ASTR 1514 1st EditionFinal Exam Study Guide Chapters: 1 - 12Half of the exam will cover material from chapter 1-12 and the other half will cover chapters 13-16CHAPTERS 13-16- High Mass stars have masses greater than 8 solar masses- High Mass stars fuse hydrogen differently - CNO (Carbon-nitrogen-oxygen) cycle – uses carbon and other nuclei as catalysts - CNO Cycle- Require a higher temperature since there is a greater repulsive force between a proton and a carbon nucleus - Our sun creates about 1.7% of Helium by this process, but in heavier stars, it is much more important- Once Hydrogen is exhausted from the core, the star leaves the main sequence, expands and cools. (Move right on the H-R diagram): Super Giants- Helium does not build up as ash in the center of these stars, so there is no degenerate corein massive stars- As High-Mass stars expand and cool, they can pass through the instability strip, where the combination of temperature and luminosity results in the stars pulsating. - Pulsating stars are extremely important when determining distances – a relationship between pulsation period and luminosity. - Iron cores of a star will not fuse, they are the limit. - Star fuses elements in order to produce the pressure needed to support the outer layers. - Nuclear binding energy plot tells you how much energy can be extracted from fusion of various elements These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Elements with higher average binding energy are more tightly bound- Iron is the most tightly bound element- The difference in total binding energy tells you how much energy is released per fusion - Ex: The binding energy of helium is much greater than for four hydrogen , so fusing four hydrogen into one helium releases a lot of energy- The triple alpha process – The difference in binding energy between carbon and three helium is less, so less energy is released. - Core Rebound- The core may not collapse indefinitely. Eventually it reaches the density of an atomic nucleus - The strong force, short range attractive force, switches a repulsive force if compressed too far- Huge numbers of neutrinos are produced, and some are trapped- The rest of the star is collapsing - Core stops, the rebounds, driving a shock wave through the star- The rebound explodes the starWhere do the Elements in the Universe come from?- Nuclearsynthesis: The development of atoms more complex than hydrogen- Big Bang: When the universe began, Includes hydrogen, helium, lithium- In stars during their lifetime: Includes all elements as light as or lighter than iron- In supernovae: Includes elements heavier than Iron. Basically we are made of star stuff. Neutron Stars- Neutron stars emit very hot X-ray radiation- Neutron stars spin very rapidly, periods ranging from 0.001 seconds to 4 seconds- Neutron stars have very strong magnetic fields. Pulsars emit a beam of light due to synchrotron radiation. 1.) Stellar Evolution has three possible endpoints- White Dwarf Star – the end-point of a medium mass star, White dwarfs are less than 1.4 solar masses- Neutron Stars – The end-point of massive stars. Neutron stars are between 1.4 and 3 solar masses.- Black Holes – The end point of very massive stars, with massive cores greater than 3 solar masses. - If the mass of a neutron star exceeds 3 solar masses it will collapse to a black hole- Not even light can escape the gravitational pull of a black hole- Can form directly from type II supernova (if massive enough) or from accretion by a neutron star in a binary system. 2.) Understanding Black holes- A black hole has mass, but it has no size. - It is a singularity, meaning you can approach a black hole close enough that the escape velocity is equal to the speed of light - Event Horizon: The radius at which the escape velocity is the speed of light- In principle, Black holes can have any mass- Ex: If we could make the Earth smaller and smaller the escape velocity would get larger and larger3.) General Relativity- The theory of general relativity was tested by observing the apparent shift of a starnear the sun during a solar eclipse. - The sun is large enough to bend space time a very little, near it’s surface.- The orbit of Mercury precesses, the axis shifts due to the bending of space near the sun. 4.) Falling into a black hole- Gravity is stronger as we get closer to the black hole, so someone falling in the black hole will fall faster and faster the closer they get to it. - Light is bent around the black hole, so we would experience some unusual opticaleffects as we got close. *Gravitational Lensing- Light is bent around the black hole, so you can see behind it- More light rays are bent in your direction, so the object is brighter than if the black hole were not there- Gravitational lensing can be used to view distant galaxies. The cluster of galaxies acts as the lens. - If you are falling into the black hole feet first, your feet will feel a stronger gravitational force than your head. - Stretching you- If you survive the stretching then after 65 days you will cross the event horizon- You would not notice anything, since the event horizon is not a hard surface or boundary. 5.) Someone observing the black hole from Earth- An observer watching you fall into a black hole will witness you falling slower and slower as you get closer to the black hole- From his perspective you never fall into the black hole, you just stop- Black holes were initially called “frozen star” because of this. 6.) Time Dilation- Clocks will run more slowly when gravity is strong- The effect of time dilation is stronger when you get closer to a black hole- We can observe time dilation from light emerging from near a black hole- Light has a frequency, which is like a clock. - Decreasing the frequency due to time dilation increases the wavelength- Called gravitational redshift. - “Tired Light” – Light loses energy fighting to get away from the black hole. 7.) Your Effect on the Black Hole- A black hole is characterized by two numbers: Mass and Spin.• See black holes through X-ray binary systems. • Neutron Stars can also be seen in binary systems- They have nearly as strong gravity as black holes, so they also emit X-Rays- Accreting neutron stars and accreting black holes are sources of X-Ray sources.Galaxy Classification- Classified according to their shape-