Formation and Motion of Galaxies

Galaxy Formation

Multiple Choice

What force causes a galaxy to form?

• Gravity

• Nuclear Fusion

• Kinetic Energy (Movement)

• Thermal Energy (Heat)

Pre-Assessment

What can you recall?

Multiple Choice

What is at the center of our Solar System?

• Earth

• The Sun

• A Black Hole

• Jupiter

Multiple Choice

In what Galaxy is Earth located?

• Andromeda

• Milky Way

• Sagittarius

• Snickers

Multiple Choice

Which of the following correctly lists bodies in space from the smallest to the largest?

• Earth, Sun, Solar System, Milky Way Galaxy, Universe

• Earth, Sun, Milky Way Galaxy, Solar System, Universe

• Sun, Earth, Solar System, Milky Way Galaxy, Universe

• Universe, Milky Way Galaxy, Sun, Solar System, Earth

What is a Galaxy?

• A group of billions of stars and their planets, gas, and dust that extends over many light-years and forms a unit within the universe.

• Held together by gravitational forces

"Discovery" of Galaxies

• Early astronomers observed these “spiral nebulae” and most believed them to be clouds of gas and stars within our own galaxy.

• In 1924, Edwin Hubble was able to measure the distance to the “Great Nebula in Andromeda” and found its distance to be much larger than the size of the Milky Way. 

Galaxy Classification

• Hubble divided galaxies into different “classes” based on their appearance.

• These are part of the "basic language" of Physics.

Spiral Galaxies

• Have long arms winding toward a bright bulge at the center.

• The difference between tightly and loosely wound spirals can be used to classify spiral galaxies.

• About 77% of the observed galaxies in the universe are spiral galaxies.

Elliptical Galaxies

• Shaped like a squished circle.

• Elliptical galaxies are classified by how stretched out they are.

• The most abundant type of galaxies found in the universe but because of their dim qualities, they're often outshone by other galaxies

Irregular Galaxies

• The catchall name given to any galaxy that does not neatly fit into one of the other categories.

• They have no defined shape nor structure and may have formed from collisions or violent activity. 

• Some of the smallest galaxies and are full of gas and dust, signifying star formation.

Learning Check!

What questions do you have?

Multiple Select

Which of the following are galaxy types?

Select all that apply.

• Spiral

• Elliptical

• Spherical

• Irregular

• Obloidal

Multiple Choice

Galaxies are classified and named according to their

• shape

• wavelength

• distance from Earth

• cosmic background radiation

Multiple Choice

Irregular galaxies are defined as having

• a rounded shape

• no real shape and are comparatively very small.

• "arms" branching from the center

Multiple Choice

Spiral galaxies are best described as

• irregular in shape with random star movement.

• regular in shape with mostly orderly star movement.

• having a huge round shape with mostly very old stars.

Multiple Choice

Elliptical galaxies can be described as having

• an uncertain shape with mostly old stars.

• a circular or elongated shape.

• a spiral structure with lots of gas & dust.

Multiple Choice

Andromeda is a galaxy close to the Milky Way. From the side, Andromeda looks like a flat disc with a bulge in the middle. From above, Andromeda has “arms” of stars that curve around the central bulge of stars. What type of galaxy is Andromeda?

• a spiral galaxy

• a planetary nebula

• an irregular galaxy

• an elliptical galaxy

Galaxies

Galaxy Formation

• Gas clouds clump together due to the gravitational pull of matter

• As the matter gets drawn together, it starts to spiral downwards into the central mass

• The center becomes squeezed typically until a black hole forms

• Over time, the galaxy might slowly stop spinning and become elliptical

• Galaxies may collide with other galaxies to form different shapes

Dark Matter

A type of physical matter that does not release any detectable light or shape. 

We see the gravitational effect of dark matter causing galaxies to spin faster than is possible given their visible matter.

Multiple Choice

What force causes a galaxy to form?

• Gravity

• Nuclear Fusion

• Kinetic Energy (Movement)

• Thermal Energy (Heat)

Multiple Choice

What is the shape of most galaxies?

• Elliptical

• Spiral

• Irregular

Multiple Choice

How does dark matter affect galaxies?

• it causes them to be hotter than expected

• it causes them to spin faster than expected

• it causes them to not be as bright as expected

Multiple Choice

What color is the most common in younger galaxies?

• red

• blue

• green

• brown

Multiple Choice

What type of galaxy is the milky way?

• Spiral

• Barred Spiral

• Elliptical

• Irregular

Multiple Choice

What usually causes an irregular galaxy?

• a surge in dark matter

• a nearby supernova explosion

• a collision with another galaxy

Life Cycle of a Star

Star Life Cycle

Death of Stars:

–What stars end up as depend on mass

Low and Medium Mass stars

•Planetary nebula --------- white dwarf

High mass stars (10 x or greater)

•Supernova --------- neutron star or black hole

Multiple Choice

The life cycles of stars are determined by their:

• mass (size)

• color

• distance from Earth

• how bright they are

Birth

Stars start out in giant clouds of dust called nebula. Gravity forces the dust to bunch together. As more and more dust bunches up, gravity gets stronger and it starts to get hot and becomes a protostar.

Watch: A Star is Born

https://www.youtube.com/watch?v=Q7MG-LahuX4

Multiple Choice

All stars begin their life as a

• Main Sequence

• Nebula

• Protostar

• Black Dwarf

Main Sequence Stars

Once a star, it will continue to burn energy and glow for billions of years. This is the state of the star for the majority of its life and is called the "main sequence". During this time a balance is met between gravity wanting to shrink the star and heat wanting to make it grow bigger. The star will remain this way until it runs out of hydroge

Multiple Choice

The core of a Red Giant collapses and becomes a ___________________.

• White Dwarf
• Blue Supergiant
• Red Supergiant
• Black Hole

Multiple Choice

A gigantic explosion that causes the death of a large star is called

• pulsar
• red giant 
• supernova
• black hole