4/3/20

ASTR 1040: Stars & Surprises with Our

• Revisit spiral pattern making in galaxy disk Super-bubble blowout in • Consider rotation curve of our galaxy, and the NGC 3709 unseen mass (dark matter) that it implies • Examine how 21-cm radio emission works: can map our galaxy (and its spiral structure) • Super-massive black hole at center of MW • Edwin Hubble using `Cepheid variables’ showed Andromeda is a distinct island universe – another Galaxy ! Prof. Juri Toomre TAs: Daniel Sega, Max Weiner Lecture 22 Thur 2 Apr 2020 zeus.colorado.edu/astr1040-toomre

Our Schedule We are Zoom-Interactive • Homework #10 due today (submit to • “Raise Hand” (Max monitors “Participants”) Canvas “Assignments”, new HW #11 available (from “Modules”) • “Send Chat” Message (Max will act) • Juri will get to your question or comment • Overview read Chap 20 “Galaxies and within at most a few minutes Foundations of Modern Cosmology” • If pressing, Unmute your mike and ask question • Then read with care 20.2 `Measuring Cosmic Distances' and 20.3 `Hubble's Law’ • We are happy to adjust “how to interact”, with your advice and experience

Clouds + dust REVISIT in Eagle

  ISM: Reddens the light A little DUST goes a long way!

Confusing to Absorbs distance & the light color

1 4/3/20

Dark and dusty stellar nurseries

Rosetta Nebula Nebula O & B star RCW 49 carving + Stellar jewels dust filaments Spitzer IR

REVISIT WHERE are we in MW? Why spiral arms? Dust makes it hard to Density waves – estimate distances stars move in and (stars dimmed) out of denser Globular clusters on regions COBE IR sky image More like ripples in a pond than arms of a pinwheel SUN Shapleys (1920) X distances to globular clusters: In dense regions, star Sun at 18 kpc from formation is more intense, so arms center (twice too far!) M51 - Whirlpool are brighter

Push and pull of gravity in disk

Gas/stars are pulled a little forward or backward toward the high density regions

Such clumping helps create a spiral pattern “traffic jam” Read with care

2 4/3/20

Density wave Stars and gas story – how spiral move through structure is built spiral wave

Gravitational instability of Star birth strongly enhanced by shock disks (gentle)

Crash/bang of star birth and recycling: rotating REMINDER through the spiral arms in the disk

Bright O & B All spiral galaxies stars are constantly changing mark the spiral pattern Cycle of starà gas M51 Whirlpool The Starà star-Gas- Galaxy Star Cycle HST

Outlining starbirth in M51 Q: Why does M51 – Whirlpool have open spiral structure, and ours is pretty ragged? visible infrared Spitzer

A: Collision with companion galaxy enhanced its spiral wave

3 4/3/20

Like Milky Way?

Questions or Comments

Break-Out Room: Meet & Greet

NGC 6118 Spiral + SN (VLT)

Stars moving in circles: orbital velocity law Reality for the Milky Way 2 • Rotation curve is MR = R x V / G flat or even rising! …faster orbit, mass radius orbital more mass inward velocity • Most of the mass of the galaxy solar system must be outside the solar circle!

• But few stars, MW rotation curve little gas there…

DARK MATTER ! probably in large halo -- outweights stars+gas by factor of about 10 !

Massive dark matter halo for MW Role of dark matter on rotation profile

• Stars and gas are embedded in a much larger dark matter halo DARK MATTER

• Dont know what dark matter is … probably not baryonic (usual protons, neutrons, electrons)

4 4/3/20

Dark matter halos for all galaxies Poll 1 Why Halo stars poor in metals • Presence revealed by rotation curves • Why are stars in the halo poor in the common (motions of stars in elements carbon, nitrogen and oxygen? galaxy)

• Dark matter extends • A. Those elements have been used up in halo beyond visible part of stars the galaxy -- mass is • B. C, N and O are biological elements, and ~10x stars and gas ! there is no life out there to make them • C. The halo stars formed before these elements • Most likely subatomic were made in abundance particles, as yet unidentified (weakly • D. Making C, N and O requires massive stars, interacting massive and these have been absent in the halo particles – WIMPs ? )

Multiple SN: Super-bubbles Super-bubbles in spiral galaxy NGC 3079

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

• If the superbubbles reaches the edge of the disk, it can blast hot gas out of the Galaxy! – Some will rain back down and mix into the galaxy HST Artist's conception/computer simulations

Super-bubbles in Large Magellanic Cloud (LMC) Q: Just HOW do we (nearby galaxy) know that MW has spiral structure?

A: Radio astronomers could map it with 21-cm line of hydrogen

5 4/3/20

Green Bank 100 m Radio Telescope VA

21 cm emission (radio)

Sampling neutral hydrogen atoms (cold)

also how MRI does it in medical imaging!

VLBA Radio Telescope Owens Valley Very Large Array (VLA) Socorro NM

VLA - Sicorro

Another view of 21 cm radio Radio mapping cool H clouds mapping in MW disk SUN o

o Beam cuts across SUN different spiral arms

o Doppler shifted radio emission

6 4/3/20

Radio map (21 cm) of spiral structure in MW in direction of Sagittarius: IR reveals a dense star cluster

SUN Ragged spiral x structure revealed

Emitted radio o waves can penetrate through GALAXY CENTER gas and dust

IR 1

Unusual activity Radio mapping at galaxy center of galactic center

Radio 3

IR 5 Sgr A*

Radio 4 VLT IR+AO Zooming in on Sagittarius A* Radio 2

7 4/3/20

Sgr A* VLT in IR + adaptive optics orbits

Star motion around black hole at galactic center

VLT: IR+AO

Sgr A* orbits Sgr A* Orbits

Keck UCLA

Rotation velocity at galaxy center

Some of central mass is stars, joined by 4.0 million (+/- 0.2) Orbits of stars solar mass indicate mass BLACK HOLE of ~4.2 million M within But further 20% sun uncertainty from 45 AU ! distance determination

Black hole still less than 1/1000 of MW mass

8 4/3/20

Question: Why no powerful jet and accretion disk near MWs supermassive black hole? Sag A* in Chandra • Modest X-ray view emission in X-rays…though other signs of activity

• Answer: maybe Exhibits it has eaten all it can – at least for outbursts, now ? but starved of fuel ?

HOW DID IT ALL BEGIN? Measuring galactic distances Edwin Hubble made Questions or Comments breakthrough using Cepheid variables to measure distance

Found Andromeda far outside Milky Way

Huge step forward in thinking about universe NGC 4414

Cepheid stars in H-R diagram Cepheid variable stars as distance • Instability strip -- indicators: region in H-R diagram standard candle with large, bright stars • Outer regions of star are unstable and tend to pulsate • Star expands and contracts, getting brighter and fainter Reminder (Fig 15.15)

Vital discovery by Henrietta Leavitt (1912)

9 4/3/20

Andromeda found to be far outside Milky Way Cepheid variable – another island universe : galaxy! stars • Edwin Hubble in 1924 identified Cepheids in Andromeda (M31) à showed they were far outside of Milky Way!

Period - • Now known distance: Luminosity 2.54 million ly (778 kp) brighter Cepheids relation • His first big discovery (more have longer periods to come) … Hubble using new 100 Hooker telescope at Mt. Wilson (above LA)

100 Hooker telescope at Mt Wilson Andromeda found to be far outside Milky Way – another island universe : galaxy!

Begins new era in 1924 ! Hubble (and Jeans) at new 100 Hooker telescope on Mt. Wilson

Andromeda – M31 (Sb) Edwin Hubble in 1924 identified Cepheids in NGC205 Andromeda (M31) à showed they were far outside of Milky Way! M32

First galaxy shown by Hubble (1924) to be a distinct island universe

2.54 million ly away 260,000 ly in diameter

10 4/3/20

LATEST IR IMAGING

Hubbles scheme to label galaxies spirals S

ellipticals E

lenticular

+ some irregulars barred spirals SB

M31 from WISE + M32 (below) + M110 (NGC 205)

Tuning fork shown with mugshots of galaxies NGC 4414 spirals Spirals ~80% of galaxies • Disks (with spiral arms) + • Spheroids (bulges+halos)

ellipticals

M100 center spirals-barred

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