SLIDE 1 ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies
- mework #6 - due Tue, Nov. 3.
- ex
ext O OBSERVIN IN es ession ion: ed ed, O , Oct. 2 . 28 i.e. i.e. morrow
, 7p
SLIDE 2 Galaxies: Ultimate Galaxies: Ultimate Recyling Recyling Plants Plants
REVIEW
SLIDE 3 Molecular clouds = Molecular clouds = star forming regions star forming regions
COLD STUFF
- Molecular CLOUDS
- Mostly atomic hydrogen,
- some helium and
- other molecules
- Dark, dusty, cold
10-30K
- Emit molecular
- emission lines
- in far IR, radio
SLIDE 4 Semi-Warm stuff Semi-Warm stuff
Dust:
– – absorbs absorbs visible visible and UV light and UV light – – Transparent Transparent to to long long wavelengths wavelengths (red, IR, radio) (red, IR, radio)
Emits IR light
Horsehead Horsehead Nebula Nebula
SLIDE 5
Hot stars ionize hydrogen and other hydrogen and other elements in the gas elements in the gas
T~ 10,000 K near hot young stars hot young stars
Ionization nebulae Ionization nebulae “ “O & B star O & B star associations associations” ”
Lagoon Nebula Lagoon Nebula
Hot stuff Hot stuff
SLIDE 6
(10 (10 ly ly across) across)
Really Hot Stuff Really Hot Stuff
Hot star Hot star winds from winds from aging stars aging stars
SLIDE 7
Supernova Supernova Remnants Remnants & & Planetary Planetary Nebula Nebula
More hot stuff More hot stuff
SLIDE 8 Some stuff is Some stuff is REALLY HOT REALLY HOT
Bubbles of hot gas blown out by blown out by SUPERNOVAE SUPERNOVAE
T = tens of millions
- f degrees K
- f degrees K
- Mixing with rest of
Mixing with rest of galactic gas galactic gas
enrichment with heavy elements heavy elements
SLIDE 9 Superbubbles Superbubbles & Fountains & Fountains
When multiple bubbles multiple bubbles join (from a cluster) they join (from a cluster) they can create can create superbubbles superbubbles. .
Superbubbles can can blast blast hot gas hot gas even even
Galaxy! Galaxy!
“Enriches Enriches” ” gas between gas between galaxies galaxies
Some will rain back down and mix into the Galaxy and mix into the Galaxy
Artists Artists’ ’ conceptions! conceptions!
SLIDE 10
Inside our Galaxy: Material is Inside our Galaxy: Material is Constantly Being Recycled Constantly Being Recycled
SLIDE 11 Summary of Galactic Recycling Summary of Galactic Recycling
- Stars make new elements by fusion
- Dying stars expel gas and new elements, producing
hot bubbles (~106 K)
- Hot gas cools, allowing atomic hydrogen clouds to
form (~100-10,000 K)
- Further cooling permits molecules to form, making
molecular clouds (~30 K)
- Gravity forms new stars (and planets) in molecular
clouds Gas Cools
From HOT
HOT to COLD COLD
SLIDE 12 Is the process of galactic recycling Is the process of galactic recycling going to continue to infinity? going to continue to infinity?
Clicker Question Clicker Question BE PREPARED TO DEFEND YOUR ANSWER
SLIDE 13 Is the process of galactic recycling Is the process of galactic recycling going to continue to infinity? going to continue to infinity?
Clicker Question Clicker Question BE PREPARED TO DEFEND YOUR ANSWER
SLIDE 14 The ages of stars suggest that the bulge The ages of stars suggest that the bulge and halo of the Milky Way formed before and halo of the Milky Way formed before many of the stars in the disk. Which would many of the stars in the disk. Which would you expect to have you expect to have more heavy metals more heavy metals (a.k.a. higher (a.k.a. higher metallicity metallicity)? )?
A.
Halo and bulge stars B.
Disk stars C.
No difference Clicker Question Clicker Question
SLIDE 15 The ages of stars suggest that the bulge The ages of stars suggest that the bulge and halo of the Milky Way formed before and halo of the Milky Way formed before many of the stars in the disk. Which would many of the stars in the disk. Which would you expect to have you expect to have more heavy metals more heavy metals (a.k.a. higher (a.k.a. higher metallicity metallicity)? )?
A.
Halo and bulge stars B.
Disk stars C.
No difference Clicker Question Clicker Question
SLIDE 16
We observe star-gas-star cycle operating in Milky Way We observe star-gas-star cycle operating in Milky Way’ ’s s disk using many different wavelengths of light disk using many different wavelengths of light
SLIDE 17
Infrared light reveals stars whose visible light is Infrared light reveals stars whose visible light is blocked by gas clouds blocked by gas clouds Infrared Visible
SLIDE 18 X-rays are observed from hot gas above and below the X-rays are observed from hot gas above and below the Milky Way Milky Way’ ’s disk s disk X-rays
We also see “point” sources – these are X-ray binaries
SLIDE 19
21 cm radio waves emitted by atomic hydrogen show 21 cm radio waves emitted by atomic hydrogen show where gas has cooled and settled into disk where gas has cooled and settled into disk Radio (21cm)
SLIDE 20
Radio waves from carbon monoxide (CO) show Radio waves from carbon monoxide (CO) show locations of molecular clouds locations of molecular clouds Radio (CO)
SLIDE 21
Long-wavelength infrared emission shows where Long-wavelength infrared emission shows where young stars are heating dust grains young stars are heating dust grains IR (dust)
SLIDE 22 Gamma rays show where cosmic rays from supernovae Gamma rays show where cosmic rays from supernovae collide with atomic nuclei in gas clouds collide with atomic nuclei in gas clouds
SLIDE 23
Outlining Outlining starbirth starbirth in M51 in M51
Visible Visible ( (Kitt Kitt Peak) Peak) Infrared Infrared (Spitzer) (Spitzer)
SLIDE 24
What Clues to Our Galaxy What Clues to Our Galaxy’ ’s s History Do Halo & Disk Stars History Do Halo & Disk Stars Hold? Hold?
SLIDE 25
Halo Stars: 0.02-0.2% heavy elements (O, Fe, …). Disk Stars: 2% heavy elements
SLIDE 26 Which stars formed first? Which stars formed first?
- A. Halo stars
- B. Disk stars
- C. All stars formed at the same time
- D. Not enough information given
Clicker Question Clicker Question
SLIDE 27 Which stars formed first? Which stars formed first?
- A. Halo stars
- B. Disk stars
- C. All stars formed at the same time
- D. Not enough information given
Clicker Question Clicker Question
SLIDE 28 Disk Stars: 2% heavy elements, stars of all ages, large fraction of young stars (Population I Population I) Halo Stars: 0.02-0.2% heavy elements (O, Fe, …),
- nly old stars. (called Population II
Population II) Halo stars formed first, then stopped
SLIDE 29 What kind of star is most likely to be a What kind of star is most likely to be a part of the part of the Halo population? Halo population?
- A. An O star
- B. An A star
- C. An M star
- D. All stars are equally likely
- E. There are no stars left in the spheroidal
- population. Only supernova remnants.
Clicker Question Clicker Question
SLIDE 30 What kind of star is most likely to be a What kind of star is most likely to be a part of the part of the Halo population? Halo population?
- A. An O star
- B. An A star
- C. An M star
- D. All stars are equally likely
- E. There are no stars left in the spheroidal
- population. Only supernova remnants.
Clicker Question Clicker Question
SLIDE 31 Disk Stars: 2% heavy elements, stars of all ages (Population I Population I) Halo Stars: 0.02-0.2% heavy elements (O, Fe, …),
- nly old stars. (called Population II
Population II) Halo stars formed first, then stopped Disk stars formed later, kept forming
SLIDE 32
How Did Our Galaxy Form? How Did Our Galaxy Form?
SLIDE 33
Our galaxy probably formed from a giant gas cloud Our galaxy probably formed from a giant gas cloud
SLIDE 34
Halo stars formed first as gravity caused cloud to contract Halo stars formed first as gravity caused cloud to contract
SLIDE 35
Remaining gas settled into spinning disk Remaining gas settled into spinning disk
SLIDE 36
Stars continuously form in disk as galaxy grows older - Stars continuously form in disk as galaxy grows older - stars remain in disk plane stars remain in disk plane
SLIDE 37 Warning: This model is
Careful study of heavy-element proportions suggests that our galaxy formed from a few different clouds.
SLIDE 38
Detailed studies: Halo stars formed in clumps that later Detailed studies: Halo stars formed in clumps that later merged merged
SLIDE 39 Galactic Creation Summary Galactic Creation Summary
What clues to our galaxy’ ’s history do s history do halo stars hold? halo stars hold?
– Halo stars are all old, with a smaller proportion of heavy elements than disk stars, indicating that the halo formed first
How did our galaxy form?
– Our galaxy formed from a few huge clouds of gas, with the halo stars forming first and the disk stars forming later, after the gas settled into a spinning disk
