# CalDay2

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Published on November 28, 2007

Author: Gavril

Source: authorstream.com

Black Holes:  Black Holes Eliot Quataert (UCB Astronomy Dept) Acknowledgment: Many Images Taken From the Web Science Fiction:  Science Fiction “Infinite Space, Infinite Terror” A Muse for Popular Culture:  A Muse for Popular Culture Twinkle, twinkle quasi-star Biggest puzzle from afar How unlike the other ones Brighter than a trillion Suns Twinkle, twinkle quasi-star How I wonder what you are! Tom Scarff’s sculpture “Black Hole” G. Gamow Slide4:  What is a black hole? Do BHs exist in Nature? YES! How do we find them? What do they look like? First, Something Simpler: Stars Pressure Balances Gravity:  First, Something Simpler: Stars Pressure Balances Gravity The Sun From www.astronomynotes.com Eluding Gravity’s Grasp :  Eluding Gravity’s Grasp Earth: Vesc = 25,000 miles/hour Sun: Vesc = 1 million miles/hour Mass M Radius R Escape Velocity “Dark Stars” Rev. John Michell (1784) & Pierre-Simon Laplace (1795):  “Dark Stars” Rev. John Michell (1784) & Pierre-Simon Laplace (1795) Speed of light ~ 1 billion miles/hour What if escape speed > speed of light? A star we couldn’t see! Earth mass: R ~ 1 inch Solar mass: R ~ 2 miles Vesc = speed of light  General Relativity, Einstein’s Theory of Gravity, Predicts Black Holes (1916):  General Relativity, Einstein’s Theory of Gravity, Predicts Black Holes (1916) Karl Schwarzschild Albert Einstein Slide9:  If an object is small enough, gravity overwhelms pressure and the object collapses. Gravity is so strong that nothing, not even light, can escape. “Radius” = 2GM/c2 ~ 2 miles for a solar mass NOT a solid surface All Mass at the Center (GR not valid there) Black Holes in GR Black Holes:  Black Holes All of the fireworks and drama originate close to the BH Far away from a BH, gravity is no different than for any other object of the same mass If a BH were to replace the sun, the orbits of planets, asteroids, moons, etc., would be unchanged. A Cosmic Vacuum Cleaner? How do we find BHs in Nature?:  How do we find BHs in Nature? “It’s black, and it looks like a hole. I’d say it’s a black hole.” Sidney Harris X-ray Binaries:  X-ray Binaries If two stars orbit close enough to each other, mass gets pulled from one and falls (accretes) onto the other. The smaller the object, the faster the gas moves and the hotter it gets. Gas falling into a BH gets very hot and emits lots of radiation in X-rays. First discovered in 1970s Matsuda How do we know it’s a BH?:  How do we know it’s a BH? Nature is tricky: couldn’t it be another small star like a neutron star or a white dwarf? Measure mass of “dark star” by motion of its companion (a star like the sun) Mass > 3 solar masses  BH ~ a dozen BHs found this way believed to be millions of ~ solar mass BHs in the galaxy formed in an explosion at the end of a massive stars’ life Chandrasekhar BIG Black Holes:  BIG Black Holes Stars in the Center of our Galaxy Eckart & Genzel BIG Black Holes:  BIG Black Holes Velocities of Stars  Mass of BH BH in our Galaxy weighs in at 3 MILLION SOLAR MASSES Nearly Every Galaxy has a Central Massive Black Hole Masses ~ Million-Billion Solar Masses; Sizes ~ solar system Most lie Dormant, waiting to strike … Quasars & “Active Galactic Nuclei”:  Quasars & “Active Galactic Nuclei” The BH outshines all of the stars in its host galaxy! Discovered in the early 60s Accreting Massive BHs Maarten Schmidt Quasars & “Active Galactic Nuclei”:  Quasars & “Active Galactic Nuclei” The BH ejects beams (“jets”) of matter & energy far outside its host galaxy into the surrounding universe Accreting Massive BHs What you should take away …:  What you should take away … Physicists said that Black Holes could exist the ultimate victory of gravity over all other forces Astronomers boldly proclaim that BHs do exist 1 Big BH per galaxy (~ million-billion solar masses) millions of little BHs per galaxy ( ~ solar mass) BHs are responsible for some of the most dramatic & energetic phenomena in the universe

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