end of ch. 13 iii. cycle of birth and death of stars: interstellar medium ch. 14
TRANSCRIPT
End of Ch. 13 III. Cycle of Birth and Death of Stars: Interstellar Medium
Ch. 14
III. Cycle of Birth and Death of Stars: Interstellar Medium
A. Interstellar Matter: Gas (mostly hydrogen) and dust
•Nebulae •Extinction and reddening
•Interstellar absorption lines •Radio observations
B. Nebulae• Emission • Reflection • Dark
C. Cycle of Birth and Death of Stars
Interstellar Medium
IIIA. Interstellar Matter: Gas (mostly hydrogen) and dust
How do we know that Interstellar Matter is there:
•Nebulae
•Extinction and reddening
•Interstellar absorption lines
•Radio observations
Extinction and Reddening: interstellar dust will make stars look
fainter and redder
Review: Absorption Spectrum
Interstellar Absorption Lines
Radio Observations: some molecules can be detected with
radiotelescopes
IIIB. Nebulae
• Emission Nebulae
• Reflection Nebulae
• Dark Nebulae
Question 1Dark nebulae are
A. Regions of space without any stars
B. Dense clouds of gas and dust that obscure the light from stars
C. Black holes
D. All the answers are correct
Question 1Dark nebulae are
A. Regions of space without any stars
B. Dense clouds of gas and dust that obscure the light from stars
C. Black holes
D. All the answers are correct
Question 2Emission nebulae are:
A. Regions of space without any stars
B. Low density gas near hot stars that show emission line spectra
C. Light from stars reflected by nearby dust
D. None of the answers are correct
Question 2Emission nebulae are:
A. Regions of space without any stars
B. Low density gas near hot stars that show emission line spectra
C. Light from stars reflected by nearby dust
Question 3Reflection nebulae are:
A. Regions of space without any stars
B. Low density gas near hot stars that show emission line spectra
C. Light from stars reflected by nearby dust
D. None of the answers are correct
Question 3Reflection nebulae are:
A. Regions of space without any stars
B. Low density gas near hot stars that show emission line spectra
C. Light from stars reflected by nearby dust
D. None of the answers are correct
Emission Spectrum
Emission Nebula (Eagle Nebula)
Hubble Space Telescope Image
Reflection Nebula
Dark Nebulae
Question 4What happens after an interstellar cloud of gas
and dust is compressed and collapses:
A. It will heat and contract
B. If it gets hot enough (10 million K) it can produce energy through hydrogen fusion
C. It can produce main sequence stars
Question 4What happens after an interstellar cloud of gas
and dust is compressed and collapses:
A. It will heat and contract
B. If it gets hot enough (10 million K) it can produce energy through hydrogen fusion
C. It can produce main sequence stars
D. All of the above
How does our galaxy recycle gas into stars?
IIIC. Cycle of Birth and Deaths of Stars• Interstellar cloud of gas and dust is
compressed and collapses to form stars
• After leaving the main sequence red giants eject their outer layers back to the interstellar medium
• Supernovae explode and eject their outer layers back to the interstellar medium
• Supernova explosions and other events can compress an interstellar cloud of gas and dust that collapses to form stars ………..
Remember Sun’s Evolutionary Process**This is an artist conception, not an HR diagram or a
real motion of the Sun
Remember mass loss in Intermediate Mass Stars
Remember Supernova explosions
Star-gas-star cycle
Recycles gas from old stars into new star systems
Ch. 14. The Milky Way
Ch. 14
Ch. 14 OUTLINEShorter than book
• 14.1 The Milky Way Revealed
• 14.2 Galactic Recycling (closely related to Ch. 13)
• 14.3 The History of the Milky Way
• 14.4 The Mysterious Galactic Center
14.1 The Milky Way Revealed
• Our Goals for Learning (not exactly like book)
• What does our galaxy look like?
• Where do stars form in our galaxy?
What does our galaxy look like?
The Milky Way galaxy appears in our sky as a faint band of light
Dusty gas clouds obscure our view because they absorb visible light
This is the interstellar medium that makes new star systems
All-Sky View at visible wavelengths plotted in galactic coordinates
What if we could see through most of that dust?
All-Sky View at visible wavelengths
All-Sky View at infrared wavelengths
Remember Extinction and Reddening: interstellar dust will make stars look fainter and redder. Dust will affect more the shorter (bluer) wavelengths and less the longer (redder) wavelengths. By looking at infrared wavelengths we can see through most of the dust.
We see our galaxy edge-on
Primary features: disk, bulge, halo, globular clusters
The Shape of our Galaxy: a flattened disk
If we could view the Milky Way from above the disk, we would see its spiral arms
Andromeda Galaxy: our twin galaxy
Our Galaxy looks like Andromeda
How do we know what our galaxy would look like if viewed from the top? Infrared and Radio observations penetrate dark interstellar clouds
Stellar Populations• Turns out that there are two types of stars in
the Galaxy– Population I: Relatively young. Similar to the
Sun. Tend to be in the galactic disk. Richer in heavy elements
– Population II: Few heavy elements, very old (12-14 billion years), tend to be in the center of the galaxy or in globular clusters
Remember CH 11 Part III
Star Clusters:
1. Two types of clusters: Open and Globular
Two types of star clusters• Open clusters:
young, contain up to several thousand stars and are found in the disk of the galaxy (Population I).
• Globular clusters: old, contain hundreds of thousands of stars, all closely packed together. They are found mainly in the halo of the galaxy (Population II).
14.2 Galactic Recycling
• Our Goals for Learning• How does our galaxy recycle gas into stars?
• Where do stars tend to form in our galaxy?
How does our galaxy recycle gas into stars?
Star-gas-star cycle
Recycles gas from old stars into new star systems
14.2 Galactic Recycling
• Where do stars tend to form in our galaxy?
14.2 Galactic Recycling
• Where do stars tend to form in our galaxy? In the Disk
Question 4What happens after an interstellar cloud of gas
and dust is compressed and collapses:
A. It will heat and contract
B. If it gets hot enough (10 million K) it can produce energy through hydrogen fusion
C. It can produce main sequence stars
Question 4What happens after an interstellar cloud of gas
and dust is compressed and collapses:
A. It will heat and contract
B. If it gets hot enough (10 million K) it can produce energy through hydrogen fusion
C. It can produce main sequence stars
D. All of the above
How does our galaxy recycle gas into stars?
Cycle of Birth and Deaths of Stars• Interstellar cloud of gas and dust is
compressed and collapses to form stars
• After leaving the main sequence red giants eject their outer layers back to the interstellar medium
• Supernovas explode and eject their outer layers back to the interstellar medium
• Supernova explosions and other events can compress an interstellar cloud of gas and dust that collapses to form stars ………..
Remember the Sun’s Evolutionary Process
Remember mass loss in Intermediate Mass Stars
Remember Supernova explosions
Star-gas-star cycle
Recycles gas from old stars into new star systems
Disk: blue stars star formation
Halo: no blue stars no star formation
Disk: emission nebulae, blue stars star formation
Halo: No emission nebulae, no blue stars no star formation
Much of star formation in disk happens in spiral arms
The Whirlpool Galaxy
Emission NebulaeBlue StarsGas Clouds
Spiral arms are waves of star formation
14.3 The History of the Milky Way
• Our Goals for Learning
• What clues to our galaxy’s history do halo stars hold?
• How did our galaxy form?
What clues to our galaxy’s history do halo stars hold?
Halo Stars: 0.02-0.2% heavy elements (O, Fe, …), only old stars
Disk Stars: 2% heavy elements, stars of all ages
Halo Stars: 0.02-0.2% heavy elements (O, Fe, …), only old stars
Disk Stars: 2% heavy elements, stars of all ages
Halo stars formed first, then stopped
Halo Stars: 0.02-0.2% heavy elements (O, Fe, …), only old stars
Disk Stars: 2% heavy elements, stars of all ages
Halo stars formed first, then stopped
Disk stars formed later, kept forming
How did our galaxy form?
Our galaxy probably formed from a giant gas cloud
Halo stars formed first as gravity caused cloud to contract
Remaining gas settled into spinning disk
Stars continuously form in disk as galaxy grows older
Note: This model is oversimplified
What have we learned?• What clues to our galaxy’s history do halo
stars hold?• The halo generally contains only old, low-mass
stars with a much smaller proportion of heavy elements than stars in the disk. Thus, halo stars must have formed early in the galaxy’s history, before the gas settled into a disk.
What have we learned?• How did our galaxy form?
• The galaxy probably began as a huge blob of gas called a protogalactic cloud. Gravity caused the cloud to shrink in size, and conservation of angular momentum caused the gas to form the spinning disk of our galaxy. Stars in the halo formed before the gas finished collapsing into the disk.
14.4 The Mysterious Galactic Center
• Our Goals for Learning• What lies in the center of our galaxy?
What lies in the center of our galaxy?
Stars at galactic centerStrange radio sources in galactic center
Stars appear to be orbiting something massive but invisible … a black hole!
Orbits of stars indicate a mass of about 4 million MSun
What have we learned?
• What lies in the center of our galaxy?
• Motions of stars near the center of our galaxy suggest that it contains a black hole about 4 million times as massive as the Sun. The black hole appears to be powering a bright source of radio emission.