Black Holes. Black Holes Gateways To The End of Time

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1 Black Holes Black Holes Gateways To The End of Time

2 There exist in the heavens therefore dark bodies, as large as and perhaps as numerous as the stars themselves. Pierre De Laplace [1796]

3 Black Hole History 1687 Sir Isaac Newton Described gravity in his publication, "Principia." 1783 John Michell Conjectured that there might be an object massive enough to have an escape velocity greater than the speed of light Simon Pierre LaPlace Predicted the existence of black holes. "...[It] is therefore possible that the largest luminous bodies in the universe may, through this cause, be invisible." -- Le Système du Monde 1915 Albert Einstein Published the Theory of General Relativity, which predicted spacetime curvature Karl Schwarzchild Used Einstein's Theory of General Relativity to define a black hole. Defined gravitational radius of black holes, later called the Schwarzchild radius Sir Arthur Eddington Relativity expert who, along with Einstein, opposed black hole theory Subrahmanyan Chandrasekhar Pioneer in theory of white dwarfs that led to an understanding of mass limits that decide whether a star will die as a white dwarf, neutron star or black hole John Wheeler Coined the term, "black hole." 1964 Jocelyn BellBurnell Discovered neutron stars that, at the time, were the densest matter found through observations Stephen Hawking Defined modern theory of black holes, which describes the final fate of black holes Cygnus X - 1 The first good black hole candidate that astronomers found. It emits x-rays and has a companion smaller than Earth but with a mass greater than that of a neutron star.

4 Relativity The hands of the clock have stayed still at half past eleven for fifty years. It is always opening time in the Sailors Arms. [Dylan Thomas, Under Milk Wood]

5 History of Relativity Galileo Galilei first described his principle of relativity in 1632 in his Dialogue Concerning the Two Chief World Systems Newton s laws of motion were published in Philosophiæ Naturalis Principia in They embodied the principle in that speed and distance are relative and time is absolute. In 1865, James Clerk Maxwell proposed that light was an electromagnetic wave, and therefore travelled at the speed c appearing in his theory of electromagnetism. In 1887, Michelson-Morley experiment demonstrated that regardless of speed or direction, observers always measure the speed of light to be the same value. Special Theory of Relativity, published by Einstein in 1905, is based on the notion that there is no such thing as absolute space or time General theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics.

6 How Fast Are You Moving Right Now? 0 m/s relative to your chair 400 m/s relative to earth center (rotation) 30,000 m/s relative to the sun (orbit) 220,000 m/s relative to the galaxy center (orbit) 370,000 m/s relative to the CMB cosmic wallpaper Relative to What?? Spring

7 Galilean Relativity Galileo Galilei first described this principle in 1632 in his Dialogue Concerning the Two Chief World Systems Imagine a passenger inside the hull of a ship, which is sailing on a perfectly smooth lake at constant speed and direction. Galileo found that to determine the speed at which the ship is travelling, the passenger and the fish must observe each other, thereby providing a frame of reference. Otherwise, it is not possible to determine the speed of the ship.

8 Special Relativity Published by Einstein in 1905 Speed of light is constant Time dilation Simultaneity Length Contraction Spacetime diagrams E = MC2

9 The special theory of relativity changes our conceptions of space and time

10 The speed of light is the same to all observers, no matter how fast they are moving

11 Speed Speed = Distance/Time Speed of Light (c) = 3X108 m/s = Distance Travelled (or Space) Time Speed of light is maximum possible speed and is 30,0000,000 m/s. If the speed of light is constant, and distance traveled is relative, then time must also be relative. Therefore, space and time are aspects of a single entity called space-time.

12 Space-Time Diagram

13 Spacetime Diagram Geodesic = shortest path between two points. Particles follow geodesics in spacetime.

14 Spacetime Diagram

15 Time dilation

16 An observer will note a slowing of clocks and a shortening of rulers that are moving with respect to the observer This effect becomes significant only if the clock or ruler is moving at a substantial fraction of the speed of light

17 Time Travel How long does it take to get to Vega? Vega is 25 light years away, assume travel is at c. Time for trip should be about 25 years. But since clocks of moving object slow down, the time elapsed on a clock taken on the trip is only

18 Twin Paradox One of a pair of twins, Betty, leaves on a high speed space journey during which she travels at a large fraction of the speed of light while the other twin, Ann, remains on the Earth. Because of time dilation, time is running more slowly in the spacecraft as seen by Ann (the earthbound twin) and Betty (the travelling twin) will find that Ann (the earthbound twin) is older when she returns from the journey. Will Betty really be younger?

19 Minkowski Diagram for Twin Effect

20 Measuring thetwin Paradox In 1971, two researchers from Washington University, borrowed 4 atomic clocks, and boarded two commercial flights and gamely flew with them around the world, first eastwards and then westwards. As airliners travel at less than millionth the speed of light, the time-warp on board was very small; about a microsecond per day s flying. On the eastwards journey, the 4 clocks came back to earth 59 nanoseconds slow relative to the a set of standard clocks at the US Naval Observatory. On the westward journey, the clocks were on average 273 nanoseconds fast. The reason for the east-west different is that the rotation of the earth produces a time dilation too. When the effect of the earth s rotation was factored in, the time dilation produced by the airliners motion confirmed Einstein s Theory of Relativity.

21 If Alpha Centauri exploded 3 second ago, could there be any effect now on Earth? Alpha Centauri is 4 light years away from earth. 1.Yes 2.No

22 Cosmic Radiation When cosmic radiation strikes the nuclei of atoms in the upper atmosphere, the produce subatomic debris. Muons are like electrons, only heavier, they take a relatively long time to decay, and most of them reach the ground. If you produced muons in a laboratory, after a few millionths of a second, nearly all of them would have decayed into electrons. In a few millionths of a second, light travels less than a km. Yet the muons are created at 20 kms altitude, and therefore ought not to make it to earth. When a muon moves at close to the speed of light, its time becomes time warped. In our frame of reference, fixed to the earth, moving-muon time becomes considerably stretched out (dilated). Instead of decaying in a few microseconds, earth-time, a muon can live long enough to reach the earth and be detected by a Geiger counter.

23 The general theory of relativity is our most accurate description of gravitation Published by Einstein in 1915, this is a theory of gravity A massive object causes space to curve and time to slow down These effects manifest themselves as a gravitational force These distortions of space and time are most noticeable in the vicinity of large masses or compact objects

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25 The theory of relativity predicts a number of phenomena, including the bending of light by gravity and the gravitational redshift, whose existence has been confirmed by observation and experiment

26 Black Holes Behold! The jaws of darkness do devour it up. [William Shakespeare]

27 The general theory of relativity predicts black holes

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31 If a stellar corpse has a mass greater than about 2 to 3 M, gravitational compression will overwhelm any and all forms of internal pressure The stellar corpse will collapse to such a high density that its escape speed exceeds the speed of light

32 Certain binary star systems probably contain black holes Black holes have been detected using indirect methods Some binary star systems contain a black hole In such a system, gases captured from the companion star by the black hole emit detectable X rays

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35 Supermassive black holes exist at the centers of most galaxies These are detected by observing the motions of material around the black hole

36 A non-rotating black hole has only a center and a surface The entire mass of a black hole is concentrated in an infinitely dense singularity The singularity is surrounded by a surface called the event horizon, where the escape speed equals the speed of light Nothing not even light can escape from inside the event horizon

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38 Falling into a black hole is an infinite voyage

39 Falling into a Black Hole Not to Scale 39

40 Falling into a Black Hole Not to Scale 40

41 Falling into a Black Hole Not to Scale 41

42 Falling into a Black Hole Not to Scale 42

43 Could a black hole somehow be connected to another part of spacetime, or even some other universe? General relativity predicts that such connections, called wormholes, can exist for rotating black holes

44 Gravitational Waves The general theory of relativity also predicts the existence of gravitational waves, which are ripples in the overall geometry of space and time produced by moving masses. On 11 February 2016, the LIGO collaboration announced the detection of gravitational waves, from a signal detected on 14 September 2015 of two black holes with masses of 29 and 36 solar masses merging about 1.3 billion light years away. During the final fraction of a second of the merge, it released more power than 50 times that of all the stars in the observable universe combined. The mass of the new black hole obtained from merging the two was 62 solar masses. Energy equivalent to three solar masses was emitted as gravitational waves.

45 The Theory of Everything Quantum Gravity: Reconciling General Relativity and Quantum Mechanics Most well known theories are String Theory and Loop Quantum Gravity Einstein said that if quantum mechanics is right, then the world is crazy. Well, Einstein was right. The world is crazy. [Daniel Greenberger, Quantum Physicist]

46 Hawking Radiation - Black holes evaporate

47 What is NASA trying to learn? NASA missions continue to search for and study black holes to determine the fate of matter as it falls into black holes, how powerful jets form, and what role black holes played in the formation of the early universe. By 2020, the Event Horizon Telescope (linked of radio telescopes around the world) Credit: NASA, ESA, and A. Schaller (for STScI) should deliver its first good portraits. What they show will help constrain the theories of black holes, and so offer telling clues about how to solve the big-small problem. 47

48 Any Questions? 48