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## Black Holes & Relativity

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**In this chapter you will discover…**• Einstein’s theory of general relativity • space and time are not separate entities • how black holes arise • surprisingly ‘simple’ theoretical properties of black holes • X rays and jets of gas are created near many black holes**Relativity**• Einstein’s vision • Theorized Time & Distance cannot be measured absolutely • Time & Distance only have meaning when measured relative to something**The “Up” Paradox**• In childhood, we regard “up” as a single direction above our head. • When we realize that people in Australia do not stand upside-down… • we revise our common sense • “up” is defined relative to the center of the Earth**What is Relative?**• A plane flies WEST from Nairobi to Quito at 1,000 mi/hr. • The Earth rotates EAST at the equator at 1,000 mi/hr. • What an observer sees depends on her/his position!**What is Relative?**• A plane flies WEST from Nairobi to Quito at 1,000 mi/hr. • The Earth rotates EAST at the equator at 1,000 mi/hr. • An observer on the Earth’s surface? => Would see the plane fly westward overhead**What is Relative?**• A plane flies WEST from Nairobi to Quito at 1,000 mi/hr. • The Earth rotates EAST at the equator at 1,000 mi/hr. • An observer far away in space? => Would see the plane not seem to move at all, and the Earth turn under it!**Motion & Reference**• Objects moving relative to one other are in different reference frames. • They experience time and measure distance & mass in different ways**Einstein’s Vision**• 1905: Special Relativity • Speed of Light is the same for ALL observers • No matter how fast they are moving! • No matter what direction they are moving!**Special Relativity Consequence**• Length is different for moving observers • Stationary observers measure longer lengths • Moving objects appear to be shorter • Time is different for moving observers • Stationary observers measure longer times • Time for Moving objects appears to be less • Energy and Mass are related (E = mc2)**A ball in moving train…**Seen from INSIDE the train, the ball simply goes UP and DOWN in a certain time tinside observer**A ball in moving train…**Seen from OUTSIDE the train, the ball goes UP and DOWN, but ALSO sideways at the speed of the train, say in a certain time toutside observer**A ball in moving train…**The faster the train is moving, the faster the ball appears to be going to an outside observer**A ball in moving train…**The faster the train is moving, the faster the ball appears to be going to an outside observer, covering a longer distance in that same time toutside observer**So what??**• Replace the Ball with a Beam of Light And… • Suppose both inside and outside observers assume the speed of light is the same**A light beam in moving train…**For the observer in the train, the light moves up and down at the speed of light, in a time tinside observer**A light beam in moving train…**For the observer OUTSIDE the train, the light travels farther ….**A light beam in moving train…**For the observer OUTSIDE the train, the light travels farther …. – but if it moves at the same speed of light – it must take longer! toutside > tinside**Consequences!**Time measured by someone moving is different than time measured by someone who isn’t! toutside observer > tinside observer**Consequences!**Time measured by someone moving is different than time measured by someone who isn’t! toutside observer > tinside observer The faster you go, the greater the difference in your perception of time vs. for someone not moving!**Proof!**• Decay of Subatomic Particles (Muons) (cf. http://www.scivee.tv/node/2415 ) • Actual Aircraft Travel (Hafele-Keating exp.) (cf. http://www.youtube.com/watch?v=gdRmCqylsME) • GPS satellites! (cf. https://www.youtube.com/watch?v=30KfPtHec4s(cf. https://www.youtube.com/watch?v=zQdIjwoi-u4 ) • Nuclear Colliders**Additional Consequences of Special Relativity**• Time as measured by stationary observer is longer • Length as measured by stationary observer is longer • Mass as measured by stationary observer is more • All compared with measurements made by moving observers…**Additional Consequences of Special Relativity**• Time is relative! (http://www.scivee.tv/node/3025) • Time Dilation (cf. http://www.scivee.tv/node/3007) • Length as measured by stationary observer is longer • Mass as measured by stationary observer is more • All compared with measurements made by moving observers…**The Doppler Shift Explained through Relativity**Speed of light is measured to be identical but… observed frequency (wavelength) is not!**Einstein’s Vision**• 1915: General Relativity • Acceleration “upward” is equivalent to gravitation “downward” • You can’t tell the difference • Matter will bend space and time**Light is affected by gravity**• According to Einstein’s Theory of Relativity, gravity is really the warping of spacetime about an object with mass. • This means that even light is affected by gravity.**Proof!**• Deflection of Starlight by the Sun • 1919 Total Solar Eclipse • Precession of Mercury’s orbit • Gravitational Redshift of light moving up • Delay in signals from Spacecraft on Mars**Radio Signals from Mars**Mars Orbiters & Landers send signals to Earth Signals travel at speed of light across solar system**Radio Signals from Mars**Signals bent by gravitation of the Sun Signals take longer to reach us than predicted**Black Holes – Theory!**• After a massive star supernova, if core mass > 3 M, force of gravity will be too strong for even neutron degeneracy to stabilize star. • The star will collapse into a singularity. • This is what we call a black hole.**Black Holes - Theory**• The star becomes infinitely small. • it creates a “hole” in the Universe • Since 3 M or more are compressed into an infinitely small space, the force of gravity NEAR to the star is HUGE!!! • WARNING!! • Newton’s Law of Gravity is no longer valid !!**Black Holes - Theory**• Defined by their event horizon • Radius inside of which light cannot escape (Schwarzschild radius)**Black Holes - Theory**• Defined by their rotation • Rapidly rotating holes will affect space around them**Black Holes - Theory**• Defined by their event horizon • Radius inside of which light cannot escape (Schwarzschild radius) • Defined by their rotation • Rapidly rotating holes will affect space around them • But how can they be observed??**Cygnus X-1**• A candidate for a *stellar-sized* black hole • ~ 11x more massive than Sun. • 8000 ly away.