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

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, please send your clicker # to TA Thomas Rogers

The Milky Way The Milky Way

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 from the center, years in the ‘Orion Arm’ Artist’s sketch

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

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: : • older stars, older stars, globular clusters globular clusters Artist’s sketch

Disk is very thin! Disk is very thin!

What Milky Way might might look like! look like! What Milky Way Spiral galaxy NGC 4414

Galaxy NGC 4565 � nearly edge-on

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

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?

Mapping the Milky Way Mapping the Milky Way • Galileo "For the Galaxy is nothing else than a congeries of • Galileo innumerable stars distributed in clusters." William & Caroline Herschel (1785): star counts • • William & Caroline Herschel – 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 s globular clusters globular clusters Shapley • 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

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

Stars in the disk all orbit in the same all orbit in the same Stars in the disk 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 of everything in the disk pulls them back in

Orbits of stars in the bulge and halo stars in the bulge and halo have have Orbits of 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

Why spiral arms? Why spiral arms? “Density waves Density waves” ” – – “ stars move in and stars move in and out of denser out of denser regions regions Like ripples in a pond ripples in a pond Like In dense regions, star star In dense regions, formation is more formation is more intense, , so so “ “arms arms” ” intense are brighter are brighter M51 - Whirlpool M51 - Whirlpool

Clicker Question Clicker Question Why do orbits of disk stars bob up and disk stars bob up and Why do orbits of 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 Why do orbits of disk stars bob up and disk stars bob up and Why do orbits of 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.

Galaxies: Ultimate Recyling Recyling Plants Plants Galaxies: Ultimate

Clicker Question Clicker Question 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 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

Contents: Cold stuff Cold stuff Contents: • Molecular CLOUDS – Mostly atomic hydrogen, some helium and other CO CO molecules Doppler Doppler Images • Dark, dusty, cold Images – 10-30K • Emit molecular emission lines in far IR, radio • Orion image Orion image here in here in • carbon monoxide (CO) (CO) carbon monoxide – colors are Doppler shifts colors are Doppler shifts –

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

Mapping Cold Cold Hydrogen Hydrogen Mapping • Even the coldest Even the coldest • hydrogen emits hydrogen emits faint emission lines faint emission lines in the RADIO RADIO in the • Change in Change in energy energy • levels of nuclear levels of nuclear configuration configuration All sky 21 cm radio mapping All sky 21 cm radio mapping • Wavelength: Wavelength: 21 cm 21 cm •

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 Nebula Nebula Horsehead

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

Hot stuff Hot stuff Ionization nebulae Ionization nebulae “O & B star O & B star “ associations” ” associations • Hot stars Hot stars excite excite • atomic transitions atomic transitions in hydrogen and in hydrogen and other light elements other light elements in the gas in the gas • T~ 10,000 K near T~ 10,000 K near • hot young stars hot young stars Lagoon Nebula Lagoon Nebula

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

A. A continuous spectrum A. 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. Absorption lines from hydrogen only from hydrogen only E. Absorption lines

Trifid nebula (M20) nebula (M20) Trifid visible Spitzer infrared visible Spitzer infrared

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

Really Hot Stuff Really Hot Stuff Hot star Hot star winds from winds from aging stars aging stars (10 ly ly across) across) (10