The Milky Way General Astronomy: Stars & Galaxies omework #6 on - - PowerPoint PPT Presentation

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The Milky Way General Astronomy: Stars & Galaxies omework #6 on - - PowerPoint PPT Presentation

Dec 28, 2023 133 likes •269 views

ASTR 1120 The Milky Way General Astronomy: 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, please send your clicker # to TA

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SLIDE 1

ASTR 1120 General Astronomy: 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

The Milky Way Size of the Milky Way

  • 100-400 billion stars
  • 100,000 light years in

diameter

  • Sun (and us) are

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

Artist’s sketch

Milky Way Anatomy – Spiral Galaxy

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SLIDE 2

Disk, Bulge & Halo

  • Disk: includes

spiral arms -- young, new star formation

  • Bulge & Halo:
  • lder stars,

globular clusters

Artist’s sketch

Disk is very thin!

What Milky Way might look like!

Spiral galaxy NGC 4414 Galaxy NGC 4565 nearly edge-on

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SLIDE 3

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

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

Clicker Question

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

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

Clicker Question

Where does most star formation occur 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

Where does most star formation occur 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

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SLIDE 4

An important Question

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

Mapping the Milky Way

  • Galileo "For the Galaxy is nothing else than a congeries of

innumerable stars distributed in clusters."

  • 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

6,500 ly 30,000 ly

Shapley’s 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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SLIDE 5

How Do Stars Orbit in Our Galaxy?

Stars in the disk all orbit in the same 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

Orbits of stars in the bulge and halo have 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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SLIDE 6

Why spiral arms?

“Density waves” – stars move in and

  • ut of denser

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

M51 - Whirlpool

Why do orbits of disk stars bob up and 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

Why do orbits of disk stars bob up and 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

Galaxies: Ultimate Recyling Plants

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SLIDE 7

Which generation of stars do you 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

Which generation of stars do you 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

Contents: 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 here in

carbon monoxide (CO)

– colors are Doppler shifts CO Doppler Images

Molecular clouds = star forming regions

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SLIDE 8

Mapping Cold Hydrogen

  • Even the coldest

hydrogen emits faint emission lines in the RADIO

  • Change in energy

levels of nuclear configuration

  • Wavelength: 21 cm

All sky 21 cm radio mapping

Semi-Warm stuff

  • Dust:

– absorbs visible and UV light – Transparent to long wavelengths (red, IR, radio)

  • Emits IR light

Horsehead Nebula

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

  • Hot stars excite

atomic transitions in hydrogen and

  • ther light elements

in the gas

  • T~ 10,000 K near

hot young stars

Ionization nebulae “O & B star associations”

Lagoon Nebula

Hot stuff

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SLIDE 9

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

  • A. A continuous spectrum
  • B. Emission lines of hydrogen plus a few other

slightly heavier elements

  • C. Emission lines of elements all the way up to

iron and a lot of heavier elements

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

Clicker Question

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

Trifid nebula (M20)

visible Spitzer infrared

Stellar nursery (Sharpless 140)

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

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SLIDE 10

(10 ly across)

Really Hot Stuff

Hot star winds from aging stars

Supernova Remnants & Planetary Nebula

More hot stuff

Some stuff is REALLY HOT

  • Bubbles of hot gas

blown out by SUPERNOVAE

  • T = tens of millions
  • f degrees K
  • Mixing with rest of

galactic gas enrichment with heavy elements

Superbubbles & Fountains

  • When multiple bubbles

join (from a cluster) they can create superbubbles.

  • Superbubbles can blast

hot gas even out of the Galaxy!

  • “Enriches” gas between

galaxies

  • Some will rain back down

and mix into the Galaxy

Artists’ conceptions!

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SLIDE 11

Edge-on view of spiral galaxy NGC 4013

  • Dust/gas in disk
  • bscures light
  • Plumes and fuzz

sticking out are “fountains” & “superbubbles” from supernovae

HST

Superbubbles in spiral galaxy NGC 3079

HST

Inside our Galaxy: Material is Constantly Being Recycled