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.

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.

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.

Betelgeuse

As a red supergiant, Betelgeuse boasts a distinctive orange color that stands out against the mostly blue stars of Orion. Its brightness varies over a period of about seven years and is unpredictable, sometimes changing in just few weeks.

Orion

Orion is one of the most easily recognized constellations with its distinctive “belt” of three bright stars. The Greeks saw the star as a hunter, but Native Americans saw a group of running deer. Syrian astronomers believed the stars formed a giant called AI Jabbar. In the northern hemisphere, you cannot see Orion in June. However, you can see it in Chile in June.

Nebula

A nebula is an enormous cloud of gas atoms and tiny particles. Nebulae are the birth place of new stars and some dying stars leave nebula as wreckage. The smallest nebula is much larger than the solar system and the largest are hundreds of light years across. Some nebula is bright while others are dark. The brightness could be due to their atoms getting affected by the energy given out by neighboring stars. Dark nebulae appear as black starless areas, since they are absorbing light from stars beyond

Big Dipper

The Big Dipper- a star group appeared in the sky in early March, 10.30 p.m., but by 3.30 a.m. It’s moved far to the west. The stars don’t really move, of course, but the earth is constantly on the go. Imagine the sky as the inside of a great hollow sphere, with the stars as fixed points on the sphere. Picture the earth as the center of that sphere.
Where you are on the earth and how the earth is moving determines which parts of the inside of the sphere you see. As the Earth revolves on its axis, the stars and constellations appear to revolve in the sky around a point directly over the axis. The earth not only revolves on its axis, but it also changes position as it orbits the Sun.
So in late September the Big Dipper will appear low in the sky. And in March of next year, it will appear to be in the same place it was this march.

Polaris

Also called the Pole Star and the North star, Polaris sits almost exactly over the North Pole. Polaris has long been important to navigators because of its position. It is located at the tip of the handle of the Little Dipper (Part of Ursa Minor)

Images of Binary star

BInary Star

A Binary star or a double star is a pair of stars that revolve around each other and are held together by gravity. The closer a pair of stars are, the faster they revolve. Some Binary stars are almost touching and go around each other in a few hours, while others, which are separated by hundreds of times the diameter of the solar system, may take a million years to orbit each other. About a quarter of all known stars belong to binary systems. Most of these, particularly the close pairs, must have been born together. In most cases, one star is large, cool and reddish while the other star is small and white hot.

Images of Neutron Star

Sirius

Sirius is the brightest star in the sky. It is at a distance of 9.5 light years from the Earth. It is also known as the Dog Star because it lies in the constellation of Canis Major, the Greater Dog. Sirius is actually a binary star and it is made of two stars that orbit around each other. Only the brighter of the two can be seen with the naked eye. Sirius was important in ancient Egypt before the calendars were developed. The appearance of Sirius coincided with the annual flooding of river Nile.

Supernova Remnant

Rings of glowing gas are all that remain of a supernova explosion. While this star ended its life in a spectacular eruption of energy and material more than 170,000 years ago, light from the catastrophe didn’t reach Earth until 1987.
Once it burned bright in the sky and then faded to the glowing rings as shown in the picture.

Eta Carinae

When super massive star Eta Carinae exploded about 150 years ago, it became the brightest object in the sky. Eta Carinae released as much light as a supernova, but it managed to survive as a star. Today the debris stretches over a distance equivalent to the diameter of our solar system. Its outer edges are moving away from the center at about 1.5 million miles per hour.

Pleiades Star Cluster

Glittering like jewels in the night sky, the Pleiades is a cluster of new stars over 4000 light years from Earth. Though only a few are visible to us, the cluster contains hundreds of stars. The bluish glow that seems to surround the stars is a cloud of interstellar gas and dust, which scatters blue light from the stars. Different people have called the cluster “Seven Sisters”, “Bunch of Grapes”, and “Sailing Stars.”