Transcript Black Holes
Scott McCumber & Samuel Taylor Black Holes THE SUCKIEST THINGS IN THE UNIVERSE General Relativity Spacetime is not a static background where Newtonian physics happens; spacetime is a dynamic fabric with definite, physical properties. The attractive force we call “gravity” is actually the way spacetime behaves when it becomes curved, or warped, around massive objects in the Universe. History… The term “black hole” was coined by physicist John Wheeler in 1967, though scientists had already been predicting black holes as a consequence of Einstein’s theory of general relativity for decades… In 1915, Karl Schwarzschild (left) derived a solution to Einstein’s field equations for the gravity of both a point mass and spherical mass. Early Descriptions Arthur Eddington further interpreted Einstein’s equations for the public, and on the subject of very dense stars, he wrote in 1926, “Firstly, the force of gravitation would be so great that light would be unable to escape from it, the rays falling back to the star like a stone to the earth. Secondly, the red shift of the spectral lines would be so great that the spectrum would be shifted out of existence. Thirdly, the mass would produce so much curvature of the space-time metric that space would close up around the star, leaving us outside (i.e., nowhere).” Through the 60’s and 70’s… In the early 1960’s, physicists Roy Kerr, Ezra Newman, Werner Israel and Brandon Carter, among others, discovered solutions for black holes showing they have mass, angular momentum and electric charge. Then in the 1970’s, Stephen Hawking shows quantum theory predicts black holes should radiate energy at a temperature proportional to the surface gravity. How do Black Holes form? When a large star has too little fuel left to maintain its temperature, it implodes and the matter left over within the star condenses to an exotic state, creating what’s known as a “stellar mass black hole.” The remnants of matter contained in the dead star must be at least 3 solar masses, or three times the mass of our sun. A singularity is then created within the heart of the dying star; this represents a point in spacetime where the gravitational pull is so strong, matter and light cannot escape. And now… for a short video: Birth of a Black Hole What We’re Left With… 3 Types of Black Holes Stellar Mass Supermassive Primordial Masses ranging from 5 to tens of solar masses Usually found at the center of large, spiral galaxies like our Milky Way Theorists believe black holes may have formed in the early Universe, less than a billion years after the big bang Outer layers of the star explode in a supernova; the interior implodes Most common type in the Universe “Intermediate” stellar black holes can have between 1001million solar masses Require gravitational forces equal to millions or billions of solar masses Possibly formed by the collapse of a dense cluster of stars Oldest supermassive black hole formed 900 million years after the Big Bang and equals 12 million solar masses These primordial or “miniature” black holes are thought to have the radius of an atomic particle, but as much mass as Mt. Everest During the big bang, some parts of the Universe are thought to have expanded more slowly than others, causing matter to condense in certain regions and create miniature black holes How do we measure Black Holes? Mass Black holes usually have stars or gas in orbit Scientists can measure the speed of the orbiting material, as well as the size of the orbit Once these two variable are known, then the laws of gravity can be used to determine the mass of the black hole X-Rays When matter falls into a black hole, it gets heated to millions of degrees K The super-heated matter emits Xrays These X-rays can be detected by special telescopes like the Chandra X-ray Observatory Misconceptions… Our sun will become a black hole. Black Holes are scary cosmic monsters that roam around eating everything in their path False; the mass of our sun is too small; the solar mass of a dead star’s core must be at least 2.8 times the mass of our sun to form a black hole. False; black holes don’t roam around, though they do spin; they exhibit the same gravity as stars with similar masses, and you would have to get close enough to a black hole to actually experience “falling in.” The information in a black hole is lost forever. Debated; while this was initially thought to be the case, physicist Leonard Susskind and others have advanced the idea that the information that falls into a black hole may actually be holographically “stored” on the surface of the black hole, with the surface area of the event horizon corresponding to the amount of information consumed by the black hole. Resources on Black Holes… Hubble Space Telescope Black Hole Encyclopedia (a good introduction for beginners): http://hubblesite.org/explore_astronomy/black_holes/home.html Frequently Asked Questions about Black Holes (written by University of Richmond physicists Ted Bunn in 1995, while he was a graduate student at Berkeley; a bit dated, but still good): http://cosmology.berkeley.edu/Education/BHfaq.html The Universe in the Classroom (The ASP’s Newsletter on Teaching Astronomy) Issue on Black Holes by John Percy: http://www.astrosociety.org/education/publications/tnl/24/24.html Chandra X-Ray Observatory Field Guide to Black Holes: http://chandra.harvard.edu/xray_sources/blackholes.html StarDate‘s Introduction to Black Holes: http://blackholes.stardate.org/ 87 Questions and Answers about Black Holes from astronomer Sten Odenwald’s Astronomy Café: http://www.astronomycafe.net/qadir/abholes.html Monsters in Galactic Nuclei (an article on supermassive black holes by John Kormendy and Gregory Shields from StarDate Magazine): http://chandra.as.utexas.edu/~kormendy/stardate.html Monster of the Milky Way (companion site to the PBS-TV NOVA episode on the black hole at the center of our Galaxy): http://www.pbs.org/wgbh/nova/blackhole/ Black Hole Math (a nice introductory booklet at the high-school math level by astronomer Sten Odenwald): http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/Black_Hole_Math.html Spacetime Wrinkles Website: http://archive.ncsa.illinois.edu/Cyberia/NumRel/NumRelHome.html The National Center for Supercomputing Applications Relativity Group (whew — what a name!) has set up an intriguing and well produced “exhibit on line” about Einstein’s theory of relativity and its astronomical implications, including some movies in which they simulate situations such as the collision of two black holes.