A nebula is the name that is given to gaseous and dust particles that are widespread throughout the galaxies. They come in all shapes and sizes and have many different names. These include: planetary nebulas, supernova remnants, and diffuse nebulas and in them include reflecting, emission and dark nebulas.
Out of these the most likely for new stars are dark nebulas and luminous nebulas which are from diffuse nebulas. Diffuse nebulas are normally very large, often many light-years wide, and have no real outline because they have a cloud-like appearance. The matter is joined together by a lot of violent disordered currents. Diffuse Nebulas are either dark or light and are seen from earth because they reflect the light of a neighbouring star and because of that they appear to shine.
In dark, diffuse nebulas or slightly luminous nebulas, obscure part of the Milky Way. This is because they are too far away to reflect or emit a lot of light so they often appear as black circles in the sky.
Some other nebulas are supernova remnants, which are not very common, but some of the most spectacular nebulas in space. They emit very strong radio waves. This is because of the huge explosions that formed them and are most likely the pulsar remnants of the original supernova.
Some of the well known nebulas in the night sky are the Great Nebula in Orion (It is the middle "star" in the sword) and is a diffuse nebula. Another is the Horsehead Nebula in Orion is also a typical diffuse nebula.
In an interstellar cloud there is often a gravitational attraction of some of the matter. There is also a collision of particles and eventually this will form a central spot in the cloud which is known as a protostar. All the matter that circles the protostar is called a planetary disc. Eventually as the matter condenses and the heat builds even more it can form a sun or a brown star.
We have a very good example of an already formed one which is the solar system.
In our case the protostar eventually became our sun and the planetary disc is all
the planets. By studying our own planetary system many planetary scientists are
starting to understand the general mechanisms that make up the structure of planetary
systems.
See Protostar
A brown star is formed when there is not enough mass to make a full fledged star (anything less than one-twentieth the suns mass won't form) and is called a brown star. These "stars" will get warm but not hat enough to start the nuclear explosions which is how a star is finally formed. It will glow a little then start to cool off. When a star forms a circle of dust and gas surrounds it. This material could eventually form planets, like our solar system, or they could form brown stars.
A sun is a circle of very hot and glowing gas. Suns are hot and concentrated enough to set off nuclear explosions which are the suns fuel.
A protostar will become a sun when its core reaches a temperature of 10 million Celsius. When the temperature is that hot triggers nuclear reactions. During this time the hydrogen atoms fuse together to form helium, releasing a lot of energy in the process. This energy is the suns fuel and it radiates outward in the form of heat and light.
Astronomers work out the brightness of a star by measuring its magnitude and how bright
it is.
Magnitude lets astronomers to place how bright different stars are seen to humans.
Because of the way our eyes see light, a lamp twenty times brighter than a second lamp
will appear less than twenty times brighter to human eyes.
This inconsistency changes the magnitude scale, and so does the habit of giving bright
stars lower magnitudes. This means the lower a star's magnitude, the more bright it is.
Stars that have a negative magnitude are the lightest of all.
See the Sun in X-ray Wavelengths
Red giant stars are stars that are getting bigger and are in the later steps of a normal star life. They have used up their hydrogen fuel and are now using their helium and much heavier parts of the stars. A lot of the carbon and particles given out from red giant stars provide fundamental chemical materials for solar systems located all over the universe.
A star transforms into a red giant when its hydrogen fuel starts to run out. The core of the star gets smaller as it starts running out of hydrogen. But the outside of the star gets bigger instead of smaller because as the hydrogen is used up in the core it starts using it up in the next layers. A red giant can grow to become 100 to 1,000 times wider than the sun. Since the surface of the star is quite cool it is a red color instead of the more common blue or white.
A supergiant star is a very big, glowing star that can be seen from far distances around space and are old stars. The difference between stars that is going to become a supergiant over a more typical star is its weight. Astronomers estimate that a star must be at least six to ten times bigger than our sun in order to have a core big enough to change into a supergiant. The added weight makes higher core temperatures in the star's early stages and the outcome is in much faster nuclear reactions than in smaller stars. A star with a mass of 20 times the weight of our sun consumes hydrogen at a rate of 20,000 times quicker than our sun. That star would use the hydrogen in its core in a few million years while a star with the suns mass would take 2,000 times longer.
After all the hydrogen in a star's core has been consumed, the outer radiation force that used to hold up the star, spreads out making the star collapse. The outer part of the star condenses enough to cause the hydrogen to fuse in the next layer from the core. When this happens it creates a burning hydrogen shell that makes the external layers, of the star, to expand while the inside gets smaller. The outer layers get colder and glow a red color as they get bigger and will eventually become a red giant.
If the weight of a red giant's core is more than around 0.7 to 1.0 times the whole weight of our sun, the core will compress until its temperature reaches 100 million Celsius or hot enough to start the fusion of the helium atoms and they will turn into carbon. The radiation released by the fusing helium makes red giant to get swell to 500 times the size of the sun or bigger and become a red supergiant. The highest output of light that one of these stars could produce matches to an absolute magnitude of about 9 or the same amount as 600,000 suns. Knowing the maximum amount of light they can produce, the bright stars allows astronomers be able to use them as "standard candles" to estimate distances to the far corners of the Milky Way or maybe even to other galaxies where red supergiants are visible.
Bigger stars, those with weights of around 20 to 60 suns, have cores at a high enough temperature to make even more energetic nuclear reactions, and they seem to move even more precisely from the main-sequence stage, right to the blue supergiant stage. The blue supergiants may have a surface temperature exceeding 30,000 Celsius or over five times hotter than the sun. After the supergiants often explode into supernovas when the nuclear fuels in their cores are all used up. Or the outer part of the star is blown away and forms a planetary nebula by a supernova explosion that goes with the collapse of the core. When the core collapses even more, the atomic nuclei and electrons, in the center, combined to form neutrons. Then the core compacts into a globe only 20 km in diameter. It's called a neutron star.
If the weight of the supergiant's core is higher than three times the whole weight of the sun, the neutron star condenses even more, becoming a black hole. Most astronomers agree that earth and everything that lives on earth are made up of matter that was blown into space from a supernova from the collapse of a supergiant star that happened over 5 billion years ago.
Planetary nebulas, or planetaries, are called this because many of them seemingly resemble planets through telescopes. Actually, they are shells of material that an old, average star, discards during a late, red giant stage during its evolution. A planetary nebula is a gas cloud that is formed when a star grows old, then expands, and sheds its outer gas layers. Planetary nebulas have the name "planetary" because the first one that ever found had a similar comparison to Uranus.
When a star can't have any more nuclear reactions, it will collapse for the last time. If the weight of the collapsed center has a bigger mass than the Chandrasekhar limit, or around 1.4 suns, the center will collapse into a neutron star or maybe a black hole. Most stars that collapse, though, have cores or centers with a mass less than 1.4 suns. The cores of all the other stars collapse to a transitional state named a degenerate electron state. The deteriorated electron core is more commonly known as a white dwarf. The outer part of the collapsed star, which is up to 90 percent of the whole mass, is blown in away during the collapsing process to a planetary nebula. It creates a circle of glowing matter surrounding the collapsed star. It is also called a planetary disc. Several thousand planetaries have been discovered in the Milky Way Galaxy alone.
A White Dwarf is old star that has used up all its nuclear fuel that it can use and has collapsed, but it still gives off light from the heat energy that was trapped inside the star when it collapsed. This is the final glowing stage in the development of low- to medium-weight stars. Depending on the weight of a star, it could go through a lot of stages, one right after the other, by using helium and after that much heavier elements for its fuel. But, in the end, all stars will, in time, reach a point where they can't support fusion reactions at all.
The density of a white dwarf could range from a hundred million to one billion kilograms, meters cubed or five thousand to fifty million times denser than earth. A star that's the size of our sun would collapse into a ball the same size as earth and it would have a density of around 109 kg/m3, or around 500,000 times that of earth. Compression of all of the matter and heat energy in a star's core makes the temperature of the center extremely hot. The concluding temperature of a big white dwarf that has a weight near the Chandrasekhar limit can have a temperature over 80,000 Celsius. The inward pressure caused by a lot of weight squeezes the atoms together. With the end result, as matter is added to a white dwarf, it actually gets smaller, not larger. This means, that the smaller white dwarfs are the biggest, while the bigger ones are the smallest.
Objects that have a temperature that is over 8,000 Celsius, give off light that is a brilliant blue-white color. As it emits light, the star loses its energy and slowly cools, changing from blue-white, to white, to yellow , to orange, and then, when it has a temperature of around 4000° C, it's a dull red. If a white dwarf cools down less than this temperature, it won't to give out visible light and would become black dwarf. Since the biggest white dwarfs are actually the smallest, they cool at a very slow speed. In fact it has been estimated that the biggest white dwarfs, those that are near the Chandrasekhar limit, would take several times the age of the milky way to cool down enough to cool down to become a black dwarf.
Astronomers think that white dwarfs are quite abundant. They may have a similar amount as
all the stars you can see at night.
Even though all white dwarfs are extremely hot early on, they are so tiny that only the
very brightest and closest ones are visible using the most powerful telescopes.
Instead, white dwarfs are usually detected as non-visible companions in binary stars.
That's a system of two gravitationally bound stars.
If the white dwarf accumulates enough material to cross the Chandrasekhar limit, it will
collapse again to become a neutron star.
See a white dwarf
A black dwarf is a burnt-out core of an old star that can not emit light any more and is believed to follow the white dwarf. It is also believed to be the final stage of medium sized stars.
As a white dwarf cools off it gives out radiation. After time the color goes from blue to white, then to yellow and then to red and then after billions of years, it doesn't shine at all in the visible side of the spectrum, so it appears black. Astronomers call these small, intense, and cold cores that have crystal-shapes, black dwarfs.
An object like this could only be spotted with technology that we have today if it were part of a double (binary) star system. It would work by two stars that revolve around a center weight, so the gravitational effect the black dwarf had on the other star would be noticeable. Since we haven't been able to do this yet, no black dwarfs have been truly identified.
Supernovas are rare, for only 5 supernovas have been visible in the Milky Way Galaxy from earth in the last 1,000 years. Some supernovas are so bright they can be seen in the day without using a telescope. A normal supernova can produce as much light and other kinds of electromagnetic radiation as billions of other stars.
After a lot of the hydrogen is used up, a star goes into a carbon-building phase. This means the fusions turn the helium into carbon. After the helium is used up most of the stars slowly cool off until they don't give out radiation any more. But if a star is 8-10 times bigger than the sun the carbon core gets crushed under its own weight. Its temperature rises high enough to fuse carbon into oxygen, neon, silicon, sulfur, and iron. The thermonuclear process in the stars core is almost finished when this happens. At this point, the external pressure that's produced by the reactions doesn't longer balance the inward gravitational attraction between the atoms. As a result, the core and the star collapse inwards making the gravitational energy into energy of movement. But only the star implodes, the atmosphere explodes outwards. The particles in the star's atmosphere start moving away from the star, making the atmosphere separate from the star. Remains from supernovas have material that may eventually become parts of new stars and planets.
The two different kinds of supernovas are Type I and Type II. The main difference is how much hydrogen is in their remains. Type I supernovas are usually older stars that have completely used up their hydrogen. Type II supernovas are usually younger stars that have exhausted the hydrogen in their core but have some left in their atmospheres. All supernova explosions make clouds of rubble and let go of a lot of energy, but Type Is usually totally demolish their parents but Type II explosions often leave the stellar center behind. Both types have glowing clouds left, are often still seen centuries later and are called supernova remnants. How much of the core left behind by a Type II supernova depends on the weight of the supernova.
If the star had a mass of around ten times the Sun the core collapses the protons and electrons turn into neutrons. The consequential result is the body is composed of only neutrons, so astronomers call it a neutron star. If the weight of the star is more than 10 suns the nuclear forces that hold up a neutron star are too weak to resist the core's gravitational pull. Then the core collapses farther than the neutron star. It collapses until all its weight could fit in a space smaller that a city on Earth. The gravity is so strong that an object would have to travel faster than the speed of light. So nothing can escape and the core attracts any matter or radiation that comes close to the core. When this happens it is called a black hole.
Astronomers learn about the final stages of huge from supernovas. Also supernovas can
give hints give to the source of the chemical elements that create stars, planets, and
even life.
A supernova in a far away galaxy can help astronomers calculate the distance, from earth,
to the galaxy.
Astronomers do this by examining the radiation that's given out from the star's
atmosphere. Then use the information they got from this to model how wide the shell is.
Then they evaluate the width of their model to the width of the shell that is seen from
Earth then calculate the approximate distance to the supernova remnant and its galaxy.
See a supernova
A neutron star is a rapidly spinning, and extremely dense star. They are made up of mostly neutrons, which are very small neutrally charged particles and live in the center of atoms. A neutron star is created when the center of a supergiant star has converted all of the material in its core to iron. At this time no further nuclear explosions can take place to create energy, so the core collapses under the its own weight. When a massive supergiant star uses up all the nuclear fuel in its core, the core colapses and compacts together under the huge gravitational forces and when this happens the star starts to spin faster. If the mass of the core is greater than approximately 1.4 times the whole mass of the sun the core will give way with such a great force that the positive protons and negative electrons in the core will all be compressed together to become neutral neutrons. When this happens there will eventually be a neutron star.
The last stage of the formation of the neutron star is when the outer part of the collapsing star caves in when the nuclear fusion in the core is all used up. The outer part of the supergiant is about eighty percent of the total mass of a supergiant. The outside doesn't become a part of the final neutron star though. When the outer part falls through the very strong gravitational field of the neutron star and falls onto the to the neutron star's surface, the material of the outer part obtains a very great amount of energy. When this highly energetic material hits the surface of the neutron star, huge thermonuclear reactions are started at the same time all over the surface of the star, which blows the outer part into a big round circle of gas and debris surrounding the newly formed neutron star. Right before the star becomes a neutron star it is five times its final weight. Most of it is blasted out into the supernova explosions that is a normal part of the formations.
After a neutron star has fully formed these are the parts. There is an atmosphere that's a few centimeters thick. It has a surface crust that's about 1 km thick, made up of iron that's 10,000 times more dense and stiff than any iron that's found on the earth. Under the iron crust is a liquid-like ocean of neutrons, which is a liquid-like material that's even denser than the crust itself, but it moves with very easily when any forces are applied (also known as it doesn't have any resistance to movement). At the center there is a core that is made up of nuclear particles that are totally unique to the neutron star.
As a neutron star gathers matter, it grow smaller, not larger. It occurs because the additional mass multiplies the gravitational pull of the star's material, which squeezes the matter even tighter together. If the mass of the collapsing core is heavier than about three times the mass of the sun, the gravitational forces will exceed the strength of the material itself so the core collapses until it is invisible. If this happens it's called a black hole.
A neutron star can also be called a pulsar. This is because the magnetic field at the neutron star's exterior, which is probably a trillion times more concentrated than the magnetic field of earth, would make electrons moving near its magnetic poles to put out energy that's in the form of radio waves and would make a signal that's sweeping across space every time the star revolves. Something that's located within the sweep of radio-frequency radiation would see a radio signal that pulses every time the star rotates . This is why neutron stars are also called pulsars because the radio signals seem to pulse because you can only see them as the star turns around to the same side.
When a neutron star is near another star the powerful gravitational field of the neutron star can deform the outer layers of the nearby star and pull material from that star to the neutron star. As it gets closer the material speeds up to very fast speeds and when it crashes into the surface the thermonuclear explosions release very powerful beams of X-rays and gamma rays.
The gravitational and nuclear forces that hold a neutron star together join to make the most intense, foreign material that's in the observable universe. Calculations expect that a neutron star is probably only 10 to 20 km in length, yet it keeps all of the mass of the supergiants, core which is at least 1.4 times the total weight of the sun. A teaspoonful of the neutron star would weigh about ten billion tons when on the surface of the earth. Even though the surface is really stiff the great gravitational forces on the star make the hills very small and only get as tall as a few centimeters high. The magnetic field of a neutron star would very compact and would spin at the same very fast speed as the neutron star itself. It is amazing that over 500 neutron stars have been found in our galaxy alone.
A black hole is a very intense space object that has been speculated to live in the universe. The gravitational field of a black hole is so powerful that, if the object is big enough, absolutely nothing, even electromagnetic radiation, is able to break away from its surrounding area. The area surrounding a black hole is encircled by a round area, which is called a horizon. In it light can go in to but not leave, which makes it appear completely black. The more we know about galactic black holes helps astronomers to learn about the how galaxies are evolved and also the connections between galaxies, black holes, and quasars. In 1994 astronomers, using the Hubble Space Telescope, found the first believable evidence that a black hole exists.
Stephen Hawking, an English physicist, has suggested that a lot of black holes could have formed in the early universe. If this is true, a lot of the black holes may be too far from other matter to be detected They could also make up a major part of the total mass of the universe. In reaction to the concept of singularities, Hawking has also said that black holes do not collapse way but form "worm holes" to other universes.
The theory that a black hole can exist was made by the astronomer that was German,
named Karl Schwarzschild, in 1916 and was based on Albert Einstein's theory of relativity.
His theory stated that the boundary of the horizon of a black hole depends on the mass
only; being 2.95 km times the mass of the body in solar units. Solar units are the
weight of the black hole divided by the weight of the sun.
Then if a black hole is electrically charged or moving his results were changed slightly.
According to general relativity, gravitation changes space and time near a black hole.
Once a body has contracted within its Schwarzschild radius, it would theoretically
collapse into a dimensionless object that has a infinite weight.
