is the center of the sun. Nuclear reactions take place here, producing energy.
has the hottest temperature
is the second inside layer. Energy travels from the core outward to this layer in the form of radiation.
is the third layer. Huge waves of energy swirl around here, carrying the heat outward.
is the outside layer of the sun. This is the visible layer, where light is emitted.
-is our ONLY source of information for distant objects (the broader universe)
A light-year is the distance that light can travel in one year.
We cannot see more than _____________ years , because ________________________________________
it is our best proxy for other stars because we can easily study it.
Properties of other stars are compared to our Sun’s:
Radius: 6.9 ¥ 108 m
Mass: 2 ¥ 1030 kg
Luminosity: 3.8 ¥ 1026 watts
Surface Temperature:5830 K
The relationship between apparent brightness and luminosity
How we can determine some distances
We estimate star temperature by the color and spectral type.
Lines in a star’s spectrum correspond to a _______ that reveals its temperature.
(Hottest) O B A F G K M (Coolest)
Star Temperature Range:
We measure mass using Newton’s version of Kepler’s 3rd Law
M1+M2=A3 / P2
plot the luminosities against the spectral types of stars
Gravitational Collapse of a Nebula
A large nebula can make a whole cluster of stars. Random motions cause the nebula to contract. The nebula heats up as gravity causes it to contract due to conservation of energy.
conservation of energy
Random motions cause the nebula to contract. The nebula heats up as gravity causes it to contract due to
Protostar Jet Formation
Rotation also causes jets of matter to shoot out along the rotation axis.
Collapse stops when fusion starts
A protostar contracts and heats until the core temperature is sufficient for hydrogen fusion, and then shrinking stops. New star achieves long-lasting state of balance because the outwards force of fusion matches the inwards collapse of gravity. Main-sequence stars are fusing hydrogen into helium in their cores, like the Sun.
If fusion never starts… Star-like objects not massive enough to start fusion are...
because mass determines core temperature.
use their core hydrogen quickly (~5 million years)
use their core hydrogen slowly (~10 billion years)
Small nuclei stick together to make a bigger one. (Sun, stars) High temperatures enable nuclear ________ to happen in the core by overpowering the repulsion between atoms.
The Sun and other low mass stars releases energy by fusing four hydrogen nuclei (4 protons) into one helium nucleus in a process called the
A star remains on the __________ as long as it can fuse hydrogen into helium in its core. Low mass stars convert hydrogen to helium by the ________ (slowly, ~10 billion years)
Low Mass Star: First Red Giant Phase
After core hydrogen is used up: The core contracts, H begins fusing to He in a shell around the core in the first giant phase. A star becomes larger, redder, and more luminous after its time on the main sequence is over.
Second Red Giant Phase
While the shell is fusing hydrogen, the inner core starts to fuse helium in the second giant phase. Helium fusion: 3 Helium atoms make 1 Carbon atom
Instability and collapse
Because a low mass star cannot undergo advance fusion of heavier elements, carbon builds up in the core and the star will never regain stability.
Fusion ends with a pulse that ejects the H and He into space as a ________
The core left behind becomes a _____________.
The leftover carbon core of a low mass star, very dense and hot
The “decaying corpse” of a star, will cool off slowly over time.
star fuses H to He at a higher rate using carbon, nitrogen, and oxygen as catalysts.
Early life stages of high-mass stars are similar to those of low-mass stars:
High Mass Star: Multiple shell fusion
High temperature nuclear fusion proceeds in a series of shells around the core.
Iron is a dead end for fusion because reactions involving iron do not release energy. Iron builds up in the core until pressure can no longer resist gravity.
The core then suddenly collapses, creating a supernova explosion.
Supernova Explosion and Remnant:
Energy released by the collapse of the core drives outer layers into space and forms elements heavier than iron, such as gold and uranium.
Black Holes and Neutron Stars:
Heavy interiors inside the remnant form Neutron Stars or Black Holes.
Neutrons collapse to the center, forming a neutron star.
Or sometime…. A BLACK HOLE!
Particles can’t be in same state in same place according to the laws of quantum physics.
-is the ball of neutrons left behind by a massive-star supernova and
about the same size as a small city, with the mass of a large star.
Jocelyn Bell noticed pulses of radio emission coming from a single part of the sky.
The pulses were coming from a spinning neutron star that emits waves in the direction of its magnetic axis.
-is an object whose gravity is so powerful that not even light can escape it.
-Some massive star supernovae can make a ________________ if enough mass falls onto the core (degeneracy pressure is exceeded).
As far as we know, gravity crushes all the matter into a single point known as a
The “surface” of a black hole is the radius at which the escape velocity equals the speed of light.
-The__________ of a 3MSun black hole is also about as big as a small city.
What we see as gravity is actually the curvature of spacetime
A black hole is like a bottomless pit of spacetime and not even light can escape it.
The Milky Way’s Galactic Center:
Stars orbiting something massive but invisible …
A SUPERMASSIVE black hole? Orbits of stars indicate a mass of about
4 million Msun.
The Big Bang and the Expanding Universe:
term coined by Fred Hoyle – 1949
Using the rate of expansion between galaxies, we can calculate that the universe is 14 billion years old. The galaxies themselves remain constant due to gravitational forces.
In the beginning…
The early universe was unfathomably hot and dense, and composed of only hydrogen and helium.
Our Cosmic Address:
Earth, Our Solar System, The Milky Way Galaxy, The Local Group, The Virgo Supercluster, The Observable Universe