When a Type II Supernova explodes the Stellar core is left over depending on its mass it will either be a _______ or __________.

If the core left behind has a mass between 1.4 and 3 M_o

it becomes a ________.

big ball of neutrons with a mass of 1.4-3 M_o

radius: 10-15km (20 mile diameter)
*About as big as Mobile is Wide

density extremely high

Sugar cube size of this stuff would weigh 200 billion lbs on Earth

Neutron Stars rotate rapidly, up to 30 times a second

Conservation of angular momentum.
It must rotate rapidly due to its smaller size.

*Ice skater example - Ice skaters spin faster and faster as they bring their arms in - the smaller the angular momentum the faster they spin.

Neutron Stars have large magnetic fields.

The neutron star has the magnetic field of the original star - its smaller size concentrates the field, making the magnetic field trillions times larger.

Also - very very hot: 1 million K at surface, emits lots of X-Rays, heat due to contraction, low luminosity due to size.

two of the following choicse are true

(has a large magnetic field)

(rotates rapidly)

Why do pulsars pulse?

Lighthouse theory:

• spinning magnetic field acts like a generator, creates and electric field
• electric field rips charged particles off surface of neutron star
• particles accelerate outward along poles of magnet, emitting radiation
• looks like it flashes when beam of light passes your line of sight.

Not all neutron stars are pulsars

but

All pulsars are neutron stars

approx 500 known pulsars

Pulsar Glitches!

Pulsars are slowing down

• period of rotation increases by a few billionths af a second each day
• Pulsar is losing energy
• Energy radiated outward is about equal to the energy lost by slowing rotation
• Estimate age of pulsar by how fast it rotates.

X-Ray Bursters

• Neutron star in a binary system
• Matter from companion falls onto neutron star
• forms an accretion disk
• slowly spirals to the surface
• as matter builds up on surface it gets hot, and very dense
• Hydrogen fusion begins over the entire surface

X-Ray Bursters cont...

like a nova except:

with a Nova you have a white dwarf (H falling on white dwarf)

HERE you have X-Ray Burster: neutron star and H falling on it.

Gamma Ray Burster

Flash of Gamma Rays lasting only a few seconds.

Possibly from merging neutron stars

Black Hole

If the core of the supernova star has a mass greater than 3M_o, no known force can stop its collapse.

3M_o the "Chandraskhar Limit" for neutron stars.

- core collapes to zero radius

- density is infinite / gravity at its surface is infinite
- Not even light can escape

Black Hole escape velocity

do not need to know formula - but do know:

• R (size of object) = size of thing you are going to try to escape
• *as R gets bigger the V_e (escape velocity) will get smaller
• If R gets smaller than V_e gets bigger

Eventually R could be so small that V_e would exceed the speed of light.

**But nothing can travel faster than the speed of light - which means you cannot get away from the Black Hole

If V_e exceeds C (speed of light) you can't escape.
It is a Black Hole.

Event Horizon

The imaginary sphere around a black hole where radius = Schwarzchild radius

**If you cross the event horizon, you cannot escape - nothing can escape

**Any event inside the event horizon can never be communicated to the universe.

Finding a Black Hole

Black holes are in a binary system

black holes strip mass off its companion

forms an accretion disk

as mass falls into the hole, it is heated and emits x-rays.

bipolar jets formed by companions mass

*a black hole ingesting mass can release a huge amount of radiation due to mass being heated as it falls

1.  mass
2. charge
3. angular momentum

A Swarzchild Black Hole has NO angular momentum

A Kerr Black Hole has angualr momentum

William and Caroline Herschel (brother and sister)

studied:

shape of Milky Way using star counts

*They thought the Milky Way was shaped like an alligator head.

Milky Way

can be confused with a cloud

Galileo discovered the Milky Way was stars

noted globular clusters mostly on one side of the sky

measured their distance using RR Lyrae Varibles

        generated a 3D map (locations of clusters)

- He believed that the center of distribution must be the    center of the galaxy (because of the effects of gravity).

- Shapely estomated the size of the galaxy at 100,000 parsecs with us at one edge.

- He believed that the galaxy was the entire universe, there was nothing else.

Milky Way

Earth is about 25,000 ly from the center of the galaxy

*we are indeed off to one side like Shapely thought

Overall shape similar to a fried egg earth is off in the white of the egg

Milky Way components

Disk Component

- stars

- open clusters

- almost all gas and dust

Nuclear Bulge (galactic bulge)

- crowded with stars

- cool low main sequence stars (K & M stars)

Milky Way Componenet cont..

Halo

- thin scattering of stars, same type as in nucleus

- globular clusters

- no gas and dust

Milky Way rotates

-stars would fall into center of galaxy without rotation

-stars are orbiting the inner galaxy

Sun moves at 220 km/s toward Hercules

-orbit radius = 8500 pc

-orbit period = 240 million yrs
(20 orbits since we were first formed)

Use Keplers 3 law to estimate mass of galaxy

  -2 X 10¹¹ M_o

Extra mass apparently Dark Mass - we don't see it

Theories for dark matter:

- black hole (unlikely)

- brown dwarfs (possible)

- low mass white dwarfs (possible)

- exotic matter (?)

General Theory of relativity that says the path of light can be changed by gravity - Thus "gravitational lensing".

*Dim white dwarfs may have been detected using gravitational lensing

Stars in galaxy can be divided into two general classes or Stellar Populations

- located in galactic disk

- metal rich (203% atoms heavier then He)

- relatively young

- circular orbits in plane of galactic disk

*Sun is population I

Metal content defines whether Pop i or Pop II

Population I stars get metal from previous generations of stars

- located in Halo and nuclear bulge

- metallic poor

- old stars

- elliptical orbits, randomly tilted

*Globular cluster stars are Population II stars.

Population II stars are older & were formed before metal were created.

Spiral Arms

- Milky way apparently has a spiral patterned shape

- Many other galaxies also

- Spiral arms are regions of high gas density and young  hot stars

- Spiral arms defines by presence of gas, dust, and O & B stars.

- lots of emission and dark nebula in the spiral arm

Milky way spiral arms found by

- plot position of O and B stars

- plot density of neutral hydrogen

-21 cm radiation (photon)

-transparent dust particles

*The Sun is in Orian Arm of spiral

Density Wave Theory

-spiral arms are stable regions of compression

-coiled wave of high density

-squeezes gas, triggers star formation

*like cars in a traffic jam

Center of the Milky Way is in Sagitarius

50,000 stars per cubic parsec

powerful radio source, Sag A

rapidly moving gases

cosmic rays

Gamma Rays emitting from galaxy center

E of gamma rays = mass of electron

gamma rays created by pair annihilation

- electrons and anti-electrons meeting, emit 2 gamma rays

Giant Black Hole in galactic core

Sag A is radio emission from the suspected black hole at the galaxy center.

Measuring Galaxies:

- several methods for measuring distance, depending on the distance

*Cepheid Variables

- period proportional to avg luminosity

- must resolve individual stars

- ***The best method***

- Hubble gets us to 25 Mpc

Tully Fisher Relation

- Rotation Speed of galaxy is proportional to its luminosity

*bigger galaxies rotate faster

*big galaxies are brighter (more stars)

-Rotation speed from Doppler Shift

- Measure apparent magnitude

- calculate distance

- good to 200 Mpc

***Only true for Spiral galaxies - not elliptical

Supernovae (Type I)

-Assume Supernovae reach same absolute magnitude

- measure apparent magnitude

- good to about 1000 Mpc

-18.9 or 19.

Velocity

Radial Velocity

- speed directly towards or away from us

- measure using Doppler Shift

- blue shift - moving towards us

- red shift - moving away from us

**only a few display blue shift

Velocity cont..

Transverse Velocity

- recall this is speed across our line of sight

- must measure distance

- must measure proper motion

**Cannot be done (galaxies too far away)

Edwin Hubble and Melton Humason

- measured radial speeds of many galaxies and their distance

- made a graph of distance on X axis and radial speed on Y axis.

Hubbles Law = more distant the galaxy, the greater the recessional speed.

Hubbles Law comes from the diagram

recessional velocity = H x distance

- H is Hubbles Constant

- H corresponds to the slope of line in diagram

- we now know Hubbles constant within 5%

*Hubbles law is now the way to measure galactic distance

V=HxD      D=V/H answer in Mpc

Galaxy Types

Edwin Hubble noted 3 types of galaxies

the normal ones - do not put out alot of energy

• Spiral
• Elliptical
• irregular

Spiral Galaxies

- Medium to large

- Central bulge, flattened disk, spiral arms, gas, dust, & young stars

Spiral Classes

SO

-very large core

-disk has no apparent spiral

- very little gas and dust

SA

- large core

- tightly wound arms

- little gas and dust

SB

- medium core

- medium wound spiral arms

- medium gas and dust

SC

- Small Core

- loosely wound arms

-lots of gas and dust - dust indicates that these are relatively young

Barred Spiral Galaxies

- Elongated structure, flattened disk, spiral arm, gas, dust, young stars

- These galaxies have a strabge bar extending from their core.

Class same as for spirals w/added letter B

SBo, SBa, SBc..

Elliptical Galaxies

- Round, no disk, very little gas, very little dust, old stars

- These have an elliptical shape

- Classed E0, E1...E7

- O Spherical Shape

- 7 Cigar Shape

Irrengular galaxies

Asymetric often with gas, dust, young stars

- No obvious pattern

- generally pretty small

- generally lots of gas and dust

Milky way has two gravitationall bound to it:

Large Magellanic Cloud and Small Magellanic Cloud

Galaxy Clusters

Collection of galaxies held together by their mutual gravitation attraction.

- the Milky Way is in the local group.
- about 50 galaxies within 1 Mpc.

- only 3 spirals, the rest are dwarf irregulars and dwarf ellipticals

*The Virgo cluster is about 17 Mpc from the Milky Way and has 2500 galaxies in volume 3 Mpc across

Irregular Galaxies

-Because galaxies occur in close clusters they often interact gravitationally.

- Cause of many Irregular Galaxies.

Many astronomers believe that the SMC used to be a barge spiral but gravitational forces within the Milky Way ruined the galaxies shape.

Galactic Cannibolism

giant galaxies absorbing smaller galaxies

- unusually bright tiny core

- 1000s times brighter than the Milky Way Core

- most energy in IR region and radio region which is indication that it is a Non-Stellar region (stars do not emit IR or radio)

-Spiral Galaxy

- Spectrum contains very broad emission lines, indicates gases rapidly rotating around a central object

*brightness varies over period of months, indicates source is light months across

Quasar

aka Quasi Stellar Object

QSOs

-star like appearance

-show a large red shift

-wavelength 5 times longer than normal indiicates large distance (billion parsecs or more)

**Quasars are the central core of a very distant galaxy

quasars sometimes appear to be double or quadrouple - due to gravitational lensing

Quasars are the core of very young galaxies

- every galaxy could have been a quasar

Every galaxy could have been a Quasar:

-when young, many stars evolve into black holes

-black holes sink to the middle of the galaxy and merge

-lots of mass falls into the black hole, lots of radiation emitted

As galaxy ages, less mass available to fall into a central black hole

Galaxy becomes a Seyfert Galaxy or BL Loc galaxy (like Seyfert but elliptical) - bright tiny core is mass falling into black hole at reduced rate.

when galaxy matures, very little mass left to fall into central black hole

now a "normal" galaxy like the Milky Way

The Big Bang

Three Basic Observations in Cosmology

• Homogeneity
• Isotropy
• Universality

Matter is uniformly spread throughout the universe

The Universe looks the same in all directions

Homogeneity, Isotropy, and Universality are embodied in the Cosmoligical Principle

-any observer in the universe sees the same general features, no matter what his location or in what direction he looks.

-the Universe can have neither edge not center

Isotropy and Homogeneity would be violated otherwise

Sloan Digital Survey

survey if 67,000 galaxies to a distance of a billion parsecs.
-Galactic clusters, filaments, and voids can be seen but on a scale larger than 300Mpc the distance is constant

*all galaxies are moving away from us

George LaMaitre, a Belgiam Priest and physics professor is credited with discovering the Big Bang Theory

"Some creation event started the universes expansion"

He derived Hubles Law 2 years before Hubble discovered it

*Consider Hubbles Law: V-HD: to everyones surprise, measurements indicated that the expansion of the universe is accelerating.

The accelerating Universe

- There must be some energy source that is causing the expansion to accelerate.

-Most stuff in the universe is dark energy

-matter as we know it is rare

-Universe is 5% "normal matter"

-25% dark matter

-70% dark energy

**we do not understand the Nature of 95% of the Universe.

Big Bang Timeline

Time t = 0 to t = .0001 second

-universe is filled with high energy gamma rays

- radiation dominated

Time t = .0001 second to 3 minutes

- gamma rays have insufficient energy to form baryon anti-baryon pairs

**All matter in the universe formed in the first 3 minutes

Time t = 3 minutes to 30 minutes

-Age of Nucleosynthesis

- He forms, trace of Li, nothing else

- Universe is virtually all H and He

Time t = 30 min to 50,000 yrs        Time t = 50,000-100 Million yr

-Nucleosynthesis ceases               -age of recombination    

-75% H and 25% He                     -Universe cool enough to allow

-Universe is opague                      e's to combine with nuclei to
                                                form neutral atom.

*Universe now transparent. It is impossible to see any photons, to see anything before this era! Universe begins the "matter era"
                                                 

Cosmic Microwave Background

Story of Arno Penzios & Robert Wilson

- Built a "horn" antennea to be ultra quiet
-picked up interference everywhere in equal directions

- freq of noise correspondes to black body w/temp 2.7K

-They detected photons from the Big Bang

    -photons traveling the universe for 14 billion years

Three pieces of evidence for the Big Bang Theory

• Virtually all galaxies getting farther away from us
  - the universe is expanding
• Cosmic Microwave Background
  -from photons present when universe became transparent
• Detailed Structure of the Cosmic Microwave Background.
  *Big Bang Theory predicts size of temp blackbodys which match observations