Transcript April 15th
Survey of the Universe Tom Burbine [email protected] Next Quiz • This Wednesday • Quiz includes material covered up to and including April 8th • Cumulative • You can bring in one 8 ½ by 11 inch piece of paper with anything written on it • If you are unhappy with any of your grades: • You can write a 10 page paper on an astronomical subject to replace it • 12 point font • Times New Roman font • Double space • No figures or plots • Due by May 1st Type Ia Supernova Lightcurve Type Ia Supernova are consistent with coming from exploding white dwarfs • No signs of hydrogen in their spectra, consistent a star that have lost their outer atmospheres of hydrogen in a stellar wind • Lightcurve matches theoretical predictions of exploding white dwarfs • Last Type Ia supernovas that occurred in our galaxy were observed by Tycho Brahe (1572) and Johannes Kepler (1604) Standard Candles • Type Ia supernovas make excellent standard candles because they have identical maximum luminosities • Their collapse and explosion occur the same way each time Products • Type Ia Supernovas are rich in elements such as carbon, oxygen, silicon, and iron • Magnetic fields in the expanding remnant can accelerate atomic nuclei to speed close to the speed of light, which are called cosmic rays Massive Stars • Greater than 8 Solar Masses • Begins life on main sequence as Blue Star • Follows the same path as a low mass star but everything occurs faster Fate of Massive Stars Light Curves of supernovae of stars undergoing core collapse Dashed red line is Type Ia supernova How do you get a Core-Collapse Supernova? • A high-mass star keeps on fusing elements into ones with larger atomic masses • Is now a Red Supergiant • Energy keeps on being released since the mass of the new nucleus is less than the original ones This stops with Iron • Fusion of Iron with another element does not release energy • Fission of Iron with another element does not release energy • So you keep on making Iron Initially • Gravity keeps on pulling the core together • The core keeps on shrinking • Electron degeneracy keeps the core together for awhile Then • The iron core becomes too massive and collapses • The iron core becomes neutrons when protons and electrons fuse together • Type I are classified based on the lack of hydrogen lines in their spectra – Type Ia are due to collapsing white dwarfs – Type Ib and Ic are due to collapsing cores of stars that have lost their hydrogen atmospheres • Type II have hydrogen lines in their spectra – Due to collapsing cores Type Ia Supernova Type II Supernova http://www.ifa.hawaii.edu/~barnes/ast110_06/tooe/1314a.jpg Supernova 1987A that exploded in Large Magellanic Cloud (a small, nearby galaxy) 168,000 light-years away Could be seen with naked eye peak magnitude +2.9 Type II Supernova remnants of different ages Cassiopeia A 300 years old Crab Nebula 1,000 years old Supernova Several thousand years old Type II Supernova explosion Hypernova explosion Hypothetical supernova explosion of a star so massive that its core collapses directly into a black hole Neutron Star • • • • Neutron stars are usually ~10 kilometers across But more massive than the Sun Made almost entirely of neutrons Electrons and protons have fused together How do you make a neutron star? • Remnant of a Supernova How do we know there are neutron stars? • The identification of Pulsars • Pulsars give out pulses of radio waves at precise intervals Pulsars • Pulsars were found at the center of supernovae remnants • Fastest pulsars are called millisecond pulsars Pulsars • Pulsars were interpreted as rotating neutron stars • Only neutron stars could rotate that fast • Strong magnetic fields can beam radiation out Conservation of Angular Momentum (M x V x R) If Radius shrinks, Rotation Velocity must increase • X-ray pulsars – generate pulses of X-ray radiation • Magnetars – neutron stars with extremely intense magnetic fields that generate intense bursts of Xray and gamma-ray radiation Black Hole • A black hole is a region where nothing can escape, even light. Black Hole • After a supernova if all the outer mass of the star is not blown off • The mass falls back on the neutron star • The gravity causes the neutron star to keep contracting http://www.astronomynotes.com/evolutn/remnants.gif Event Horizon • Event Horizon is the boundary between the inside and outside of the Black Hole • Within the Event Horizon, the escape velocity is greater than the speed of light • Nothing can escape once it enters the Event Horizon How do calculate the radius of the Event Horizon? • • • • It is called the Schwarzschild Radius Radius = 2GM/c2 This is a variation of the escape velocity formula Escape velocity = square root (2GMplanet/Rplanet) Black Hole Sizes • A Black Hole with the mass of the Earth would have a radius of ~0.009 meters • A Black Hole with the mass of the Sun would have a radius of ~3 kilometers Anything with mass curves space Can you see a Black Hole? No • Black Holes do not emit any light • So you must see them indirectly • You need to see the effects of their gravity Accretion disk – flat disk of gas or other material held in orbit around a body before it falls onto the body Evidence • The white area is the core of a Galaxy • Inside the core there is a brown spiralshaped disk. • It weighs a hundred thousand times as much as our Sun. http://helios.augustana.edu/~dr/img/ngc4261.jpg Evidence • Because it is rotating we can measure its radii and speed, and hence determine its mass. • This object is about as large as our solar system, but weighs 1,200,000,000 times as much as our sun. • Gravity is about one million times as strong as on the sun. • Almost certainly this object is a black hole. • http://documentaryheaven.com/whos-afraid-of-abig-black-hole/ Any Questions?