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omework #6 on Mas ring As onom due on Tuesday, ov. 03, by 5p - - PowerPoint PPT Presentation

Mar 18, 2023 382 likes •837 views

ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies omework #6 on Mas ring As onom due on Tuesday, ov. 03, by 5p If your CU clicker grade is 0 and you have been in class,

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ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies

  • mework #6
  • n Masring Asonom

due on Tuesday, ov. 03, by 5p

If your CU clicker grade is 0 and you have been in class, please send your clicker # to TA Thomas Rogers

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The Milky Way The Milky Way

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Size of the Milky Way Size of the Milky Way

  • 100-400

100-400 billion stars

  • 100,000 light years in

diameter

  • Sun (and us) are

located ~28,000 light ~28,000 light years years from the center, in the ‘Orion Arm’

Artist’s sketch

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Milky Way Milky Way Anatomy Anatomy – – Spiral Galaxy Spiral Galaxy

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Disk, Bulge & Halo Disk, Bulge & Halo

  • Disk

Disk: :

includes includes spiral arms spiral arms

  • young, new star

young, new star formation formation

  • Bulge & Halo

Bulge & Halo: :

  • lder stars,
  • lder stars,

globular clusters globular clusters

Artist’s sketch

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SLIDE 6

Disk is very thin! Disk is very thin!

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SLIDE 7

What Milky Way What Milky Way might might look like! look like!

Spiral galaxy NGC 4414

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SLIDE 8

Galaxy NGC 4565 nearly edge-on

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What kind of object lie in the What kind of object lie in the halo halo of our

  • f our

Galaxy? Galaxy?

  • A. O and B stars.
  • B. Gas and dust.
  • C. Globular clusters
  • D. Open clusters.
  • E. All of the above.

Clicker Question Clicker Question

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SLIDE 10

What kind of object lie in the What kind of object lie in the halo halo of our

  • f our

Galaxy? Galaxy?

  • A. O and B stars.
  • B. Gas and dust.
  • C. Globular clusters
  • D. Open clusters.
  • E. All of the above.

Clicker Question Clicker Question

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Where does most star formation occur Where does most star formation occur in the Milky Way today in the Milky Way today? ?

  • A. In the halo
  • B. In the bulge
  • C. In the spiral arms
  • D. In the Galactic center
  • E. Uniformly throughout the Milky

Way

Clicker Question Clicker Question

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SLIDE 12

Where does most star formation occur Where does most star formation occur in the Milky Way today in the Milky Way today? ?

  • A. In the halo
  • B. In the bulge
  • C. In the spiral arms
  • D. In the Galactic center
  • E. Uniformly throughout the Milky

Way

Clicker Question Clicker Question

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An important Question An important Question

How do we know all we know How do we know all we know about the Milky Way? about the Milky Way?

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Mapping the Milky Way Mapping the Milky Way

  • Galileo

Galileo "For the Galaxy is nothing else than a congeries of innumerable stars distributed in clusters."

  • William & Caroline Herschel

William & Caroline Herschel (1785): star counts

– Counted stars along 683 lines of sight using their 48-inch telescope.

Conclusion: Sun is in the center and MW width is about 5 times its thickness

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SLIDE 15

6,500 ly 30,000 ly

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Shapley Shapley’ ’s s globular clusters globular clusters

  • Harlow Shapely measured distances to globular clusters

– These appeared to be centered on a location tens of thousands of light-years from the Sun.

Conclusion: Sun not in center, about 2/3 out

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How Do Stars Orbit in Our Galaxy? How Do Stars Orbit in Our Galaxy?

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Stars in the disk Stars in the disk all orbit in the same all orbit in the same direction with a little up-and-down motion direction with a little up-and-down motion

  • If they get too far above or below the disk, the gravity
  • f everything in the disk pulls them back in
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Orbits of Orbits of stars in the bulge and halo stars in the bulge and halo have have random orientations random orientations

  • Evidence points to bulge and halo formed before

the disk existed

– Their orbits not affected (much) by the gravity of the disk

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Why spiral arms? Why spiral arms?

“ “Density waves Density waves” ” – – stars move in and stars move in and

  • ut of denser
  • ut of denser

regions regions Like Like ripples in a pond ripples in a pond In dense regions, In dense regions, star star formation is more formation is more intense intense, , so so “ “arms arms” ” are brighter are brighter

M51 - Whirlpool M51 - Whirlpool

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Why do orbits of Why do orbits of disk stars bob up and disk stars bob up and down? down?

  • A. They’re stuck to the interstellar medium

which moves like that because of its density.

  • B. The gravity of disk stars pulls toward disk
  • C. The halo stars push them back into disk
  • D. Their orbits carry them out but then they

bounce off the edge of the Galaxy and head back in.

  • E. The density waves in the spiral arms kick

them out of the disk.

Clicker Question Clicker Question

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SLIDE 23

Why do orbits of Why do orbits of disk stars bob up and disk stars bob up and down? down?

  • A. They’re stuck to the interstellar medium

which moves like that because of its density.

  • B. The gravity of disk stars pulls toward disk
  • C. The halo stars push them back into disk
  • D. Their orbits carry them out but then they

bounce off the edge of the Galaxy and head back in.

  • E. The density waves in the spiral arms kick

them out of the disk.

Clicker Question Clicker Question

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SLIDE 24

Galaxies: Ultimate Galaxies: Ultimate Recyling Recyling Plants Plants

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Which generation of stars do you Which generation of stars do you expect to be more metal-rich? expect to be more metal-rich?

  • A. Older population of stars (i.e. stars

formed a very long time ago)

  • B. Younger population of stars (i.e.

formed more recently)

  • C. No difference

Clicker Question Clicker Question

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Which generation of stars do you Which generation of stars do you expect to be more metal-rich? expect to be more metal-rich?

  • A. Older population of stars (i.e. stars

formed a very long time ago)

  • B. Younger population of stars (i.e.

formed more recently)

  • C. No difference

Clicker Question Clicker Question

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Contents: Contents: Cold stuff 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

  • Orion image

Orion image here in here in carbon monoxide carbon monoxide (CO) (CO)

– – colors are Doppler shifts colors are Doppler shifts CO CO Doppler Doppler Images Images

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Molecular clouds = Molecular clouds = star forming regions star forming regions

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Mapping Mapping Cold Cold Hydrogen Hydrogen

  • Even the coldest

Even the coldest hydrogen emits hydrogen emits faint emission lines faint emission lines in the in the RADIO RADIO

  • Change in

Change in energy energy levels of nuclear levels of nuclear configuration configuration

  • Wavelength:

Wavelength: 21 cm 21 cm

All sky 21 cm radio mapping All sky 21 cm radio mapping

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Semi-Warm stuff Semi-Warm stuff

  • Dust:

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

Emits IR light

Horsehead Horsehead Nebula Nebula

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Dust+dark Dust+dark molecular molecular clouds clouds Horsehead Horsehead in close-up in close-up VLT VLT (Very Large (Very Large Telescope) Telescope)

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  • Hot stars

Hot stars excite excite atomic transitions atomic transitions in hydrogen and in hydrogen and

  • ther light elements
  • ther light elements

in the gas in the gas

  • T~ 10,000 K near

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

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If we took a spectrum of the gas in an If we took a spectrum of the gas in an ionization nebula, what should we ionization nebula, what should we expect to see? expect to see?

A. A. A continuous spectrum A continuous spectrum B. B. Emission lines of hydrogen plus a few other Emission lines of hydrogen plus a few other slightly heavier elements slightly heavier elements C.

  • C. Emission lines of

Emission lines of elements all the way up to elements all the way up to iron and iron and a lot of heavier elements a lot of heavier elements D.

  • D. Absorption lines of a number of elements

Absorption lines of a number of elements E. E. Absorption lines Absorption lines from hydrogen only from hydrogen only

Clicker Question Clicker Question

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A. A. A continuous spectrum A continuous spectrum B. B. Emission lines of hydrogen plus a few other slightly heavier Emission lines of hydrogen plus a few other slightly heavier elements elements C. C. Emission lines of Emission lines of elements all the way up to iron and elements all the way up to iron and a lot of a lot of heavier elements heavier elements D. D. Absorption lines of a number of elements Absorption lines of a number of elements E. E. Absorption lines Absorption lines from hydrogen only from hydrogen only

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Trifid Trifid nebula (M20) nebula (M20)

visible visible Spitzer infrared Spitzer infrared

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Stellar nursery ( Stellar nursery (Sharpless Sharpless 140) 140)

Spitzer IR image shows deeply embedded Spitzer IR image shows deeply embedded O-type stars within dark dust cloud encasing them O-type stars within dark dust cloud encasing them

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SLIDE 37

(10 (10 ly ly across) across)

Really Hot Stuff Really Hot Stuff

Hot star Hot star winds from winds from aging stars aging stars

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Supernova Supernova Remnants Remnants & & Planetary Planetary Nebula Nebula

More hot stuff More hot stuff

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Some stuff is Some stuff is REALLY HOT REALLY HOT

  • Bubbles of hot gas

Bubbles of hot gas blown out by blown out by SUPERNOVAE SUPERNOVAE

  • T = tens of millions

T = tens of millions

  • f degrees K
  • f degrees K
  • Mixing with rest of

Mixing with rest of galactic gas galactic gas

  • enrichment with

enrichment with heavy elements heavy elements

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Superbubbles Superbubbles & Fountains & Fountains

  • When

When multiple bubbles multiple bubbles join (from a cluster) they join (from a cluster) they can create can create superbubbles superbubbles. .

  • Superbubbles

Superbubbles can can blast blast hot gas hot gas even even

  • ut of the
  • ut of the

Galaxy! Galaxy!

  • “

“Enriches Enriches” ” gas between gas between galaxies galaxies

  • Some will rain back down

Some will rain back down and mix into the Galaxy and mix into the Galaxy

Artists Artists’ ’ conceptions! conceptions!

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Edge-on view of spiral galaxy Edge-on view of spiral galaxy NGC 4013

NGC 4013

  • Dust/gas in disk

Dust/gas in disk

  • bscures light
  • bscures light
  • Plumes and fuzz

Plumes and fuzz sticking out are sticking out are “ “fountains fountains” ” & & “ “superbubbles superbubbles” ” from supernovae from supernovae

HST HST

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SLIDE 42

Superbubbles Superbubbles

in spiral galaxy NGC 3079 in spiral galaxy NGC 3079

HST HST

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Inside our Galaxy: Material is Inside our Galaxy: Material is Constantly Being Recycled Constantly Being Recycled