Star Birth, 6 November 2013!Opening question: What does protoplanetary mean? !1.It describes something that is going to be a planet, but is not yet. !A.Planets condense out of disks of nebulosity around new stars over a.several hundred million years. !Fundamental processes of Star Birth: !2.Stars (usually clusters of stars) form anywhere there is a dense enough A.concentration of material in a nebula.!As the early stars are formed and radiate out energy, they cut out a hollow B.in the nebula.!Planets form in a disk of nebulosity around the star. !C.The gas and dust around the star sometimes joins the star, but most of it is D.blown away. !Astronomers can find unseen objects around stars by seeing if they move 3.irregularly due to a gravitational pull from an object or if the star's light is blocked by it.!If an object exerts a gravitational pull on a star, the star becomes red shifted A.and blue shifted and its motion across the sky wobbles. !Brown dwarfs which aren't stars or planets form in the nebula as well: !4.They are less that two percent of the mass of the sun – which is the A.minimum mass it takes to make a star. !Another way to say this is that they are less that 80 times the mass of a.Jupiter. !Brown dwarfs are basically big Jupiters (Gas giants). !B.These objects are studied by both stellar and planetary astronomers. !a.Brown dwarfs are studied by stellar astronomers. !1.Gas giants are usually studied by planetary astronomers. !2.These two divisions will say there is a difference between the two, but 3.no one can say what the difference is (there is not a significant difference).!These are in the space on Take A Nebula, Condense and Stir between C.planets and stars. !About a thousand of these are now known. !D.For an object to be a star is must be performing hydrogen fusion.!5.This is a nuclear reaction (nuclear fusion), as opposed to a weaker chemical A.reaction. !Chemical reactions take place in the electrons cells surrounding the a.nucleus of atoms, whereas nuclear reactions take place in the nucleus. !Nuclear bombs and energy plants are more powerful that their chemical b.counterparts. !H-bombs are humans imitating the processes of stars. !1.Hydrogen fusion, aka proton-proton chain reactions!B.A hydrogen nucleus is a proton.!a.Hydrogen that undergoes hydrogen fusion is ionized, meaning that it 1.has no electrons. !At low temperature and low pressure, when hydrogen proton are b.moving slowly, protons repel each other with their like magnetic charges. !At high temperatures and high pressure, the speed of protons is fast c.enough to overcome their magnetic repulsion, and hydrogen nuclei can fuse. !The net reaction is four hydrogen atoms making 1 helium atom plus d.energy. !You do not need to know the steps of this reaction, but you need to 1.know there are many steps, each producing energy and eventually 1 helium. !Most of the radiant energy seen in the universe (like in nebulae, stars, e.and galaxies) comes from this proton-proton chain reaction. !There is some other energy in the universe, mostly from the big bang, 1.but the vast majority of light you see is from the proton proton chain !If an object has hydrogen fusion, it is a star. If it used to have hydrogen C.fusion but doesn't anymore, it used to be a star. If it doesn't have hydrogen fusion but it will in the future, it will become a star in the future. !In objects less than 80 times the mass of Jupiter or less than 2 percent the D.mass of the sun, there is not enough temperature and density in the core to produce hydrogen fusion. !The star itself is putting out lots of material in all directions, but all of it is 6.reabsorbed except at the disk and a bit at the poles (bipolar outflow).!1-15-51 is a young star which still has bipolar outflow. !A.There is also an intense amount of infrared light around it!a.Astronomers understand this bipolar outflow. Later in this course, there B.will be instances of bipolar outflow that astronomers do not understand in pulsars and quasars. !This is the best current model for star birth: !7.What this chart does not show is the reason for so much material being A.propelled out of the proton star in the first place. !There are several ideas for why this might be which haven't been proven a.or disproven. ! !b.New born stars always seem to be from a disk. !8.This is how our solar systems and other solar systems formed.!A.This disk has been spotted in the infrared, radio, and sometimes visible light. !B.The disk was first seen clearly around the star beta pictoris. !C.In infrared light, astronomers could see a big, uneven, protoplanetary a.disk.!T Tauri is a type of new star still laced up in a lot of nebulosity in a disk D.shape. !It is an irregular variable star, which means it does not have any a.periodicity and behaves unpredictably. !These types of stars almost always get brighter because they are eating b.through the surrounding nebula which obscures their light from earth. !In some new stars, astronomers cannot see a disk. This is probably because E.the disk is seen face on, so it appear as a circle rather than a line.!In any part of the protoplanetary disks, some of the nebula is falling in towards 9.ProtostarInfrared gasAcceleratingcore gasAcceleratingmolecular gasInfalling dustInfrared photonProtostargas accretion diskthe new star and being subjected to variable amounts of heat from the star. !You can see the effects of heat on various parts of a nebula as it falls into A.the new star. !Some of the dust is vaporized into a transparent gas. !a.The condition of gas is also strongly determined by the temperature and b.pressure. !A hot star will ionize a great deal of hydrogen around it, causing the 1.area to look pink. !The Bubble Nebula: !B.A lot of nebulae are bubbles, but this nebula is called the bubble nebula. !a.There is a bright star in the slightly off center in the bubble. !b.The hot star pushes away nebulosity. !c.The bubble is thickest where the gas is densest. !1.A clump of nebulosity starts off big, shrinks to get higher density and 10.pressure, which sparks fusion. This sends the object to the main sequence where it stays for 98% of its career as a star. !Stars don't move up or down the main sequence, they move to or from it.!A.If a nebula condenses to the point where astronomers can gage its a.surface temperature, then it is a star. !If you can see a star's luminosity, the gas and dust around it must be 1.thin enough to show that information.!Stars
View Full Document
Unlocking...