Astronomy Unit 4: Galaxies Flashcards

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Questions and Answers

Astronomers estimate that 50 billion to 1 trillion galaxies exist within our universe.

True (A)

What are the 4 main parts of a spiral galaxy?

A halo, bulge, dish, and arms

The Milky Way galaxy is home to our Solar System.

True (A)

How do scientists know that dark matter exists?

<p>Gravitational lensing</p> Signup and view all the answers

Edwin Hubble used a telescope and observed fuzzy blobs of light off in the distance; he realized that these lights were what?

<p>Galaxies</p> Signup and view all the answers

Closed clusters are groups of closely grouped stars that are located along the spiral disk of a galaxy.

<p>False (B)</p> Signup and view all the answers

Galaxies are classified by their shape and size into 5 major groups.

<p>False (B)</p> Signup and view all the answers

Accretion is defined as what?

<p>Gravity that pulls matter in a spiraling matter</p> Signup and view all the answers

Which type of galaxy is a spherical cluster of stars with extraordinary brightness and little dust and gas?

<p>Elliptical galaxies</p> Signup and view all the answers

What best describes the black hole status within the Milky Way?

<p>There is a supermassive black hole that is about 15 million miles across</p> Signup and view all the answers

Many galaxies' gravity source is in the form of black holes.

<p>True (A)</p> Signup and view all the answers

Redshifts are what?

<p>Galaxies that are moving farther apart</p> Signup and view all the answers

Black holes have the strongest force of gravity in the universe.

<p>True (A)</p> Signup and view all the answers

A cluster of galaxies containing very few galaxies is known as what?

<p>Poor cluster</p> Signup and view all the answers

A globular cluster is a group of older stars that cluster together.

<p>True (A)</p> Signup and view all the answers

Describe the Milky Way. What does it contain?

<p>The Milky Way is a 13.5 billion-year-old, average-sized, barred spiral galaxy. It contains four main spiral arms (Perseus, Cygnus, Centaurus, Sagittarius) and approximately 500 billion stars.</p> Signup and view all the answers

How are galaxies organized and distributed within the universe?

<p>Galaxies are typically organized into clusters and distributed across the universe. In clusters, galaxies are held together by the force of gravity. If a cluster contains numerous galaxies, then it is a supercluster. The Milky Way is a part of the Local Group cluster which contains more than 50 other galaxies.</p> Signup and view all the answers

How is gravity important to the galaxies within our universe?

<p>Gravity binds everything together; it keeps galaxy clusters intact. Gravity also forms galaxies into different shapes: spiral, elliptical, and irregular.</p> Signup and view all the answers

How do galaxies vary?

<p>Galaxies vary in many ways. They come in different shapes: spiral, elliptical, and irregular. Spiral galaxies look like flying saucers; elliptical galaxies are circular; irregular galaxies do not have a defined shape. Spiral galaxies contain nebulae; elliptical galaxies do not. Spiral galaxies are constantly making new stars, whereas elliptical galaxies do not make new stars. Galaxies also come in different colors. Spiral galaxies are blue; elliptical galaxies are red.</p> Signup and view all the answers

What forces shape the stars in galaxies?

<p>Gravity is what causes stars to form. During accretion, gravity pulls matter into a core, which can be a star, planet, or black hole.</p> Signup and view all the answers

How do galaxies change over time?

<p>Galaxies change as time passes. Young galaxies are not well organized, but eventually become organized into different clusters. Young galaxies are spiral-shaped; older galaxies are elliptical shaped. Additionally, galaxies change colors, from blue to red, as they get older. The color change is because younger galaxies form new stars (giving off ultraviolet and blue light), whereas older galaxies contain old stars (giving off red light) and create fewer new stars.</p> Signup and view all the answers

How are galaxies created?

<p>There are two theories about how galaxies were formed after the Big Bang. According to one theory, gravity pulled gas and dust together to make stars and planets, which were drawn together to create galaxies. According to the second theory, the universe already contained 'clumps' of matter, that gathered together to form galaxies. This second theory is supported by Hubble Space Telescope photographs of 'clumps' which may be developing into new galaxies. Additionally, small galaxies are often consumed up by larger ones, including the Milky Way.</p> Signup and view all the answers

Flashcards

Number of galaxies

There are an estimated 50 billion to 1 trillion galaxies in the observable universe.

Galaxy Types

Galaxies are categorized by their shapes (spiral, elliptical, irregular) and sizes.

Spiral Galaxy Structure

Spiral galaxies have a halo, bulge, disk, and spiral arms.

Milky Way

Our galaxy, a barred spiral galaxy. It has about 500 billion stars and 4 spiral arms.

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Dark Matter

Matter that cannot be seen directly but is inferred from its gravitational effects, such as gravitational lensing.

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Galaxy Formation Theory 1

Galaxies formed from the gravitational attraction of gas and dust.

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Galaxy Formation Theory 2

Pre-existing clumps of matter combined to form galaxies.

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Galactic Evolution

Galaxies change over time, often from less to more organized structure.

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Hubble's galaxies

Hubble identified distant 'fuzzy blobs' as galaxies.

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Galaxy Clusters

Groups of galaxies held together by gravity.

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Superclusters

Clusters of galaxy clusters.

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Poor Cluster

A cluster of galaxies containing relatively few of them.

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Black Hole

A region of spacetime with extreme gravity, from which nothing, not even light, can escape.

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Galaxy Movement

Galaxies are moving away from each other

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Milky Way Black Hole

A supermassive black hole in the center of the Milky Way.

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Accretion

Gravitational process where matter spirals inwards, potentially forming stars, planets, or black holes.

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Star Formation

The process where stars are born from gravitational forces, with newer stars found in spiral galaxies, older in ellipticals.

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Local Group

The group of galaxies, including the Milky Way, that are close together.

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Redshift

A phenomenon where the light from distant galaxies is shifted towards the red end of the spectrum.

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Galactic merging

Smaller galaxies combine to form larger ones, like the Milky Way.

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Study Notes

Overview of Galaxies

  • Estimated existence of 50 billion to 1 trillion galaxies in the universe.
  • Galaxies are categorized by shape and size with specific classifications.

Structure of Spiral Galaxies

  • Composed of a halo, bulge, disk, and spiral arms.
  • The Milky Way is classified as a barred spiral galaxy containing about 500 billion stars and four main spiral arms (Perseus, Cygnus, Centaurus, Sagittarius).

Dark Matter and Gravity

  • Dark matter is inferred from gravitational lensing phenomena.
  • Gravity plays a crucial role in maintaining galaxy structure and formation, shaping galaxies into spiral, elliptical, or irregular forms.

Edwin Hubble's Contributions

  • Hubble identified distant "fuzzy blobs" as galaxies, expanding our understanding of the universe.

Black Holes

  • The Milky Way houses a supermassive black hole approximately 15 million miles across.
  • Many galaxies contain black holes as a source of significant gravitational force.

Galaxy Clusters

  • A 'poor cluster' refers to a cluster with very few galaxies.
  • Superclusters contain numerous galaxies and are held together by gravity.
  • The Milky Way is part of the Local Group, consisting of over 50 other galaxies.

Star Formation and Accretion

  • Accretion refers to the gravitational process where matter spirals inward, potentially forming stars, planets, or black holes.
  • Stars form through gravitational forces, with newer stars typical of spiral galaxies and older stars prevalent in elliptical galaxies.

Galactic Evolution

  • Galaxies evolve over time, starting as less organized and developing into structured clusters.
  • Young spiral galaxies may transition into older elliptical galaxies, with color changes from blue (indicating active star formation) to red (indicating older, less active stars).

Theories of Galaxy Formation

  • Two primary theories exist regarding galaxy formation post-Big Bang:
    • Gravity attracted gas and dust to form galaxies.
    • Pre-existing "clumps" of matter coalesced into galaxies, supported by Hubble Space Telescope images showing these clumps.
  • Smaller galaxies often merge into larger ones, such as the Milky Way.

Galaxy Movement

  • Redshifts indicate that galaxies are moving farther away from each other, a key observation in understanding the expanding universe.

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