Astronomy Unit 4: Galaxies

What are the 4 main parts of a spiral galaxy?

A halo, bulge, dish, and arms

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

Elliptical galaxies

True/False: Closed clusters are groups of closely grouped stars that are located along the spiral disk of a galaxy

False

Redshifts are what?

Galaxies that are moving father apart

True/False: Galaxies are classified by their shape and size into 5 major groups

False

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

Galaxies

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

Poor cluster

How are galaxies organized and distributed within the universe?

Galaxies are typically organized into clusters and distributed (not scattered randomly) 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.

How do scientists know that dark matter exists?

Gravitational lensing

Accretion is defined as what?

Gravity that pulls matter in a spiraling matter

True/False: A globular cluster is a group of older stars that cluster together

True

True/False: Astronomers estimate that 50 billion to 1 trillion galaxies exist within our universe

True

True/False: Black holes have the strongest force of gravity in the universe

True

True/False: Many galaxies' gravity source is in the form of black holes

True

True/False: The Milky Way galaxy is home to our Solar System

True

How was Hubble important to our understanding of galaxies?

Edwin Hubble was important in advancing our understanding of galaxies. In the 1920s, he discovered that there are other galaxies in the universe. Hubble was also able to classify spiral galaxies based on their tightness and nuclear bulge size. Additionally, he discovered that the distance to a galaxy is directly correlated to the size of its redshift. This discovery was arguably the most crucial discovery in astronomical history; it informed us that our universe is ever expanding.

How do galaxies change over time?

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.

How do galaxies vary?

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.

How do gravity and dark matter shape the galaxies and affect their environment?

Gravity and dark matter shape galaxies and affect our environment. Black holes are often the center of galaxies. They are made of dark matter and are the strongest force of a galaxy's gravity. Stars orbit around black holes and dark matter within a galaxy. In a whirlpool-like motion, black holes suck in nearby stars and gas. When black holes consume substances too quickly, they can form quasars: extremely high velocity and luminosity bursts of energy. Gravity and dark matter cause galaxies to take different shapes: spiral, elliptical, and irregular. Additionally, gravity from neighboring galaxies can distort each others' shapes.

How is gravity important to the galaxies within our universe?

Gravity binds everything together; it keeps galaxy clusters intact. Gravity also forms galaxies into different shapes: spiral, elliptical, and irregular.

What forces shape the stars in galaxies?

Gravity is what causes stars to form. During accretion, gravity pulls matter into a core, which can be a star, planet or black hole.

Describe the Milky Way. What does it contain?

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.

How does the Milky Way compare with other galaxies within the universe?

The Milky Way, a member of the "Local Group," is different than other galaxies in the universe. First, it is brighter than most galaxies that we have been able to see. Second, the Milky Way is a barred spiral galaxy; unlike typical spiral galaxies, barred spiral galaxies have flat discs in their centers. Third, it is a medium size galaxy with a diameter of about 100,000 light years. In comparison, the large size Andromeda galaxy (which is the nearest spiral galaxy) is approximately 220,000 light years in diameter, and the small size Canis Major Dwarf is about 5,000 light years in diameter. Fourth, the Milky Way contains roughly 200 billion stars, compared to Andromeda's one trillion stars. Fifth, both the Milky Way and Andromeda galaxies have grown in size by consuming other smaller galaxies. Interestingly, in approximately 5 billion years, the Milky Way and Andromeda galaxies are expected to merge. Sixth, both the Milky Way and Andromeda galaxies are thought to have black holes at their centers.

How are galaxies created?

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.

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

There is a supermassive black hole that is about 15 million miles across