Seven Brightest Objects in the Sky Study Guide

Seven brightest objects in the sky o Sun o Moon o Mars o Mercury o Jupiter o Venus o Saturn Androcentric: man is the center of the universe Geocentric: Earth is the center of the universe Age of universe: 14 billion years Age of sun: 5 billion years Age of earth: 4.5 billion years # of years humans have been around: 100,000 years There are 100 billion stars in the Milky Way The term galaxy comes from the Greek word “galaxias” meaning milky circle The name of our cluster of galaxies is called a supercluster, which contains 70 galaxies In 1929, Edwin Hubble proposed the idea that the universe was expanding o Said that all galaxies outside the local group are moving away from us, and the farther away they are, the faster they’re going Einstein’s E=mc^2 concerns energy and mass; energy has been transformed into mass AU is an astronomical unit, distance between earth and sun o 1 AU = 1.5 x 10^11 = 150 million km o Jupiter lies about 5.2 AUs from the sun o Mars is about 1.5 AU from the sun o 0.01 AU between Earth and moon Humans → Earth → solar system → Milky Way → local group → local supercluster Gravity keeps stars, planets, and galaxies in motion Dark energy keeps the universe expanding o Dominant form of energy in the universe Hydrogen and helium are the two lightest elements in the universe, which represent 98% of the solar system o Sun is made up of these elements o Formed from the Big Bang Carbon, oxygen, gold, and other heavy metals come from an explosion of stars known as a supernova Light is electromagnetic radiation o Radio waves o Infrared o X-ray o Ultraviolet Light year: distance light travels in one year o Speed of light is C = 3.0 x 10^8 m/s o 10 trillion km o Diameter of the Milky Way is about 100,000 light years Sirius, which is 8 light years away, is the brightest star in the sky Andromeda is the closest galaxy, which is 2.5 million light years away Speed of a planet’s rotation = 1000 km/hr Speed of a planet’s revolution = 100,000 km/ht Speed of sun = 70,000 km/hr Speed of galaxy = 300,000 km/hr Dark matter affects the motion of objects moving in that region; not many stars; located in the halo of the galaxy There is no center of the universe because everything is equally spread out The raisins in a cake model explains the expansion of the universe o Place raisins 1 cm apart from each other o The raisins spread during baking o Farthest things move fastest The farthest galaxy that modern telescopes are capable of seeing are up to 10 billion light years away Expansion of the universe suggests that Dark Energy is present The stars visible just after sunset are different from those visible just before sunrise because Earth rotates once a day No one on Earth can see the constellation Orion in June because Earth revolves around the Sun once each year The stars of Orion’s belt rise in the east and set in the west because Earth rotates once a day The solar system is located halfway between the center and edge of the visible disk of the galaxy Galaxy: a collection of a few hundred million to a trillion or more stars, bound together by gravity Stars made most of the oxygen nuclei in the solar system Big Bang: the event that marked the beginning of the expansion of the universe When we say the universe is expanding, we mean that the average distance between galaxies is increasing with time Nuclear fusion: the process of combining lighter weight nuclei to make heavier nuclei Sun and Earth formed in September The moon orbits the Sun once a year The patterns of the stars in our sky look the same every year because the stars in the constellations are so far away It takes one year for Earth to complete one orbit around the sun It takes 230 million years for the solar system to complete one orbit The distribution of the mass of the Milky Way is determined by studying the rotation of the galaxy The solar system travels 170,000 light years in one orbit Solar system is moving toward the star Vega at 70,000 km/hr Constellations are a group of stars that form a pattern o Constellations change because stars move o A region in the sky as seen from Earth 360 degrees in a circle 60 arcminutes in a degree 60 arcseconds in an arcminute 3,600 arcseconds in a degree Polaris, the North Star, can be found above the North Pole o Will no longer be the North Star in 1,000 years because of Earth’s precession Earth’s axis causes the seasons o If Earth had no inclination, seasons would be very extreme and the sun would always be on the horizon at the poles Precession - rotation of axis; 26,000 years per cycle Everything rises in the east because of the Earth’s counterclockwise rotation o The moon rises in the east and sets in the west because Earth rotates once a day Full moon o Rises at 6pm o Max at midnight o Sets at 6am Waxing gibbous o Rises at 3pm o Max at 9pm o Sets at 3am 1st quarter o Rises at noon o Max a 6pm o Sets at midnight Waxing crescent o Rises at 9am o Max at 3pm o Sets at 9pm New moon o Rises at 6am o Max at noon o Sets at 6pm Waning crescent o Rises at 3am o Max at 9am o Sets at 3pm 3rd quarter o Rises at midnight o Max at 6am o Sets at noon Waning gibbous o Rises at 9pm o Max at 3am o Sets at 9am All moons except full and new can be seen during the day Requirements for solar eclipse include new moon and node, for lunar eclipse include full moon and node o Sun, Earth, Moon must be nearly perfectly aligned Three types of solar eclipses are total, partial, annular In order for there to be a total eclipse, the Moon’s umbra must touch the area where you are located Saros cycle is the predicting of a solar eclipse o Each cycle lasts for 18 years and 11 ⅓ days o The next solar eclipse in the US is April 8th 2024 Retrograde motion is the apparent reversed motion of an object o Mars has caused the most controversy  When this happens to Mars, Earth is catching up with and passing by Mars in their respective orbits o Happens when Earth passes another planet, then the planet appears to move backward with respect to the background stars. But this is apparent as the planet’s true motion has not changed o Sun never goes through this Parallax refers to the fact that objects appear to be in different positions from different perspectives o A parallax angle of 1 second represents a distance of 3.26 light years o The closer the star is to us, the more parallax it exhibits o The farther a star is to us, the less parallax it exhibits Stellar parallax is the slight back-and-forth shifting of star positions that occurs as we view the stars from different positions in Earth’s orbit of the sun Certain constellations are visible in the evening only at certain times of the year because our evening view of space depends on where Earth is located in its orbit around the sun 2,000 stars are visible to the naked eye on a dark, clear night The point directly over the head is called the zenith If we have a new moon today, the next full moon will be in two weeks The Greeks rejected the idea that the Earth orbits the Sun because they could not measure a change in stars’ positions on the sky Celestial sphere o Earth is placed at the center of this o When we look in the sky, the stars all appear to be located on this o Does not physically exist o Process of science has 4 parts: o Observation o Interpretation o Measurement o Formulation Julius Caesar suggested the idea of having a leap year every four years Gregorian calendar o Named after Pope Gregory XIII who suggested that 5 days needed to be removed from the calendar, so October 5-10 were taken off Three aspects of ancient Greek science o Mathematics o Understanding the supernatural without gods and goddesses o Observation and reasoning Ptolemy explained the retrograde motion of planets by explaining that Mars moves in 2 circles, one around itself and one around the sun Ptolemy had the planets orbiting the Earth in perfect circles in his model of the universe to explain that planets sometimes appear to move westward, rather than eastward, relative to the stars in our sky The Big Three of the 16th century revolution in astronomy o Copernicus  Born in Poland  Learned the tables of planetary motion based on Ptolemaic model were inaccurate, so he wanted to find a better way  Sun-centered model for retrograde motion to determine the layout of the solar system  Copernican model didn’t work because it still used perfect circles o Tycho Brahe  Compiled the most accurate 1 arcminute with naked eye measurements  Still could not detect stellar parallax, still thought Earth was center of solar system  Hired Kepler  Recorded a nova, a bright star that appeared one evening and lasted for 18 months  May have solicited funds from wealthy donors to support science o Kepler  First tried to match Tycho’s observations with circular orbits  Kepler’s predicted positions differed from Tycho’s observations by only about 8 arcminutes, which led him to abandon the idea of circular orbits  Discovered the orbits are ellipses, which have foci, major/long axis, semimajor axis, minor/short axis, and eccentricity  Could not predict Mars’s orbit, which led him to consider an ellipse for orbit Galileo o Earth could not be moving because objects in air would be left behind o Noncircular orbits are not as perfect as heavens should be o If Earth were really orbiting the sun, we’d detect stellar parallax o Challenged the idea that objects in the heavens were perfect by observing sunspots on the Sun and mountains on the moon Kepler’s three laws o Planets move in an ellipse with sun at 1 focal point o Planets sweep out equal areas in equal time o P^2 = a^3; more distant planets orbit the sun at slower speeds  P = period, time of the cycle or year  A = average distance between sun and planet; AU units  Venus orbits the Sun at a slower average speed than Mercury  If a planet were discovered with an average distance from the sun of 100 AU, its period would be 1000 years  A planet that is twice as from from the Sun as Earth should have a period of more than 2 Earth years An asteroid with an orbital period of 8 years lies at an average distance from the Sun equal to 4 AU # of stars known with time o Ancient times: 1,000 o 1600: 2,000 o 1712: 3,000 o 1918: 250,000 o Now: 16 million During the European Dark Ages, the scientific work of the ancient Greeks was preserved and further developed by scholars in Baghdad, Iraq The Muslim fast of Ramadan occurs during the ninth month of the lunar calendar, between new moons The Mediterranean and the Middle East is the part of the world that led to modern science which emerged from ancient civilizations The ancient goal of astrology was to predict future events affecting nature and people The ancient Greeks were the first people known to try to explain nature with models based on reason and mathematics, without resort to the supernatural Earth is moving fastest in its orbit during the winter because it is closest to the sun Perihelion: planet is closest to the sun, moving fastest Aphelion: plane is farthest from the sun, moving slowest Jupiter has the Galilean moons If Venus is in its full phase, then Earth would also be in its full phase Within the past 500 years, humans first learned that the Earth is not the center of the universe Four fundamental forces o Gravity o Electromagnetic o Strong nuclear o Weak nuclear Vector: magnitude, direction o Example: o Velocity Scalar: magnitude, temperature o Example: o Speed Velocity: change (displacement) over time Difference between speed and velocity Acceleration = change in velocity / change in time Change in acceleration / change in time is called jerk Centripetal acceleration is acceleration directly toward the center when spinning in a circle o Orbital motion results from this Force = mass x acceleration Newton’s universal gravitation equation is Fg = Gm1m2 / R2 Mass is the same anywhere in the universe, but weight changes depending where the body is. For example weight is different on the moon than on earth or at higher altitudes  Gravity for humans on earth is 9.8 m/s^2 and goes downward Speed tells us how far something will go in a certain amount of time Velocity tells us both speed and direction Momentum = mass x velocity The acceleration of gravity causes falling objects to fall faster by 9.8 m/s or 10 m/s with each passing second Newton’s laws o First - In the absence of a net force, an object will move with constant velocity; objects at rest tend to remain at rest o Second – what happens to an object when a net force is present; f=ma; a net force will change an object’s momentum o Third – every force is always paired with an equal and opposite reaction force Two types of planets – terrestrial and jovian Albedo = % of light reflected 3 greenhouse gases are CO2, CH4, H2O planetesimal – accumulation of mass, few km in diameter, dust, rocks, pebbles protoplanets – keep getting bigger, takes a billion years, bigger than planetesimal convection – hot interior comes to surface and cools down metal and fast rotation help determine if a planet will have a strong magnetic field  which protects us from charged particles from the sun jovian planets are large planets, are orbited by many moons and rings, and have fast rotation Uranus and Neptune are blue because of the presence of Methane Jupiter and Saturn are made mostly of hydrogen and helium, while Uranus and Neptune are made mostly of hydrogen compounds/rock as well as hydrogen and helium Over 160 moons orbit the Jovian planets Small moons have no geological activity, medium have it in the past, large have it ongoing Sun o Radius = 108x radius of Earth and mass = 333,000x mass of Earth o Composition = Hydrogen and helium o Sun spots = cooler regions o Solar flares = releases of gas from sun o Solar wind = particles from sun o Pressure and temperature highest at the core at 10^ K o Each second, 600 tons of hydrogen  transformed by fusion into 596 tons of helium  leaves 4 million tons of mass converted into energy Mercury o Made of metal and rock; large iron core, desolate, cratered o Not much atmosphere o Very hot during the day (425 degrees C) and very cold at night (-170 degrees C) o 0.39 Au from the sun o radius is 0.38 radius of the earth, mass is 0.055 mass of earth o inclination at 0.0 degrees, albedo at 0.06, eccentricity is 0.206 o year 88 days, day 58.6 days Venus o 470 degrees C day and night o nearly identical in size to Earth o surface hidden by sulfuric clouds o hellish conditions due to an extreme greenhouse gas effect; presence of volcanoes o 0.72 Au from the sun o radius is 0.95 radius of earth, mass is .082 mass of earth o inclination at 177.3 degrees; no seasons o sun rises west o year is 224.67 days, day is 116.8 days o eccentricity is 0.007 Earth o Only surface of liquid water in solar system o Surprisingly large moon o Pangaea – all continents were together at some point o Core – highest density, center, iron and nickel o Mantle – medium density, rocky material o Crust- lower density, rock, surface o Lithosphere – coolest edge of the mantle o Impact cratering – meteor crater from asteroids, erosion destroys original crater o Volcanism – when molten rock (magma) finds a path thru lithosphere to the surface; called lava after it reaches the surface o Tectonics – structure of the crust; breaking of plates  earthquakes o Erosion – weather that destroys the surface like ice, wind, water o 77% nitrogen, 21% oxygen, 2% other The Moon o Some volcanic activity 3 billion years ago must have flooded lunar craters, creating the Lunar Maria o Now geologically dead o 17% of the surface is Lunar Maria o 83% of the surface is highlands, which are heavily cratered Mars o 0.107 mass of Earth, 0.53 radius of earth, eccentricity of 0.1 o 1 year = 1.88 earth years; 1 day = 24 hours 39 minutes o mainly rocks and minerals o habitat like an Earth desert o liquid H2O once present  now dried up riverbeds o giant volcanoes, huge canyons, polar caps o atmosphere is 90% CO2 o seasonal winds create huge dust storms o two moons are Phobus and Deines, which are captured planeteismals o inclination at 23.45 degrees  seasons Jupiter o 5.2 AU from the sun o mass is 318x mass of earth, density is 1.33 g/cm^3 o mostly hydrogen and helium o ammonium sulfide clouds reflect red and brown light o Great Red Spot – storm twice as big as Earth, has existed for at least 3 centuries o Ammonia, highest and coldest layer, reflects white o 1 day = 10 hours o core of rock, metals, metallic hydrogen Moons of Jupiter o Io  Size of our moon  Most volcanically active object in the solar system  heat because of tidal heating, which refers to when orbit energy is dissipated as heat in either the surface or interior of a planet; moon creating friction from squishing and stretching o Europa  Covered by H2O ice  Twice as much water than on Earth o Ganymede  Largest moon in solar system  Clear evidence of geological activity  Tidal heating  Craters and smooth regions  Water/ice surface o Calisto  Cratered ice ball   No tidal heating Magnetic field Saturn o 9.54 Au from sun o mass 95x mass of earth, density is 0.71 g/cm^3 o mostly hydrogen and helium o core of rock and metals o giant and gaseous; has rings o 1 day = 10.5 hours o Cassini spacecraft currently studying it o Rings are divided into categories of A, B, and C o Rings are ice coated particles Saturn’s Moon Titan o Only moon with a thick atmosphere o Consists of mostly nitrogen with some argon, methane, and ethane o Methane and ethane rain o Rocks made of ice Uranus o Core of rock and metals, water, methane, ammonia o lower pressure  no metallic hydrogen o made of H/He gas and hydrogen compounds o inclination at 97.86 degrees because something hit it o 1 year is 84 earth years o albedo is 0.66 o 27 moons o blue because of methane presence; absorbs red light and reflects blue light Neptune o Core of rock and metals, water, methane, ammonia o Lower pressure  no metallic hydrogen o Mathematically discovered o Inclination at 29.56 degrees o 1 year is 164.8 earth years o Triton, its moon, rotates backwards  it has recent volcanic activity Comet – chunk of ice with some rock inside, originates from Pluto Asteroid – rocky leftover planetesimal, smaller are more common, Ceres is largest, smaller than 2km in diameter Meteoroid – smaller asteroid, from boulder to pebble size Meteor – flash of light of a meteoroid burning in the atmosphere Meteorite – meteor that hits Earth and survives Asteroid belt is between Mars and Jupiter No terrestrial planets past Mars because of the high magnetic field and gravitational pull in the outer solar system Two types of meteorites o Primitive – simple rock and metal, 4.6 billion years old, remnants of early solar system o Secondary/processed – pieces of the mantle or crust, parts of a planet, some iron, 100 million years old, volcanic activity Comets o Coma – comet itself, atmosphere that comes from heated nucleus o Tails  Plasma – gas escaping coma, pushed by solar wind  Dust – pushed by photons Oort cloud – comets on random orbits extending to about 50,000 AU Kuiper belt – closer than oort cloud, where Pluto is, comets on orderly orbits at 30-100 AU, in disk of solar system Pluto o Moons are Charon, Hydra, Nix o Orbit is tilted and very elliptical o Not terrestrial nor jovian o Made of ice and rock o Mass is 0.002 mass of earth o Eccentricity at 0.25 o Inclination at 17 degrees o Big comet o Eris brought on the farewell o Dwarf Eris o Twice as far from the sun as Pluto o 5% bigger in size, 27% more mass o moon is Dysnomia o dwarf Iridium layer – thin layer containing iridium, deposited 65 million years ago, rare for Earth but common for asteroids, layer below has dinosaur remains When the comet/asteroid hit earth 65 million years ago, 99% of organisms died Of that 1% that survived, 75% went extinct Those mammals that survived lived underground and ate decayed material from before, known as subterranean mammals Jovian planets attract comets and large asteroids but could shoot bigger ones toward us faster Plasma refers to charged particles giving off light, such as lightning Parts of the sun o Solar wind – charged particles o Corona – sun’s outer atmosphere, source of sun’s x-rays, seen during a total solar eclipse o Chromosphere – middle layer of atmosphere where UV radiation takes place o Photosphere – sun’s visible surface, 6000 Kelvin, where sunspots are seen o Convention zone – energy transported by gas upward o Radiation zone – where photons move outward o Core – 10-15 million Kelvin, where nuclear fusion occurs o Core  radiation zone  convention zone  photosphere  chromosphere It takes hundreds of thousands of years for nuclear energy of the core to reach the surface Three scientific techniques to figure out what’s happening in the sun o Mathematical models o Solar vibrations o Neutrino observations Sunspots – regions of intense magnetic fields and cooler temperatures Solar prominences – gas and particles from chromosphere Solar flares – undergo change  particles move outward, high in x-rays A coronal mass ejection is a release of plasma and magnetic field from the corona, following solar flares and occur during a solar prominence; eruptions from the Sun’s surface o CMEs can be bigger than Earth o Most that hit Earth do not have an impact because they’re small o A huge one can setback human progress with technology because general electricity would be wiped out The sunspot cycle is 10-11 years The causes of sunspots include: o Magnetic field convection  magnetic field brought to surface o Magnetic field rotation  faster at the equator, stretches and bends magnetic field A star is 75% hydrogen and 25% helium Luminosity is the amount of power energy per time, and it’s measured in watts Apparent brightness is how bright the star is on Earth, measured in b for brightness Brightness = luminosity / pi x d^2 the luminosity of the sun is 3.9 x 10^26 w the Greeks rated stars based on their brightness from 1 to 6, 1 being the dimmest and 6 the brightest apparent magnitude is observed brightness from earth (m) absolute magnitude is the apparent magnitude if the star is at a distance of 10 parsecs the spectral type listing from hottest to coolest star is OBAFGKM (oh be a fine girl kiss me) the sun is a G star three types of binary stars o visual – 2 stars seen by a telescope o eclipsing – light is reduced when one star passes in front of other o spectrotropic – blue/red shifts  blue is getting hotter and moving toward us, red is getting cooler and moving away from us types of stars o giants/supergiants – large in radius and luminosity o main sequence – fusion of hydrogen into helium in core, more common, lives longer lives o white dwarf – leftover core, smallest, hot but less luminous stars along the main sequence are fusing hydrogen and helium in their cores stellar masses decrease as a star moves down the main sequence Star A. B. C. D. E. low mass stars are more common than high mass stars and live longer star clusters are useful to study because: o they are the same distance from Earth, all in the same place in the sky o all stars in cluster formed at the same time two types of clusters o open – found in the disk of the galaxy, young stars, several thousand, more energetic, hot and blue; example is Piedes o globular – found in the halo , several hundreds, older, tired and red Mv mv Spectral type Luminosity class Spica -3.6 +0.9 B1 V Antares -4.5 +0.9 M1 I Sirius +1.4 -1.4 A1 V Cen A +4.4 0.0 G2 V Aldebara -0.2 +0.9 K5 III n Antares has the greatest luminosity, looks reddest in color, is most distant, has lowest surface temperature, has largest radius Sirius looks brightest in the sky, looks bluest in color Spica emits the most UV light per unit area, has the highest surface temperature Cen A is most similar to the sun mv – Mv = distance m – M > 0  close, negative number m – M < 0  far, positive number Hubble Space Telescope used a reflection based telescope and is based in space where there is little light pollution and atmospheric turbulence that would have caused stars to twinkle The frost line is the distance in the solar nebula from the central protostar where it is cold enough for hydrogen compounds to condense into solid ice An infrared photon has less energy than an x-ray photon, but travels at the same speed Longer wavelengths means lower frequency and lower energy Doppler effect o Frequency of sound is higher on approach o Frequency of sound is lower on departure o Wavelength of light is lower when coming toward o Wavelength of light is higher when moving away Everything looks red through a red filter because the filter transmits red light and absorbs other colors A star emitting visible light is hotter than a star emitting infrared light Stefan-Boltzman Law – hotter objects emit more intense light per area Wien’s Law – hotter objects emit photons with higher energy Nuclear fusion occurs in the sun’s core Asteroids appear as straight lines across a background of stars in long exposure images Nitrogen is the most abundant gas in Titan’s atmosphere Jupiter’s strong magnetic field is generated in the metallic hydrogen layer Pluto’s mountains must be made of water ice Small asteroids aren’t spherical because the force of gravity is less than the resistance of rock to deform The plasma tail always points directly away from the sun Comets with very long orbital periods come from the Oort cloud Comets are frozen balls of ice and dust The Huygens spacecraft landed on Titan Saturn’s rings are water ice Most photons that leave the Sun’s surface lie in the visible region of the electromagnetic spectrum Sun generates energy via nuclear fusion Neutrinos formed in the early universe before atoms could form; they are continually being produced in the nuclear reaction of stars and Earth 3% of the total energy of the sun is in the form of neutrinos only 1/3 of the expected neutrino count is observed because electron neutrons can turn into muon neutrinos, meaning they can turn into each other Birth of a star needs: o Gravity - 10^7 K needed for fusion in the core o Equilibrium of:  Outward  Inward Best places for stars to form are clouds of dust that are cold (10-30 K) and dense Stars are formed in clusters protostar - a star that has not finished forming; not enough mass for fusion o Two parts  Disk - collisions cause gas to form this; spins, goes thru angular momentum  Jets - gas and particles are ejected from the star Massive stars live shorter lives because fusion temperature is higher in a massive star, so it burns out faster o Sun is a low-mass star A star is less massive than 8% of the mass of the Sun. It does not have enough gravitational compression to start fusion and typically becomes a brown dwarf Masses of newborn stars have a lower limit of 0.08 (mass of the Sun) and an upper limit of 300 (mass of the Sun) Electron/neutron degeneracy pressure - particles can’t be in the same state in the same, not depending on the heat content Low mass stars have a mass of less than 2 (mass of the Sun) Steps of the red giant stage o Outer layers expand → more solar wind o Core actually compresses → becomes helium Process of the death of a low-mass star o Becomes a white dwarf → leftover core converted to carbon o Planetary nebula o White dwarf can become a black dwarf with a large amount of carbon Typical size of a Red Supergiant is hundreds of times the size of the Sun Equation for helium core fusion o 3 4/2 He → 12/6 C Helium flash - when the core becomes helium; the core quickly heats up and expands as helium fusion begins all at once throughout the core Planetary nebula - expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star CNO cycle - high-mass main-sequence stars fuse hydrogen to helium at a higher rate using carbon, nitrogen, and oxygen as catalysts; a greater core temperature enables hydrogen nuclei to overcome greater repulsion; hydrogen fusion proceeds in high-mass stars A star becomes a supergiant by Iron is unique because it’s the highest element by fusion, but lowest by fission; it cannot release energy by either fission or fusion What happens to the iron core? A high mass star can end its life in three ways, which are white dwarf (highest mass), neutron star, and black hole (lowest mass) The typical luminosity of a supernova is 10^11 luminosity of the Sun Life of a main-sequence star o ←-0.1-----------1-------------10--------------100-------> (mass) ------------------main-sequence stars--------------------Red giant supergiant Planetary nebula supernovae White dwarf neutron star black hole ------------0.5------------------3--------------------10-------A low-mass star like the Sun leaves behind white dwarfs at the end of their lives Characteristics of a white dwarf o higher mass white dwarfs are small because of gravity Hot when it first forms because it was recently inside a star, slowly cools with time o High density o Large in mass, small in size → so gravity is very strong near the surface o No fusion to maintain heat and pressure inside, so pressure that opposes gravity must come from degeneracy pressure  Degeneracy pressure in white dwarves comes from closely packed electrons  A white dwarf exists in a balanced state because the outward push of electron degeneracy pressure matches the inward crush of gravity Source of a white dwarf’s stability Chandrasekhar Limit - as white dwarf approaches 1.4M of the sun, electrons must move at nearly the speed of light (impossible); if it reaches it, it explodes o Also known as the white dwarf limit o “The electron speeds would reach the speed of light in a white dwarf with a mass of about 1.4 times the mass of the sun. Because neither electrons nor anything else can travel faster than the speed of light, no white dwarf can have a greater mass than the sun.” White dwarf supernovae are important because they’re used to measure the expansion of the Universe How do white dwarf supernovae come about? Two types of supernovae o Type I - no hydrogen line (spectra)  Type 1A - white dwarf supernovae Carbon fusion suddenly begins as white dwarf in close binary system reaches white dwarf limit, causing a total explosion  Type 1B, 1C Iron core of massive star reaches white dwarf limit and collapses into a neutron star, causing an explosion o Type 2 - hydrogen line (spectra)  Type IIP, IIN, IIL Neutron stars - a ball of neutrons created by the collapse of the iron core in a massive supernova. They are dense with an incredibly high gravitational pull o Neutron degeneracy pressure for neutron stars, instead of electron degeneracy pressure for white dwarves, because neutrons are closely packed In 1967, Jocelyn Bell detected radio pulses (radio-astronomy) of a period of 1.337301 seconds. At first, they were called the LGM source named for little green men o Now referred to as pulsars Pulsars are neutron stars that beam radiation along a magnetic axis that is not aligned with the rotation axis o They sit at the center of two supernova remnants, the Vela Nebula and crab Nebula o Neutron stars that are left behind by the supernova explosions o They are neutron stars because no other massive object could spin so fast A red giant is cooler and brighter o Helium fusion results in the production of carbon Stars that are at least several times the mass of the Sun end their lives with supernovae Iron has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission 3 helium nuclei fuse together when making carbon Brown dwarf located at the right lower corner of the H-R diagram; cool and dim Gas between the stars is the interstellar medium The closest supernova in the last 4 centuries was seen in 1987, known as Supernova 1987A Can’t see large or small magellenic clouds in the northern hemisphere Nuclear fusion and gravitational contraction are the two processes that can generate energy to help a star maintain its internal thermal pressure The cloud must radiate much of its thermal energy so that a gravitationally collapsing cloud can continue to collapse A main-sequence star is hotter and dimmer than it when it was a protostar The protostar is brighter than the main-sequence star because it is much larger in radius When a large molecular cloud gives birth to a cluster of stars, a few massive stars will form, live, and die before the majority of the star’s clusters complete their protostar stage Brown dwarfs outnumber all ordinary stars H-R diagrams of globular clusters provide evidence to help understand the life tracks of low-mass stars A 1 solar-mass red giant is more luminous than a 1 solar-mass main-sequence star because fusion reactions are producing energy at a greater rate in the red giant Carbon fusion occur in high-mass stars but not low-mass because the cores of low-mass stars never got hot enough for carbon fusion Heavier elements require higher temperature for fusion The sudden collapse of an iron core into a compact ball of neutrons marks the beginning of a supernova If the star Betelgeuse were to supernova tomorrow as seen from Earth, it would remain a dot of light but would suddenly become so bright that, for a few weeks, we’d be able to see this dot in the daytime Elements with atomic mass numbers divisible by 4 (oxygen 16, neon 20, magnesium 24) are more abundant in the universe because at the end of a high-mass star’s life, it produces new elements through a series of helium capture reactions A spinning neutron star has been observed as the center of a supernova remnant Planetary nebula formation is more common than a star blowing up as a supernova You discover a binary star system in which one star is a 15 M main-sequence star and the other is a 10 M giant. A star system like was created as the giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion The interstellar clouds called molecular clouds are the cool clouds in which stars form Sun Sun Most interstellar clouds remain stable in size because the force of gravity is opposed by thermal pressure within the cloud The infrared part of the EM spectrum gives us our best views of stars forming in dusty clouds A cold, dense gas cloud is likely to give birth to stars 10 million K is required before hydrogen fusion can begin in a star A 1 solar mass star spends the longest time in the protostellar phase of life Brown dwarfs o Are supported against further gravitational collapse by degeneracy pressure o Form like ordinary stars but are too low mass to sustain nuclear fusion in their cores o All brown dwarfs have masses less than 8% that of our Sun Jets help slow the rotation rate of the protostar by carrying away some of its angular momentum About 2 solar masses separate low mass stars from intermediate mass stars Stars with masses greater than 150 times our Sun cannot form because they would generate so much energy that they would blow off their outer layers A star becomes a main-sequence star when the rate of hydrogen fusion in the star’s core is high enough to sustain gravitational equilibrium A brown dwarf will remain a brown dwarf forever A neutron star has a density higher than the density of a white dwarf The Sun formed within a large molecular cloud A close binary consists of two stars that orbit each other every few days A brown dwarf is a star so small in mass that its core never gets hot enough to sustain nuclear fusion reactions Most of the gas remaining from the process of star formation is swept into interstellar space by a protostellar wind Planets may form within the protostellar disk that surrounds a forming star A star with a mass below 0.08 has its gravitational contraction stopped by degeneracy pressure A red giant star increases in size and fuses hydrogen in a shell around its core During the red giant phase, a star’s pressure and gravity is out of equilibrium M stars are the most common When a main-sequence star exhausts its core hydrogen fuel supply, the core shrinks while the rest of the star expands Helium and carbon would require the highest temperature in order to proceed with a reaction The ultimate fate of our Sun is to become a white dwarf that will slowly cool with time A star spends 90% of its life on the main sequence When a star exhausts its core hydrogen supply, its core contracts but its outer layers expand and the star becomes bigger and brighter After the planetary nebula stage, the star becomes a white dwarf Protostar → main sequence → red giant → white dwarf : stages of life for one solar mass star Most interstellar dust grains are produced in the atmospheres of red giant stars Need to know the mass of a star to predict whether it will fuse oxygen into heavier elements in its core Low-mass stores don’t go through the CNO cycle because the core temperatures are too low Gold was produced during the supernova explosions of high-mass stars When the gravity of a massive star’s collapsing core is able to overcome neutron degeneracy pressure, the core contracts and becomes a black hole Stars that end their lives with supernovae are stars that are more massive than 8 times the mass of the Sun After a supernova event occuring in a high-mass star, a neutron star or a black hole is left behind A white dwarf is the exposed core of a star that has died and shed its outer layers in a planetary nebula Accretion ? Carbon fusion in white dwarves releases more energy than a helium flash in low-mass red giants Close binaries that contain accreting neutron stars are often called x-ray binaries Black holes o Event horizon – point of no return; edge of a black hole o Schwarzchild radius – measure of the radius of the event horizon surrounding a non-rotating black hole; depends on the mass and proportional to it o Singularity – center of black hole where gravity crushes all matter Two arguments that black holes exist o High-energy x-rays from the distant regions of space o Has to be something that holds a galaxy together Wormhole – black hole that connects to another place in the universe Hawking process – black hole emits particles and black body radiation and slowly dies; o Proceeds matter-antimatter annihilation, when a postiron comes in contact with an electron o Vacuum fluctuations cause a particle-antiparticle pair to appear close to the event horizon of the black hole Gamma ray bursts o They come from distant galaxies o They are the most powerful explosions o When found in the universe, they signify the formation of black holes Three processes that cause gamma ray bursts o Hypernova – supernova that forms a black hole o Distant galaxies forming new star o Collisions in binary systems Galaxy o Group of stars o Dark matter – spread throughout the halo o Gas and dust held together by gravity It’s difficult to study the Milky Way Galaxy because we are in it – nobody has ever seen it from the outside Until the early 20th century, scientists thought that the Milky Way was the entire universe Milky way o Spreads 100,000 light years across o Consists of disk, bulge, halo, globular cluster Galaxies in the local group o Milky Way o Andromeda o Magellenic clouds (large and small) – but these can only be seen in the southern hemisphere; they are two small galaxies that orbit the Milky Way Stars in the disk tend to be younger, move in the same direction, appear plainer Stars in the halo and bulge are older, move dramatically, have large amplitude There are no new stars in the halo and bulge because cold and dense clouds are needed for formation, but it’s too hot in these places Dark matter – consists of 25% of the universe, located in the halo o We know it is there because the orbital speed of stars in the halo is faster than expected Star dust in a galaxy tends to make the light more red because the blue light is scattered away Stars form in the spiral arms and ionization nebulae Formation of the milky way o Protogalactic cloud – huge collapsing cloud of intergalactic gas o Stars of the bulge and halo – motion not uniform because gravity was not uniform when they formed (heat is too high for new stars) o Disk flattens and spins to make young stars (angular momentum) Galactic center can be found in the constellation Sagittarius o It’s a super massive black hole in the center of the galaxy o 4 x 10^6 mass of the sun four major arms of the milky way o Sagittarius – center of galaxy, can be seen in the summer o Perseus – seen in the winter o Centaurus – not seen in visible light o Cygnus – not seen in visible light General relativity says that time-space can be warped by mass If we could view our galaxy from a distance of several hundred thousand light years away, it would look like a flattened disk with a central bulge and spiral arms Interstellar medium – the gas and dust found between the stars in the Milky Way o Prevents us from seeing most of the visible and UV light from the galactic disk The Sun is found in the galactic disk, slightly over halfway out from the center By applying Newton’s version of Kepler’s third law to the Sun’s Orbit around the center of the Galaxy, we can figure out the total mass of the Milky Way that is contained within the Sun’s orbital path On a dark summer night in the northern hemisphere, we can see the Milky Way but we cannot see the center of the Milky Way because the interstellar dust and gas absorbs and scatters visible light before it can reach us from the center Globular clusters lie in the halo of our galaxy The Sun is 27,000 light years from the center of the galaxy Orbits of stars in the halo are elliptical with random orientations It takes the Sun 200 million years to orbit the center of the Milky Way Disk stars orbit in the same plane in the same direction The circular but relatively flat portion of the galaxy is the disk The first portion of the galaxy to form was the halo A tightly packed group of a few hundred thousand very old stars is a globular cluster A spiral arm stands out in a photo of a galaxy because it shines brightly with light from massive young stars and glowing clouds of gas and dust Our Milky Way is a spiral galaxy Stars orbiting in the bulge near the galaxy’s center can have orbits highly inclined to the galactic plane The star-gas-star cycle increases the abundance of heavy elements in the Milky Way X-ray binaries, young stars, and high-mass red supergiants can be found in the disk Blue stars are found in or near star-forming clouds Spiral arms are bright because they contain more hot young stars than other parts of the disk Cosmic rays are subatomic particles that travel close to the speed of light The star-gas-star cycle is the continuous recycling of gas in the galactic disk between stars and the interstellar medium Most star formation occurs in the Milky Way All elements other than hydrogen and helium are considered heavy Low-mass stars transport newly formed elements in the interstellar medium when they form planetary nebulae Protogalactic cloud – a cloud of hydrogen and helium that contracts to become a galaxy Most stars in the halo are very old Disk stars o Youngest stars o The Sun o Stars that all orbit in nearly the same plane o High-mass stars Halo stars o Oldest stars Globular clusters Stars with the smallest abundance of heavy elements Stars whose orbit can be inclined at any angle The galaxy consists of a large, nearly flat disk with a central bulge, all surrounded by a vast halo The disk of the Milky Way is 1000 light years thick We cannot see far into the disk with visible light because our view is blocked by dark, dusty clouds Suppose that we look at a photograph of many galaxies. If all these galaxies formed at the same time, the galaxy that is farthest away is the youngest in the picture Lenticular galaxies have a disk and a spheroidal component but no spiral arms Spiral and lenticular galaxies have a clearly defined disk component Elliptical galaxies are redder and rounder than spiral galaxies Elliptical galaxies are the most massive galaxies in the universe A standard candle is an object whose luminosity we know Edwin Hubble measured the distance to the Andromeda galaxy by applying the periodluminosity relation to Cepheid (a type of standard candle) variables in Andromeda A quasar is the extremely bright center of a distant galaxy, thought to be powered by a supermassive black hole Galaxy collisions should have been more common in the past than they are today because galaxies were closer together in the past Astronomers use the Hubble constant (H) to estimate the age of the universe as the inverse of H is proportional to the age of the universe A white dwarf supernova is the most accurate way to determine the distance to a very distant galaxy Velocity and distance are the two quantities Hubble compared to discover the expansion of the universe Dark matter is dark because it emits no radiation of any wavelength Evidence for dark matter o X-ray observations of hot gas in galaxy clusters o The broad absorption lines found in the spectra of elliptical galaxies o The flat rotation curves of spiral galaxies o Gravitational lensing around galaxy clusters The expansion of the universe is not evidence for dark matter Physicists have shown that the electromagnetic and weak forces are the same force under conditions of very high temperature 10^-43 seconds after the Big Bang was Planck Time o Planck time – the time at which our current theories become completely unable to describe conditions any earlier in the universe The formation of protons happened first after the Big Bang According to the Big Bang theory, we live in a universe of matter rather than antimatter because during the first 0.001 seconds after the Big Bang, particles and antiparticles were o o o made in almost but not perfectly equal numbers. Everything annihilated except the very slight excess of matter particles The simple question posed by Olbers’ paradox is “Why is the sky dark at night?” Measuring the amount of distortion caused by gravitational lensing to determine the mass of a cluster of galaxies doesn’t depend on Newton’s law of gravity WIMPs make up the majority of dark matter Galaxies appear to be distributed in chains and sheets that surround great voids – describes how galaxies are distributed on large scales in the universe A GUT (grand unified theory) refers to theories that unify the strong force, electromagnetic force, and weak force Dark energy causes the universe to accelerate Hubble said that the further away a galaxy is, the faster it is moving away Three major types of galaxies o Spiral galaxy  Example is the Milky Way  Sa – tightly bound spiral  Sb – moderately bound spiral  Sc – loosely bound spiral  The tighter the spiral, the larger the central region o Elliptical galaxy  Orange, cooler, football shaped, old stars, more common in huge clusters  No disk  E0  E7 – E0 is more circular while E7 is more elongated o Irregular galaxy  Inward o Lenticular galaxies are hybrids of spiral and elliptical disk and spheroidal, but don’t have spiral arms Hubble’s Law - V = Ho D o D = distance to the galaxy in mpc o V = velocity of the galaxy away from us, km/sec o Ho = constant/slope in km/sec/mpc Radar ranging – the method of finding a target range continuously with a radar, observing objects by reflecting microwaves off target objects and analyzing the reflections Main-sequence fitting – determines distances between stars using HR diagram. It compares: o The location of the main sequence for the cluster stars placed on the HR diagram where apparent magnitude is used as the y-axis variable o The location of the main sequence for nearby stars whose distances are wellknown from parallax where absolute magnitude is used as the y-axis variable Cepheid variable stars with longer periods have greater luminosities White dwarf supernovae are good standard candles because they are so bright they can be detected even in very distant galaxies (because they are so young) and are very common Cosmological principle – the universe looks about the same no matter where you are in it o Matter is evenly distributed on very large scales in the universe o No center and no edges Lookback time – how long it takes for light to reach o If an object is 1 billion lightyears away, then that’s what it looked like 1 billion years ago Cosmological redshift – the wavelength of the emitted radiation is lengthened due to the expansion of the Universe; everything is redder than it should be Cosmological horizon – 13.6 billion light years away  farthest away we can see something The two factors that affect the formation of a galaxy o Spin of angular momentum (spiral galaxy) o Density of protogalactic center Dark matter – found in the halo, influenced by gravity, 20% of the universe If the center of a galaxy is unusually bright, we call it an active galactic nucleus. Quasars are the most luminous examples Three pieces of evidence that dark matter is present in clusters of galaxies o Orbital speed of galaxies is faster than they should be o Temperature of hot gas; E=mc^2 o Gravitational lensing – the bending of light rays by gravity Dark matter might be made of hydrogen and helium WIMP – weakly interacting massive particles; neutrino-like particle that doesn’t interact with itself or others MACHO – massive compact halo objects Critical density – density of matter that halts expansion Expansion patterns of the universe o Recollapsing – gravity wins, “big crunch,” closed universe as it closes in on itself o Critical – gravity slows expansion but does not stop it, flat universe o Coasting – supported by Hubble, critical density is never reached, end up with linear expansion o Accelerating – dark energy allows expansion, “big chill” Eras after the Big Bang o Planck – no theory of quantum gravity, all forces may have been unified o GUT – began when gravity became distinct from other forces, ended when a strong force became distinct from electroweak force o Electroweak – gravity became distinct from other forces; strong, weak, and electromagnetic forces may have been unified into GUT force o Particle – amounts of matter and antimatter are nearly equal o Nucleosynthesis – began when matter annihilates remaining antimatter at 0.001 seconds o Nuclei – helium nuclei formed at age 3 minutes, the universe became too cool to blast helium apart o Atoms – background radiation is released, atoms formed at age 380,000 years o Galaxies – present day, the first stars and galaxies formed by 1 billion years after the Big Bang Hydrogen fusion into helium o Method of energy generation used by the sun o Produces the outward flow of photons and neutrinos form the core of a star o Needs a temperature of the core to be 10 million K CNO cycle o allows for many of the organic compounds we need for life to be created Helium fusion o When a 1-solar mass star stabilizes as a giant for about a billion years, this occurs in its central core o Leads to the production of carbon Matter-antimatter annihilation o Hawking radiation proceeds with this process, which is that black holes will die out over time o Happens when a postiron comes in contact with an electron Gravitational contraction o This method of energy generation provides the source of energy for a protostar o Provided the energy that made the Sun hot in the first place General relativity o Explains how time-space can be warped by mass Radiation pressure o Wins out when a main-sequence star becomes a red giant Electron degeneracy pressure o A quantum mechanical effect that says no two electrons can exist close together o Overcomes complete gravitational contraction in a white-dwarf Neutron degeneracy pressure o Overcomes complete gravitational contraction in a neutron star Black hole o Outer reaches – event horizon o Radius – Schwarzchild o Center - singularity