physics solar system to cosmos
Ladder step 5: Distant galaxies
1 - Approximate scaling law for disk galaxies: Tully-Fisher relation between rotational velocity and absolute luminosity o Rotation rate and observed brightness gives us distance o Current limit: distant galaxies (up to few billion of light years) 2 - white dwarf binary supernova (type Ia) o explosion emits almost always the same energy, again giving us distance indication o they are very rare
Protostar to Star
1.Cloud collapses to form protostars, heating up as it shrinks. It moves left, up on HR diagram 2.Collapse continues, temperature stabilises as convection circulates energy outwards. Moves downwards 3.As core temperature reaches million K, fusion begins but our protostar is still not stable, still collapsing. Moves left on HR diagram. 4.Stellar thermostats keeps luminosity, temperature stable. Hydrogen to helium fusion. Main sequence - sheds cocoons of gas
Properties of black hole
1.Information that has made the black hole is lost beyond the event horizon. 2. It is electrically neutral 3. the collapsing stellar core rotates faster and faster as it shrinks in size
Pulsars
A fluctuating source of radio waves, that results from a neutron star spinning rapidly. the collapse of a neutron star makes its magnetic field lines running through the core tighter, amplifying the strength of the magnetic field. this then sends out radiation along the magnetic poles. they send out radiation like light houses.
Patterns of motion in large bodies
All planetary orbits are nearly circular and lie nearly in the same plane All planets orbit the Sun in the same direction Most planets rotate in the same direction in which they orbit, with fairly small axis tilts. The sun also rotates in this direction, Most of the solar system's large moon exhibit similar properties in their orbits around their planets such as orbiting in their planet's equatorial plane in the same direction direction as the planet rotates
Kepler's second law
As a planet moves around its orbit, it sweeps out equal areas in equal times. this means the planet travels faster when it is nearer to the sun and slower when it is further away
Centre of mass
As momentum is conserved, orbiting objects orbit around their centre of mass. the bigger the mass, the closer the balance point is to it
Asteroids and Comets
Asteroids are rocky bodies that orbit the Sun much like planets but they are much smaller. Most known asteroids are found within the asteroid belt between the orbits of Mars and Jupiter. Comets are made largely of ices mixed with rocks. They orbit the Sun in either the Kuiper belt or the Oort cloud
Apparent magnitude
Compare how bright stars appear in the sky. A star of magnitude of 4 is dimmer than a star of magnitude 1. Each difference in magnitude is a difference of exactly 100 in brightness. Stars can have fractional apparent magnitudes and an apparent magnitudes less than 1.
Universal law of gravitation
Every mass attracts every other mass. attraction is directly proportional to the product of their masses. Attraction is inversely proportional to the square of the distanced between their centres. when comparing big mass and a small mass, the small mass is so tiny it can essentially be ignored. this law allows us to weigh distant objects by observing the period and measuring the separation of the two objects
Terrestrial planets formation
Formed in the warm, inner regions of the gas disk Formed far enough from the centre to allow metals and rocks to form into seeds. Smaller as there is less rocks and metals in the gaseous cloud Formed through the process of accretion: 1. Microscopic particles "bumped" into each other and held together by electrostatic force 2. As they grew, gravity aided the accretion process, making them into larger planetesimals 3. They grew larger - however as they grew, their speed and gravitational forces grew too, making more destructive collisions. Only the largest planetesimals could survive these and grow into the terrestrial planets
Differentiation
Gravity pulls high-density material to centre Lower density material rises to surface Material ends up separated by density
Black hole
Happens when gravity is stronger than pressure. this happened when the neutrons are traveling at the speed of light but it still isn't fast enough! Collapse of a massive star core concentrates all the mass in a single point Space time continuum is torn (singularity is created) Black holes are black because gravity is so strong even light cannot escape. only massive stars have enough gravity to collapse to a black hole after core fusion ends. there is no standard 'state' of matter here; a singularity has zero volute and infinite density
Critical universe
In the case of gravitational attraction that was not quite strong enough to reverse the expansion in the absence of a repulsive force, the expansion would decelerate forever, leading to a universe that would never collapse but would expand ever more slowly as time progressed. This is called a critical universe, because this is what would occur if the total density of the universe was the critical density and only matter (and not dark energy)
Recollapsing universe
In the case of strong gravitational attraction and no repulsive force, the expansion would continually slow down with time and eventually would stop and reverse. Galaxies would come crashing back together and the universe would end in a fiery "Big Crunch". The final state would look much like the big band
Magnetic field requirements
Molten, electrically conducting interior Convection Moderately rapid rotation
Kepler's third law
More distant planets orbit the Sun at slower average speeds, obeying the relationship p^2=a^3. p= orbital period in years, a= the semi-major axis of the orbit in AU
Formation of Jovian planets
Occurred beyond the frost line -> cold enough for ices to condense. More solid material and more ice rich composition. Because the planetesimals were larger, their gravitational forces were big enough to capture hydrogen and helium gas. This added gas made their gravity even stronger, allowing them to capture more gas and grow bigger -> they eventually bore little resemblance to the icy seeds they grew from. This also explains the large moon of jovian planets. The same process of heating, spinning and flattering occurred with the gas attracted to young jovian planets Moons that accreted from rich planetesimals ended up with nearly circular orbits going in the same direction as their planet's rotation and lying close to their planet's equitorial plane
Nebula theory
Our solar system was formed from the gravitational collapse of a giant interstellar gas cloud - the solar nebula. Is orderly as a collapsing gas clouds tends to heat up, spin faster, and flatten out as it shrinks in size. Speed increased due to conservation of momentum, collisions caused it to flatten into disk
Distance from Sun
Planets close to the sun are too hot for rain, snow, ice and so have less erosion Hot planets have more difficulty retaining an atmosphere Planets far from the Sun are too cold for rain, limiting erosion Planet with liquid water have the most erosion
Effects of Rotation
Planets with slower rotations have less weather, less erosion, and a weak magnetic field. Planets with faster rotation have more weather, more erosion, and a stronger magnetic field
Quasars
SMBHs in action •Appear as extremely blue stars ⇒ must be very hot •Brightness variations rapid and dramatic ⇒ must be fairly small (only light days across) •Some have very high redshifts (= large distances) ⇒ must be extremely bright •These are the most luminous AGNs •Some show jets or huge radio "lobes" many times larger than the host galaxy (huge amounts of energy) •Quasars are very luminous -visble across billions of light years
Role of planetary size
Smaller worlds would cool off faster and harden earlier. Larger worlds remain warm inside, promoting volcanism and tectonics. Larger worlds also have more erosion because their gravity retains an atmosphere.
4 factors effecting the atmosphere
Solar brightening • ]The Sun very gradually grows brighter with time, increasing the amount of sunlight warming the planets Changes in Axis Tilt •Larger tilt creates more extreme seasons, while smaller tilt keeps polar regions colder •Small gravitational tugs from other bodies in solar system causes Earth's axis tilt to vary between 22 and 25 degrees Changes in Reflectivity •Higher reflectivity tends to cool a planet, while lower reflectivity leads to warming Changes in Greenhouse Gases •An increase in greenhouse gases leads to warming, while a decrease leads to cooling
Measuring temperature
Spectral lines: oComplex atoms or molecules (more electrons, ore atoms) are fragile oFragile types are easily destroyed by collisions in high temperature regions - high temp = high energy of particles oIf there are signs of fragile atoms and molecules, that is absorption lines, the temperature must be low oLevels of ionisation reveals the star's temperature oAbsorption lines in a spectrum tell us level of ionisation
Active Galatic Nuclei
Super massive black hones in the process of growing are called Active Galactic Nuclei (AGN) Gas clouds gall into core of galaxy and form an accretion disk around a SMBH Inner regions of accretion disk hotter than outer - spectrum of temperatures AGN light come from hot accretion disk outside the event horizon of a SMBH
Two types of planets
Terrestrial planets are the four planets of the inner solar system. they are relatively small and dense, with rocky surfaces and an abundance of metals in their cores. they have few moons, if any, and no rings. Jovian planets are the four large planets of the outer solar system. They are much larger in size and lower in average density than the terrestrial planets. They have rings and many moons. They lack solid surfaces are are made mostly of hydrogen, helium and hydrogen compounds.
How does gravity cause tides?
The moon causes tides as the moon's gravity pulls harder on the near side of the Earth than the far side. Differences in the Moon's gravitational pull stretches Earth Tidal friction gradually slows Earth's rotation (and makes the moon move further from Earth) Tidal friction causes the moon to 'lock' in synchronous rotation and rotate at the same speed as Earth (hence why we only see one side) There is a budge on both sides of the planet - the force on the backside is less than the force in the centre The tidal force is the change in gravity over distance + the overall effect is to stretch an object
Kepler's first law
The orbit of each planet around the sun is an ellipse with the Sun at one focus
Geological processes that have shaped mars
There is ice below the surface of Mars - icey polar caps (Carbon Dioxide ice and Water ice). They evaporate during summer. The biggest volcano in the solar system is on the surface of Mars - Olympus Mons. The amount of crating differs greatly across Mars' surface Many early craters have been erased. Valles Mariners (valleys on Mars) is thought to originate from techtonics that no longer exist
Tidal force: Spaghettification
Tidal force near event horizon for a stellar black hole is very strong. Supermassive black holes gentler near the event horizon because Schwarzschild radius is much bigger R(Schwarzschild) ~ M(BH) (proportional) Tidal force (event horizon) ~ G h/M^2 (black hole)
Time dilation near event horizon
Time passes more slowly because of strong gravitational field
Exceptions to the rules
Uranus rotates on its side, and Venus rotates backwards. Small moons have unusual orbits. Earth has one of the largest moons in our solar system
How to measure age of a star cluster?
We can determine their ages by plotting an H-R diagram. Stars lie along the main sequence until they trail off to the right. This means the cluster is old enough for the hotter/bigger/more luminous stars to have stopped hydrogen fusion and instead transformed into giants (fusing other elements)
Standard Candles
White dwarf supernovae are exploded white dwarf stars that have reached the 1.4M sun limit. they have the same luminosity. they are all very bright and can be detected from galaxies billion of light years away.
Why do more massive stars have shorter lives?
a star's lifetime depends on both its mass and luminosity Its mass determines how much hydrogen fuel the star initially contains in its core. It's luminosity determines how rapidly the star uses up its fuel. Massive stars start their lives with more hydrogen, but they fuse this hydrogen into helium so rapidly they end up with shorter lives. Massive stars are so rare as they die quickly, and there are also less formed.
Gravitational potential energy
in space, an object or gas cloud has more gravitation energy when it is spread out than when it contracts - a contracting cloud converts gravitational potential energy to thermal
Stars in spirals moving in space
oDisk stars move in near-circular orbits, up and down through the disk (merry go round) oLots of gas and bright stars - can get star formation oBulge and halo star: stars swarm like bees. No gas. oOrbits of stars in the bulge and halo have random orientations oEvidence suggests that the bulge and halo formed before the disk existed. Their orbits are not affected much but the gravity of the disk oStars in the disk all orbit in the same direction a little up and down motion oIf they get too far above or below the disk, the gravity of everything in the disk pulls them back in - but they go too far and end up on the other side
Ladder step 1: The solar system. Radar ranging
oIdea: send radar signal, wait to receive it back (minutes to hours) oSignals travels for twice distance, radio waves propagates at speed of light
Ladder step 2: Nearby stars. Parallax
oRecap of idea: Nearby stars positions relative to background changes as Earth orbits around the Sun oParallax distance (parsec = star with parallax of one arcsec = 3.26 light years) oCurrent limit: Our galaxy (~100,000 parsec thanks to GAIA) •After we know their distance, we can work out their absolute brightness from their apparent brightness
What causes arms in spiral galaxies
oSpiral density waves - the arms are not solid structures, they are areas of higher density of stars oAssociated waves of molecule could collapse and star formation oLong lasting oSpiral arms do not wind up over time - the arms do not collapse into the bulge
White dwarfs
the "dead" core of a giant that has stopped nuclear fusion. they are hot because they are essentially exposed stellar cores, but dim as they lack an energy source and only radiate their leftover heat into space
inverse square law for light
the amount of light received per unit are decreases with increasing distance by the square of the distance
apparent brightness
the amount of starlight reaching Earth (energy person second per square metre)
Thermal energy
the collective kinetic energy of many particles. thermal energy is a measure of the total kinetic energy of all the particles in a substance. it therefore depends on both temperature and density.
Schwarszchild Radius
the distance from a black hole where nothing can escape. it is not a physical surface, just a dark outline. the Schwarzschild radius is 3km per solar mass. If any star (or any object) became a black hole, its gravity would be different only near the event horizon
Clearing the Nebula
they hydrogen and helium gas was cleared out by a combination of intense radiation from the young sun and the solar wind - a stream of charged particles (such as protons and electrons), continually blown outwards . If the gas has remained longer, it would cool till even the hydrogen compounds in the inner solar system condensed into ice. Terrestrial planets would accreted iced, hydrogen gas and helium gas, changing their basic nature. If the gases had been blown out earlier, the raw materials of planets could be swept away before planets could fully form. When charged particles were blown out, they transferred the Sun's angular momentum to the nebula, which was blown into interstella space. This left the sun with less angular momentum, leaving the sun with less angular momentum and a slow rotation
luminosity
total amount of power (energy per second) the star radiates into space
Features of venus
•"Earth's twin" as similar in size and topography •Due to its thick atmosphere must use radar mapping •Venus has impact craters, but fewer than the Moon, Mercury, or Mars - objects more likely to burn up in atmosphere •And contains shield volcanoes •It is unclear if Venus has tectonics •Venus' fractured and contorted surface indicates tectonic stresses, but no recently •If rotation affects tectonics, Venus' slow rotation will affect its ability to have techtonics
Galaxy group (village)
•1-5 large galaxies •various dwarf satellites •we live in the local group: o large galaxies: MW + Andromeda o dwarf: ~50 galaxies which orbit one of the large galaxies or orbit the group as a whole
Globular Clusters
•100,000 to million stars •tightly bound into a ball. Stars are very dense in core •tend to be quite old (but not always) (some are as old as universe)
Open clusters
•100s to 1000s of stars •loosely bound together by gravity (if at all) •usually young - older clusters are pulled apart by galactic tides
Galaxy clusters (cities)
•10s-100s of large galaxies, thousands of dwarfs •elliptical galaxies much more common here •clusters are the most massive gravitationally-bound objects in the universe •nearest cluster is the Virgo cluster, 50 mega light years away
Star life: Stage 1: Main Sequence
•90% of its life spent on the main sequence •fusing hydrogen into helium the core (T=15 million K for the Sun) •Stellar thermostat keeps luminosity and temperature stable (10 billion years for the Sun). Convection regulates temperature. •When the core first runs out of hydrogen, the core will start to collapse as it is not able to fight the force of gravity. •There is helium now in the collapsing core from hydrogen fusion. As the core collapses, it heats up but it is still not hot enough for helium fusion to occur (100 million K needed) •No more fusion in core, no more heat, lower thermal pressure, gravity causes core collapse -> core temperature starts to heat up (T ~50 million K). •Layers above the core must collapse (and heat up) too. Now it is hot enough for hydrogen fusion in shell around core. •This causes outer layers of star expand as hydrogen "shell burning" is closer to surface of the star •High temperature without as much mass above it to keep pressure balanced •Outer layers of star "puff up" and cool off meaning radiation can leave more easily Stage 2: Red Giants
Earth
•An oasis of life •The only surface liquid water in the solar system •A surprisingly large moon
Andromeda's blue shift
•Andromeda is actually blueshifted and is falling towards us at a velocity of -300km/s •We will collide in 2-5 billion years •The local gravity between the two galaxies has overcome the Hubble expansion so that space is not expanding locally o (Nor galaxies are expanding because gravitationally bound)
How does a star form from a cloud of gas?
•Anything that has a mass attracts anything with other mass - gravity! They contract down to the centre of gravity 1.Interstellar gas cloud starts to contract 2.It gets smaller and denser 3.And smaller and denser and hotter until hydrogen fusion begins - when core reaches at least 5 million degrees
Doppler shift
•Audible version is familiar: objects coming toward us have higher pitch = higher frequency = smaller wavelength of sound. Objects moving away = lower pitch = smaller frequency = longer wavelength •Light from objects coming towards us is blueshifted •Bluer = smaller wavelength = higher frequency. Objects moving away are redshifted •Shift in astronomy can be large - pink hydrogen can be redshifted to infrared or even radio wavelengths. •Shifted colours / wavelengths can be converted into the red /blueshift into a speed of motion •Doppler effect used to measure the speed of bright objects in space
Star life: Stage four: Double-shell Red giant
•Carbon core starts collapsing and heats up(needs to get to 600 million K) •Two fusing shells oInner shell fusing He -> C oOuter shell fusing H -> He •Energy generation becomes much higher again •Outer layers lift and cool again •Star becomes every luminous Double-Shell fusion - red giant. •Carbon fusion should start at 600 million K, but electron degeneracy pressure become a factor before the core reaches that temperature
Stages of collapse
•Cloud starts to collapse due to its own gravity •Spins faster, may fragment (conservation of angular momentum). M x V x R = Constant •Heats up as it collapses (conservation of energy). Gravitational Energy -> Kinetic Energy. Kinetic Energy -> Thermal Energy •Flattens into a disk (conservation of momentum). Collisions between particles average out motions and orbits. Directions averages out - cloud flattens. Speeds average out - orbits become circular
Creating heavy metals
•Elements heavier than iron don't generate energy through fusion •But you can fuse them if you add enough energy (endothermic reaction) •Supernovae create a lot of energy •All elements heavier than iron (gold, uranium, silver, elad, etc) originated in a supernova •All heavy elements are created and dispersed through the galaxy by stars •Without supernovae, nothing heavier than carbon can form •Our atoms were once parts of stars that expolodedd more than 4.6 billion years ago, whose remains were swpt up into the cloud out of which our Sun (and solar system) formed
Galaxy formation
•Galaxies form from giant gas clouds 1. Gravitational instability - Gravity pulls mass together, creating over densities 2. Disk formation - Angular momentum decides whether it's a disk or a spheroid. If a gas cloud does not have any rotational velocity, just in-falling velocity, it is possible to form a spheroid shape. This does require essential 0 rotational velocity though - most things do have some sort of angular velocity 3. Hierarchical growth - multiple gas clouds collide together. Large galaxies formed out of smaller galaxies. Gas clouds collapse into their own gravity, but also multiple gas clouds collapse into a central point. Old stars orbit in random direction [halo] gas clouds collide, form spinning disk. New stars continuously form in disk as galaxy grows older. Small galaxies, gas clouds continually "eat" by larger galaxies - galactic cannibalism.
Clustering of galaxies
•Galaxies found preferentially together o Galaxy groups o Galaxy clusters •It is always gravity holding it together
Galactic collisions
•Gas clouds are much more bigger than stars - more likely to collide. Collisions are almost certain •Stars are very small, so a chance of a collision are tiny due to their elliptical orbit •If two galaxies (stars and gas) collide, the stars would pass through each other but the gas clouds collide •New stars form from compressed gas clouds
Saturn
•Giant and gaseous like Jupiter •Spectacular rings •Many moons, including cloudy Titan •Rings are not solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon.
How to measure change in space (grav waves)
•Grav wave periodically changes the mirror positions (and hence distance laser light travels) •This bring the x and y waves in and out of phase •Measure the period of intensity of the recombined laser light - measure grav waves
What is the origins of clustering?
•Gravity is an attractive force •Overdense regions become more dense: galaxy clusters acquire mass over time •Matter is pulled away from underdense regions: void size grows over time. •Most of the matter in the Universe is dark matter. We can understand clustering with computer simulations that include gravity only (DM - only simulations) •Simulations of the large scale structures produced by Dark matter look a lot like the distribution of galaxies
Star life: Stage 3: Horizontal Branch
•Happily fusing helium to carbon as a Horizontal Branch Star •Core stabilises, luminosity decreases oOuter layers stopped being pushed out •Gravitational equilibrium is restored •R=10Rsun •50 million years
Hubble's law
•Hubble showed universe appears to be expanding •The slope of the line is the Hubble constant. •Ho = 70 km/s/Mpc. Written as Ho as the value changes on when/where you are in the universe. Ho means it's the here and now. •Hubble's law says that the further away we look in the universe, the faster things are moving. •Look at features we know, then see how their wavelength has changed from what we know intrinsically
Formation of elliptical galaxies
•If enough spiral galaxies collide, they will form an elliptical galaxy due to conservation of angular momentum •Most likely the Milky Way and our closet large neighbour Andromeda will collide, and the Triangulum galaxy to boot •Set to happen in ~4 billion years time
Nuclear fusion regarding Iron
•Iron nucleus is most tightly bound possible •Iron does not release energy through fusion or fission •There is no way iron can produce any energy to push back against the crush of gravity in the star's core •When pressure is large enough, iron atoms get compressed into pure neutrons •Protons + electrons -> neutrons + neutrinos •Regular matter becomes neutronium nothing but neutrons •This takes less than 0.01 seconds for the entire core •Electron degeneracy pressure - gone - core collapses Eventually neutron degeneracy pressure stops the collapse abruptly
Mars
•Looks almost Earth-like, but smaller so doesn't have atmosphere •Giant volcanoes, a huge canyon, polar caps, more •Water flowed in distant past; could there have been life?
Star life: Stage 5: Planetary nebula
•Low mass stars: oTemperature never gets high enough for carbon fusion oShell fusion becomes violent ♣(no stellar thermostat) ♣outer layers blown off: planetary nebula formed
Star life: Stage 6: White Dwarf
•Low mass stars: oTiny (earth sized) hot (10,000K) oDensity is ~1ton/cm3 oCools over tens of billions of years
Gas recycling
•Lower mass stars return gas to interstellar space through stellar winds and planetary nebula. Throw back about half •High mass stars have strong stellar winds that blow bubbles of hot gas •X rays from hot gas in supernova remnants reveal newly made heavy elements •Multiple supernovae create huge hot bubbles that can blow out of the disk. Gas clouds cooling in the halo can rain back down on the disk •Gravity forms stars out of the gas in molecular clouds, completing the star-gas-star cycle
Mercury
•Made of metal and rock; large iron core •Desolate, cratered; long, tall, steep cliffs - there is nothing to smooth over impact craters. On earth, water, wind and earth would change them. •Very hot, very cold: 425C (day), -170C (night), due to the slow rotation.
Cloud core to protostar
•Meanwhile, centre of disk is getting very hot and dense •Densest parts of cloud become opaque. Light can't escape. Heat is trapped •Can't cool as efficiently •Collapsing clouds spin up, form stars, disks and jets •Once a protostar becomes opaque, it starts to heat up •An ordinary solid object cools off and fades from blue hot to red hot as it radiates energy •A gas sphere held together by its own gravity contracts as it radiates, growing every hotter •Gravitational energy -> thermal energy. Protostar gets hotter and denser. Some energy radiated, some stays in protostar
Jupiter
•Much farther from Sun than inner planets •Mostly made from helium and hydrogen; no solid surface •300 times more massive than Earth •Many moons, rings •Jupiter's moons are almost like small planets. Io has active volcanoes all over, Europa has a possible subsurface ocean, Ganymede is the largest moon in the solar system, Callisto is a large, cratered ice ball.
Venus
•Nearly identical in size to Earth; surface hidden by clouds •Hellish conditions due to extreme greenhouse effect - atmosphere almost 100% Carbon dioxide. •Even hotter than Mercury: 470C, day and night
Star life: Stage 2: Red Giants
•No more core fusion - thermostat is broken! •As core collapses, hydrogen shell fuses faster and faster - more energy created •More pressure, less gravity - star becomes larger, cooler, but brighter •Core is continuing to shrink getting denser and hotter •Meanwhile, back in core - helium fusion oWhen core contracts enough to heat to 100 million K, helium starts to fuse into carbon oHelium "flash" - "triple alpha" fusion: He+ He+ He -> C + energy oAfter the helium flash, the core expands, and the H fusion in shell decreases •After the helium flash, a carbon core forms. This produces a sudostable state
The Big Strech
•Not an explosion of galaxies through space from a centre. •The fabric of space between galaxies is stretching, carrying the galaxies away from one another. •The galaxies themselves don't expand due to gravitational forces •Even though everything is moving away from us, it does not make us the centre of the universe. Every galaxy sees every other galaxy moving away.
Sun
•Over 99.9% of solar system's mass •Made mostly of H/He gas (plasma) •Converts 4 million tons of mass into energy each second •Contains sunspots which are cooler areas
How long do different stars take to form?
•Protostars of difference masses follow different life tracks towards the main sequence •Massive stars form fast, form first - new globular clusters contain a lot of big OB stars - OB stars can live their entire lives before M-dwarf even reach the Main sequence •Massive star radiation, winds can affect the formation of less massive stars - bigger stars can push away smaller stars •Supernova from massive stars may trigger collapse of adjacent areas in molecular cloud •Massive stars "carve out" holes in dense molecular clouds •Winds, supernovae from these stars help form other stars in other parts of the cloud
Mutliwavelength observations
•Required as there is dust in the way of optical observations •Infrared: Some IR penetrates dust that obscured optical. Longer wavelength IR from dust reradiating absorbed light •Radio: Emission from hydrogen and molecules in space. Reveals molecular clouds in which stars form •X-Rays: High temperature gas (and X-ray binaries) (when super hot gas emits x rays)
Ladder step 3: Distance stars. Main sequence fit
•Requires the knowledge from nearby stars •Main sequence fit idea o Temperature/colour gives stellar type, in turn mass and absolute luminosity o From observed brightness possible to infer distance o Current limit: Nearest galaxies (Need to identify indivudal stars within star clusters)
Neptune
•Similar to Uranus (except for axis tilt) •Many moons
Redshift
•Since the universe is expanding, light traveling through the universe "feels" the stretch as it travel •Redshift = z = how much longer the light's wavelength is now than when emitted (then) •the distance between galaxies has stretched between the olight being emitted and detected. Distance is now 1.05 x larger than when light left the galaxy
Clustering of stars
•Single stars are rare: oBinary/triple/multiple oStar clusters: ♣ Open clusters ♣ Globular clusters
Uranus
•Smaller than Jupiter/ Saturn; much larger than Earth •Made of hydrogen and helium, and hydrogen compounds •Extreme axis tilt •Moons and rings
Ladder step 4: Nearby galaxies
•Some variable stars such as Cepheids, have tight relation between period of oscillation and absolute luminosity •Measuring period and observed brightness gives us distance •Current limit: Nearby galaxies (need to be able to identify individual stars in non-crowded environment)
What causes the arms?
•Spiral density waves •Associated waves of molecular could collapse and star formation •Long lasting •Spiral arms do not wind up over time! •Gas clouds compress in spiral arms, new stars form •Blue stars burn out before they can leave the arm •Lower mass stars live long enough to leave spiral arm
Spiral structure
•Stars move on elliptical orbits by themselves •Spiral arms are a pattern, not a physical structure. Stars move in and out of arms •Some spirals have an elongated bulge called a bar, and hence called a barred spiral
Lifetime of stars
•Stars spend 90% of their lives on Main Sequence - fixed in the place its fusing hydrogen into helium in their core oMassive (O,B) stars live only 3-10 million years oSun (G- type star) lives 10 giga years oLow-mass (K,M) stars live 1012 years
Effects of atmospheres
•They create pressure that determines whether liquid water can exist on surface •They absorb and scatter light •They create wind, weather, and climate •They interact with the solar wind to create a magnetosphere - charged particles cannot reach the ground •They can make planetary surfaces warmer through the greenhouse effect
Irregular galaxies
•Unsure what they are - could be: o Formation o Transition (crashed into something else and interacting) o Fails •Often lots of stellar births - companions to larger galaxies and get messed around by tidal formation, which means gas is compressed, creating star formation
Elliptical galaxies
•Very few young stars •Very little cool gas/ dust •Reddish colour = old stars, red giants, red main sequence •All bulge/halo - no disk
Mass of stars
•You cannot measure mass for single stars •Binary stars are fairly common (~80% of stars in galaxy) •By analysing the motion you can tell how much gravitational attraction there is, and therefore find the mass of the stars •Newton's Version of Kepler's Third Law: oThe period2 is equal to 4 pi2 divided by G (a constant) times the distance between stars cubed divided by the mass
The Cosmic Web
•created through computer simulations of how the dark matter interacts with gravity •regular matter clusters where dark matter is densest. This is where galaxies form. •Dark matter is the 'scaffold' of the structure of the universe
Virgo's cluster redshift
•the Milky Way is falling towards the Virgo Cluster at ~300 km/s, but galaxies in Virgo appear redshifted in Virgo appear redshifted at ~1500 km/s. •Virgo's mass is pulling us towards it, against, the expansion of spacetime (Hubble's Law), but the space is still expanding between us •We will never actually reach Virgo because space is expanding faster than we are falling
Galaxy stellar mass function
•uncertain measurement, but clearly small galaxies (~tens billion stars) are 100x to 1000x more common than giant galaxies (thousand billion stars)
