘cloud’). He didn’t know what they were and ended up classing both galaxies and nebulae as nebulae. Today we know these to be different.

Question 3

What was The Great Debate in 1920?

Answer 3

In 1920, The Great Debate between Shapley and Curtis for our galaxy containing everything vs seperate galaxies. Hubble resolved the debate in 1924 using a 100inch telescope to observe Cepheid (regular frequency of brightness relative to its luminosity) variable stars in the Andromeda Nebula (M31).

Question 4

How many galaxies are there in the universe?

Answer 4

Approximately 100 thousand million.

Question 5

What are the types of galaxies?

Answer 5

Spiral-Bar
Irregular
Elliptical
Spiral
Lenticular

Question 6

What are spiral galaxies?

Answer 6

Spiral disks are relatively blue (hot, massive, young stars) and are still forming stars. Spiral tend to be a flat rotating disk with stars moving in all the same directions.

Question 7

What are lenticular galaxies?

Answer 7

Lenticular (lens-shaped) Galaxies = antenna galaxy - lie between spirals and ellipticals.

Question 8

What are elliptical galaxies?

Answer 8

Ellipticals tend to be much older so tend to be red due to the dominant population of odler lower-mass stars. Not much new star formation.

Question 9

What is a Density Wave?

Answer 9

As a Density Wave passes, gas is compressed leading to enhanced rates of star formation. Therefore a spiral is just a density wave which is why newer stars are predominantly in the arms.

Question 10

Where do you find newer stars in galaxies?

Answer 10

UV light is mainly from massive, hot young stars which are concentrated in the arms, older stars seen in red light (VIS = visible) are less concentrated in arms.

Question 11

What is Dark Matter?

Answer 11

Stars furthest out from centre of galaxy move as quickly as those nearest the centre. For the stars to move that quickly and not fly off into deep space it is postulated that ‘dark matter’ is holding it all together. It’s necessary for galaxies to form in the expanding universe.

Question 12

What are our neighbouring galaxies?

Answer 12

There are about 30 galaxies in our local group of galaxies including our milky way, andromeda (2.5m light years), the Magellenic cloud (being pulled into our own galaxy).

Question 13

What are Active Galactic Nuclei?

Answer 13

AGN emit light of 10,000 galaxies in a size small than solar system.

Powered by accretion (material falling onto) disk surrounding a supermassive black hole. As gas moves through that disk it gives off light.

Question 14

What is a supermassive black hole?

Answer 14

All large galaxies appear to contain a supermassive black hole at the centre.

One possibility is that SMBH are made by merging a pair of galaxies (to achieve 1bn solar masses).

Question 15

What do AGNs consist of?

Answer 15

Blazars, Quasars, Radio.

Question 16

What is a blazar?

Answer 16

The jet of light coming straight towards us is known as a blazar i.e. we are looking straight down onto the AGN.

Question 17

What are quasars?

Answer 17

Most luminous objects in the Universe (10-10,000 x brighter than galaxies)

Question 18

Which comes first the galaxy or the SMBH?

Answer 18

There is a link but we don’t know what that link is yet.

Question 19

What are radio galaxies?

Answer 19

Emit large amount radio emission

Emit jets of radiation extending millions of light years.

Question 20

When you view both redshift and blueshift light together what does this mean?

Answer 20

You are viewing something that is moving both towards and away from you i.e. cyclical.

Blue towards you, red away from you, both is cyclical.

Question 21

How hot is the material when it hits a SMBH?

Answer 21

As material is accelerated by gravity towards the black hole it slams into the accretion disk heating it to c100,000degs.

Radiation is emitted in visible –> UV –> X-rays.

Question 22

What is a parsec?

Answer 22

Parsec measures distance to objects outside of solar system by measuring a disc w/ radius of 1AU and how it appears to subtend (form at a particular point) at an angel of 1 arc second.

Astronomers don’t use “light years” but use “pc” (parsec).

1 light year = 0.3 parsecs (or 1 AU = 4.8 x 10(-6) parsecs).

Question 23

What is an arcsecond?

Answer 23

Arcsecond = 1/3,600 degree.

Question 24

How many stars are within our own galaxy?

Answer 24

Approximately 300 billion stars.

Question 25

What is a globular cluster?

Answer 25

Globular Clusters are”small towns of stars” (if you accept City being the Milkyway Galaxy).

Typically contain c50k stars. Globular Clusters move symmetrically under gravitational influence of the Galaxy.

Question 26

How far away is Earth from the centre of the Milky Way?

Answer 26

We are about 27,000 light years from centre of galaxy (which is 100,000 light years across).

Question 27

How do we measure the size of the galaxy?

Answer 27

RR Lyrae variable stars pulsate (with the same average luminosity) - i.e. appear fainter, must be further away. As we know how bright they should be we can measure how far they are depening on how bright they are.

Question 28

How do we measure distance of objects outside our galaxy?

Answer 28

Delta Cephids - used to measure things outside of our galaxy.

Question 29

What is the Galaxy Rotation Curve?

Answer 29

The stars at the very edge of galaxy are moving faster than at centre due to relative pull of gravity from nearby objects - more objects pull at the edge making the stars moving faster - as seen on Galaxy rotation curve.

Question 30

How do we galaxy rotation?

Answer 30

Can observe rotation through techniques such as Doppler shift and observing radio waves.