Gravity and Black Holes Einstein’s Discoveries Albert Einstein •Albert Einstein was very famous physicist and mathematician in the early 1900’s •Escaped from Nazi Germany in the 1930’s and came to America •Worked as a patent officer, with science being his “part time job” •Einstein created the theory of general relativity and completely changed how scientists thought about light, gravity, and the universe Albert Einstein •Much of what Einstein did is way too difficult for even me to understand! •Today we’ll cover the basics and talk about how his work applies to astronomy •E=mc2 •Gravity •Black holes •Dark matter Speed of Light •Light travels a at specific speed: 300,000,000 m/s or 670,616,629 mph In math terms, we write the speed of light as “c” Light always travels the same speed, no matter what! 3 +2 = 5 mph 3 mph c ?? 2 mph c! E=mc2 •Anyone know what this means? •E=mc2 means that energy (E) is equal to something’s mass (m) times the speed of light squared (c2) •Energy is measured in Joules (J) •1 Joule is the amount of energy you would use to lift an apple 3 feet in the air How much energy do you have? Let’s figure out how much energy you are! 1) What’s your weight in Kg: 1Kg=2.2lbs Ex) 120lbs = 120/2.2 = 54.5 Kg 2) Square the speed of light: c2 = 300,000,0002 m2/s2 = 9*1016 m2/s2 3) Multiply your weight times c2 Ex) 54.5kg * 9*1016 m2/s2 = 5*1018 Joules! What is gravity? •Gravity is the force with which objects attract each other •Isaac Newton came up with the theory of gravity •Newton watched an apple fall from a tree and wondered why? •Force of gravity on Earth: F = m*g m is mass (in Kg) g is the acceleration due to gravity (m/s2) On Earth, g = 10m/s What is gravity? •Gravity is the reason why we stick to Earth •Gravity always points down towards the center of the Earth •Gravity makes objects fall at the same speed no matter how heavy they are •Gravity is different on different planets: On the moon: g = 1.5 m/s2 On the sun: g = 276 m/s2 Law of Gravitation •Everything in the universe attracts everything else with some amount of gravity •Gravitational attraction: F = G*M*m/r2 G is Newton’s gravitational constant M and m are the masses of two objects R is the distance between them r M The strength of gravity is directly proportional to the objects mass and inversely proportional to its size! m How does gravity work? •Gravity makes our world go ‘round, literally! •Scientists know very little about how gravity works! •We see proof of it working every day, but can’t explain why it works the way it does •Einstein came up with an idea of why it works…… How does gravity work? •Before we can understand how it works, we need to understand Einstein’s idea of spacetime •We live in a 4 dimensional world: 3 spatial dimensions, 1 time dimension •If you combine these you get spacetime! Einstein’s idea of gravity •You can think of space time as a flat sheet of rubber that is bendable (like a trampoline) •Space time can be bent my big objects (just like a person jumping on the trampoline) DEMO! Einstein’s idea of gravity •Gravity is not produced by an object “pulling” on you •Gravity is the result of an object bending spacetime, turning spacetime in that area into a funnel shape Einstein’s idea of gravity •Heavy objects such as planets, stars and galaxies bend spacetime •The moon revolves around Earth because its sitting inside the funnel of spacetime earth created •The planets revolve around the sun because the planets are caught up in the funnel of spacetime the sun created Movie Time! (gravity) Einstein’s idea of gravity •This is a cool idea, but how do we know it’s true? •We have seen light bend in spacetime! Real Photo Black Holes •Einstein’s ideas about the speed of light and gravity had very important implications to astronomy •With his ideas, we can sort of understand black holes! •A black hole is a very massive region of curved spacetime from which light cannot escape! (remember light travels at a finite speed) Artist view Black Holes •Black holes don’t suck!!!! •They are NOT like a giant vacuum in outerspace! •Black holes bend spacetime into a funnel like shape, causing objects and even light to fall inside of it! Formation of black holes •Black holes are formed when a very big star dies and explodes! Formation of black holes •After the star explodes, gravity pulls the material back until it’s super compact •The black hole collects more mass and the gravity keeps getting stronger until it is so strong that nothing can escape its pull! F = G*M*m/r2 M = huge R = tiny => F is gigantic! Artist view Radio & X-ray Jets Event Horizon Black Hole Unstable Zone Accretion Disk Artist view Where are black holes? •Most Black holes are found at the center of galaxies •We know they exist because we can see them! •The closer things get to a black hole, the faster they rotate around it •This movement heats up the surrounding material and glows very brightly NGC 1097 M 64 Two types of black holes There are two basic types of black holes: •Stellar-mass black holes are small black holes that weigh the same as about 1 star. •They can exist anywhere in space •Supermassive black weigh as much as 100 million stars and are at the center of galaxies NGC 1097 M 64 Death by black hole? •What do you think would happen if you could travel into a black hole? You get Spaghettified!! Artist view Movie Time! (BH) Gravity and Dark matter •On day 1 we saw that 96% of the universe is made of things we don’t understand! Proof that dark matter exists •“Proof” that dark matter exists can be found in galaxies if you understand how gravity and black holes work •Black holes bend spacetime into a funnel shape, so stars orbiting the center of a galaxy should act as if they are trapped inside a funnel Demo: Funnel (galaxy) marble (star) hole in funnel (black hole) Roll a marble on the inside of your funnel and watch how the speed at which it circles the center changes as it falls closer to the hole. What do you observe? Proof that dark matter exists •Scientists predict that stars closer to the black hole will orbit faster than those farther away Speed of stars orbit •Observations say this is not true! All stars in a galaxy orbit at about the same speed! Event horizon Black hole Proof that dark matter exists •Physics says velocity (speed of star’s orbit) is proportional to the amount of mass (weight) in the region near that star V= √(G*M*m)/R V= velocity G=gravitational constant M= mass of BH m=mass of star region R=radius (distance to BH) •Since G is a constant, the distance from the black hole to the star doesn’t change, and we can measure the mass of the BH, the only way to make V go up is to increase the mass of the star region (m)! •Therefore, there must be some “invisible” matter (dark matter) near the edges of galaxies making stars orbit faster than theory predicts! The search for gravity waves •This is all very fascinating, but how do we know it’s true? •Scientists are hard at work trying to figure out exactly how black holes work and prove that gravity is really a result of the manipulation of space time •Like we saw in the video, objects moving through spacetime create ripples in space called gravity waves •If we could “observe” or measure these waves, we could fully prove Einstein’s Theory of Relativity What are gravity waves? •When an object moves through space, it creates ripples in spacetime. •Similar to dropping a pebble into water What are gravity waves? Black holes cause objects to rotate very quickly, causing large amounts of gravity waves LIGO: A new kind of telescope LIGO is a ground based “telescope” used to search for gravity waves Two telescopes: one in Louisiana, one in Washington L-shaped buildings 2.5 miles long on each side How does LIGO work? Laser Detector Gravity waves Laser Detector When a gravity wave passes though the detector, spacetime is bent, causing the laser beam to travel a further distance and take more time to reach the detector What have we found? To date, LIGO has not detected any gravity waves  Their influence on spacetime is so small that our instruments are not precise enough yet to detect it Enhanced LIGO Advance LIGO Summary •Einstein was a genius who told us that mass=energy, the speed of light is constant, and gravity is the result of curved spacetime •Black holes form after a giant star dies, and have gravity so strong that light cannot escape its pull •To prove Einstein’s theories, we are currently searching for gravity waves using LIGO