Any model of Solar System formation must explain the following facts: 1.All the orbits of the planets are prograde (i.e. if seen from above the North pole of the Sun they all revolve in a counter-clockwise direction). 2.All the planets (except Pluto) have orbital planes that are inclined by less than 6 degrees with respect to each other (i.e. all in the same plane). 3.Terrestrial planets are dense, rocky and small, while jovian planets are gaseous and large.Solar System Solar system formed about 4.6 billion year ago, when gravity pulled together low-density cloud of interstellar gas and dust (called a nebula) Initially the cloud was about several light years across. A small overdensity in the cloud caused the contraction to begin and the overdensity to grow, thus producing a faster contraction Initially, most of the motions of the cloud particles were random, yet the nebula had a net rotation. As collapse proceeded, the rotation speed of the cloud gradually increased due to conservation of angular momentum. conservation of angular momentum Gravitational collapse was much more efficient along the spin axis, so the rotating ball collapsed into thin disk with a diameter of 200 AU (0.003 light years) (twice Pluto's orbit), aka solar nebula with most of the mass concentrated near the center. As the cloud contracted, its gravitational potential energy was converted into kinetic energy of the individual gas particles. Collisions between particles converted this energy into heat (random motions). The solar nebula became hottest near the center where much of the mass was collected to form the protosun (the cloud of gas that became Sun).NatSci102/lectures/solarsysform.htm At some point the central temperature rose to 10 million K. The collisions among the atoms were so violent that nuclear reactions began: the Sun was born as a star, containing 99.8% of the total mass The great temperature differences between the hot inner regions and the cool outer regions of the disk determined what of condensates were available for planet formation at each location from the center. The inner nebula was rich in heavy solid grains and deficient in ices and gases. The outskirts are rich in ice, H, and He (gas even at very low temp.). Around the Sun a thin disk gives birth to the planets, moons, asteroids and comets. Jupiter is the biggest planet in terms of mass and volume. Mercury is the smallest. Solar System About 4.5 billion years ago, the Earths moon is believed to have been formed from material ejected when a collision occurred between a Mars-size object and the Earth. Kuiper belt Kuiper belt, beyond Neptune, much larger; In addition to asteroids it is the source of short-period comets and contains dwarf planets Asteroid belt Asteroid belt situated between Mars and Jupiter, contains millions of asteroids. Comets Comets are irregular objects a few kilometres across comprising frozen gases (ice), rocky materials, and dust. Observable comets travel around the Sun in sharply elliptical orbits with periods ranging from a few years to thousands of years. As they draw near to the Sun the gases in the comet are vaporized, forming the distinctive comet tail that can be millions of kilometres long and always points away from the Sun. Asteroids Asteroids consist of metals and rocky material. Those of size less than 300 km have irregular shape because their gravity is too weak to compress them into spheres. our Asteroids and comets are both celestial bodies orbiting our Sun, and they both can have unusual orbits, sometimes straying close to Earth or the other planets. They are both leftovers made from materials from the formation of our Solar System 4.5 billion years ago The stability of a star depends on the equilibrium between two opposing forces. The equilibrium depends on the gravitation which can collapse the star and the radiation pressure which can make the star expand. This equilibrium is gained through nuclear fusion which provides the energy the star needs to keep it hot so that the star's radiation pressure is high enough to oppose gravitational contraction. hydrostatic equilibrium When this is balanced the star is in a state of hydrostatic equilibrium and will remain stable for up to billions of years. Stars Stars initially form when gravity causes the gas in a nebula to condense. As the atoms move towards one another, they lose gravitational PE that is converted into KE. This raises the temperature of the atoms which then form a protostar. When the mass of the protostar is large enough, the temperature and pressure at the centre will be sufficient for hydrogen to fuse into helium, with the release of very large amounts of energy the star has ignited. This applies to all layers of the Sun. Gravity pulls outer layers in, gas and radiation pressure pushes them out. The fusing of hydrogen into helium takes up the majority of a stars lifetime and is the reason why there are far more main sequence stars than those in other phases of their life-cycle. It is pretty hot at the center!!!! As the hydrogen is used up the star will eventually undergo changes that will move it from the main sequence. During these changes the colour of the star alters as its surface temperature rises or falls and it will change size accordingly. The original mass of material in the star determines how the star will change during its lifetime. At the beginning of a star's life cycle the star consists mainly of hydrogen; 98% hydrogen. All stars follow a simple hydrogen burning: hydrogen fuses into helium, in order to maintain an equilibrium between gravity and pressure. Story about our sun Nuclear Fusion within stars: Nuclear Fusion within stars: hydrogen burning: hydrogen fuses into helium. Stars consist mainly of hydrogen, which is used for the fusion reactions that produce almost all of their energy. 3.Two helium-3 nuclei fuse to produce the helium-4 nucleus. Two protons are released 2. The deuterium nucleus fuses with another proton, and produces a helium-3 nucleus. 1.Two protons fuse to form a deuterium, and releases a positron and a neutrino. Each positron is annihilated to create 2 ray photons. stars of greater than four solar masses CNO For stars of greater than four solar masses undergo CNO cycle. Sun-like stars protonproton chain For Sun-like stars the process advances through the protonproton chain The fusing of hydrogen into helium takes up the majority of a stars lifetime and is the reason why there are far more main sequence stars than those in other phases of their life-cycle. Again, four protons are used to undergo the fusion process; carbon-12 is both one of the fuels and one of the products. Two positrons, two neutrinos and three gamma-ray photons are also emitted in the overall process. Thus, in order to produce a helium nucleus, four hydrogen nuclei are used in total (six are used in the fusion reactions and two are generated). Despite the difficulties in assessing whether stars exist singly or in groups of two or more, it is thought that around fifty per cent of the stars nearest to the Sun are part of a star system comprising two or more stars. Binary stars Binary stars consist of two stars that rotate about a common centre of mass. They are important in astrophysics because their interactions allow us to measure properties that we have no other way of investigating. For example, careful measurement of the motion of the stars in a binary system allows their masses to be estimated. Groups of stars Star Star is a massive body of plasma/gas held together by gravity, with fusion going on at its center, giving off electromagnetic radiation. There is an equilibrium between radiation/gas pressure and gravitational pressure called hydrostatic equilibrium Stellar cluster Stellar cluster is a group of stars held together by gravitation in same region of space, created roughly at the same time from the same nebula. The Pleiades is a stellar cluster of about 500 stars that can be seen with the naked eye Open clusters Open clusters consist of up to several hundred stars that are younger than ten billion years and may still contain some gas and dust. They are located within our galaxy, the Milky Way, and so lie within a single plane. Globular clusters Globular clusters contain many more stars and are older than eleven billion years and, therefore, contain very little gas and dust. There are 150 known globular clusters lying just outside the Milky Way in its galactic halo. Globular clusters are essentially spherically shaped. The galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component. Several distinct components of galaxies comprise the halo: the galactic spheroid (stars) the galactic corona (hot gas, i.e. a plasma) the dark matter halo. Clusters Clusters : Gravitationally bound system of galaxies/stars. Constellation Constellation is a pattern formed by stars that are in the same general direction when viewed from the Earth. Such stars are not held together by gravity. Regions of intergalactic cloud of dust and gas are called nebulae. As all stars are born out of nebulae, these regions are known as stellar nurseries. There are two different origins of nebulae. The first origin of nebulae occurred in the matter era around years after the Big Bang. Dust and gas clouds were formed when nuclei captured electrons electrostatically and produced the hydrogen atoms that gravitated together. The second origin of nebulae is from the matter which has been ejected from a supernova explosion. The Crab Nebula is a remnant of such a supernova. Other nebulae can form in the final, red giant, stage of a low mass star such as the Sun. Nebula Galaxy Galaxy is a huge group of stars, dust, and gas held together by gravity, often containing billions of stars, measuring many light years across. Some galaxies exist in isolation but the majority of them come in clusters containing from a few dozen to a few thousand members. The Milky Way is part of a cluster of about 30 galaxies called the Local Group which includes Andromeda and Triangulum. Regular clusters Regular clusters consist of a concentrated core and are spherical in shape. Irregular clusters Irregular clusters have no apparent shape and a lower concentration of galaxies within them. Since the launch of the Hubble Space Telescope it has been observed that even larger structures, superclusters, form a network of sheets and filaments; approximately 90% of galaxies can be found within these. In between the clusters there are voids that are apparently empty of galaxies. The Andromeda galaxy with two smaller satellite galaxies. Spiral galaxies Spiral galaxies the most common class of galaxies (both The Milky Way and Andromeda). They have a flat rotating disc-shape with spiral arms spreading out from a central galactic bulge that contains the greatest density of stars. It is increasingly speculated that, at the centre of the galactic bulge, there is a black hole. The spiral arms contain many young blue stars and a great deal of dust and gas. Other galaxies are elliptical in shape, being ovoid or spherical these contain much less gas and dust than spiral galaxies; they are thought to have been formed from collisions between spiral galaxies. Irregular galaxies are shapeless and may have been stretched by the presence of other massive galaxies the Milky Way appears to be having this effect on some nearby dwarf galaxies. The astronomical unit (AU): the average distance between the Sun and the Earth. It is really only useful when dealing with the distances of planets from the Sun. Astronomical distances Resulting from the huge distances involved in astronomical measurements, some unique, non-SI units have been developed. This avoids using large powers of ten and allows astrophysicists to gain a feel for relative sizes and distances. 1 light-second = (3.0 10 m/s)(1.0 s) = 3.0 10 8 m = 3.0 10 5 km 1 light-minute = 18 10 6 km 1 light-year (ly) 1 ly = 9.46 m l0 13 km. The EarthMoon distance is 384,000 km = 1.28 light-seconds. The EarthSun distance is 150,000,000 km = 8.3 light-minutes. 1 AU= 1.50 m 8 light minutes 1 parsec (pc): This is the most commonly used unit of distance in astrophysics. 1 pc= 3.26 ly = 3.09 m Distances between nearby stars are measured in pc, while distances between distant stars within a galaxy will be in kiloparsecs (kpc), and those between galaxies in megaparsecs (Mpc) or gigaparsecs (Gpc). For small angles: Parallax Method Parallax Method relies on the apparent movement of the nearby star against the background of further stars as the earth orbits the sun. It is the most direct measure of distance. close star two apparent positions of a close star with respect to position of distant stars as seen by an observer in both January and July are compared and recorded to find angle p 1 pc = 3.09 X m One parsec is a distance corresponding to a parallax of one arc second' 1 AU = m Parsec is short for parallax arcsecond when talking about stars, parallax is very, very small number. Parallaxes are expressed in seconds. Parallax has its limits The farther away an object gets, the smaller its shift. Eventually, the shift is too small to see. Even the nearest star has a tiny parallax! First measured in 1838 The closest bright star Alpha Centauri 4.3 light-year 0.75 pcstate.edu/~pogge/Ast162/Movie s/parallax.gif There is a limit to the distance that can be measured using stellar parallax parallax angles of less than 0.01 arcsecond are difficult to measure from the surface of the Earth because of the absorption and scattering of light by the atmosphere. Turbulence in the atmosphere also limits the resolution because it causes stars to twinkle. In 1989, the satellite Hipparcos (an acronym for High Precision Parallax Collecting Satellite) was launched by the European Space Agency (ESA). Being outside the atmosphere, Hipparcos was able to measure the parallaxes of stars with an accuracy of arcsecsond (to distances 1000 pc); its mission was completed in Gaia, Hipparcoss successor, was launched in 2013 and is charged with the task of producing an accurate three-dimensional map showing the positions of about a billion stars in the Milky Way. This is about one per cent of the total number of stars in the galaxy! Gaia is able to resolve a parallax angle of 10 microarcsecond measuring stars at a distance of pc. limits because of small parallaxes: d 100 pc from Earth d 1000 pc from Hipparcos d pc from Gaia To understand the nature, to interpret many beautiful phenomena you have to have a tool. We are introducing something that we know all about and then well compare the nature with that ideal case!!!!!!! A black body A black body is a theoretical object that absorbs 100% of the radiation that that is incident upon them it. Because there is no reflection or transmission it appears perfectly black. Such bodies would also behave as perfect emitters of radiation, emitting the maximum amount of radiation possible at their temperature. This type of radiation consists of every wavelength possible but containing different amounts of energy at each wavelength for a particular temperature. Black bodies in thermal equilibrium Black bodies in thermal equilibrium emit energy to balance the energy they absorb and remain at a constant temperature. temperature The only parameter that determines how much EM radiation the black body radiates for the given wavelength is its temperature. That is why the radiation emitted by an blackbody is often called thermal radiation. The hotter the blackbody, the more EM radiation at all wavelengths. emitsPlancks Wiens law Black body emits energy according to Plancks and Wiens law are not Although stars are not perfect black-bodies they are capable of emitting and absorbing all wavelengths of electromagnetic radiation. In practice no material has been found to absorb all incoming radiation, but carbon in its graphite form absorbs all but about 3%. It is also a perfect emitter of radiation. radiation spectrum black-body radiation. Stars and planets radiation spectrum is approximately the same as black-body radiation. Wiens law: Wavelength at which the intensity of the radiation is a maximum max, is: Blackbody radiation Planck's Law Planck's Law predicts the radiation of a blackbody at different temperatures. intensity of radiation as a function of wavelength. It gives intensity of radiation as a function of wavelength. only It depends only upon the temperature of the black body. The peak emission from the blackbody moves to shorter wavelengths as the temperature increases (Wiens law) The hotter the blackbody the more energy emitted per unite area at all wavelengths. Note that the peak shifts with temperature. Except for their surfaces, stars behave as blackbodies Except for their surfaces, stars behave as blackbodies. Luminosity Luminosity of a star is the total power radiated by a star. L = A T 4 (W) Stefan-Boltzmanns law A is surface area of the star, T surface temperature (K), is Stefan-Boltzmann constant. (Apparent) brightness (b) (Apparent) brightness (b) is the power from the star received per square meter of the Earths surface L is luminosity of the star; d its distance from the Earth Can be measured, for example, by using a telescope and a charge-coupled device ? IB Photometer!!! Internet When we assume that a star is spherical we can use this equation in the form: L = 4R 2 T 4 (W) R is the radius of the star If we regard stars as black body, then luminosity is (total energy per second) Some data for the variable star Betelgeuse are given below. Average apparent brightness = 1.6 10 7 Wm 2 Radius = 790 solar radii EarthBetelgeuse separation = 138 pc The luminosity of the Sun is 3.8 W and it has a surface temperature of 5800 K. (a) Calculate the distance between the Earth and Betelgeuse in metres. (b) Determine, in terms of the luminosity of the Sun, the luminosity of Betelgeuse. (c) Calculate the surface temperature of Betelgeuse. For a star, state the meaning of the following terms: (a) (i) Luminosity (ii) Apparent brightness (c)Distances to some stars can be measured by using the method of stellar parallax. (i) Outline this method. (ii) Modern techniques enable the measurement from Earths surface of stellar parallax angles as small as 5.0 10 3 arcsecond. Calculate the maximum distance that can be measured using the method of stellar parallax. (i) The luminosity is the total power emitted by the star. (ii) The apparent brightness is the incident power per unit area received at the surface of the Earth. (i) The angular position of the star against the background of fixed stars is measured at six month intervals. The distance d is then found using the relationship d = 1/p Since both are red (the same color), the spectra peak at the same wavelength. By Wien's law Star A is 9 times brighter and as they are the same distance away from Earth. Star A is 9 times more luminous: So, Star A is three times bigger than star B. Suppose I observe with my telescope two red stars A and B that are part of a binary star system. Star A is 9 times brighter than star B. What can we say about their relative sizes and temperatures? then they both have the same temperature. L = 4 R 2 T 4 (W) By Wien's law Suppose I observe with my telescope two stars, C and D, that form a binary star pair. Star C has a spectral peak at 350 nm - deep violet Star D has a spectral peak at 700 nm - deep red What are the temperatures of the stars? If both stars are equally bright (which means in this case they have equal luminosities since the stars are part of a pair the same distance away), what are the relative sizes of stars C and D? Star C is 4 times smaller than star D. The Sun, our favorite star! WE CAN SEE IT REALLY WELL. The Sun is the basis for all of our knowledge of stars. Why? Today we will take a journey to the center of the Sun, starting with what we can see and ending up deep in the core. Overview of Solar Structure Main Parts: The Sun is made of mostly HYDROGEN and HELIUM The Corona Outer layer of the Sun Millions of degrees but very diffuse Extends millions of kilometers into space Hot and energetic, gives off lots of x rays! Outer layer of the Sun Millions of degrees but very diffuse Extends millions of kilometers into space Hot and energetic, gives off lots of x rays! Mass is ejected into space as the solar wind The solar wind streams off of the Sun in all directions at speeds of about 400 km/s (about 1 million miles per hour). The source of the solar wind is the Sun's hot corona. The temperature of the corona is so high that the Sun's gravity cannot hold on to it. The Sun has intense magnetic fields The magnetic fields release energy from the Sun Release seen in sunspots, flares, coronal mass ejections & other phenomena This twisting leads to the loopy structures we see! Flares BE AMAZED! Earth to scale. Yes, really. BE AMAZED! The Sun has an 11-year solar cycle Minimum Maximum The Suns magnetic fields create sunspots Visible Sunspots! Ultraviolet nm Ultraviolet 284 nm Ultraviolet 195 nm Ultraviolet -174 nm temperature is about 5800 K Remember how the temperature and color of stars are related? The temperature of our Sun gives it its yellowish color! Our Sun is really yellowish green, but our atmosphere absorbs and scatters some of the blue light. Sunshine = Energy from Fusion E = mc 2 Energy Mass Speed of Light Speed of light is BIG-- so a little mass can turn into a LOT of energy! review: The next two layers of the Sun are all about getting the energy being made in the core out into space! It takes a lot of time, but we get it eventually. The next two layers of the Sun are all about getting the energy being made in the core out into space! It takes a lot of time, but we get it eventually. Gravity compresses and heats the center of the sun At the core nuclear reactions take place The Sun is a giant nuclear reactor Energy flows from the core outward, but how does it get out and end up as sunshine? How does energy get from one place to another? 1.Convection 3.Radiation 2.Conduction Convection and Radiation are most important for the Sun! Hot stuff risesCool stuff sinks! BOILING Metal of a pan heats by conduction heat travels through the atoms of the pan Not very important for stars! Photons can scatter off of unbound electrons When they scatter, the photons share their energy with the electrons The electrons get hotter Ionized gas Really high resolution spectrum of the Sun: lots of absorption lines! Outer layers of the Sun are cooler than interior Interior opaque part of Sun produces a thermal spectrum, while cooler outer layers produce absorption lines! Hot source makes a continuous thermal spectrum Light passing through a cloud of cooler gas gets some light absorbed out: ABSORPTION SPECTRUM How Much Fusion a Second? Einsteins formula E = m c 2 The luminosity of the Sun is 4 x Watts So The Sun loses 4 million tons of mass per second! The Sun Takes About 4 Weeks to Rotate We know diameter & mass Density = mass / volume Density = 1.4 times water! Low density + Hot temperature The Sun is a ball of gas! What is the sun made of? Determined from study of spectrum and atomic spectra in the laboratory 74% Hydrogen 25% Helium 1% All other elements Particles emitted by the sun detected on the Earth confirm picture of the Sun given in this power point. Good night. Very important thing is the question of mass That question can be translating into question: What are binary stars ???????? star A large ball of gas that creates and emits its own radiation. Binary Stars >60% of Stars are in Binary Systems two balls not necessarily gas, not necessarily emitting radiation Can be white dwarf, even black hole Contains two (or sometimes more) stars which orbit around their common center of mass. Importance - only when a star is in a binary system that we have the possibility of deriving its true mass. The period watching the system for many years. The distance between the two stars - if we know the distance to the system and their separation in the sky. the masses can be derived. The more unequal the masses are, the more it shifts toward the more massive star. The masses of many single stars can then be determined by extrapolations made from the observation of binaries. Visual binary Visual binary: a system of stars that can be seen as two separate stars with a telescope and sometimes with the unaided eye They are sufficiently close to Earth and the stars are well enough separated. Sirius A, brightest star in the night sky and its companion first white dwarf star to be discovered Sirius B. Hubble image of the Sirius binary system. Sirius B can be clearly distinguished (lower left) Spectroscopic binary: A binary-star system which from Earth appears as a single star, but whose light spectrum (spectral lines) shows periodic splitting and shifting of spectral lines due to Doppler effect as two stars orbit one another. have patience Eclipsing binary: (Rare) binary-star system in which the two stars are too close to be seen separately but is aligned in such a way that from Earth we periodically observe changes in brightness as each star successively passes in front of the other, that is, eclipses the other Algol known colloquially as the Demon Star, is a bright star in the constellation Perseus. It is one of the best known eclipsing binaries, the first such star to be discovered. NASA X-ray Binaries A special class of binary stars is the X-ray binaries, so-called because they emit X-rays. X-ray binaries are made up of a normal star and a collapsed star (a white dwarf, neutron star, or black hole). These pairs of stars produce X-rays if the stars are close enough together that material is pulled off the normal star by the gravity of the dense, collapsed star. The X-rays come from the area around the collapsed star where the material that is falling toward it is heated to very high temperatures (over a million degrees!). An animation of an eclipsing binary system undergoing mass transfer.