ASTR 1120 REVIEW General Astronomy: Stars & Galaxies - - PowerPoint PPT Presentation

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ASTR 1120 REVIEW General Astronomy: Stars & Galaxies - - PowerPoint PPT Presentation

Feb 07, 2024 309 likes •445 views

ASTR 1120 REVIEW General Astronomy: Stars & Galaxies NNOUNCEMENTS Midterm #3 this Thursday 11/17; covering lect. 15-21 (and corresponding reading in Ch. 19-22) last part of class today will be review HW #8 due today, 5pm

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SLIDE 1

ASTR 1120 General Astronomy: Stars & Galaxies

NNOUNCEMENTS

  • Midterm #3 this Thursday 11/17;

covering lect. 15-21 (and corresponding reading in Ch. 19-22)

  • last part of class today will be review
  • HW #8 due today, 5pm
  • HW #9 due Tue, 12/01, by 5pm

ALTERNATE FINAL on Monday, Dec.7th, 5:30pm- 7:00pm, in Muenzinger E131 Numerical simulations of structure formation

REVIEW

Lessons from Imaginary Universes

  • Cold (Slow) dark matter

works better than hot (fast) dark matter

  • Neutrinos are too fast–

structure would be smeared out

  • What is slow and dark

enough? We don’t know yet!

– Particle experiments under way…..

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SLIDE 2

Dark Matter and the Fate of the Universe

  • Expansion begins with the Big Bang (we’ll talk about

this after the break)

  • At that point, everything in the universe is flung

apart at outrageous speeds!

  • Several different models for Past and Future

depending upon the amount of dark matter

Very important diagram

“Average distance between galaxies”

measure of “expansion factor

  • f Universe”

Hubble constant NOW sets how fast universe is expanding NOW Big Bang = when distance zero TIME SIZE

NOW

The expansion rate of the universe is not necessarily constant for all time

  • GRAVITY should SLOW

expansion rate deceleration

  • Different models for

different amounts of dark matter

– Let’s ignore accelerating for now

Since gravity is what pulls everything back in, there must be a magic number

  • Just the right amount of mass (in our current

universe) to slow down expansion but not enough to cause recollapse

  • We call this exact amount of matter, the

CRITICAL DENSITY ~10-29 grams/cm3 = a few atoms in a closet

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SLIDE 3

Critical Universe

  • Density of

matter = “critical density”

  • Will expand

forever, but more and more slowly with time

Flat Universe

Recollapsing Universe

  • Dark matter

density is greater than “critical density”

  • Expansion will

stop in the future, will collapse back in

– Big Crunch – Oscillations?

Closed Universe

Coasting Universe

  • The universe

has always expanded at the same rate (no deceleration due to gravity!)

  • The age of the

Universe = 1/Ho

Open Universe

Three models for fates of universe

CLOSED OPEN FLAT

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SLIDE 4

Which model predicts the youngest age for the universe today?

  • A. Recollapsing

(closed)

  • B. Critical

(flat)

  • C. Coasting

(open)

Clicker Question

  • A. Recollapsing
  • Age of universe is

how far to left curves hit horizontal axis (distance between galaxies = 0)

What determines the future average distance between galaxies?

  • A. The rate of expansion, with a slower expansion

rate meaning a greater average distance

  • B. The rate of expansion, with a faster expansion

rate meaning a greater average distance

  • C. Only on the density of matter in the universe.

Clicker Question

What determines the future average distance between galaxies?

  • A. The rate of expansion, with a slower expansion

rate meaning a greater average distance

  • B. The rate of expansion, with a faster expansion

rate meaning a greater average distance

  • C. Only on the density of matter in the universe.

Clicker Question

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SLIDE 5

Which model has the slowest future rate of expansion?

  • A. Recollapsing
  • B. Critical
  • C. Coasting

Clicker Question

Which model has the slowest future rate of expansion?

  • A. Recollapsing
  • B. Critical
  • C. Coasting

Clicker Question

  • Recollapse to big crunch:

– Crushing heat – Destruction of all matter – Rebirth?

  • Eternal expansion:

– Cold, galaxies dimming – Star formation slowing – Everything winds up as a brown dwarf, black dwarf, neutron star or black hole

What is the fate of the Universe? Is there enough dark matter to recollapse the universe?

Baryonic matter: only a few % of critical density Dark matter: only about 25% of what is needed

  • Universe should be in between the “coasting”

and “critical” models

The Universe will expand forever

Which is it?

… and with an unexpected twist…

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SLIDE 6

A New Twist for the 21st Century

  • Scientists using white

dwarf supernovae to measure distances discovered something quite strange

Using supernovae to determine the fate of the Universe

  • Redshifts of the

supernovae gives their vertical position

– Space has stretched since they gave off their light

  • Apparent

brightness gives their horizontal position

– Dimmer=more distant = high lookback

Supernovae are not consistent even with the expectations of a coasting universe!!!

Universe is accelerating?!?!

How can the universe be accelerating???????

A force that counteracts gravity? “Dark energy”– outweighs every other form of mass/energy! Truly an unknown force in all of physics The Cosmological Constant actually exists!

(“Einstein’s Greatest Blunder” )

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SLIDE 7

Four models for fates of universe

CLOSED OPEN FLAT ACCELERATING

What is meant by “dark energy”?

  • A. The energy associated with dark matter through

E=mc2

  • B. An unknown form of energy that counteracts

gravity and causes the expansion of the universe to accelerate.

  • C. Any unknown force that acts like gravity
  • D. Highly energetic particles that are believed to

constitute dark matter

  • E. The total energy in the universe after the Big

Bang but before the first stars

Clicker Question

What is meant by “dark energy”?

  • A. The energy associated with dark matter through

E=mc2

  • B. An unknown form of energy that counteracts

gravity and causes the expansion of the universe to accelerate.

  • C. Any unknown force that acts like gravity
  • D. Highly energetic particles that are believed to

constitute dark matter

  • E. The total energy in the universe after the Big

Bang but before the first stars

Clicker Question

REVIEW FOR MIDTERM III to follow…..

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SLIDE 8

Disk, Bulge & Halo

  • Disk: includes

spiral arms -- young, new star formation

  • Bulge & Halo:
  • lder stars,

globular clusters

Artist’s sketch

Disk is very thin!

Galaxies: Ultimate Recyling Plants

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SLIDE 9

Summary of Galactic Recycling

  • Stars make new elements by fusion
  • Dying stars expel gas and new elements, producing

hot bubbles (~106 K)

  • Hot gas cools, allowing atomic hydrogen clouds to

form (~100-10,000 K)

  • Further cooling permits molecules to form, making

molecular clouds (~30 K)

  • Gravity forms new stars (and planets) in molecular

clouds Gas Cools

From HOT to COLD

We observe star-gas-star cycle operating in Milky Way’s disk using many different wavelengths of light

Dark matter halo for galaxies

  • Dark matter extends

beyond visible part of the galaxy -- mass is ~10x stars and gas!

  • Probably not normal

mass that we know of (protons, neutrons, electrons).

  • Most likely subatomic

particles, as yet unidentified (weakly interacting massive particles – WIMPs?)

Stars appear to be

  • rbiting something

massive but invisible … a black hole! Orbits of stars indicate a mass of about 3-4 million Msun within 600 RSchwarzchild

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SLIDE 10

Summary “Distance Ladder” to measure universe

Different standard candles are useful for different distances

v = Ho d

Velocity of Recession (Doppler Shift) Hubble’s Constant Distance (km/sec) (km/sec/Mpc) (Mpc)

“Hubble’s Law”

velocity distance

Best current values for expansion

Ho = 71 +/- 4 km/s/Mpc

Balloon analogy for expanding universe

  • Each dot on the

balloon can be thought of as a galaxy. As the balloon expands, galaxies move farther away from each other

Forming a disk with spiral

  • As more material

collapses, angular momentum spins it into a disk

  • Stars now formed

in dense spiral arms – disk stars are younger!

Angular momentum of protogalactic cloud important in spiral galaxy formation

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SLIDE 11

Making ellipticals

1. Higher density: much faster star formation uses up all the gas

– Nothing left to make a disk

  • r

2. Lower spin

– Gas used up before angular momentum took

  • ver
  • Now we see a sphere
  • f old stars

Or perhaps a different scenario….

  • Spiral galaxy collisions

destroy disks, leave behind elliptical

  • Burst of star formation

uses up all the gas

  • Leftovers: train wreck
  • Ellipticals more common

in dense galaxy clusters (centers of clusters contain central dominant galaxies) NGC 4038/39 Antennae

AGNs Central Engines

How do AGNs emit so much light in so little space?

  • They are powered by

accretion disks around supermassive black holes

  • In some AGNs, huge

jets of material are shot

  • ut at the poles. These

jets are strong radio sources.

JET DISK

REVIEW

“Central Engine” -- artist’s conception

  • Accretion disk

around super- massive black hole

  • Disk itself may or

may not be obscured by dust

  • If bright nucleus is

visible, looks like a quasar, if not, then its a radio galaxy

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SLIDE 12

Prototypical “radio galaxy”

Giant elliptical galaxy NGC 5128 with dust lane (from spiral galaxy?) + Centaurus A radio source (color lobes)