Galaxies & Deep Space This is NGC It’s a typical spiral galaxy in the constellation Coma Berenices, is about 55,000 light-years in diameter and approximately 60 million light-years away from Earth. What is a galaxy? A galaxy is a system of stars, interstellar dust and dark matter all caught in the gravity of a supermassive black hole.

Galaxies & Deep Space This is an image from the Hubble Space Telescope using the Ultra Deep Field View. All the galaxies in this picture fit inside the tiny red square beside the moon there. How many Galaxies are there? There are 100’s of billions of galaxies in the observable universe. A billion is such a large number that it would take you nearly 32 years to count to it one Mississippi at a time!

Galaxies & Deep Space This is what the Milky Way looks like. Is it a real picture?? It is a real picture actually! But it’s not the Milky Way. Why don’t we have a picture of our won galaxy like this ? Our arms just aren’t long enough to take a selfie! There’s no technology that can travel fast enough and far enough to take a picture of the Milky Way. Voyager has been travelling for 36 years and it only recently left our solar system!

We’re about here

 Draw 4 pictures of the stages of galaxy collision.  They don’t have to be right, just have a guess! Before Collision Starting to Collide Mashed up!After Collision

 0GaBQ494E

Ellipticals Most galaxies without spiral arms tend to be either irregular or elliptical. It’s actually really rare that you’ll see a perfectly round galaxy. This is just because elliptical galaxies like this tend to collect matter randomly and be a little disordered. The stars in an elliptical galaxy don’t follow any specific orbit and tend to be fairly chaotic. Because of this the combined effect of gravity causes the centre to be really bright and dense.

Spiral Galaxies Spiral galaxies are less dense than elliptical ones as they tend to be more ordered.

Spiral galaxies Spiral galaxies are made up of a circular disk with a big bulge in the centre.

Spiral Bulge This is an image of Messier 81, a galaxy with a classical bulge. Notice that the spiral structure ends at the start of the bulge. The centre of a galaxy like this tends to be a kind of reddish colour. This is because all the old stars gather here. Old stars tend to be big and red but they’re not the hottest or the brightest! We’ll look at this later.

Spiral arms This is M51, considered to be a classic example of a spiral galaxy. At a distance of about 30 million light years from Earth, it is also one of the brightest spirals in the night sky. Do we remember what triggers stars to form? The arms in a spiral galaxy are the star-forming region due to the gravity shockwaves they cause. They crush the gas and dust in the star-forming nebula and begin chain reactions that cause the birth of stars. That’s why the arms are so bright.

Spiral Galaxies Do the arms move around the black hole in the center? Yep! It takes a really really long time though! Our solar system is 4.6 billion years old and it’s only gone around about 20 times! That’s just us though, the closer you are to the black hole, the faster you spin. This is because of centrifugal motion. We’ve seen this with our own solar system.

Barred Spiral Some spiral galaxies have a kind of bar going through the middle of them like this. We just called these “Barred Spiral Galaxies”. Do you remember from the Hubble pitchfork how we classify these? SB(a,b or c) What do you think this guy should be? SBc

How did the bar get there? NGC 1300, viewed nearly face- on by the Hubble Space Telescope image. Two thirds of all spiral galaxies are Barred Spirals. How do you think the bar forms in the middle? Well we’re not actually sure! Most people seem to think the bar acts as a kind of channel for all the gas in the arms to reach the centre. This results in an Active Galactic Nucleus which is a hive of activity!

Active Galactic Nuclei Active galactic nuclei are really dense clusters of stars spitting out energy like a big radiation fountain. This is another Hubble Space Telescope image of a light-year-long jet being ejected from the active nucleus of the active galaxy M87, a radio galaxy. The blue synchrotron radiation of the jet contrasts with the yellow starlight from the host galaxy.

Lenticular Galaxies These guys are kind of at a halfway point between elliptical galaxies and spiral ones. They have arms but they’re just not long enough to spiral. See the how the bar can still form though?

Irregulars These guys tend to show up after a nasty bump with another galaxy. They’re messy and don’t really have any proper shape but they’re probably the most colourful and pretty! (you’ll see soon). When two galaxies collide they create tons and tons of shockwaves. What do you think this means? SO MANY STARS

Irregular galaxies The Hubble Space Telescope’s best ever image of the Antennae Galaxies.

Irregular Galaxies This is one of the most active star forming regions in the night sky. The Large Magellanic Cloud, a nearby satellite of the milky way.

The HR diagram The Hertzsprung-Russell diagram shows the relationship between brightness and temperature of a star. Are the biggest stars always the hottest? Actually no! The main sequence is the big line that our sun follows too. These are suns which are just fusing hydrogen.

Supernovae What is a supernova? A supernova is a stellar explosion that’s so bright it can briefly outshine a galaxy. How do supernovae happen? They happen when a sun reaches the end of it’s lifetime. The most common is when a white dwarf starts to accrete matter from a neighbour star, sending it’s mass over the limit and causing a type 1a supernova. This is the crab nebula. It’s a big stellar wind left over from a supernova.

Hubble caught this guy getting ready to explode.

Type II supernovae Type II supernovae happen when a giant star skips the white dwarf stage and just goes boom when it’s at it’s biggest and baddest stage. These events are pretty rare but absolutely huge! A star has to be at least 8 times bigger than our sun to go supernova like this. They usually leave behind a neutron star and sometimes a black hole. This is the eskimo nebula. They probably called it that because it looks like a dude with a big fluffy hood.

Cat’s eye nebula

Planetary Nebulae As big stars flash through their lifetimes they leave behind these masterpieces.

Betelgeuse Betelgeuse is the shoulder of Orion. She’s a massive red supergiant set to go supernova any day now! Betelgeuse is about 600 times wider than our sun so when it does go supernova it’s sure going to be bright!!