Galaxies, Characteristics of Stars, Stellar Formation

Elliptical Galaxy

(E): Characterized by a smooth, ball shaped appearance. Contains old stars and very little gas or dust. Classified by the shape of the "ball", which ranges from E0 (round) to E7 (oval). Stars in this galaxy move like a swarm of bees; in randomly oriented orbits.

What are the two leading theories on how galaxies form?

-Galaxies were formed when clouds and dust collapsed under their own gravitational pull and allowed stars to form. -The universe originally contained small "lumps" of matter that clumped together to form galaxies.

Globular Cluster

A ball-shaped group of hundreds of thousands of stars.

Name the three "galactic neighbors" of the Milky Way.

Andromeda, The Large Magellanic Cloud, The Small Magellanic Cloud

How do astronomers classify galaxies?

Astronomers classify galaxies by their shape.

Yellow stars

Medium hot, not as bright

Milky Way

The Galaxy in which our solar system is located. A medium sized galaxy; contains several billion stars.

How big is the Milky Way in diameter?

The Milky Way is 100,000 light years in diameter. (See 8 above)

Absolute magnitude

The actual brightness of a star. Usually absolute magnitude is used instead of apparent.

What is the approximate surface temperature of the sun?

The approximate surface temperature of the sun is 5,500 K.

Sun-like stars (like G main sequence) are located at the: top bottom left right center

center

Irregular Galaxy

(Irr): Not spiral or elliptical galaxy. They are usually smaller with no definite shape. Usually has very hot, young stars mixed with lots of dust. Often has active regions of star formation. Stars and dust are spread randomly.

Planetary Nebula

A nebula that is formed by a star collapsing. As the star collapses, the bloated outer layer is ejected, producing a cloud of gas. The gas cloud is heated from the hot, central star, causing it to glow.

How long does it take from light to travel from the Sun to Earth?

It takes light eight minutes to travel from the Sun to Earth.

Death of Massive Stars

Massive stars turn into red supergiants after their main sequence stage. They later end their lives in a supernova. After a supernova, the remnants of massive stars can turn into black holes.

What types of waves were used to study the "foggy" Milky Way?

Radio and infrared waves were used to study the "foggy" Milky Way because they can travel through the dust of the Milky Way and reach telescopes on Earth.

Blue stars

Really HOT and bright

What is the color of stars with the lowest surface temperature?

Red stars have the lowest temperature.

Bright stars are located at the: top bottom left right center

top

Hot, bright stars are located at the: top bottom left right center

top left

Spiral Galaxy

(S and SB): Consists of a flattened disk with spiral arms, a central bulge and a halo. Classified by the size of the bulge and tightness and appearance around the arms. Younger stars are found at the spiral arms or around the bulge. Older stars are found in the bulge. "Density waves" squeeze clouds of interstellar gas together to trigger new star formation.

What is in the middle of the Milky Way?

A black hole is located in the middle of the Milky Way.

Protostar

A developing star not yet ready to go through nuclear fusion.

Lenticular Galaxy

A galaxy in between an elliptical and a spiral galaxy. Contains very red stars. Stellar formation has stopped.

Red stars

Cool and dim

Supergiant/Giant Star

Large and bright stars but with very cool temperatures only if they are red giants/supergiants!. Located on top/middle right side of HR Diagram. Towards the end of the life of a star. When hydrogen fusion stops in the core of the main sequence star, there is no outward pressure or energy source so it begins to contract. As the core contracts, it grows hotter and converts gravitational energy into heat energy. Some of the energy is radiated outward and the hydrogen fusion in outer shell increases, expanding the outer layer. Star grows to be hundreds of times larger than it was in its main sequence stage. Star appears red because as it expands, the surface cools. Produces energy by consuming hydrogen and helium.

How many comets did Messier discover?

Messier discovered 20 comets.

Why is Sirius brighter than Betelgeuse?

Sirius is brighter than Betelgeuse because it is much closer to Earth.

What factor affects the luminosity of a star?

Size affects the luminosity of a star.

Luminosity

The amount of energy given off by a star. The luminosity of stars are relative to the luminosity of our sun (1). If star X has a luminosity of .1, it is 1/10 the luminosity of the sun's.

All galaxies have the following three traits in common:

They are composed of dust, gas, and stars. They are held together by the force of gravity.They have individual stars and star clusters circling the outer area (halo).

Blue stars have ________ amounts of energy .

greater (higher temperatures)

Hot stars are located at the: top bottom left right center

left

Red stars have _______ energy.

less (cooler temperatures)

The three basic shapes of galaxies are

spiral, elliptical, and irregular.

Main Sequence Star

90% of all stars are main sequence stars because this is the longest phase of their lives and most stars spend most of their lives as this type of star. Towards the beginning of the life of a star. Hydrogen is combining and changing (hydrogen fusion) in the star. To be considered a main sequence star, the star has to have an equally balanced outward pressure and inward force of gravity (the gases increase in motion due to hydrogen fusion, causing an increase in outward pressure and eventually balancing with the inward pressure). Hydrogen fusion increases the outward pressure and keeps the star from collapsing. Ranges on the HR Diagram from top left corner to bottom right corner.

Galaxy

A cluster of stars, gas, dust and other celestial bodies held together by gravity.

Nebula

A dark, cool, cloud with interstellar matter. The birthplace of stars. Composed of dust and gases. Some nebulae begin to contract because they get very dense, and a shock wave can trigger the contraction. Gravity squeezes particles and pulls them toward the center of the nebulae. When the nebulae shrinks, gravitational energy is turned into heat energy.

The Hertzsprung-Russell (HR) Diagram

A diagram that graphs the relationship between a star's temperature/spectral class and absolute magnitude/luminosity. Can show us the color of a star, and what type of star it is.

The Local Group

A group of dozens of galaxies that travel through space as a single unit because they are bound together by their mutual gravitational pull.

Supernova

A huge explosion with which massive stars end their lives. It occurs when a star consumes all of its fuel, and the star collapses due to no heat engine generating gas pressure. The collapse leads to a huge shock wave moving outwards, destroying the star and blasting the outer shell into space. During this explosion, the star becomes millions of times brighter.

Death of Medium-Mass Stars

After the main sequence phase, a star will turn into a red giant. The star later turns into a white dwarf, but in between being a red giant and turning into a white dwarf, it turns into a planetary nebula.

Black Hole

An object smaller and denser than neutron stars. It is very hot, and has very strong amounts of gravity so no light can escape from its surface. When something moves near a black hole, it is sucked in by its gravity and it will disappear forever. Massive stars can turn into black holes when they are remnants of a supernova and they collapse.

How many galaxies are thought to exist, based on current scientific observations?

Around 100 billion galaxies are thought to exist.

What will happen to white dwarf stars as they cool off?

As white dwarf stars cool off, they will change color and turn red. Cool stars are not white; they are red. Therefore, if the star is cooling off, it will change to the color of cool stars, which is red. White dwarf stars would move to the red side of the HR diagram.

Summarize the expected future of the Universe.

Astronomers expect that the Universe will still live on, but it will be very different from how it is today. Stars will burn out, and galaxies will gradually fade from sight because they are moving away from us. Giant black holes will dominate the hearts of galaxies, dead stars will disintegrate and the Universe will only have a thin mixture of radiation and subatomic particles.

Why do astronomers like to study the Andromeda Galaxy (M31)?

Astronomers like to study the Andromeda Galaxy (M31) because it is so large that big telescopes can reveal many of its individual stars. It is also far enough away that astronomers can see its overall structure and composition.

What type of star has a high temperature and a high luminosity?

Blue giants have a high temperature and a high luminosity.

What is the color of stars with the highest surface temperature?

Blue stars have the highest surface temperature.

List the color of stars from hottest to coolest.

Blue, white, yellow-green, yellow, light orange, orange, red.

The Hubble Telescope contains spectrographs to analyze data from stars. By separating the colors of light from a star, what can astronomers determine about the star?

By separating the colors of light from a star, astronomers can determine its temperature, motion, composition and age.

Explain how Charles Messier "accidentally" discovered galaxies.

Charles Messier "accidentally" discovered galaxies when he was searching for comets, but he found many blurry objects that didn't change position over time, unlike comets. These blurry objects ended up being galaxies.

Edwin Hubble devised one system to classify galaxies. What did his system include? Exclude?

Edwin Hubble's system to classify galaxies included spiral and elliptical galaxies, but excluded irregular ones.

Even if two stars have the same brightness, does it mean they are the same temperatures?

Even if two stars have the same brightness, it does not mean they are the same temperature. The brightness of a star does not affect its temperature, so you can have a cool, bright star, but you can also have a cool, dim one. Therefore, even if two stars have the same brightness, one could be hotter or cooler than the other.

Apparent magnitude

How bright a star appears.

If Sirius and Betelgeuse were the same distance from Earth, which one would be brighter?

If Sirius and Betelgeuse were the same distance from Earth, Betelgeuse would be brighter.

Even if two stars have the same color, are they the same temperature?

If two stars have the same color, it means they are the same temperature. The temperature of a star affects its color. As a result, you cannot have a cool, red star while having a hot, red star. Therefore, if two stars are the same color, they will be the same temperature.

How long does it take the sun to orbit the center of the galaxy?

It takes the sun 200 million years to orbit the center of our galaxy.

Most of the stars on the HR Diagram are classified as which type of star?

Most of the stars on the HR Diagram are classified as main sequence stars.

How far across is our galaxy?

Our galaxy is 90,000 light years across. (See 19 below)

Our solar system is a part of what galaxy?

Our solar system is a part of the Milky Way galaxy.

Explain how the solar system is moving in relation to our galaxy.

Our solar system is revolving around the center of our galaxy.

What type of star has a low temperature but a high luminosity?

Red supergiants have a low temperature but a high luminosity.

Dwarf Stars

Small and dim but very hot stars. Typically the end of a star's life cycle.

What type of star has a low temperature and a low luminosity?

Some main sequence stars have a low temperature and a low luminosity.

Death of Low-Mass Stars

Stars remain main-sequence stars for a long period of time because they consume their fuel at a slow rate. They do not turn into red giants because the star never gets hot enough and never gets to a high enough pressure to fuse helium, so its only source of energy is hydrogen. They will consume all of their hydrogen fuel and collapse into a white dwarf star.

What factor affects the color of a star?

Temperature affects the color of a star.

What is meant by the "orientation of a galaxy"?

The "orientation of a galaxy" means the angle at which we view a galaxy.

What has the Hubble Telescope shown us about galaxies?

The Hubble Telescope has shown us that different types of galaxies evolved at different rates. Elliptical galaxies formed shortly after the Big Bang, while spiral galaxies took longer to form.

Magnitude

The brightness of a celestial body (usually stars). The lower the number, the brighter the star is.

What is the largest type of galaxy in our universe?

The largest type of galaxy in our universe is a giant elliptical galaxy. They contain more than a million stars, and span as much as one million light years. They also have "supermassive" black holes at their center, like some spiral galaxies.

Is the surface temperature of white dwarf stars higher or lower than red supergiants?

The surface temperatures of white dwarf stars are higher than red supergiants.

What type of star has a high temperature but a low luminosity?

White dwarf stars have a high temperature but a low luminosity.

Has the Milky Way "gobbled up" any other galaxies?

Yes, the Milky Way has "gobbled up" other galaxies. It is currently in the process of "gobbling up" two small galaxies.

Cool, dim stars are located at the: top bottom left right center

bottom right