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321
Astronomy
Undergraduate 2
12/05/2013
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Term
8 light minutes
 Definition
how far away is the sun
Term
. Where the inward gravitational force is balanced by outward heat pressure.
 Definition
The Sun is in hydrostatic equilibrium.
Term
The radiation zone is relatively transparent; the cooler convection zone is opaque
 Definition
energy transport in the solar interior
Term
corona
 Definition
highest temperature and lowest density (suns atmosphere)
Term
solar wind
 Definition
ionized particles that flow outward from the Sun into space
Term
chromosphere and photosphere of the Sun
 Definition
Spectral analysis can tell us what elements are present, but only in the
Term
solar corona
 Definition
can be seen during eclipse if both photosphere and chromosphere are blocked:
Term
SOHO: Solar and Heliospheric Observatory
 Definition
Orbits at Earth’s outside the magnetosphere
Multiple instruments measure magnetic field, corona, vibrations, and ultraviolet emissions
Term
sunspots
 Definition
First to be studied by Galileo in 1613
Appear dark because slightly cooler than surroundings
Term
Umbra – dark center – 4500 K
Penumbra – lighter surround – 5500 K

Can change in size and shape
May form in groups over several days
Lasts about 50 days (group)
Individual spots can lasts 1- 100 days
 Definition
Two parts to Sunspots
Term
pairs of magnetic field lines
 Definition
sunspots are linked by
Term
magnetic field lines are distorted by Sun’s differential rotation.
 Definition
Sunspots originate when
Term
11

This is really a 22-year cycle, because the spots switch polarities between the northern and southern hemispheres every 11 years.
 Definition
The Sun has an ___year sunspot cycle, during which sunspot numbers rise, fall, and then rise again.
Term
Maunder minimum
 Definition
Few, if any, sunspots (during the late 1600s and early 1700s).
Term
prominences
flares
coronal mass ejections
 Definition
There are three types of active regions in order of least energetic to most energetic:
Term
Solar prominence
 Definition
loop or sheet of ejected gas due to instability in magnetic field of sunspots.
Can last for days or weeks and can extend 10 times the diameter of the Earth out from the Sun.
Term
Solar flare
 Definition
- larger explosion and more violent. Emits similar amount of energy to a prominence, but in seconds or minutes rather than days or weeks: less understood.
Term
During solar min – once per week During solar max – three per day
 Definition
Coronal mass ejection occurs when a large “bubble” of ionized gas escapes into space.
Term
coronal mass ejections
 Definition
If orientated correctly can merge with magnetic field and dump energy, overloading satellites causing disruption in communications and power outages.
Term
Strong nuclear force: Keeps nucleus together; short range; very strong
Weak nuclear force: Responsible for beta decay; short range (1-2 proton diameters); weak
Electromagnetic: Much stronger than gravity, but either attractive or repulsive; infinite in range
Gravity: Very weak, always attractive and infinite in range
 Definition
Physicists recognize four fundamental forces in nature:
Term
Nuclear fusion – the combination of two light nuclei into heavier ones
In the case of the Sun – two hydrogen nuclei (protons) into helium
 Definition
Where does the heat come from in the Sun? What powers the Sun?
Term
The helium stays in the core.
All hydrogen burning stars use this to create their energy.
The neutrinos escape without interacting.
 Definition
The ultimate result of the process: hydrogen to helium with energy and neutrinos as a by product
4(1H) → 4He + energy + 2 neutrinos
Term
Our Sun has enough for a 10-billion-year lifetime
It is halfway through its lifetime (5 billion years)
 Definition
Sun must convert 4.3 million tons of matter into energy every second.
Term
This is called the Solar Neutrino Problem.
 Definition
Neutrino problem – discrepancy between predicted (theoretical) and observed (experimental).
Term
: core, radiation zone, convection zone, photosphere, chromosphere, transition region, corona, solar wind
 Definition
Main interior regions of Sun
Term
parallax
 Definition
Stellar distances can be measured using
Term
parallax
 Definition
apparent motion of object against distant background from two vantage points
Term
Proxima Centauri
 Definition
Nearest star to the Sun:
Term
Mass
Radius
Luminosity
 Definition
Intrinsic properties of Stars
Term
Distance
Brightness (absolute and apparent)
Proper Motion
Stellar Class
Temperature
 Definition
Other properties of stars
Term
luminosity
 Definition
is a the amount of the total power radiated by a star (energy radiated per second). (unit W
Term
apparent brightness
 Definition
is how bright a star appears because of its distance from Earth.
Term
apparent magnitude
Larger magnitudes are fainter. Smaller magnitudes are brighter
 Definition
Apparent brightness is measured using a magnitude scale. It is called
Term
The intensity of the light decreases by the square of the distance away from a light source.
 Definition
Light is an inverse square law
Term
Absolute Magnitude (M)
 Definition
Luminosity is related to absolute brightness. It is also measured in magnitude, which is also a log scale.
Term
absolute magnitude.
 Definition
If we know a star’s apparent magnitude and its distance from us, we can calculate its
Term
negative – star is closer than 10 pc
positive – star is farther than 10 pc
 Definition
The distance modulus equation is mainly used to calculate a star’s absolute magnitude.
Term
Red stars are relatively cool, while blue ones are hotter.
 Definition
The color of a star is indicative of its temperature
Term
Blackbody radiation
 Definition
the radiation of stars is
Term
stella spectra
 Definition
are much more informative than the blackbody curves
Term
O B A F G K M
 Definition
There are seven general categories of stellar spectra (spectral class), corresponding to different temperatures.
From highest to lowest temperature, those categories are:
Term
Her thesis, Stellar Atmospheres, A contribution to the Observational Study of High Temperature in the Reversing Layer of Stars was labeled at the time and for many years afterwards as "the most brilliant Ph.D. thesis ever written in astronomy."
 Definition
In 1925, Payne became the first person, woman or man, to receive an Ph.D. in astronomy from Harvard.
Term
spectral lines
 Definition
give the composition of the star
Term
G0, G1, G2, G3, G4, G5, G6, G7, G8, G9, K0, K1, …
 Definition
Each category of spectral class can be subdivided into 10 subclasses using number 0-9:
Term
interferometry
 Definition
A few very large, very close stars can be imaged directly using
Term
Giant stars have radii between 10 and 100 times the Sun’s
 Definition
Dwarf stars have radii equal to, or less than, the Sun’s
Term
stellar luminosity against surface temperature.
 Definition
The H-R diagram plots
Term
stars
 Definition
About 90% of stars lie on the main sequence; 9% are red giants and 1% are white dwarfs.
Term
Ia: Brightest Supergiants
Ib: Supergiants
II: Bright giants
III. Normal giants
IV: Subgiants
V: Main sequence stars
 Definition
luminosity class
Term
Spectroscopic parallax
 Definition
Has nothing to do with parallax, but does use spectroscopy in finding the distance to a star.
Term
spectroscopic binaries
 Definition
use the spectral lines to give the motion of the stars relative to each other using the Doppler shift.
Term
eclipsing binaries
 Definition
can be measured using the changes in luminosity.
Term
mass
 Definition
is the main determinant of where and how long a star will be on the Main Sequence and how long it will live.
Term
luminosity class
 Definition
can distinguish giant star from main-sequence one in the same spectral class
Term
spectroscopic parallax
 Definition
is a new tool use to find distance using the H-R diagram
Term
Measurements of binary-star systems
 Definition
allow stellar masses to be measured directly
Term
Star formation happens when part of a dust cloud begins to contract under its own(weight) gravitational force; as it collapses, it heats up. If enough mass collapses to heat the center to temperatures needed for nuclear fusion, a star is born.
 Definition
star formation
Term
star formation
 Definition
Rotation can also interfere with gravitational collapse, as can magnetism. Clouds may very well contract in a distorted way
Term
Shockwave
Star(s) moving close to the cloud
Death of a nearby Sun-like star (planetary nebula)
Supernova
Density waves in galactic spiral arms
Galaxy collisions
 Definition
What can trigger a part of the interstellar cloud to collapse?
Term
As the interstellar cloud contracts, gravitational instabilities cause it to fragment into smaller pieces.
The pieces themselves continue to fall inward and fragment, eventually forming many tens or hundreds of individual stars.
 Definition
Stage 1: Interstellar Cloud
Term
Individual cloud fragments begin to collapse. Once the density is high enough, there is no further fragmentation.
 Definition
Stage 2: Cloud fragmentation
Term
The interior of the fragment has begun heating and is about 10,000 K.
 Definition
Stage 3: Fragmentation ceases and protostars formation begins (protostellar disk)
Term
The core of the cloud is now a protostar and can be placed on the H-R diagram. This is the embroynic stage of a star. (When it first begins to resemble a star.)
Has high luminosity and radius because it is still large, still collapsing. Low temperature due to large size.
 Definition
Stage 4: Protostar
Term
Star continues to collapse increasing slightly in temperature and decreasing in radius. Overall it is decreasing in luminosity as it heads toward the main sequence.
 Definition
Stage 5: Protostellar evolution
Term
Named for Japanese astrophysicist in the 60’s.
Planetary formation has begun, but the protostar is still not in equilibrium—all heating comes from the gravitational collapse

Protostars in this stage often exhibit violent surface activity, T-Tauri phase. This is due to the fact they are not in equilibrium and vary in brightness.

The protostar’s luminosity decreases even as its temperature rises because it is becoming more compact.
 Definition
Stages 4-6: Haysashi Track (Track to Main Sequence)
Term
At the end of stage 6, the star has contracted enough to heat core to 10 million K and nuclear fusion begins.
This increases the temperature of the star overall and luminosity increases slightly.
Star then begins to stabilize itself from the beginning of fusion until its reaches equilibrium.
 Definition
Stage 6: Newborn Star
Term
Star has reach hydrostatic equilibrium and enters onto the main sequence. It will remain there as long as it has hydrogen to fuse.
How much mass the collapsed cloud contained in formation determines the mass for the star and where it is on the main sequence.
 Definition
Stage 7: Main Sequence
Term
ZAMS (zero age main sequence) –
 Definition
where a star end up on the main sequence predicted by theory because of its mass.
Term
Once they reach it, they are in equilibrium and do not move until their fuel begins to run out.
 Definition
Most important: Stars do not move along the Main Sequence
Term
emission nebulae
 Definition
are heated by the formation of stars nearb
Term
Protostars (T-Tauri)
 Definition
are believed to have very strong winds, which clear out an area around the star roughly the size of the solar system.
Term
brown dwarf
 Definition
If the mass of the “failed star” is about 12 Jupiter masses or more, it is luminous when first formed, and is called a
Term
brown dwarfs
 Definition
are difficult to observe directly, as they are very dim. Radiate in the infrared.
Term
Protostellar collisions
 Definition
In the congested environment of a young cluster, star formation is a competitive and violent process.
Term
Open Clusters
Globular Clusters
 Definition
Two types of Star Cluster:
Term
Loosely bound
A few parsec across
10s to 100s of stars
Found in plane of galaxy
Young
 Definition
Open Cluster:
Term
Tightly bound
50 parsecs across
Thousands to millions of stars
Found in halo of galaxy
old
 Definition
Globular Cluster:
Term
subgiant branch
 Definition
Star moves off the main sequence to the
Term
No longer in stable equilibrium and changes luminosity class (IV Subgiants) as it heads for the red giant region.
Continues shrinking in core and expanding outer layers.
Temperature is decreasing and radius slightly increases.
 Definition
Stage 8: The Sub-Giant Branch
Term
As the core continues to shrink, the outer layers of the star expand and cool. (Not much T change)
Despite its cooler temperature, its luminosity increases enormously due to its large size. (100 times than main sequence)
 Definition
Stage 9: The Red-Giant Branch
Term
Once the core temperature has risen to 100 million K, the helium in the core starts to fuse into carbon.
The helium flash: (end of stage 9)
Begins to fuse helium into carbon extremely rapidly, increasing temperature. The core expands, the shell (H) contracts (lower luminosity), and density drops.
The star must again adjust to reach equilibrium and stops expanding. This takes about 100,000 years.
 Definition
Stage 10: Helium fusion
Term
Star again uses up the fuel in the core and there is no heat from fusion so gravity takes over and the core (C ash) collapses.
The star is now similar to its condition just as it left the Main Sequence, except now there are two burning shells, H and He
 Definition
Stage 11: Back to the giant branch (Asymptotic Branch)
Term
Betelgeuse and Antares
 Definition
The star has become a red giant for the second time. This is the Asymptotic Branch. ____ and _____ are examples
Term
There is no more outward fusion pressure being generated in the core, which continues to contract.
The shells are still burning and helium flashes can occur here causing outer layers to pulsate from the heating and cooling.
This causes the envelope to be ejected.
 Definition
Stage 12: Planetary nebula
Term
A small, extremely dense carbon core (1 cm² = 1000 kg = 1ton)
An envelope about the size of our solar system.
Layers are ejected at 10 km/s and takes less than a few million years to eject material
 Definition
the deaths of a low mass star. the star now has two parts.
Term
planetary nebula
 Definition
the envelope is called a
Term
Once the nebula has gone, the remaining core is extremely dense and extremely hot, but quite small.
It is luminous only due to its high temperature.
As the white dwarf cools, its size does not change significantly; it simply gets dimmer and dimmer, and finally ceases to glow.
 Definition
Stage 13 : White dwarf
Term
Cold, dense, burned-out ember in space that no longer radiates.
Not found – not enough time in the universe for one to cool off
 Definition
Stage 14: Black dwarf
Term
Electron degeneracy – the pressure produced by the resistance of electrons to further compress because electrons cannot be in the same quantum state
 Definition
A white dwarf is in hydrostatic equilibrium, but is not undergoing nuclear fusion. How?
Term
Electron degeneracy
 Definition
the pressure produced by the resistance of electrons to further compress because electrons cannot be in the same quantum state
Term
makes no sharp moves on the H-R diagram—it moves smoothly back and forth.
 Definition
A 4-solar-mass star
Term
can fuse carbon to oxygen. Its path across the H-R diagram is essentially a straight line—it stays at just about the same luminosity as it cools off.
 Definition
A 4-8 solar-mass star
Term
can fuse oxygen to neon
 Definition
An 8-12 solar mass star
Term
they no longer become white dwarfs.
 Definition
Above 12 solar masses
Term
can begin to fuse He while still on the main sequence. (Rigel)
 Definition
Stars 15 solar masses
Term
already left the Main Sequence, while many of the least massive have not even reached it yet.
 Definition
After 10 million years, the most massive stars have
Term
point on the main sequence of an H-R diagram for a cluster where stars have moved toward the red giant stage indicating age.
After 100 million years, a distinct main-sequence turnoff begins to develop. This shows the highest-mass stars that are still on the Main Sequence.
After 1 billion years, the main-sequence turnoff is much clearer.
 Definition
Main sequence turnoff point –
Term
they are stars that have formed much more recently, probably from the merger of smaller stars.
 Definition
The “blue stragglers” in the are not exceptions to our model;
Term
sirius
 Definition
is the brightest star in the northern sky and has been recorded throughout history. But there is a mystery!
Term
If the stars in a binary-star system are relatively widely separated, their evolution proceeds much as it would have if they were not companions.
If they are closer, it is possible for material to transfer from one star to another, leading to unusual evolutionary paths, including movement on the main sequence.
 Definition
the evolution of binary star systems
Term
spectroscopic binaries
 Definition
use the spectral lines to give the motion of the stars relative to each other using the Doppler shift.
Term
eclipsing binaries
 Definition
can be measured using the changes in luminosity.
Term
mass
 Definition
is the main determinant of where and how long a star will be on the Main Sequence and how long it will live.
Term
luminosity class
 Definition
can distinguish giant star from main-sequence one in the same spectral class
Term
spectroscopic parallax
 Definition
is a new tool use to find distance using the H-R diagram
Term
Measurements of binary-star systems
 Definition
allow stellar masses to be measured directly
Term
Star formation happens when part of a dust cloud begins to contract under its own(weight) gravitational force; as it collapses, it heats up. If enough mass collapses to heat the center to temperatures needed for nuclear fusion, a star is born.
 Definition
star formation
Term
star formation
 Definition
Rotation can also interfere with gravitational collapse, as can magnetism. Clouds may very well contract in a distorted way
Term
Shockwave
Star(s) moving close to the cloud
Death of a nearby Sun-like star (planetary nebula)
Supernova
Density waves in galactic spiral arms
Galaxy collisions
 Definition
What can trigger a part of the interstellar cloud to collapse?
Term
As the interstellar cloud contracts, gravitational instabilities cause it to fragment into smaller pieces.
The pieces themselves continue to fall inward and fragment, eventually forming many tens or hundreds of individual stars.
 Definition
Stage 1: Interstellar Cloud
Term
Individual cloud fragments begin to collapse. Once the density is high enough, there is no further fragmentation.
 Definition
Stage 2: Cloud fragmentation
Term
The interior of the fragment has begun heating and is about 10,000 K.
 Definition
Stage 3: Fragmentation ceases and protostars formation begins (protostellar disk)
Term
The core of the cloud is now a protostar and can be placed on the H-R diagram. This is the embroynic stage of a star. (When it first begins to resemble a star.)
Has high luminosity and radius because it is still large, still collapsing. Low temperature due to large size.
 Definition
Stage 4: Protostar
Term
Star continues to collapse increasing slightly in temperature and decreasing in radius. Overall it is decreasing in luminosity as it heads toward the main sequence.
 Definition
Stage 5: Protostellar evolution
Term
Named for Japanese astrophysicist in the 60’s.
Planetary formation has begun, but the protostar is still not in equilibrium—all heating comes from the gravitational collapse

Protostars in this stage often exhibit violent surface activity, T-Tauri phase. This is due to the fact they are not in equilibrium and vary in brightness.

The protostar’s luminosity decreases even as its temperature rises because it is becoming more compact.
 Definition
Stages 4-6: Haysashi Track (Track to Main Sequence)
Term
At the end of stage 6, the star has contracted enough to heat core to 10 million K and nuclear fusion begins.
This increases the temperature of the star overall and luminosity increases slightly.
Star then begins to stabilize itself from the beginning of fusion until its reaches equilibrium.
 Definition
Stage 6: Newborn Star
Term
Star has reach hydrostatic equilibrium and enters onto the main sequence. It will remain there as long as it has hydrogen to fuse.
How much mass the collapsed cloud contained in formation determines the mass for the star and where it is on the main sequence.
 Definition
Stage 7: Main Sequence
Term
ZAMS (zero age main sequence) –
 Definition
where a star end up on the main sequence predicted by theory because of its mass.
Term
Once they reach it, they are in equilibrium and do not move until their fuel begins to run out.
 Definition
Most important: Stars do not move along the Main Sequence
Term
emission nebulae
 Definition
are heated by the formation of stars nearb
Term
Protostars (T-Tauri)
 Definition
are believed to have very strong winds, which clear out an area around the star roughly the size of the solar system.
Term
brown dwarf
 Definition
If the mass of the “failed star” is about 12 Jupiter masses or more, it is luminous when first formed, and is called a
Term
brown dwarfs
 Definition
are difficult to observe directly, as they are very dim. Radiate in the infrared.
Term
Protostellar collisions
 Definition
In the congested environment of a young cluster, star formation is a competitive and violent process.
Term
Open Clusters
Globular Clusters
 Definition
Two types of Star Cluster:
Term
Loosely bound
A few parsec across
10s to 100s of stars
Found in plane of galaxy
Young
 Definition
Open Cluster:
Term
Tightly bound
50 parsecs across
Thousands to millions of stars
Found in halo of galaxy
old
 Definition
Globular Cluster:
Term
subgiant branch
 Definition
Star moves off the main sequence to the
Term
No longer in stable equilibrium and changes luminosity class (IV Subgiants) as it heads for the red giant region.
Continues shrinking in core and expanding outer layers.
Temperature is decreasing and radius slightly increases.
 Definition
Stage 8: The Sub-Giant Branch
Term
As the core continues to shrink, the outer layers of the star expand and cool. (Not much T change)
Despite its cooler temperature, its luminosity increases enormously due to its large size. (100 times than main sequence)
 Definition
Stage 9: The Red-Giant Branch
Term
Once the core temperature has risen to 100 million K, the helium in the core starts to fuse into carbon.
The helium flash: (end of stage 9)
Begins to fuse helium into carbon extremely rapidly, increasing temperature. The core expands, the shell (H) contracts (lower luminosity), and density drops.
The star must again adjust to reach equilibrium and stops expanding. This takes about 100,000 years.
 Definition
Stage 10: Helium fusion
Term
Star again uses up the fuel in the core and there is no heat from fusion so gravity takes over and the core (C ash) collapses.
The star is now similar to its condition just as it left the Main Sequence, except now there are two burning shells, H and He
 Definition
Stage 11: Back to the giant branch (Asymptotic Branch)
Term
Betelgeuse and Antares
 Definition
The star has become a red giant for the second time. This is the Asymptotic Branch. ____ and _____ are examples
Term
There is no more outward fusion pressure being generated in the core, which continues to contract.
The shells are still burning and helium flashes can occur here causing outer layers to pulsate from the heating and cooling.
This causes the envelope to be ejected.
 Definition
Stage 12: Planetary nebula
Term
A small, extremely dense carbon core (1 cm² = 1000 kg = 1ton)
An envelope about the size of our solar system.
Layers are ejected at 10 km/s and takes less than a few million years to eject material
 Definition
the deaths of a low mass star. the star now has two parts.
Term
planetary nebula
 Definition
the envelope is called a
Term
Once the nebula has gone, the remaining core is extremely dense and extremely hot, but quite small.
It is luminous only due to its high temperature.
As the white dwarf cools, its size does not change significantly; it simply gets dimmer and dimmer, and finally ceases to glow.
 Definition
Stage 13 : White dwarf
Term
Cold, dense, burned-out ember in space that no longer radiates.
Not found – not enough time in the universe for one to cool off
 Definition
Stage 14: Black dwarf
Term
Electron degeneracy – the pressure produced by the resistance of electrons to further compress because electrons cannot be in the same quantum state
 Definition
A white dwarf is in hydrostatic equilibrium, but is not undergoing nuclear fusion. How?
Term
Electron degeneracy
 Definition
the pressure produced by the resistance of electrons to further compress because electrons cannot be in the same quantum state
Term
makes no sharp moves on the H-R diagram—it moves smoothly back and forth.
 Definition
A 4-solar-mass star
Term
can fuse carbon to oxygen. Its path across the H-R diagram is essentially a straight line—it stays at just about the same luminosity as it cools off.
 Definition
A 4-8 solar-mass star
Term
can fuse oxygen to neon
 Definition
An 8-12 solar mass star
Term
they no longer become white dwarfs.
 Definition
Above 12 solar masses
Term
can begin to fuse He while still on the main sequence. (Rigel)
 Definition
Stars 15 solar masses
Term
already left the Main Sequence, while many of the least massive have not even reached it yet.
 Definition
After 10 million years, the most massive stars have
Term
point on the main sequence of an H-R diagram for a cluster where stars have moved toward the red giant stage indicating age.
After 100 million years, a distinct main-sequence turnoff begins to develop. This shows the highest-mass stars that are still on the Main Sequence.
After 1 billion years, the main-sequence turnoff is much clearer.
 Definition
Main sequence turnoff point –
Term
they are stars that have formed much more recently, probably from the merger of smaller stars.
 Definition
The “blue stragglers” in the are not exceptions to our model;
Term
sirius
 Definition
is the brightest star in the northern sky and has been recorded throughout history. But there is a mystery!
Term
If the stars in a binary-star system are relatively widely separated, their evolution proceeds much as it would have if they were not companions.
If they are closer, it is possible for material to transfer from one star to another, leading to unusual evolutionary paths, including movement on the main sequence.
 Definition
the evolution of binary star systems
Term
detached binary
 Definition
, each star has its own Roche lobe: stars are different masses and formed separately
Term
semidetached binary
 Definition
one star can transfer mass to the other. As they evolve one can overflows its Roche lobe and transfers mass. This increase in mass can move a star up on the main sequence due to mass transfer of companion star.
Term
Nova
 Definition
a white dwarf that suddenly increases in luminosity and then slowly decreases back to its original luminosity
Term
nova
 Definition
result from the accretion of hydrogen onto a white dwarf star from a companion body
Term
repeated novas
 Definition
A white dwarf that is part binary system can undergo
Term
Type I - carbon-detonation supernova (binary)
Type II - death of a high-mass star
 Definition
There are two different types of supernovae, both equally common:
Term
white dwarfs
 Definition
are supported by electron degeneracy, not thermal pressure. Limit to pressure electrons can exert, above which they cannot support the star.
This max mass limit is called the Chandrasekhar Limit, which is 1.4 solar masses.
Term
when the core has fused to iron, no more fusion can take place.
 Definition
Iron is the crossing point
Term
and more than a million times as bright as a nova:
 Definition
A supernova is incredibly luminous
Term
Neutron star
Black Hole
This is dependent on mass
 Definition
What is left after behind after the stellar explosion:
Term
The Crab nebula (M1)
 Definition
is a remnant from a supernova explosion that Chinese astronomers observed in the year 1054.
Term
there are 81 stable and 10 radioactive elements
 Definition
Elements up to iron are formed in the cores of high mass stars.
Term
These elements are released into space during a supernova type II.
 Definition
During the supernova type II explosion the elements above iron are formed.
Term
Iron is the most stable nucleus, so it can not be fused.
 Definition
All of the elements up to iron are formed within the cores of stars
Term
star stuff
 Definition
These elements are blown out into space and from this 2nd generation stars are born.
Term
After a Type I supernova
 Definition
little or nothing remains of the original star. Enriches space with carbon.
Term
After a Type II supernova
 Definition
, part of the core, remnant, may survive. It is very dense—as dense as an atomic nucleus—and is called a neutron star.
Term
neutron degeneracy.
 Definition
A neutron star is held in equilibrium against gravity by
Term
10 billion tons
 Definition
If you weigh 150 lbs and could stand on a neutron star, you would weigh
Term
rotation
 Definition
as the parent star collapses, the neutron core spins very rapidly, conserving angular momentum. Typical periods are fractions of a second. (Pulsars)
Term
magnetic field
 Definition
again as a result of the collapse, the neutron star’s magnetic field becomes enormously strong, trillions times the Earth. (Magnetars)
Term
gravity
 Definition
the high density of these objects give it high gravity
Term
Jocelyn Bell
 Definition
The first pulsar was discovered in 1967 by
Term
Strong jets of matter are emitted at the magnetic poles due to fast rotation. If the rotation axis is not the same as the magnetic axis, the two beams will sweep out circular paths. If the Earth lies in one of those paths, we will see the star pulse.
 Definition
But why would a neutron star pulse?
Term
all pulsars are neutron stars, but not all neutron stars are observed as pulsars.
 Definition
Pulsars are a subclass of neutron stars. So
Term
magnastars
 Definition
A subclass of newly formed neutron star with extremely powerful magnetic fields a thousand trillion times stronger than Earth's.
Term
the millisecond pulsar.
 Definition
Most pulsars have periods between 0.03 and 0.3 seconds, but a new class of pulsar was discovered in the early 1980s:
Term
Two types:
Long GRB (longer than 2 s)
Hypernova - a collaspsing star into a black hole

Short GRB (less than 2 s) – more difficult to detect
Star quakes in a magnetar (burst just 2/10ths of a second long has as much energy as the sun releases in 1,000 years)
Binary neutron stars collide and merge
 Definition
gamma ray bursts
Term
3 solar masses
 Definition
The mass of a neutron star cannot exceed about
Term
black- gravitaitonal force (Black hole)
 Definition
is so intense that even light cannot escape
Term
Schwarzschild radius
 Definition
The radius an object would have to be compressed for the escape speed to be speed of light.
Term
Event horizon
 Definition
– imaginary sphere around singularity of a collapsed star in which no event inside can be seen.
Term
Space time warps or curves in the presence of mass, and in doing so redefines straight lines (the path a light beam would take):
A planet orbits due to the warp in space time from its parent star.
The higher the mass the larger the warp and deeper the hole.
 Definition
How do black holes make a hole?
Term
space time is warped
 Definition
The more mass in an area of space the more
Term
“indentation” caused by the mass becomes infinitely deep to a point of singularity. This is where density and gravity are infinite. At this point gravity has won the battle that the star has fought all its life.
 Definition
A black hole occurs when the
Term
This is called an Einstein-Rosen Bridge.
 Definition
It has been theorized that matter that falls into a black hole may be emitted by another black hole in some kind of parallel universe
Term
This type of Einstein-Rosen Bridge is called a wormhole.
 Definition
Or perhaps our universe is warped or curved sufficiently that one black hole may connect with another black hole elsewhere in our universe.
Term
black holes
 Definition
Matter encountering a black hole (near event horizon) will experience enormous tidal forces that will both heat it enough to radiate, and tear it apart. Object is pulled in atom by atom.
Term
. This is called time dilation. This is an effect of special relativity (Einstein – 1905).
 Definition
Black holes also affect time. The closer one comes to a gravitational body or travels at high speed, times slows down
Term
This is called a gravitational redshift—
 Definition
Similarly, a photon escaping from the vicinity of a black hole will use up a lot of energy doing so; it cannot slow down (speed of light constant), but its wavelength gets longer and longer to lower energies
Term
black hole
 Definition
The effect the holes have on the star’s orbit. The companion will orbit around an unseen object. In this case, the mass of the unseen object can be calculated from the orbits of the binary system. From the mass, we can tell if it is a black hole.
Term
Cygnus X-1
 Definition
is a very strong black-hole candidate:
Term
General relativity
 Definition
predicts that objects should lose energy by emitting gravitational waves. The amount of energy carried by these waves is tiny, and these waves have not yet been observed directly.
Term
The two detectors are located in Hanford, Washington (shown here) and Livingston, Louisiana.
 Definition
This figure shows LIGO, the Laser Interferometric Gravity-wave Observatory, designed to detect gravitational waves. It has been operating since 2003, but no waves have been detected yet.
Term
neutron stars
 Definition
are very dense, spin rapidly, and have intense magnetic fields.
Term
X-ray burster or a millisecond pulsar.
 Definition
A neutron star in a close binary may become an
Term
Gamma-ray bursts
 Definition
are due to two neutron stars colliding or magnetars (Short GRB) or hypernova (Long GRB).
Term
the Schwarzschild radius.
 Definition
The distance from the event horizon to the singularity is called
Term
gravitational red shift and time dilation.
 Definition
A object entering black hole would be subject to extreme
Term
x-rays
 Definition
Material approaching a black hole will emit strong
Term
galaxy
 Definition
gravitational bound collection of stars and interstellar material (gas and dust).
Term
Milky Way
 Definition
Named for band in the sky that we see that looks like milk – Hera’s milk (Jupiter’s wife)
Term
. The Andromeda Galaxy
the milky way is also a spiral galaxy
 Definition
our closest spiral neighbor, probably resembles the Milky Way fairly closely.
Term
Distance to Sun from center – 30,000 ly
Thickness of galaxy – 13,000 ly
Total distance across galaxy – 100,000 ly
 Definition
structure of the milky way
Term
Galactic halo
Galactic bulge
Galactic disk
 Definition
3 park galactic structure
Term
galactic halo
 Definition
(oldest – formed early in galaxy formation)
Contains globular clusters (old stars) –appears red
Stars have random orbits
Essentially spherical
No gas and dust
Term
galactic disks
 Definition
Star formation regions - youngest stars located here – appears blue
Moves in circular orbits
Highly flattened
Contains gas and dust
Spiral arms
Term
galactic bulge
 Definition
(mix of halo and disk)
Contains the galactic center
Contains a mix of older and younger stars (appears yellow)
Random orbits
Football shaped
Contains gas and dust
Term
the infrared view
 Definition
of our galaxy shows much more detail of the galactic center than the visible-light view does, as infrared is not absorbed as much by gas and dust.
Term
All stars have the same brightness
Sun is in the center
 Definition
William Herschel first attempted to measure the Milky Way. He counted stars to make map of galaxy in 18th century. He assumed:
Term
The spectral classification system (OBAFGKM) by Cannon and Payne
The period–luminosity relationship of Cepheid variable stars by Leavitt
 Definition
Some of the discoveries and innovations made by these women include:
Term
harvard women
 Definition
Their work enabled the advances made by Shapley and Hubble as well as Hertzsprung and Russell, among others
Term
Henrietta Leavitt (1868-1921
 Definition
Studied photographic plates of LMC and SMC
Classified 1,777 variable stars - 47 Cepheid variables
Harvard College Observatory
Term
cataclysmic variables.
 Definition
We have already encountered variable stars- star whose luminosity varies in brightness. Novae, supernovae, and related phenomena are called
Term
– periodic variation in brightness
 Definition
Intrinsic variables or variable stars
Term
RR Lyrae stars and Cepheids.
 Definition
Two types of intrinsic variables have been found:
Term
unstable star that oscillates - not in hydrostatic equilibrium.
 Definition
Cepheid variable
Term
Period Luminosity Relationship (1908-1912)
 Definition
Henrietta Leavitt Cepheids with longer periods are intrinsically more luminous than those with shorter periods
Term
RR Lyrae stars
 Definition
all have about the same luminosity although less luminous than Cepheids so are harder to see. By knowing their apparent magnitude allows us to calculate the distance.
Term
Cepheids
 Definition
have a luminosity that is strongly correlated with the period of their oscillations; once the period is measured, the luminosity is known and we can proceed as above
Term
RR lyrae
 Definition
are more common, but have a smaller range in which distance can be found; therefore Cepheids are use for the period luminosity relationship
Term
Harlow Shapley (1885-1972)
 Definition
Studied variable stars in globular clusters and determined that they map out a spherical shape.
1914- used globular clusters to (incorrectly) measure the size of the Milky Way 300,000 ly -100 kpc across (actual – 100,000 ly)
Recalibrated the absolute magnitude scale for Cepheids - revised the value of the distance to the SMC to 95,000 ly - 32 kpc - less than the diameter of the Milky Way
Term
Shapely
 Definition
mapped out the galactic halo using variable stars are found in globular clusters. These clusters are not all in the plane of the galaxy, so they are not obscured by dust and can be measured.
Term
This led to the great debate of 1920 between Harlow Shapley and Heber Curtis (Lick Observatory astronomer).
 Definition
It was debated whether these nebula were inside the Milky Way or other galaxies.
Term
Huber Curtis
 Definition
Spiral nebulae - external galaxies outside of Milky Way

Sun at center of galaxy 10 kpc across
Term
Harlow Shapley
 Definition
Everything in the universe in the Milky Way

Sun located 17 kpc from center of galaxy and 100 kpc across
Term
edwin hubble
 Definition
Rival of Harlow Shapley and attended the Great Debate
Studied Cepheids in Andromeda (M-31) 1923-1924
Using period luminosity relationship found distance
1925 - distance from Earth – 300 kpc ~ 1million ly (2.5 million ly)
This proved that Andromeda that it was a separate galaxy.
Term
Orbital Motion:
 Definition
Rotation depends on distance from center. Does not rotate like a solid body
Term
The mass can be calculate using Newton’s modification of Kepler’s Third Law:
 Definition
the mass of the milky way galaxy
Term
dark matter
 Definition
This unaccounted matter we can not see its called dark matter.
What could this “dark matter” be? It is dark at all wavelengths, not just the visible.
All candidates dealing with normal matter have been eliminated.
Could be an exotic subatomic particle that has yet to be discovered.
This is still one of the big mysteries in astronomy.
Term
A stellar density a million times higher than near Earth.
A ring of molecular gas 400 pc across
Strong magnetic fields
A rotating ring or disk of matter a few parsecs across
A strong X-ray source at the center (Sgr A)
 Definition
The galactic center is in the direction of Sagittarius and has:
Term
The galactic rotation curve
 Definition
shows large amounts of undetectable mass at large radii called dark matter.
Term
spiral (S)/spiral barred (SB), elliptical (E), and irregular (Irr).
 Definition
The types of galaxies are
Term
spiral galaxies
 Definition
are classified according to the size of their central bulge: The components of spiral galaxies are the same as in our own galaxy: disk, core, halo, bulge, and spiral arms
Term
hubbles galaxy classifications
 Definition
Type Sa has the largest central bulge, Type Sb is smaller, and Type Sc is the smallest.
Type Sa tends to have the most tightly bound spiral arms with Types Sb and Sc progressively less tight, although the correlation is not perfect
Term
The Sombrero galaxy
 Definition
with its large central bulge, is a type Sa. We cannot see the spiral arms, as they are edge-on.
Term
barrred spiral
 Definition
the milky way has what galactic classification
Term
galactic classification
 Definition
SBa has the least amount of barring, with SBc with the most. Milky Way is an SBb
Term
Elliptical galaxies
 Definition
have no spiral arms and no disk. They come in many sizes, from giant ellipticals of trillions of stars, down to dwarf ellipticals of less than a million stars.
Term
ellipticals
 Definition
are classified according to their shape from E0 (almost spherical) to E7 (the most elongated):
Term
Tully–Fisher
 Definition
s a relationship between a spiral galaxy’s rotational velocity (which can be measured using the Doppler effect) to its luminosity. The higher the rotational velocity, the more luminous
Term
Type I supernovae
 Definition
all have about the same luminosity, as the process by which they happen doesn’t allow for much variation. They can be used as “standard candles”—objects whose absolute magnitude is known, and which can therefore be used to determine distance using their apparent magnitude.
Term
local group
Consists of about 45 galaxies.
There are three spirals in this group—the Milky Way and Andromeda (M31) being the largest, and M33, a smaller spiral. Most are dwarf elliptical and some irregular galaxies.
 Definition
The galaxy cluster of which we are a part is the
Term
Andromeda
 Definition
is blue shifted and will collide with the Milky Way. Changes will be seen in about 2 billion years.
The collision will occur as our Sun runs out of fuel.
Term
Sagittarius Dwarf galaxy
 Definition
is blue shifted and will collide with the Milky Way in about 100 million years. The Milky Way is not in danger because our galaxy is so much larger. This galaxy has collided with us several times before and survived! Why? One possibility is that it contains a great deal of low-density dark matter that hold it together gravitationally during these collisions.
Term
virgo cluster
 Definition
it is much larger than the Local Group, containing about 3500 galaxies.
Term
Edwin Hubble
 Definition
By studying spectrums of galaxies, he calculated their velocities by the red shift using the Doppler effect.
Using period luminosity relationship found distance.
Noticed a relationship between red shift and distance of galaxies.
Term
Hubble’s Law
 Definition
Galaxies further away have larger velocities

Proved that the universe is expanding
Hubble’s determination of Hubble’s constant - Ho (slope) - 500 km/sec/Mpc
Term
Tully Fisher, Supernova Type Ia, and Cepheid variables
 Definition
Today Hubble’s constant is found using several distance techniques
Term
Hubble's law
 Definition
can also be used as a distance marker for objects. Once the red shift is known for an object and placed on the graph, distance can be found.
Term
active galaxies
 Definition
About 20–25% of galaxies don’t fit well into the Hubble scheme—they are far too luminous. Such galaxies are called
Term
high luminosity
nonstellar energy emission
variable energy output, indicating small nucleus
jets and other signs of explosive activity
broad emission lines, indicating rapid rotation
These galaxies are all now know to be the same thing.
 Definition
Active galactic nuclei have some or all of the following properties:
Term
Quasars (quasi-stellar objects- QSO
 Definition
starlike radio source with observed red shift that indicates an extremely large distance.
Term
Cepheid variable stars and Type I supernovae. This are used to find distances
 Definition
Objects of relatively uniform luminosities are called “standard candles”; examples include
Term
hubble's law
 Definition
Galaxies recede from us faster the farther away they are. This is used to find the greatest distances
Term
Active galaxies
 Definition
contain supermassive black holes in their centers; infalling matter converts to energy, powering the galaxy
Term
helmi stream
 Definition
a group of stars that remains after its mini-galaxy was devoured by the Milky Way some six to nine billion years ago.
Term
elliptical galaxy
 Definition
Mergers of two spiral galaxies probably result in an
Term
galactic bulge
 Definition
The mass of the central black hole is well correlated with the mass of the
Term
10 billion years ago
 Definition
The end of the quasar epoch seems to have been about
Term
"clumps"
 Definition
The filaments and voids show that the universe is not uniformly distributed, but are in
Term
The Sloan Digital Sky Survey (SDSS)
 Definition
was done by a dedicated telescope situated in New Mexico. Its purpose - to measure hundreds of millions of celestial objects. Approximately one million of these also have their redshifts measured, making possible very detailed redshift maps.
Term
galaxy masses
 Definition
Galaxy masses can be determined by
Term
galactic lensing
 Definition
Quasars can be used as probes of intervening space, especially if there is
Term
the Sloan Great Wall
It stretches 300 Mpc across and is 1000 Mpc away from Earth.
 Definition
is the largest structure in the Universe
Term
the Cosmological Principle
 Definition
On the largest cosmic scales, the Universe is both homogeneous and isotropic.
Term
Isotropy
 Definition
means that there is no preferred direction in the Universe. That is, from your current location, no matter which direction you look, the Universe will look the same.
.
Term
homogeneity
 Definition
means that there is no preferred location in the Universe. That is, no matter where you are in the Universe, if you look at the Universe, it will look the same.
Term
Abbe Georges Lemaitre
 Definition
first suggested the universe originated from a singular point
Term
George Gamow
 Definition
developed the big bang theory in additional detail and was one of the first champions of the theory. Many of his details were incorrect, but he got the essential idea right.
Term
Ralph Alpher, Robert Herman, and George Gamow in 1948.
 Definition
The big bang theory predicts Cosmic Microwave Background (CMB). At the time of the big bang the universe its filled with high energy radiation (gamma rays). So there should be a cosmic background that radiates everywhere. The existence of the CMB radiation was first predicted by
Term
cosmic microwave background

the were awarded nobel prize
 Definition
It was accidentally found in 1965 by Arno Penzias and Robert Wilson (Bell Telephone Lab in Murray Hill, New Jersey). The antenna built to communicate with Earth-orbiting satellites always had a “noise” that came from all directions and at all times, and was always the same. They were detecting photons left over from the Big Bang.
Term
COBE and WMAP
 Definition
only with instruments such as ____ and ____ can cosmologists detect fluctuations in the cosmic microwave background temperature.
Term
Wilkinson Microwave Anisotropy Probe (WMAP)
 Definition
The NASA Explorer mission that launched June 2001 to make fundamental measurements of cosmology -- the study of the properties of our universe as a whole.
Term
anisotropy”. Tiny variations in the intensity of the CMB
 Definition
The CMB was found to have intrinsic
Term
Ω < Ω0 Open geometry
 Definition
expands forever-cold death
Term
Ω = Ω0 Flat geometry
 Definition
corresponds to the critical density
Term
Ω > Ω0 Closed geometry
 Definition
– collapse “Big Crunch”
Term
open universe
 Definition
omega < 1 and the universe has a negative curvature
Term
flat universe
 Definition
omega = 1 and the universe has Euclidean geometry
Term
closed universe
 Definition
omega > 1 and the universe has a positive curvature
Term
there is insufficient mass to cause the expansion of the Universe to stop. So a low mass/low energy Universe has negative curvature. The Universe in that case has no bounds, and will expand forever.
 Definition
If space has negative curvature
Term
there is exactly enough mass to cause the expansion to stop, but only after an infinite amount of time. Thus, the Universe has no bounds in that case and will also expand forever, but with the rate of expansion gradually approaching zero after an infinite amount of time.
 Definition
If space has no curvature (it is flat)
Term
there is more than enough mass to stop the present expansion of the Universe. So a high mass/high energy Universe has positive curvature. The Universe in this case is not infinite, but it has no end (just as the area on the surface of a sphere is not infinite but there is no point on the sphere that could be called the "end"). The expansion will eventually stop and turn into a contraction. Thus, at some point in the future the galaxies will stop receding from each other and begin approaching each other as the Universe collapses on itself.
 Definition
If space has positive curvature
Term
flat with only a 2 percent margin of error
 Definition
WMAP has confirmed with very high accuracy and precision that the universe is
Term
"biggest blunder.“
 Definition
When Edwin Hubble found that the universe is expanding, Einstein removed the constant from his theory and is rumored to have called it his
Term
dark energy
 Definition
Einstein's cosmological constant has been resurrected in the form of
Term
homogeneous and isotropic.
 Definition
On scales larger than a few hundred megaparsecs, the Universe is
Term
big bang
 Definition
The Universe began about 13.8 million years ago, in a
Term
geometry
 Definition
Cosmic microwave background may lend clues to
Term
50,000 years after the big bang
 Definition
As the Universe cooled, it went from being radiation dominated to being matter dominated. This happened
Term
10−43 seconds after the Big Bang. This is called the Planck era
 Definition
We cannot predict anything about what happened before the Big Bang or the first
Term
GUT (Grand Unified Theory) era.
 Definition
At the end of the Planck era, the gravitational force “freezes out” from all the others. The next era is the
Term
quark era
 Definition
after the gut era is the
Term
quark era
 Definition
during this era all the elementary particles were in equilibrium with radiation.
Term
lepton era
 Definition
after the quark era was the
Term
nuclear era
 Definition
after the lepton era is the
Term
up, down, charm, strange, top, bottom
 Definition
The four fundamental forces and the particles on which they act. There are six types of quarks
Term
electron, muon, tau, and neutrinos associated with each). All matter is made of quarks and leptons.
 Definition
six types of leptons
Term
the electroweak theory
 Definition
The theories of the weak and electromagnetic forces have been successfully unified in what is called
Term
string theory
 Definition
the idea that elementary particles are oscillations of little loops of “string,” rather than being point particles. This avoids the unphysical results that arise when point particles interact. It does, however, require that the strings exist in 11-dimensional space. The extra seven dimensions are assumed to be very small.
Term
The horizon problem:
 Definition
When observed in diametrically opposite directions from Earth, cosmic background radiation and temperature appears the same (homogeneous and isotropic) even though there hasn’t been enough time since the Big Bang for them to be in thermal contact.
Term
alan guth
 Definition
American physicist and cosmologist, proposed that many features of our universe, including how it came to be so uniform and why it began so close to the critical density, can be explained by a new cosmological model which he called inflation. Inflation is a modification of the conventional big bang theory, proposing that the expansion of the universe was propelled by a repulsive gravitational force generated by an exotic form of matter.
Term
This is the epoch of inflation.
 Definition
Between the GUT epoch and the quark epoch, some parts of the Universe may have found themselves stuck in the unified condition longer than they should have been. This resulted in an extreme period of inflation, as shown on the graph. Between 10−35 s and 10−32 s, this part of the Universe expanded by a factor of 1050!
Term
radiation dominated
 Definition
At present the Universe is matter dominated; at its creation it was
Term
pair production
 Definition
Matter was created by
Term
gravity
 Definition
“froze out” first, then the strong force, then the weak and electromagnetic forces.
Term
primordial nucleosynthesis
 Definition
Most helium, and nearly all deuterium, in the Universe was created during
Term
radiation and matter decoupled
 Definition
When the temperature became low enough for atoms to form
Term
inflation
 Definition
Horizon and flatness problems can be solved by
Term
2/3 of the density comes from dark energy, and dark matter makes up most of the rest.
 Definition
The density of the Universe appears to be the critical density;
Term
Carl Sagan (1934-1996
 Definition
was the first person to explain the history of the universe in one year-as a "Cosmic Calendar"-in his television series, Cosmos.
Term
Urey–Miller experiment
 Definition
first done in the 1930s, that demonstrated the formation of amino acids from the gases present in the early Earth’s atmosphere, excited by lightning.
Term
The Murchison meteorite
 Definition
which fell in Australia, contains 12 different amino acids found in Earthly life, although some of them are slightly different in form.
Term
Mars: possibly past life
Europa and Titan: possible life
Enceledus: known precursors to life
 Definition
Life as we know it: carbon-based, originated in liquid water
Is such life likely to be found elsewhere in our Solar System?
Term
extremophiles
 Definition
survive in environments long thought impossible—here, hydrothermal vents emitting boiling water rich in sulfur.
Term
The Drake Equation
 Definition
was developed by Frank Drake in 1961 as a way to focus on the factors which determine how many intelligent, communicating civilizations there are in our galaxy.
Term
the Pioneer 10 spacecraft
 Definition
We have already launched interstellar probes.
Term
the Green Bank radio telescope
 Definition
used to search for extraterrestrial signals in the mid-1990s (SETI). The inset is a test using the Pioneer 10 spacecraft; no true extraterrestrial signal has ever been found.
Term
particulate, galactic, stellar, planetary, chemical, biological, and cultural.
 Definition
The history of the universe can be divided into phases:
Term
the drake equation
 Definition
can be used to estimate the total number of intelligent civilizations in our galaxy, although a number of its factors are extremely uncertain.
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