Astro Final
What's at the Galactic nucleus, at the heart of the Galactic center? What do we observe? How can we tell what's happening there?
At the very center is the Galactic nucleus Sgr A* powerful radio and X-ray source supermassive Black Hole
what can cause a Gamma-ray burst?
Collision of two neutron stars or two black holes or a black hole swallowing a neutron star.
What is the order of the elements in a star?
H, He, C, O, Ne, Si, Fe
What is the Galactic Halo? What is it made of?
Most of the Halo (99%) are isolated stars The rest are in Globular Clusters Including some intermediate-mass Black Holes Stars and clusters in the inner Halo shell revolve the same way as the disk Stars in the outer shell orbit the opposite way Halo stars (especially the ones further out) are metal-poor and old Some created in the very early Universe
What do we call the remnant of an intermediate mass star? What's special about it?
We call the remnant of an intermediate mass star a white dwarf and it is special because: they can create powerful explosions when they are found in close binary systems (nova).
What is escape velocity?
the velocity needed to leave the atmosphere The speed needed to break free of a planet's gravitational pool.
What is a standard candle? What standard candle do we use to find the most distant galaxies?-
- an object whose known luminosity can be used to deduce the distance to a galaxy - supernova
What are irregular galaxies made of? What kind of stars are in them?
- contain gas, dust, young and old stars - Smaller and less massive than Spirals
What is gravitational lensing and what does it tell us?
- distoration of appearance of an object by a source of gravity between it and its observer
What is a Quasar? How can we tell something is a Quasar? How did we first find it?
- starlike object with a large redshift Quasars have redshift of 6% − 90% of the sol (�) The farthest ones are 10 − 13 gigayears away from us The greater the redshift the fartherthe object the farther back in time we see it we can follow the history of Quasars using their redshift
What is the Hubble classification? How many Galactic types? What are the subtype of Spirals? What kind is the Milky Way?
- the classification of galaxies according to their appearances into one of four categories- spiral, barred spiral, elliptical, irregulars sup of spirals- Sa, Sb, Sc flocculent spirals (not tight), grand design spirals milky way-
How large are Elliptical galaxies? What kind of stars are in them? Why?
- the largest and smallest galaxies in the Universe - Giant Ellipticals are rare, Dwarf Ellipticals common 10 trillion millions - can be rounded or increasingly elongated (oval) - contain mostly old, low mass, long living stars barely any star formation
What are the Bars in galaxies? How are stars moving in them?
-a spiral galaxy with a bar of stars crossing through the center bulge Barred Spiral galaxies have less mass than unbarred ones Stars move back and forth through the bar We classify them the same way as unbarred
. What is the Cosmic Background Radiation? What kind of energy output is it? What does it tell us about the Universe and its history?
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How do AGN simultaneously explain everything about Quasars, Blazars, and other similar objects of that, including their huge redshift/distance?
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What are the grouping of galaxies named? What's ours? How large is it? Who's in it?
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What are the major parts of our galaxy? What kind of galaxy is it?
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What did galaxies other than the Milky Way look like to us? What changed that made us understand what they really were?
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What is the Big Bang Hypothesis? What is it based on (how did we come to think of it)?
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What is the explanation for the energy emanating from Quasars? Where else have we seen this mechanism?
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What is the explanation to Hubble's law? What analogy did we use for it?
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What two things do we get from the collision of two NS?
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Where is our Solar system in the Galaxy? How far out and relative to the spiral arms? How did we find out at first?
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What are the "big picture" five scenarios for the evolution (birth-life-death) of stars?
1. Mass too low 2. Small mass 3. Intermediate mass 4. Large mass → neutron stars 5. Large mass → black holes.
What are the "big picture" five scenarios for Close Binary stars?
1. Star + WD → nova 2. Star + WD → Supernova type Ia 3. Star + NS → X-ray pulsators 4. NS + NS → collisions → elements created 5. Star + BH → accretion disk and jets of gas accretions also occurs with WD and NS
What are the five main implication, discussed in class, of Special Relativity (which observer sees what)?
1. Your description of physical reality is the same regardless of the (constant) velocity at which you move. 2. Regardless of your speed or direction, you always measure the speed of light to be the same. 3. The length of an object decreases as its speed increases (think of the train) 4. Clocks that you see as moving run more slowly than do clocks you see at rest. 5. The mass of an object increases as it moves faster.
What's a Type Ia Supernova (associated with a WD)? What happens and why?
A Type Ia supernova is when a white dwarf blows apart completely. It occur in white dwarfs that are part of a semi-detached binary star system. To trigger a Type Ia supernova, a swollen giant companion star dumps gas onto a white dwarf that is close to the Chandrasekhar limit (1.4 solar masses). When the added gas causes the white dwarf's mass to cross that limit, the increased pressure deep inside the dwarf enables carbon fusion to begin in the core. The rate of carbon fusion skyrockets, and with no outer layers to absorb the energy, the star blows up. What we see is the fallout from a gigantic thermonuclear explosion.
Does a WD generate energy by itself? Is it easy to observe? What will happen to it eventually?
A White Dwarf does not generate energy by itself. As billions of years pass, an isolated white dwarf radiates its own energy into space, cooling and decreasing in luminosity. It's not easy to observe White Dwarfs directly because they are very faint. Eventually, the white dwarf will radiate away all of its heat, becoming cooler/redder. After billions of years of radiating away their heat, the interior temperatures of white dwarfs will decrease to about 4000K, and the carbon and oxygen in them will solidify, transforming them into giant crystals.
What is a White Dwarf made of? How large is it? How dense? How large can it get?
A White Dwarf is made of degenerate gases rich in oxygen and carbon, and is covered with a thin coating of hydrogen and helium. It's roughly the size of Earth and its density is typically 10^9 kg/m^3. It can only get as heavy as 1.4 solar mass, which is the Chandrasekhar limit. Above the Chandrasekhar limit, the degenerate matter cannot exert enough outward force to prevent the core from collapsing further.
What is a Black Hole? What is the basic idea behind it in terms of General Relativity?
A black hole is when the gravitational force of an object is so great that it overcomes all opposing repulsive forces or pressures (like neutron degeneracy pressure), forcing the object to collapse in on itself. Its gravitational attraction then becomes so strong that nothing - not even light - can escape from it. General relativity predicts the fate of massive star cores - black holes. → All matter warps space around itself. When matter gets sufficiently dense, it actually causes space near it to curve so much that it closes in on itself. Such regions out of which no matter or any form of electromagnetic radiation can leave are called black holes. A collapsing neutron star becomes so dense that it ceases to consist of neutrons. General relativity predicts that in creating a black hole, matter compresses to infinite density (and zero volume), a state called singularity. Basically... matter in black holes becomes incredibly dense and compact.
What is a Nova? What happens and how does it happen?
A nova is when a white dwarf suddenly becomes between 10^4 and 10^6 times brighter than usual, and then gradually declines over a stretch of several months or more. Novae occur in close binary systems that contain a white dwarf. The ordinary companion star fills its Roche lobe, so it gradually deposits fresh hydrogen onto the white dwarf. This new mass becomes a dense layer covering the hot surface of the white dwarf. As more gas is deposited and compressed, the temperature in the hydrogen layer continues to increase. Finally, at about 10^7K, hydrogen fusion ignites throughout the layer, blowing it into interstellar space. This explosion is the nova. After a nova, fusion ceases on the white dwarf.
What is a planetary nebula? What type of star's death is it a part of? What stage of death?
A planetary nebula is the dust and gas that expands at the last stages of a star's life. It is a part of an intermediate-mass star's death, and it occurs at the final stage which begins with a "thermal runaway" in the helium shell. After all the helium in the core has been used up, the star now shines due to shell hydrogen fusion and shell helium fusion: The core shrinks and outer layers expand. Luminosity increases and surface temperature decreases: star moves up and to the right on the H-R diagram (become supergiant). As expanding star loses a lot of mass, there is less contraction at the core and fusion stops. The star now undergoes a series of outbursts (helium flashes). Eventually the star sheds its outer layers to form a planetary nebula. Much of the mass gets ejected (around 80%). Only the hot interior remains.
What is a Type II Supernova (associated with a high-mass star)? What happens and why?
A type II supernova occurs when the buildup of an inert core of iron nuclei and electrons signals the impending violent death of a massive star. After silicon fuses into iron, fusion stops because iron cannot fuel thermonuclear reactions. Because iron atoms do not fuse and emit energy, the electrons in the core must now support the star's outer layers by the strength of electron degeneracy pressure alone. Soon, however, the continued deposition of fresh iron from the silicon-fusing shell causes the core's mass to exceed the Chandrasekhar limit. Electron degeneracy suddenly fails to support the star's enormous weight, and the core collapses. When the core collapses, a rapid series of cataclysms is triggered that tears the star apart in a few seconds. Core collapses → temperature exceeds 5 billion K. Gamma-ray photons associated with this intense heat have so much energy that they begin to break apart the iron nuclei, a process called photodisintegration. As the density continues to climb, the electrons in the core are forced to combine with the core's protons to produce neutrons, and the process releases a flood of neutrinos. The matter inside the core is so dense that its newly created neutrinos cannot immediately escape from the star's core. They slam into nearby particles, providing a pressure pushing outward from the core. The outer layers that are falling in collide with the hard core and absorb the outflowing neutrino energy. The impact (between the layers and the neutrinos) stops the core's rebound, while causing the infalling matter to reverse course. A tremendous volume of matter begins to move back up towards the surface. This matter accelerates rapidly, encounters less resistance and soon forms an outgoing shock wave. After a few hours, this shock wave reaches the surface, lifting the star's outer layers away in a mighty blast. This explosion is extremely bright: up to 10^6 times as luminous as Supergiant.
What happens after Silicon is fused into Iron? Why?
After silicon is fused into iron, the star becomes a luminous supergiant. Each stage of fusion adds a new shell of matter outside the core, creating a structure that resembles the layers of an enormous onion. The fusion-generated photons in all of these shells, as well as i the core, push the outer layers of the star farther and farther outward. The star expands to become a luminous supergiant, almost as wide as Jupiter's orbit around the Sun. High-mass main sequence stars evolve into luminous supergiant stars that are brighter than 10^5 solar luminosity, emit winds throughout most of their existence, and have mass-loss rates that exceed those of giants. After silicon is fused into iron, fusion stages in the cores of high-mass stars ends. Iron cannot fuel further thermonuclear reactions, because the protons and neutrons inside iron nuclei are already so tightly bound together that no further energy can be extracted by using still more particles with them.
How did we map the Galaxy? What part of the spectrum did we use and how did we use it?
Almost every kind of radiation gets absorbed by gas So we observe the gas Use a rare radio-wave occurrence 21cm Map how everything moves towards/away from us We can also observe nearby OB associations and HII regions our galaxy contains ~ 200 Billion stars organized mainly in two spiral arms Perseus and Scutum Centaurus We are located between the Perseus and Sagittarius arms, arms spiral out of a bar made of stars, gas, dust, Bar is surrounded by the central bulge, Inside the bulge is the galactic nucleus
What is the difference between constellations and asterisms?
An Asterism is simply an easily recognizable pattern of stars. The same pattern is often known by many different names to different peoples. A constellation is a defined area of the sky.
What is an accretion disk? In what type of systems do we see it?
An accretion disk is a disklike flow of gas, plasma, dust, or particles around any astronomical object in which the material orbiting in the gravitational field of the object loses energy and angular momentum as it slowly spirals inward. The formation of stars and planets and the powerful emissions from quasars, radio galaxies, X-ray binaries, and probably also Type Ia supernovas all involve accretion disks. Black holes too.... Accretions also occurs with WD and NS.
What can we say about the movement of stars at the very edge of the disk or beyond? What does that mean?
Beyond the edge of the disk, stars move around more rapidly gravitational pull What's pulling? Whatever it is, we can't see it: Dark Matter Massive Compact Halo Objects - MACHO
How large can a BH get? What are Supermassive Black Holes? Where do we see them?
Black holes range in mass up to billions of solar masses. They curb their own growth however once they accumulate about 10 billion times the mass of the sun. Early in the life of the universe, black holes could have formed from the condensation of vast amounts of gas and also from the collisions of stars during the process of galaxy formation, thereby creating supermassive black holes, each with millions or billions of solar masses. They can be found at the center of most spiral galaxies.
What are Cosmic Rays?
Cosmic rays are particles flying through space at speeds that exceed 90% the speed of light. They are primarily hydrogen nuclei. A few percent are electrons and positrons (positively charged electrons). Less than 1% are nuclei of more massive, non hydrogen elements.
What is a galaxy? What's in it? What keeps it together?
Each galaxy is an enormous grouping of stars, gas, and dust bound together by gravitation.
What is Electron-Degeneracy? What does it mean to be in this state? What object is?
Electron degeneracy is a result of the extreme pressure inside a white dwarf. T he electrons are compressed so tightly that they are forced into higher energy states (degenerate state). The high-energy electrons create an outward pressure that opposes the white dwarf's gravitational pressure and keeps it in an equilibrium state. Degeneracy: special state when pressure is not coupled to temperature. White Dwarfs are in this degenerate state because: the fast-moving high-energy electrons provide a pressure which is independent of temperature. Even as the temperature of a white dwarf falls toward absolute zero, the Pauli exclusion principle demands that the high-velocity electrons keep moving at the same speed. Hence, the pressure exerted by the electrons remains constant as the temperature falls
What are the various ways for stars to maintain balance depending on their evolution stage?
From protostar to remnant. Gravity pulls in - pressure pushes out. Protostar: Heat from contraction. Star: Heat from fusion (plasma). White dwarf: electron-degeneracy pressure. Neutron star: neutron-degeneracy pressure.
What are Superclusters? How are they "arranged" across the Universe?
Galactic Clusters exist in Superclusters The clusters in a Supercluster are not gravitationally bound - they drift apart Typical Supercluster size: hundreds of millions lyr across Since the 1980s big parts of the sky were mapped Superclusters located near bubblelike voids sponge-like structure
Why would galaxies collide? What happens when they do? What are Starburst galaxies?
Galaxies in cluster are gravitationally bound occasionally collide In galactic collisions stars never collide, but gas does galaxy may lose gas hot intergalactic gas galaxy may keep compressed gas galaxy-wide galaxy-wide starburst galaxy( a galaxy where there is an unusually high rate of star formation)
What is the main idea about space, mass and light behind General Relativity? What are the implications for time and mass?
General relativity explains how matter warps spacetime, creating gravitational attraction. The greater the mass, the more the distortion or curvature. The curvature of spacetime creates attraction between all pieces of matter in the universe (gravitational force). Another result of general relativity is that time slows down in the presence of matter. The greater the concentration of matter, the slower clocks tick. For ex, time passes more slowly for us here on Earth's surface than it would for astronauts on the Moon, which has less mass than Earth. The curvature of spacetime also changes the path and wavelength of light that passes near any matter. Light travels along trajectories in space called geodesics. Geodesics are sufficiently curved to cause light from stars behind the sun to arc around it (verification of GR theory). (the warping of space by matter causes light to be deflected) → ex, star-light's path being bent by the sun. Some tests that have been conducted: measuring the bending of light by the sun, redshifts from compact objects, trajectories near large masses of objects like Mercury or binaries.
What is the Hubble Constant? How does it relate to the age of the Universe?
H0 = 73.8 km/sec/Mpc is the Hubble Constant How do we know the distances to other galaxies? If we know absolute Magnitude (M) same as Luminosity apparent magnitude (m) what we observe distance to find the absolute magnitude we use a "standard candle" like a Supernova Explaining Hubble's Law: The Universe must be expanding Every cluster sees all other clusters receding from it. The ones farther out recede faster Spacetime itself is growing, carrying the galaxies with it and stretching the wavelengths!
What are the spiral arms? What analogy did we use to describe them? How are stars forming them? Why do we see them so distinctly?
How are Spirals created? In Flocculent galaxies these are regions of star formation, appearing and disappearing In Grand Design galaxies these are density compression waves analogy? Spirals have only 5% more stars than in between the arms We see them because they contain bright O and B stars that shine onto the gas surrounding them Barred Spiral galaxies have less mass than unbarred ones Stars move back and forth through the bar We classify them the same way as unbarred
How does the fusion work in a high-mass star? What fuses into what (at first and at the end)? How long does it all take?
How the fusion works: nucleosynthesis → the process of converting lower-mass elements into higher-mass ones. When helium fusion ends in the core of a high-mass star, carbon fusion begins (at 600 million K), producing such elements as neon and magnesium. When the star compresses itself enough to elevate its central temperature to 1.2 billion K, neon fusion occurs, creating oxygen and magnesium. Oxygen fusion then begins (at 1.5 billion K), producing sulfur, silicon, and phosphorus. Each cycle of fusion happens faster, because there are less particles to fuse and the temperature increases. For example: (for a star that was initially 25 solar masses on the main sequence) carbon fusion occurs for 600 years, neon fusion for 1 year, and oxygen fusion for only 6 months. After core oxygen fusion, gravitational compression forces the central temperature up to 2.7 billion K, and silicon fusion begins. This thermonuclear process proceeds so furiously that the entire core supply of silicon in a 25 solar mass star is converted into iron in 1 day.
How can we tell how far a galaxy is?
Hubble knew that he could calculate the distance to M31 by using the characteristics of the fluctuating light of Cepheid variable stars. M31 (Andromeda) → Cepheid variable star → pulsation + apparent magnitude → distance The distances to even more remote galaxies have been determined from observations of Type Ia supernovae in them.
What is the Cosmological redshift Hubble discovered? What does it tell us?
In the 1920 Hubble and Humason took the Spectra of various galaxies Doppler redshift galaxies are moving away, receding from us Hubble calculated the distances Redshift tells us how fast galaxies are moving distant clusters/superclusters move away faster than nearby ones
What happens to light near the various compact objects (WD, NS)?
Light leaving the vicinity of a white dwarf curves and redshifts more, whereas near a neutron star, some of the photons actually return to the star's surface. Inside a black hole, all light remains trapped. Most photons curve back in, except those that fly straight upward, which become infinitely redshifted, thereby disappearing.
What happens in a Binary Pulsar (NS + NS, and NS + Star)?
NS + NS: Some pulsars exist as part of a binary. Many binary pulsars pull mass onto themselves from their companions. This infall causes the pulsar to speed up. As a result, some pulsars spin nearly a thousand times per second and are called millisecond pulsars. NS + Star: Some pulsars have compact massive companions, which are often also neutron stars. Observations of binary pulsars with neutron star companions reveal that the two bodies are spiraling toward each other as predicted by Einstein's general relativity theory. The theory also predicts that these two pulsars should be precessing (the directions that their rotation axes point should be changing). Gas from the filled Roche-lobe flows onto the NS. H fuses to He on the surface of NS. He explodes, and then BAM → strong X-ray beams. Same as nova but with a NS, instead of a WD.
When is Neutron degeneracy insufficient? What does it mean? What happens then?
Neutron degeneracy is insufficient when the mass of the star exceeds the Oppenheimer-Volkov limit (3 solar mass). Above this limit, neutron degeneracy pressure cannot support the overbearing weight of the star's matter pressing in from all sides. What happens: A, Neutron stars just above the limit may become quark stars. When pressure on them is great enough, neutrons can become so compressed that they dissolve into their constituent quarks. Quarks obey the Pauli exclusion principle (identical quarks cannot occupy the same place at the same time). So, quarks create a pressure that resists collapse creating quark stars. B, If the remnant core from a supernova is above the mass limit of neutron stars, then it may collapse into a black hole. If the stellar corpse has slightly greater than 3 solar mass, so much matter becomes crushed into such a small volume that the repulsion created by the Pauli exclusion principle on its neutrons is overcome. The remnant therefore collapses further and the escape velocity exceeds the speed of light. Nothing can travel faster than light, therefore nothing can leave such a collapsed object → tada! black hole.
What is a Neutron star? What's it made of? How large is it? How dense? How large can it get?
Neutron stars are compact objects that are created in the cores of massive stars during supernova explosions. The core of the star collapses, and crushes together every proton with a corresponding electron turning each electron-proton pair into a neutron. The neutrons, however, can often stop the collapse and remain as a neutron star. They're made entirely of neutrons. They are 200 million times denser than matter found in a white dwarf. 1 tbs of wd weighs 5 tons, while 1 tbs of ns weighs 1 billion tons. A 2 solar mass neutron star would have a diameter of only 20km (12 mi) and would fit inside any major city on Earth. It can get as large as 3 solar mass (minimum: 1.4 solar mass).
What is Neutron-Degeneracy? What does it mean to be in that state? What object is?
Neutrons in neutron stars are in this neutron-degeneracy state. Quantum mechanics restricts the number of neutrons that can have low energy. Each neutron must occupy its own energy state. When neutrons are packed together, as they are in a neutron star, the number of available low energy states is too small and many neutrons are forced into high energy states. These high energy neutrons make up the entire pressure supporting the neutron star. Because the pressure arises from this quantum mechanical effect, it is insensitive to temperature, i.e., the pressure doesn't go down as the star cools. Similar to electron degeneracy pressure but, because the neutron is much more massive than the electron, neutron degeneracy pressure is much larger and can support stars more massive than the Chandrasekhar mass limit.
What is a Pulsar? How was it discovered?
Pulsars are spinning objects, rotating tens, hundreds, or thousands of times/sec. They are actually rotating neutron stars. It was discovered by a Cambridge student, Jocelyn Bell, who detected regular pulses from one particular location in the sky through the radio telescope she was using.
What is Sgr A*? How large is it? What does it do?
Sgr A* powerful radio and X-ray source
What is the difference between a sidereal and synodic year?
Sidereal is in respect with the stars and synodic is in respect with the sun.
What type of star is a Luminous Supergiant? (what was it on the main sequence)?
Stars that are more massive than 8 solar masses become luminous supergiants through a series of fusion reactions.
What does the Galactic center look like? What's in it?
The Galactic center is an interesting place As we go in, more stars occupy space (a given volume) A million stars as bright as Betelgeuse near the center At the very center, lots of IR emission A grouping of powerful radio sources Hot and ultrahot gas, rapidly moving objects, SNR At the very center is the Galactic nucleus Sgr A* powerful radio and X-ray source - Supermassive Black Hole
How are things moving in the various parts of the Galaxy? How long does it take the Sun to circle the disk? What kind of rotation do we see in the Galaxy?
The Galaxy is a dynamic place Everything - gas and stars - is constantly moving - Disk revolves around the galactic center - Stars in the bulge revolve in a different way - Halo Stars pass through the Disk and back Stars at different distances from the center move in different speeds Differential Rotation The Sun takes ~ 230 mega years to complete one revolution around the galactic center The Sun also goes up and down, passing through the disk every ~ 33 mega years Differential rotation as we go out from the center, stars move more or less with the same speed stars further in complete a rotation more quickly Far from the disk's center, we expect stars to move more slowly, due to Kepler's Third law The opposite is happening
What was created during the Big Bang? How long ago was it?
The Hypothesis is a basis for a scenario of how the Universe developed, explaining various observations
What is the event horizon? What happens there?
The event horizon is the spherical boundary separating the black hole from the outside. What happens there: When an object reaches the event horizon, it disappears. What is theorized is is that the singularity's gravitational pull is so massive that molecules are broken up into the smallest sub-atomic particles. Everything basically "dematerializes" at the event horizon, creating the dark region that we see. More answer: What's special about an event horizon is that once anything, matter or even light, passes beyond the event horizon, it can never escape from the black hole, and will continue falling towards the center of the black hole, which is called a singularity. This is because at that point, the gravitational field of the black hole is so strong that nothing, not even light, can reach the escape velocity necessary to leave the black hole. Because of this, it's impossible to get any information out of a black hole, so we can't really know what's beyond an event horizon
What is the latest supernova we could readily observe (the one discussed in class)?
The latest supernova we can observe is SN 1987A. It was discovered in the Large Magellanic Cloud galaxy in 1987. It's exciting because it gave astronomers a rare opportunity to study the death of a nearby massive star using modern equipment, allowing them to test the Stellar Structure theory.
Why is the Neutron star spinning and why is it pulsing? What do we end up seeing?
The neutron star spins because of conservation of angular momentum. The rotation rate of collapsing stars increases, because the total amount of angular momentum in an isolated system always remains constant. To conserve angular momentum, the core of a high-mass main sequence star rotating once a month, spins faster than once a second when it collapses to the size of a neutron star. Neutron stars pulse because they have very intense magnetic fields. The magnetic field of a neutron star is very concentrated, the same way as stalks of wheat in a field become concentrated when you gather them in a bundle. As the neutron star rotates, its powerful magnetic field rapidly changes direction. The star creates intense electric fields, which act on protons and electrons near its surface. The powerful electric fields channel these charged particles, causing them to flow out from the neutron star's polar regions. As the particles stream along the field, they accelerate and emit energy. The result is two very thin beams of radiation that pour out of the neutron star's north and south magnetic polar regions and sweep through space - a pulsar.
What's left after a Supernova? What happens to the outer shells? The core?
The outer layers of the star are blown off in the explosion, leaving a contracting core of the star after the supernova. The shock waves and material that fly out from the supernova can cause the formation of new stars. There are many beautiful images of supernova remnants, the expanding shell of gas made up of the outer layers of the original star. What happens to the star after the supernova depends on how big it was to begin with. If the star was only a few times bigger than the Sun, the core will shrink into a tiny neutron star only a few miles across. If the star was much bigger than the Sun, the core will shrink down to a black hole.
What is differential rotation?
The rotation of a body in which different parts of the body have different periods of rotation. This is true of the sun, Jovian planets, and the disk of the galaxy.
3. How long is the life of a red dwarf? Why? How do they die?
They remain on the main sequence for trillions of years - much longer than the current age of the universe - because fusion in the cores of red dwarfs is so slow. The fusion progresses very slowly due to the low temperatures in the dwarf's core. - remain in main sequence for trillions of years - fade out (die) when Hydrogen is depleted - low mass star- .08m-.4m
what are the two types of Black Holes we talked about?
Two types of black holes: Nonrotating: Schwarzschild black hole. A nonrotating black hole has only two notable features: its singularity and its boundary. Its mass, called a singularity because it's so dense, collects at its center. Rotating: Kerr black hole. The singularity of a Kerr black hole is located in an infinitely thin ring around the center of the hole. There is a doughnut-shaped region, called the ergoregion, just outside the event horizon, in which nothing can remain at rest. Space in the ergoregion is being curved or pulled around by the rotating black hole (chocolate in blender example).
Where do Supernovae happen in the galaxy? Are they frequent events? How do we find their remnants?
Vigorous stellar evolution in our Milky Way occurs primarily in the Galaxy's disk, because stars there continue to form in the giant molecular clouds. There should be about 5 supernovae exploding in our galaxy each century. Many supernova remnants in our Galaxy can be detected only at nonvisible wavelengths, ranging from X rays through radio waves. Radio searches are more fruitful than visual searches. More than 3100 remnants in our Galaxy and in others have been discovered by radio astronomers.
How do we know Black Holes exist? What are X-ray Binaries and what do they have to do with BH?
X-ray binaries are a class of binary stars that are luminous in X-rays. The technique for detecting black holes formed from collapsing stars is based on the interaction between the black hole and its binary companion. When one star in a close binary becomes a black hole, its gravitational attraction pulls off some of its companion's atmosphere. However, such black holes have diameters of only a few km, so there isn't enough room for all the gas to go straight in → accretion disk (like water swirling around a drain).. Magnetic fields in the disk help pull debris inward. Calculations reveal that this gas is compressed and thereby heated so much from the collisions of its particles that it gives off X rays.
What is dark matter? What are MACHO?
the as yet decided undetected matter in the universe that is underluminous and different from ordinary matter Massive Compact Halo Objects - MACHO
What is the Hubble Law? What does it mean?
the farther away you are, the faster you move away from us: × 2 the distance × 2 the speed This "Flow" of galaxies applies to Superclusters and a bit less to clusters The Hubble Law recessional velocity=Ho x difference H0 = 73.8 km/sec/Mpc is the Hubble Constant
