Galaxies

Our Solar System – a Speck in the Milky Way

•Our galaxy is about ____________in diameter▫What’s a ly again?

• It is _______________thick at its widest point near the core

•Our solar system is very tiny compared to the whole Milky Way

•A beam of light from the Sun would take _____________ to cross the entire Milky Way▫But it takes only _________to get to Neptune!

:o

Our Milky WayOur Milky Way

•Looks like two fried eggs stuck back to back (from the side)

•Looks like a giant whirlpool (from the top)

•Our Sun takes about 220 million years to travel once around the centre of the galaxy

•This means that in millions of years, people will see different stars at night

•If our solar system was a single bean, the Milky Way would be a bit larger than the area of Lake Superior

_________________ Galaxy

•One of the ______________ galaxies to us

•You can see it from Britain

•It is __________________ away

Oooo-aaaah!•The most distant galaxies are _____________________ away

•When light left them, the Earth did not exist!!

Properties of Galaxies

•All galaxies contain _________, ______________ and ____________

•More dust means more ___________▫Stars form from dust and gases present in

_________________▫__________________ galaxies have less dust

because it has all been used up in star-making

Properties of Galaxies1. Black Hole

▫ It is a region of space where ____________ is so strong that nothing (not even light) can escape

▫ It’s believed that each galaxy contains __________ supermassive black hold at the _____________

Milky Way: at centre, many stars are orbiting around a point in space that seems empty

▫ Affects its surroundings by __________________ Can pull a star right into it, destroying the star

This will increase the ____________ of the black hole Milky Way: ours has a mass of ____________________

stars like our Sun▫ When two galaxies collide, the black holes will

_____

Properties of Galaxies2. Dark Matter

▫ It is matter in the universe that is ___________ It does not interact with _______or other

radiation▫ Astronomers think that __________ of the

universe is filled with dark matter Why?

Unexpected _______________ of galaxies▫ Milky Way: stars revolve around centre so fast,

they should be flung off but aren’t

▫ Most of the ______________ in the universe is thought to be produced by ________________

Properties of Galaxies3. Star Clusters

▫ This is a ______________________ of stars▫ Has a concentration of stars in a smallish

region of space▫ Two types:

1. ______________ Cluster Contains a few hundred to a few thousand stars One of the _____________star groups in a galaxy

2. ____________________ Cluster Contains hundreds of thousands of stars,

drawn together by the stars’ gravity One of the _____________star groups in a galaxy

Properties of GalaxiesOpen Cluster Globular Cluster

Galaxy Shapes

•Galaxies are commonly classified according to four main shapes:

1. __________________________2. __________________________3. __________________________4. __________________________

Galaxy Shapes1. Spiral & Barred Spiral

▫ Have spiral-shaped _____coming out from the centre

▫ Half of all spiral galaxies have a bar across the ________

These are called barred spiral galaxies (E.g.: Milky Way)

▫ A typical spiral galaxy completes a full rotation once about every __________________________

▫ Most spiral galaxies have hundreds to thousands of star _____________________

Due to the dust and gases between stars (breeding ground for new stars)

▫ At the core, has a “_______________” with mostly old stars (not enough dust an gases here)

Galaxy Shapes

3. Elliptical Galaxies▫ Looks like a _________________________▫ Can look almost _______________▫ Can look ___________________________▫ Can look long and cylindrical like a

_________▫ Happens when spiral galaxies _________▫ These are the _____________galaxies▫ Don’t have a lot of dust fewer young

stars

Galaxy Shapes

4. Irregular Galaxies▫ Neither spiral nor elliptical▫ No ________________shape▫ May have happened because...

Two galaxies ____________________ Two galaxies got _______ enough that the

gravity of one ______________ stars from the other

Galaxy ShapesSpiral Galaxy Barred Spiral Galaxy

Galaxy ShapesElliptical Galaxy Irregular Galaxy

Learning Checkpoint

1. What is a galaxy?2. What is thought to be at the very centre

of all galaxies?3. What is dark matter?4. Sketch the general shape of a spiral

galaxy as viewed from the side and then as viewed from above.

5. State one possible way that elliptical galaxies form.

Galaxy Clusters•The universe does not end at the Milky

Way!•The Milky Way is part of a group of

________ galaxies▫This is called a galaxy cluster▫Ours is called the ___________________

More than _____________ stars are inside it•The Local Group is part of the Local

Cluster•The Local Cluster is part of the Local

Supercluster...

Galaxy ClusterMiss Strilchuk

700 Main Street WestHamiltonOntarioCanadaEarth

Milky WayLocal GroupLocal Cluster

Local SuperclusterThe Universe