1Massive Stars AfterThe Main SequenceExplosions, Neutron Stars andBlackHolesIt’s all about gravity……Eskimo Nebula2Ant NebulaWhat’s really going on?3Three thousand light-years away, a dying star throws off shells of glowing gas. This image from the HubbleSpace Telescope reveals The Cat's Eye Nebula to be one of the most complex planetary nebulae known. Infact, the features seen in the Cat's Eye are so complex that astronomers suspect the bright central object mayactually be a binary star system.The primary source of energy for aWhite Dwarf• A) Nuclear fusion• B) Nuclear fission• C) gravitational contraction• D) stored heat, cooling passively• E) chemical heat4Formation of Heavy Elements• Hydrogen and a little helium were formed shortly after theBig Bang• All other elements were formed inside stars!• Low-mass stars create carbon and oxygen in their cores at theend of their lifespan, thanks to the higher temperatures andpressures present in a red giant star• High-mass stars produce heavier elements like silicon,magnesium, etc., by nuclear fusion in their cores– Temperatures are much higher– Pressures are much greater• Highest-mass elements (heavier than iron) must be created insupernovae, the death of high-mass starsThe Lifespan of a Massive Star5Layers of Fusion Reactions• As a massive star burns its hydrogen,helium is left behind, like ashes in afireplace• Eventually the temperature climbs enoughso that the helium begins to burn, fusinginto Carbon. Hydrogen continues to burnin a shell around the helium core• Carbon is left behind until it too starts tofuse into heavier elements.• A nested shell-like structure forms.• Once iron forms in the core, the end isnear…Core Collapse of Massive Stars• Iron cannot be fused into any heavierelement, so it collects at the center ofthe star• Gravity pulls the core of the star to asize smaller than the Earth’s diameter!• The core compresses so much thatprotons and electrons merge intoneutrons. At this point, there are noelectrons to provide degeneracypressure. The bottom brick has beenpulled out of our foundation.6Core Collapse of Massive Stars• The core collapses, and the layersabove fall rapidly toward the center,where they collide with the corematerial and “bounce”• The “bounced material collides withthe remaining infalling gas, raisingtemperatures high enough to set off amassive fusion reaction. The star thenexplodes.• This is a supernova!Before and After – a Supernova7X-Ray Image Visible-UV Image8pressure densityRadial velocityAzimuthal velocity•Most luminous EM events inthe universe•Short (few sec) gamma rayburst•Longer optical afterglow•2 kinds (short and long)•(1)Massive star death•(2)Collisions of dead starsA massive star forms metals heavier than iron a) At the end of it’s main sequence lifetimeb) During the red super giant phasec) During a supernovad) never9Supernova Remnant• The supernova hasleft behind arapidly expandingshell of heavyelements that werecreated in theexplosion.• Gold, uranium andother heavies alloriginated in asupernovaexplosion!The Crab Nebula10Types of Supernovae• Type Ia: The explosion thatresults from a white dwarfexceeding the ChandrasekharLimit (1.4 solar masses)• Type II: Supernovae resultingfrom core collapse• Less common:– Type Ib and Ic: Results fromcore collapse, but lackshydrogen, lost to stellar windsor other processesStellar Corpses• A type II supernova leaves behind the collapsed coreof neutrons that started the explosion, a neutron star.• If the neutron star is massive enough, it can collapse,forming a black hole…11Interior Structure of a Neutron StarBlack