Two Ways to search for extra solar planets

1. Directly

2. Gravitational Lensing

1. this is the preferable method but not often used

2.o   Einstein’s general theory of relativity

Observed three planets

One object’s gravity bends or brightens the light of a more distant object

Indirectly

o   Measurements of stellar positions

o   How much they “wobble” shows the effects of another planet’s gravity

o   Can detect the mass of the other planet

o   Examines changes in Doppler shifts

o   Motions cause shifts from red to blue end of the spectrum

o   Can use period with star’s mass and Newton’s version of Kepler’s third law to calculate planets orbital distance

o   Used in majority of discoveries

o   Can tell us if a star has more than one planet

o   Better for large mass planets

o   Amount of shift depends on planet’s mass

o   Acceleration depends on mass

o   Changes in a star’s brightness when a star passes in front (transit) or behind it (ellipse)

o   Measures the combined light from star and planet

o   Look for dip in brightness

o   Advantages: take spectrum and find elements

o   Disadvantages: only works for edge-on orbits

·         Orbit close to their stars

·         Highly elliptic orbits

o   May be a result of the young planet being flung into that orbit

o   Many are very massive (bigger than Jupiter)

·         Large Jovian planets that orbit close to their star

o   Ammonia, water vapor, and gas cannot form

o   Helium and hydrogen atmosphere

o   May be rare, but easiest to detect

o   Disadvantages: only works for edge-on orbits

Something maybe fundamentally wrong with our system

                                          i.    Gradually shrinking sun gives off heat as potential energy turns to thermal

                                        ii.    This could not keep going for 25 millon years and the solar system was proven older than that

·         Nuclear Fission

                                          i.    Requires high temperatures

                                        ii.    Gravitation equilibrium: balances pressure with gravity

                                       iii.    Keeps core hot and dense

                                       iv.    Sun born 4.5 billon years ago

·         3000 times the mass of the Earth

·         Plasma

·         Hydrogen and helium

·         Sunspots: dark splotches on the Earth

·         Luminosity: sun’s power output

·         Solar wind: charged particles that blow outward from the sun

                                          i.    Comes from coronal holes

a.    Gravity

b.    Weak: stronger than gravity

c.    Electromagnetic: important to nuclear fusion as preventative

d.    Strong force: binds protons and neutrons together into atomic nuclei

                                          i.    Only force strong enough to overcome electromagnetic 

a.    Nuclei collide and protons and neutrons stick together by strong force

                                          i.    Higher the temp, the harder the collisions

b.    Proton-proton chain: collisions between protons

                                          i.    Two heliums fuse=protons and energy

·         If the fusion rate varied, it would affect the sun’s luminosity

·         If the core temperature rose, protons would collide with more energy

·         The core would expand and cool and then return to its normal size- fusion rate returns to normal

a.    Math models

                                          i.    Primary way

b.    Solar vibrations

                                          i.    Observe and look for Doppler shifts

c.    Solar Neutrinos

                                          i.    Produced by fusion

                                        ii.    Particle that passes through anything

                                       iii.    Their elusiveness makes it difficult to capture and count

·         Problem: disagreement between model predictions and actual observations

·         Answer: neutrinos going undetected

a.    Cooler

b.    Magnetic lines confine cool gas

c.    Scientist can map magnetic fields by looking for spectral lines

d.    Eventually lines weaken and sunspots dissolve

e.    Sunspot cycle: 11 years

f.     Coronal mass ejection: much more material than usually associated with solar flares

g.    Solar prominences: giant loops

h.    Solar flares: send bursts of xrays and fast-moving particles into space

Stars information

1. Apparent brightness

2. Luminosity

1. how bright stars look in our sky

2. the total amount of power emitted into space

brightness is inversely related to distance

Apparent Brightness

a.    Smaller angle=farther away

b.    Larger angle= closer

c.    D=1/p

d.    Dx32.6 = # of LY away

a.    Compare ot luminosity of the sun

b.    Our sun in the middle

c.    More dim stars than luminous

Brightness as it Appears is apparent 

Absolute is as it would be 10 parsecs from earth 

a.    Surface temperature: comparing blue and red light

                                          i.    Only surface temperature can be measured directly

b.    Color of star can tell you a lot about the temperature

c.    Spectral lines:

                                          i.    Temperatures determined by spectral lines are more accurate

1.    Spectral type

a.    O B A F G K M

                                                                                          i.    Oh be a fine boy and kiss me

b.    Hot to cold

2.    Subcategories:

a.    1-9

b.    Larger the number, the cooler the star

Measuring Stellar Masses

Binary Star types (stars that orbit each other)

                                          i.    Visual binary

1.    Pair of stars we can see distinctly

                                        ii.    Eclipsing binary

1.    Orbit in the plane of our line of sight

2.    When one eclipses, the apparent brightness drops

3.    When neither Is ellipsed, we can see combined light

                                       iii.    If neither visual or eclipsing, we measure Doppler Shifts-called spectroscopic binary

can only measure orbit if they have orbital distance and period

a.    Need luminosity and spectral type

b.    Temperature decreases from left to right

c.    Luminosity up and down

a.    Denoted by Roman numeral

b.    Represents area of the H-R diagram

c.    Ex of full classification G2V

a.    Stellar masses decrease down main-sequence

b.    Mass is most important element in fusion

c.    Mass and solar temperature: a star must be luminous and large or luminous with a large solar temperature

d.    We can calculate mass just by knowing star’s spectral type

a.    More massive- shorter lives-burn helium faster

b.    Smaller-longer lifetimes

1. Reddish in color

2. nearing the end of their lives

Giants and super-giants out of fuel

exposed solar core

all stars in a  cluster are about the same distance from Earth

            2. all formed about the same time

Two Type of Clusters

1. Open Clusters

2. Gobular

1a.    Found in disks

b.    Modest size

c.    Young stars

d.    Famous: Seven sisters

2.a.    Halo

b.    Oldest in the universe

c.    Densely packed

a.    Main-sequence turnoff point: where star diverges from standard main-sequence

b.    The age of a cluster is its lifetime of stars at M-S turnoff point

a.    .08 MassSun<stars<150 MassSun

b.    Stars<.08MassSun ….Brown Dwarf- “failed star”

·         Stars<.4MassSun : Never helium burn

·         Stars>.4 MassSun: core contracts, outer layers expand, core is hot enough for helium fusion

·         Algol Paradox: complications from close binary systems

·         Mass-exchange: gas giant’s outer layers spill to another star

o   By tidal force

·         Exposed core of a dead star

·         Cools with time

·         Degeneracy pressure (like Brown Dwarfs)

·         Actually, electron degeneracy pressure

·         Density very high

·         More massive is smaller

·         White Dwarf Limit: 1.4 Solar Masses

a.    In a close binary system can gain mass from its companion

b.    The clump must rotate conserving angular momentum and forming an accretion disk

a.    With more accreting gas

b.    Heat and pressure rise

c.    Hydrogen fusion suddenly ignites

d.    Becomes a NOVA

e.    Accretion resumes after and the process can repeats itself

I.              Difference between white dwarf and supernova and massive star supernova

a.    WD supernova’s luminosity fades slowly massive star supernova more complicated

·         Neutron star is a ball of neutrons created by the collapse of an iron core in a massive star supernova

·         Resists gravity by neutron degeneracy pressure

·         Paper clip size of neutron star would equal weight of Mt. Everest

·         Fit in a hometown

a.    Rapidly pulsing radio sources

b.    Neutron stars left behind by supernova explosions

arise because neutron star is spinning rapidly because of conservation of angular momentum

c.    All pulsars are neutron stars but not all neutron stars are pulsars

d.    They must be neutron stars because no other object could spin so fast

a.    Can spring brilliantly back into life

                                          i.    Close binaries that contain accreting neutron stars are often called XRAY binaries-pulses

                                        ii.    Material builds up, temperature rises, helium fusion to make carbon and heavier elements- bursts of energy

                                       iii.    Called xray binaries

·         The gravity in a stellar corpse becomes so strong that nothing can prevent the corpse from collapsing under its own weight into a BLACK HOLE

·         Nothing can escape from a black hole

·         Spacetime= space and time bound in a 4D space

·         If you enter into a black hole, you never return

a.    Nothing that passes can ever escape

b.    “size” of black hole= size of event horizon

c.    Event horizon is a sphere with a Scwarzchild radius

d.    More massive blackhole=smaller radius

e.    Collapsing star becomes a black hole when it shrinks smaller that swarzchild radius

f.     All matter condenses to the point of SINGULARITY

Why do black holes exist

Formations and Observations

a.    Formation

                                          i.    When mass of white dwarf exceeds 1.4 solar masses, it will collapse

                                        ii.    Mass may rise above neutron star limit

                                       iii.    The more the star collapses, the stronger gravity gets- the star collapses to black hole

II.            Observations

a.    Difficult to detect

b.    Emit xray radiation

·         Sending photons

·         Carry so much energy that they are difficult to focus

·         Come randomly from all directions in space

·         Gammaray bursts come from exploding stars

·         Most of stars reside in the disk

·         Clouds of interstellar gas and dust known collectively as interstellar medium fill galactic disk

a.    Orbit in a roughly circular path (stars in disk)

b.    Stars in bulge or halo soar high above and below on random orbits

a.    Sun’s orbit is fairly typical of disk

b.    We use sun’s orbital velocity and distance from galactic center to determine mass of our galaxy within sun’s orbit

c.    Orbital speeds are the same great distances from galactic center and distributed throughout the halo

·         Gradually changes chemical composition of interstellar medium

·         Universe born with only hydrogen and helium

·         More heavy elements

a.    Star-gas-star cycle:

b.    Low mass stars have weak stellar winds which don’t blow much into space

c.    High mass stars: gas ejected into space and sweeps gas in a bubble around exploding stars

d.    Supernova generates shockwaves: waves of pressure

e.    Supernova remnant: aftermath of shockwave

f.     Cosmic rays

g.    Atomic hydrogen gas

                                          i.    Cool

                                        ii.    Part of the cooling cloud

h.    Detect radio transmission at 21-cm line coming from all directions telling us gas is evenly distributed throughout galactic disks

i.      Molecular clouds: cool cloud of atomic hydrogen gives birth to cluster of clouds

a.    1-9

b.    Larger the number, the cooler the star

Where are stars in the milky way?

a. ionization nebulae

b. spirals arms

c. spiral density waves

a.    Ionization nebulae: wispy blobs of gas near hot stars

b.    Spiral arms: newly formed stars: home to molecular could and clusters of ionization nebulae

c.    Spiral density Waves: produce spiral arms

a.    Disks population: young and old stars with heavy elements

b.    Spherical population: stars in halo and bulge

                                          i.    Spherical, low in mass

a.    Doesn’t have cold, dense clouds

b.    Very old

c.    No young stars

d.    Contain fewer heavy elements

a.    Acquired with conservation of angular momentum

                                          i.    This is why stars orbit in same plane

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  • We plot the stars of a cluster on an H-R diagram.
  • Main-sequence turnoff point: the point where the main sequence of a cluster diverges from the standard main sequence.
  • The age of the cluster is always equal to the lifetime of stars at its main-sequence turnoff point.
  • Most open clusters are very young, with few older than 5 billion years. Globular clusters are older than 10 billion years.
  • The first stars probably began to form when the universe was a billion years old.

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  • Open Clusters: modest size, always found in the disk of the galaxy, young stars, several thousand stars, about 30 light years across.
  • Globular Clusters: densely packed, found in the halo, oldest stars in the universe, more than a million stars in a ball about 60 to 150 light years across.

•  
  • Most dependable method for finding the mass of a star depends on Newton’s version of Kepler’s third law (this can only be applied when one object is orbiting another). Thus, we want a binary star system (about half of all stars are in a binary system).

Binary Star Systems 

1. Visual 

2. Eclipsing

1.we can see distinctly with a telescope that there are two stars orbiting each other. We may see the star slowly shifting position.

2. a pair of stars that orbit in the plan of our line of sight. When neither is eclipsed, we can see the combined light of both stars. A light curve that shows the apparent brightness over time will show a pattern of the eclipse.

•  
  • Measuring masses in binary systems is done by using Newton’s version of Kepler’s third law if we can measure both the orbital period and separation of the two stars.

•  
  • When measuring temperatures of a star, we use the surface temperature because they are the only temperatures that are directly measurable. Interior temperatures are only inferred from mathematical models.
  • Measuring temperature is easier than measuring luminosity because distance doesn’t affect it.
  • Color and Temperature:
  • They come in different colors because they emit thermal radiation.
  • Surface temperature can be measured by comparing a star’s apparent brightness in two different colors of light. By measuring how much blue vs. red light a star emits, temperature can be found.
  • Spectral Type and Temperature:
  • Because stellar dust can affect the apparent color of stars, spectral lines are generally more accurate.
  • Stars that display spectral lines of ionized material must be very hot because ionization requires extremely high temperatures. Spectral lines with molecules must be relatively cool or they would break up into atoms.
  • Star Spectrum (hottest to coolest)
  • O, B, A, F, G, K, M (Oh, be a fine girl, kill me.)
  • Brown dwarfs are usually colder than M (L and T are now included)
  • The spectrum is divided into numbers to specify
  • The range of temperatures is much narrower than the range of luminosities (3,000 K – 40,000 K).
  • Cool, red stars are much more common than hot, blue stars.