Disk Galaxies – Including the Milky Way.

M51 – A typical spiral-disk galaxy

The M81 group of galaxies M82 M81 Satellite galaxy

M81 group showing hydrogen emission at radio wavelengths

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

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

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

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.

Why is M82 producing stars so rapidly? 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 M

The interaction between M81 and M82 caused molecular clouds to collide in M82 For Friday, read about tidal forces. Tides on the Earth– Chapter & Tides from Black Holes – Chapter Galaxy interaction – Chapter 19.2 There will be a quiz on this on Friday.

Where are we in the Milky Way?

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)

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.

Lexington Financial Center is 410 feet tall.

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.

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.

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?

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

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?

1.4.5 trillion years billion years million years 4.450,000 years

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.

The nearest stars to the Sun.

Barnard’s Star

Brightest stars in the sky

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

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.

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

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.