galaxies. objectives identify three types of galaxies. describe the contents and characteristics of...
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Galaxies
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Objectives
• Identify three types of galaxies.
• Describe the contents and characteristics of galaxies.
• Explain why looking at distant galaxies reveals what young galaxies looked like..
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Solar System
What is a Galaxy ?Distance from Earth to Sun = 93,000,000 miles = 8 light-minutes
Size of Solar System = 5.5 light-hours
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What is a Galaxy?Stellar Region
30light-years
Sun(solar system
too small to beseen on this scale)
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What is a Galaxy?
A Galaxy is:
100,000 light-years
a massivecollection ofstars, gas, and dust kept togetherby gravity
Sun’s Stellar Region
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What is a Galaxy?
If our solar system was the size
of a cell inthe human body,
our galaxywould still
measure overone mile across.
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Contents of Galaxies
• Gas Clouds A large clouds of gas and dust in interstellar space is called a nebula.
• Star Clusters A globular cluster is a tight group of stars that looks like a ball and contains up to 1 million stars.
• An open cluster is a group of stars that are close together relative to surrounding stars.
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• Contents of Galaxies• Quasars
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There are two main classes of galaxies organized by Hubble
ELIPTICAL• Spherical galaxies
classified on a scale of 0 to 7• The number indicates
how egg-shaped the ellipse is - 0 means a ball shape, and 7 looks like a dish
SPIRAL• Central nucleus
surrounded by arms of stars
• Spiral or barred spiral• The bar is a dense
area of stars that extends along the diameter of the galaxy
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Types of GalaxiesSpiral disk-like appearance with arms of stars and dust forming a spiral pattern
Barred Spiral similar to spirals but with a bright bar of stars and gas through the center
Elliptical elliptically-shaped, with less gas and dust than spirals; no disk or “arms”
Irregular neither elliptical nor spiral in shape; gas and dust as in spirals but no defined “arms”
Peculiar distorted form of one of the above types, often due to collision with another galaxy or similar catastrophic event
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Where did they come from?
• Galaxies first formed in the densest spots in the Universe.
• By the time the Universe was a few hundred million years old, the densest regions had ceased expanding and began to collapse
• Matter in these areas did not expand rapidly with the big bang
• These areas formed dense groups of rotating stars which became galaxies
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Where did they come from?
• A gigantic star formed at the center of the star cluster from the inflowing matter.
• Stars containing more than about 100 times the mass of the Sun are unstable. If slightly compressed, they collapse faster and faster until a black hole forms.
• In every observed galaxy, supermassive black holes have been found.
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Classification of Galaxies
Hubble Tuning Fork
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The Hubble Tuning Fork• After he discovered what galaxies really were, Edwin
Hubble became the first person to classify galaxies. • Astronomers use his system, called the "Hubble
Tuning Fork," even today. – First, Hubble divided the galaxies into two general
categories: elliptical and spiral galaxies. • Elliptical galaxies are shaped like ellipses, and
spiral galaxies are shaped like spirals, with arms winding in to a bright center.
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The Hubble Tuning Fork
• Elliptical galaxies are classified by how round or flat they look.
• An E0 galaxy is very round and an E7 galaxy is very flat.
• In detail, the number after the "E" is determined by the galaxy's ellipticity - the ratio of the ellipse's major axis to minor axis.
• Galaxies with higher ellipticities have higher numbers.
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The Hubble Tuning Fork
• Hubble noticed that some spiral galaxies have a bright line, or bar, running through them.
• He called these galaxies "barred spiral galaxies."
• Galaxies with spiral arms, but without the bar, are just called "spiral galaxies."
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The Hubble Tuning Fork
• Spiral galaxies are further classified by how tightly their arms are wound.
• Type a galaxies have their arms wound very tightly and have large central bulges.
• Type c galaxies have very their arms would loosely and have small central bulges.
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The Hubble Tuning Fork
• Some galaxies are a transition type between the elliptical and spiral galaxies, labeled S0 on the tuning fork.
• These are called "lenticular galaxies." • Lenticular galaxies have a central bulge and a
disk but no spiral arms.
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The Hubble Tuning Fork
• The third class of galaxies is irregular galaxies. • Irregular galaxies are neither spiral nor
elliptical, and can have any number of shapes. • They are frequently the product of two
galaxies colliding with each other, or at least affecting each other through the force of gravity.
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• For each slide, write the type of galaxy as classified by the Hubble Tuning Fork diagram.
• 1• 2• 3• 4• 5• 6• 7• 8• 9• 10• 11• 12• 13• 14• 15
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Spiral
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Spiral
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Lenticular Spiral
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Barred Spiral
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Elliptical
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SpiralMilky Way galaxy - Spiral
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Barred Spiral
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Barred Spiral
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Elliptical
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Irregular
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Elliptical
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Spiral
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Irregular
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Lenticular Spiral
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Spiral
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Milky Way Galaxy = Our Home•Our solar system is located in a spiral galaxy called the Milky Way. •From the side, the Milky Way appears to be a narrow disk with a bulge in the middle. •The galaxy’s spiral structure is visible only from above or below.
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The Milky Way Galaxy• The Milky Way might contain one trillion
stars.
• The visible disk of stars is about 100,000 light-years across.
• The Sun is located about 26,000 light-years from the galaxy's center in one of the spiral arms.
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The Milky Way Galaxy
• In the galaxy, all stars orbit around a central region, or core.
• It takes about 225 million years for Sun to orbit the center of the Milky Way.
• The last time our solar system was in its current position was during the Triassic Period, when dinosaurs first appeared on Earth!
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The Milky Way Galaxy
• The Milky Way often is classified as a normal spiral galaxy.
• However, recent evidence suggests that it might be a barred spiral.
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The Milky Way Galaxy• You can, see the Milky Way stretching across
the sky as a misty band of faint light. • You can see the brightest part of the Milky
Way if you look low in the southern sky on a moonless summer night.
• Like many other galaxies, the Milky Way has a supermassive black hole at its center.
• This black hole might be more than 2.5 millions times as massive as the Sun.
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The Milky Way Galaxy
• Evidence for the existence of the black hole comes from observing the orbit of a star near the galaxy's center.
• Additional evidence includes X-ray emissions detected by the Chandra X-ray Observatory.