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Announcements. Reading for next class: Chapter 20 Cosmos Assignment 2, Due Wednesday, April 14 Angel Quiz. Questions:. Black Holes Star-Gas-Star cycle Halo, halo stars, halo vs. bulge, halo vs disk Spiral arms Do dying stars come back as the same star? superbubbles. Halo Stars:

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Announcements

Announcements

  • Reading for next class: Chapter 20

  • Cosmos Assignment 2,Due Wednesday, April 14

    • Angel Quiz


Questions

Questions:

  • Black Holes

  • Star-Gas-Star cycle

  • Halo, halo stars, halo vs. bulge, halo vs disk

  • Spiral arms

  • Do dying stars come back as the same star?

  • superbubbles


Milky way

Halo Stars:

0.02-0.2% heavy elements (O, Fe, …)

only old stars

Disk Stars:

2% heavy elements

stars of all ages


What do your classmates see

What do your classmates see?

To answer this need to know a little of Einstein’s theory of Motion and Gravity:

  • Gravity is Motion in Warped Space - Time

  • You can’t tell the difference between acceleration by gravity and any other constant acceleration

  • E = mc2, energy and mass are same thing measured in different units


Mass warps space time warped space time tells mass how to move

Mass warps Space - TimeWarped Space - Time tells Mass how to Move

Forget time, think just about warped space


Orbits in warped space time

Orbits in Warped Space - Time

c = circular, e = elliptical, u = unbounded


Elevator rocket

Elevator & Rocket


Gravity acceleration light beam in an elevator or gravity

Gravity = AccelerationLight Beam in an Elevator or Gravity


Gravity attracts light light generates gravity

Gravity Attracts LightLight generates Gravity

Reasonable since E = mc2

  • Black Holes Gravity attracts light

  • Light loses energy escaping from environs of a Black Hole. Convert radiation energy to gravitational potential energy.

  • Escaping Light is redshifted to longer wavelengths and periods


Your classmates would see you slow down as you approached the bh event horizon

Your classmates would see you slow down as you approached the BH event horizon

  • Can use period of light as a clock

  • Redshifted light oscillates with a longer period

  • Time appears to run slower near event horizon

  • You would appear to stop and hover (& fade out) as you approached the Event Horizozn


What would you notice as you passed the event horizon

What would you notice as you passed the Event Horizon

Nothing special

  • For you time does not slow down in a BH.

  • You quickly crash into the previous matter inside the BH(But you couldn’t tell us about it)


What can we know about black holes

What can we know about Black Holes?

  • Nothing can escape from inside an Event Horizon

  • Long range forces can exert influence outside Event Horizon

    • Gravity

    • Electric Force

  • Can determine:

    • Mass

    • Charge

    • Spin


Mini black holes can evaporate

Mini Black Holes can Evaporate

Mini BH produce strong tides (stellar BH don’t have strong enough tides)

  • Lose energy by work of tidal gravity on material outside the event horizon

  • Since energy = mass, they lose mass and get smaller

  • Evaporate


The milky way our galaxy

The Milky Way,our galaxy

Beginning of Unit IV: Cosmology

Milky Way - chapter 19


What does my building look like

What does my building look like?


Milky way small portion from the winter sky

Milky Waysmall portion from the winter sky


First idea count stars in different directions more stars larger extent what assumption is made

First Idea: Count stars in different directions,more stars -> larger extent.What Assumption is made?

Sun

Kapteyn Model of Milky Way, 1922


Question 1 what assumptions were made

Question 1:What Assumptions were made?

  • Stars are clustered in a disk

  • Stars are evenly distributed in space

  • Stars are clustered near the Sun

  • We see all the stars in the Milky Way


Question 1 what assumptions were made1

Question 1:What Assumptions were made?

  • Stars are clustered in a disk

  • Stars are evenly distributed in space

  • Stars are clustered near the Sun

  • We see all the stars in the Milky Way


What was missing

What was missing?

  • We don’t see all the stars, because some are hidden by interstellar clouds of gas & dust

  • The stars are not evenly distributed in space (but this is not as important)


Mosaic view does give good idea of mw structure

Mosaic View, does give good idea of MW structure

All-Sky View


Familiar constellations

Familiar Constellations


Milky way

Dusty gas clouds obscure our view because they absorb visible light

This gas is the

interstellar

medium that

makes new stars


Milky way

Infrared light passes more easily through dusty gas clouds

This gas is the interstellar medium that makes new stars


Milky way

Infrared Light


Milky way has disk shape

Milky Way has DISK shape

  • Stars are concentrated into a disk, but some stars above and below the disk

  • Neutral Hydrogen gas is concentrated in disk


Milky way cartoon

MilkyWayCartoon


Stars in the disk orbit in the same direction with a little bobbing up down

Stars in the disk orbit in the same direction with a little bobbing up & down


Stars in the bulge halo have randomly oriented orbits

Stars in the bulge & halo have randomly oriented orbits


Question 2

Question 2:

Why do orbits of disk stars bob up and down?

A. They’re stuck to the interstellar medium

B. Gravity of disk stars pulls toward disk

C. Halo stars knock them back into disk


Question 21

Question 2:

Why do orbits of disk stars bob up and down?

A.They’re stuck to the interstellar medium

B. Gravity of disk stars pulls toward disk

C.Halo stars knock them back into disk


Life of a galaxy gas star gas cycle

Life of a Galaxy:Gas -> Star -> Gas cycle

  • Gas clumps together by gravity -> stars

  • Stars produce heavy elements by fusion

  • Stars die and return processed gas to space

  • Enriched gas clumps together by gravity

  • New stars


Life of a galaxy gas star gas cycle1

Life of a Galaxy:Gas -> Star -> Gas cycle

Hot, ionized gas - one million K

Warm neutral gas - 10,000 K (most is here)

Cool neutral gas - 100 K

Molecular clouds - 30 K

Molecular cores - 6 K

Gas Cools

STAR FORMATION


Milky way

X-ray map of sky shows hot gas high above and far below galactic disk


Milky way

X-ray map of sky shows hot gas high above and far below galactic disk

Hot gas eventually cools to form atomic hydrogen and settles into disk


Milky way

Additional cooling makes the gas cold enough to form molecules

Hot gas eventually cools to form atomic hydrogen and settles into disk


Milky way

Additional cooling makes the gas cold enough to form molecules

Darkest regions of Milky Way correspond to these dense clouds.

That is where stars form!


Hot blue massive ms stars heat and ionize the gas around them

Hot, Blue, Massive MS starsheat and ionize the gas around them


Massive hot blue ms stars ionize the gas around them

Massive, hot, blue MS stars ionize the gas around them

Produce ionization nebula


Recycling stellar material low mass stars blow off winds eject envelopes

Recycling Stellar Material-Low mass stars blow off winds & eject envelopes


Recycling stellar material high mass stars explode as supernova

Recycling stellar Material -High mass stars explode as supernova


Recycling stellar material

Recycling Stellar Material

Stellar Winds and Supernova return stellar material, as hot gas, to the Interstellar Medium (gas between the stars) ENRICHED in Heavy Elementsproduced during nuclear fusion & supernova explosions


Gas star gas cycle

Gas -> Star -> Gas cycle


Milky way

Disk: ionization nebula & blue stars = star formationHalo: no ionization nebula or blue stars = no star formation


Milky way

Halo Stars:

0.02-0.2% heavy elements (O, Fe, …)

only old stars

Disk Stars:

2% heavy elements

stars of all ages


Where do stars form

Where do stars form?

Much of star formation in disk happens in

spiral arms

Whirlpool Galaxy


Question 3 how can we study the center of the milky way

Question 3: How can we study the Center of the Milky Way?

  • By observing it in x-rays

  • By observing it in ultraviolet light

  • By observing it in visible light

  • By observing it in infrared light

  • By observing it in radio light

    Choose all that apply


Question 3 how can we study the center of the milky way1

Question 3: How can we study the Center of the Milky Way?

  • By observing it in (very energetic) x-rays

  • By observing it in ultraviolet light

  • By observing it in visible light

  • By observing it in infrared light

  • By observing it in radio light

    Choose all that apply


Center of the milky way

Center of the Milky Way


Question 4 will stars move faster closer to the center or farther away from it

Question 4: Will stars move faster closer to the center or farther away from it?

  • Closer

  • Farther

  • The same at all distances


What happens in the solar system

What happens in the Solar System?


Star motions near the center of the milky way

Star Motions near the Center of the Milky Way


Star motions near the center of the milky way1

Star Motions near the Center of the Milky Way


What did we observe

What did we observe?

  • Stars moved fastest closest to the center

  • Similar Solar System

  • Speed decreases as 1/D

  • Point mass at Center of Galaxy

  • From velocity & distance can determine the MassM (inside distance D) = V2 D / G

  • Supermassive Black Hole, M ~3-4x106 Msun


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