Life of a Star
Before looking at how a star collapses to become a black hole, let’s look at its life. Stars are formed inside vast clouds of gas and dust to drift together to form clumps called protostars. Each protostar shrinks until its center becomes so dense that nuclear reactions begin inside it, and it starts to shine. The Orion nebula, a huge cloud of gas and dust is lit by the light of nearby stars. Stars come in different sizes. The Sun is a pretty average star, which glows yellow. Larger stars glow blue or white because they are hotter, but they don’t shine for as long. Smaller stars glow Orange or red. They are cooler and last longer.
After thousands of millions of years, the nuclear reactions in the sun will stop. Gravity will then squeeze the core, creating heat that will make the outer layers swell, swallowing Earth. The outer layers will drift into space, leaving a planet-sized star called a White dwarf.
Formation of Black Holes
Karl Schwarzschild predicted that a Black hole would be formed when a massive star stopped shining and collapsed in on itself. The gravity would be so large that the material would become more and more dense, making the gravity still stronger. Gravity would eventually become so great that the star would keep collapsing past its gravitational field! In 1939, American astrophysicists Robert Oppenheimer and Hartland Snyder used mathematics to show that this collapse would happen.
Gravitational Radius
The French Mathematician Pierre Laplace used Newton’s laws to calculate the size of a body that would stop light from escaping. Karl Schwarzschild calculated at what distance from the center of a body the escape velocity would be the speed of light. He used Einstein’s relativity theory. Remember that the force of gravity between two objects gets greater as the objects get close together. At a certain distance from a body, the gravity becomes so great that the escape velocity becomes greater than the Speed of light.
Schwarzschild calculated the relationship between this distance from a body’s center and the mass of the body. This distance is known as the Schwarzschild radius. For bodies such as planets and stars, Schwarzschild’s radius is mush smaller than the body. For example for Earth it is less than one half of an inch, and it is about one and a half miles for the sun.
Schwarzschild’s theory was that a black hole was formed if the gravitational radius of a body was larger than its actual radius. This means a body would have to be squeezed into an extremely tiny space. For example, Earth would have to be squashed to the size of a pea for it to become a Black hole.
Theoretical Black Hole
Armed with Einstein’s theories, the German astronomer Karl Schwarzschild (1873-1916) developed the idea of the black hole as we know it today. He did not call it a black hole. This term was first used in the late 1960s by the American physicist John Wheeler. Before Wheeler, they were called “Frozen stars”.Reference for Technorati
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Changing the Rules
There are two important differences between Laplace’s idea of a dark star and the modern idea of a Black hole. The differences are due to two important discoveries of modern astrophysics. The first discovery is that nothing can travel faster than light. This means that if light cannot escape from a massive star, nothing can. This also means that a dark star is a hole, because nothing that is pulled in by the star’s gravity can never escape. The second difference is that Laplace used Newton’s law of gravity as the basis of his work. Modern astrophysics says that these laws do not work in and around Black holes.
Dark Stars
Pierre Laplace (1749-1827), a French mathematician and astronomer, was one of the first people suggest that black holes could exist. As an expert on celestial Mechanics, he knew how the planets and moons move around the sun. In his book, Exposition of the System of the world, published in 1795, Laplace made an amazing prediction. Laplace realized that if a star were massive enough, its escape velocity would be greater than the speed of light. So he calculated how big a star would have to be, if it had the same overall density as Earth, to have an escape velocity equal to the speed of light. He calculated that the star would have to be 250 times the diameter of the Sun. Laplace predicted that a star of this size would have such an enormous gravitational pull that light particles would have such an enormous gravitational pull that light particles would never leave its surface. The star would be invisible.
Light and gravity
When Sir Isaac Newton devised his Law of universal Gravitation, he also suggested that light was subjected to the pull of gravity. On Earth, light always travels in a straight line, unless it hits an object. But light does bend as it passes close to bodies with very strong gravitational fields, such as very massive stars. This shows that the things we take for granted on Earth do not necessarily apply when super strong gravity is at work.
Black Hole
A black hole is a place in space where gravity is so super strong that nothing can escape it not even light. When scientists call a black hole a giant cosmic vacuum, they do not mean it sucks up anything that comes near it. However, anything passing close to a black hole will be affected by its strong gravitational pull. Astronomers think that events become very strange both near and inside black holes. The known world ceases to exist, time slows down, space is warped, and the accepted laws of physics no longer apply. No one should go into a mysterious black hole to investigate, because they would never return.
In most great mysteries, such as UFOs, science tries to explain the strange things that people claim to have seen. In the case of black holes, however things are the other way around. Scientists predicted the existence of black holes long before there was any real evidence that they existed. In fact, the very nature of black holes means they cannot be seen to be believed!
Varying Heights
Astronauts become 1-2 inches taller while they are in space. Without Earth’s gravity tugging on their bodies, the vertebrae in their spines stretch out. The extra height is only temporary, though. Astronauts shrink back to their normal size after returning to Earth.
Life in the slow lane
Time slows down when traveling at great speed in space, so space travelers age more slowly than they do on Earth. Albert Einstein figured this out
In 1905, long before we started flying in space. Einstein knew the speed of light never changes as it is constant. Time however, is relative said Einstein. It can change. It changes according to the speed of what is measuring it. The faster the speed, the slower time passes. In fact, a very accurate clock aboard a space shuttle was measured after its return to Earth it lost 2.95 x 10^-10 seconds for each second of the trip. If the shuttle had been traveling near the speed of light and had been gone for several years, the time loss would have been bigger. So if you went on a very long space trip and our space craft could travel close to speed of light we would be younger than our current same-age friends when we returned to Earth.
Weight on different Planets
Planet Earth Weight Multiply by Our Space Weight
Mercury ----- x .38 =
Venus ----- x .91 =
Earth ----- x 1.00 =
Mars ----- x .38 =
Jupiter ----- x 2.34 =
Saturn ----- x .93 =
Uranus ----- x .79 =
Neptune ----- x 1.14 =
Pluto ----- x .04 =
Relative theory of Einstein
Einstein made other predictions in his General Theory of Relativity. He said that in super strong gravitational fields, time passes more slowly than it does outside the field. And as gravity becomes infinitely strong, time actually slows to a stop. He also said that all laws of geometry would no longer be true because three-dimensional space would be changed and distorted. For example, the geometry rule that the area of a square is equal to its length multiplied by its width would not be true in super strong gravity.
Einstein’s other great theory, the special Theory of relativity, predicted that the passing of time and the measurement of distance change as movement becomes faster and faster. The effects of this become noticeable only as the speed of light is approached. This would have the consequences for black holes, since objects that fall into black holes would begin to go as fast as the speed of light.
Mass and Weight
Mass and weight are often confused. In physics, the mass of an object is the amount of matter in it. Mass is measured in kilograms (kg). Weight is the pull of gravity on an object. Weight is a force. It is measured by both the mass and gravity. It is measured in units called Newton (N). The mass of an object is always the same, but its weight can change.
Escape Velocity
Imagine throwing any object straight up. The Earth’s gravity would gradually slow it down and make it fall back to Earth. But if the object was thrown upward fast enough, gravity would not be able to stop it escaping into space. The minimum speed needed for this to happen is called Escape Velocity is 25,000 miles per hour. Space Rockets must accelerate to a minimum of 17,000 miles per hour to stay in orbit around Earth. They must travel faster to escape from Earth.
Astrophysics
Astrophysics is the branch of astronomy that describes the physical characteristics of things in the Universe. Two of the characteristics that astrophysicists study are Gravity and Light
Nature of light
Light travels in waves of particles called photons. Eyes detect light. Some objects, such as stars, can be seen because they make light. Other objects, such as planets of this book, can be seen because light bounces off them. Light travels very fast. In the vacuum of space, the speed of light is 186,282 miles (300,000 kilometers) per second. Its sped decreases when it passes through substances, such as air and glass.
Gravity
Gravity is a force that attracts every object that has mass towards every other object that has mass towards every other object. Mass is the amount of matter an object, or body contains. The amount of gravitational pull between two bodies depends on the mass of the two bodies and the distance between them. The greater the masses the greater the force. The further the distance between them, the smaller the force. The amount of gravitational pull between bodies is very massive, such as a planet.
This is called the Law of Universal Gravitation. It was first written by the English scientist Sir Isaac Newton (1642-1727). This law of gravity explains how the gravitational pull between bodies causes the planets to orbit the sun. A body has a gravitational field around it. Any other object in the field experiences a pull from the body, which pulls the object towards it.
Unsolved Mysteries
For centuries, people have been puzzled and fascinated by mysterious places, creatures, and events. Why have ships and planes vanished without a trace when crossing Bermuda Triangle? Are some houses really haunted by ghosts? Does the Abominable Snowmen actually exist? What secrets are held by a black hole? Read on my future posts to know about some of these facts.
Halley
Halley’s Comet zooms by Earth regularly, and so it has a chance a tiny one of colliding with our planet. During a flyby, the famous chunk of ice is easy to spot, even without a telescope. For example, there are reports from 240 B.C., when ancient Chinese stargazers saw it without any problem.
Here’s a timeline that shows some of the world changing events that happened between Halley’s visits. As you will see, Halley doesn’t appear at exactly even intervals. By computing the averages time between visits what year would you except the comet to turn up next?
1338- Hundred Years war starts between England and France on 1301 Visit.
1405- Chinese Sailors explore the Indian Ocean on 1378 Visit.
1492- Columbus sets sail to find a route to Asia through the Pacific.
on 1456 visit.
1910- World War I begins on 1910 visit.
1986- First Official U.S. observation of Martin Luther king Jr. Day, in honor of slain civil rights leader, space shuttle Challenger explodes
Meteor Master
Hero who could spot and stop Doomsday Meteor would be Carolyn Shoemaker. Since 1983, she has discovered more than 800 asteroids and 32 comets, some of which cross Earth’s orbit. Mrs. Shoemaker is already a hero in the eyes of world astronomers. Working with her husband, Gene, and David Levy, she discovered Comet Shoemaker-Levy 9.
Jupiter’s gravity had grabbed the comet and forced it to orbit the gas giant instead of the Sun. The powerful gravity ripped the comet into 21 pieces, all of which slammed into Jupiter in 1994. The spectacular crash gave astronomers an exciting glimpse at the chemistry of Jupiter’s mysterious atmosphere.
Stick Man
It’s a map of galaxies! In 1986, astronomer Margaret Geller led a team of researchers to pinpoint the location of more than 1,000 nearby galaxies. The map shows that galaxies are not evenly spaced in the universe, but grouped together in narrow bands with large spaces or voids between them. Geller nicknamed the image the “Stick Man” because it resembled a stick figure with arms outstretched.
Andromeda
The closest major galaxy to Earth, the spiral-shaped AndromedaGalaxy is the most distant object visible to the naked eye. It lies about 2.5 million light-years from Earth and contains over 200 billion stars.
Hang Ten
The circle of sky is divided into 360 degrees. The “hang ten” sign shows about a 20-degree distance when holding your hand out at arm’s length. This is roughly the length of the Big Dipper. A closed fist measures about 10 degrees, and one finger equals one degree. At night, identify a major constellation, like Orion or Ursa Major.
