disk galaxies – including the milky way.. m51 – a typical spiral-disk galaxy

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Disk Galaxies – Including the Milky Way.

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Page 1: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

Disk Galaxies – Including the Milky Way.

Page 2: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

M51 – A typical spiral-disk galaxy

Page 3: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

The M81 group of galaxies

M82

M81

Satellite galaxy

Satellite galaxy

Page 4: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

M81 group showing hydrogen

emission at radio

wavelengths

Page 5: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy
Page 6: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy
Page 7: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy
Page 8: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

Composite image of M 81. Blue shows X-Ray observations(high energy), pink infrared (dust)

Page 9: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy
Page 10: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

M 82. It has a disk and lots of gas and dust around.

Page 11: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

M82 composite: Blue-Xrays, Red-Infrared, White-optical

Page 12: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

• M 82 is smaller than M 81 yet it is producing stars at an enormous rate. Ten times faster than the Milky Way is producing stars.

• Most of the erupted gas is coming from supernova explosions. This is star formation on steroids.

• Why do you think this little galaxy is producing stars so rapidly? Think about the mechanisms for producing stars.

Page 13: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

Why is M82 producing stars so rapidly?

1 2 3

33% 33%33%

1. Stars form out of gas clouds, so it must have an extra large amount of gas

2. In smaller galaxies the gas clouds are closer together, because the galaxy is small

3. Something must have forced more gas cloud collisions in M82

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Page 14: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

The interaction between M81 and M82 caused molecular clouds to collide in M82

• For Friday, read about tidal forces.• Tides on the Earth– Chapter 3.6.1 & 3.6.2• Tides from Black Holes – Chapter 15.5.4• Galaxy interaction – Chapter 19.2

• There will be a quiz on this on Friday.

Page 15: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy
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Page 25: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

Where are we in the Milky Way?

Page 26: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

It is important to understand the scale that we are talking about here.

• Shrink the solar system to the diameter of a human hair (about 0.1 millimeters)

• Alpha Centauri would be about 1 meter away

• The Milky Way, which has a diameter of 100,000 light years would have a diameter of 20 km, on this scale (about 13 miles)

Page 27: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy
Page 28: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

• The thickness of the disk changes some but it is about 1000 light years thick.

• On this scale that is about 200 meters. That is about 700 feet. Or the height of a 70 story building.

Page 29: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

Lexington Financial Center is 410 feet tall.

Page 30: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

• The thickness of the disk changes some but it is about 1000 light years thick.

• On this scale that is about 200 meters. That is about 700 feet. Or the height of a 70 story building.

• The Sun orbits the Milky Way at a speed of 220 km/s and it completes one orbit in about 300 million years.

• On this scale, the Solar System moves the width of a hair every year.

Page 31: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

• In 10 years it moves one millimeter• In 10,000 years, the amount of time that

human civilization has existed on Earth, the Solar system moved 1 meter.

• Since the Sun formed (~4.6 billion years ago) it has completed around 15 trips. Depending on the size of the orbit you use.

Page 32: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

So try to picture this..

• The solar system is the width of a hair.• The Milky Way is about 3 times the size of New Circle

Drive.• It has a thickness almost 2 times the height of the

largest building in Lexington.• And the distance from us to the next closest star is

about 1 meter.• What about are closest big neighbor, the Andromeda

Galaxy?

Page 33: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

On our scale, the Andromeda Galaxy would be a city, a little bigger than Lexington and 300 miles away.

Page 34: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

• That’s about the distance to St. Louis.

• Remember, our solar system is the width of a hair and it is moving about 1 meter every 10,000 years.

• So on this scale, Andromeda is about 450 km away, or 450,000 meters away.

• How long would it take the Sun to reach Andromeda?

Page 35: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

How long would it take the Sun to reach Andromeda?

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25% 25%25%25%1. 4.5 trillion years2. 4.5 billion years3. 4.5 million years4. 450,000 years

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Page 36: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

At the Sun’s speed it would take about 4.5 billion years.

• And remember, the Sun and solar system is moving 220 km/s. That is 528,000 miles/hour!

• At that speed it would take 2 minute, 43 seconds to fly around the Earth.

• Our Milky Way galaxy and the Andromeda galaxy are going to collide in the future. It will take about 7 to 8 billion years to reach Andromeda.

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The nearest stars to the Sun.

Page 40: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

Barnard’s Star

Page 41: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

Brightest stars in the sky

Page 42: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

From the two H-R diagrams what can you conclude about the types of stars in the Galaxy?

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33% 33%33%1. Most stars must be low

mass because that is what we find near us

2. Most stars must be high mass because throughout the galaxy we mostly see luminous stars

3. If we combine the two H-R diagrams there are about the same number of high and low mass stars in the Galaxy

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Page 43: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

• We see a lot of high mass or luminous evolved stars in the sky. This is because they have extremely large luminosity. They can be readily seen at great distances.

• The stars in our little volume of the Galaxy are almost completely, low mass stars.

• This means if we increased the volume that we are using to search for stars, we would start to bring in a few high mass stars, but the number of low mass stars would skyrocket.

• Most stars in the Galaxy are low-mass, red dwarfs. ~90% of all stars.

Page 44: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

Why are there so many little red stars in the Galaxy?

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33% 33%33%1. Little low mass stars

live much longer than high mass stars

2. Star forming regions make more low mass stars than high mass

3. It is the combination of 1 & 2

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Page 45: Disk Galaxies – Including the Milky Way.. M51 – A typical spiral-disk galaxy

• In young stars clusters, there are typically 5 – 10 really massive, luminous stars. But there might be several hundred or more low mass stars.

• The massive stars die rapidly. The really small stars (less massive than the Sun) have never died since the start of the universe.

• Both are important.