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The Crab Nebula was formed when it's host star exploded as a supernova [See related question]

a nebula is classified by a planetary nebulae

What basically happens is that the "dying star" has enormous energy production at the end of its life, due to a kind of instability. The resulting heat will fuse lighter elements into heavier elements - resulting in production of elements at least up to element number 92 (uranium).

This process is known as planetary differentiation, and it is believed to have occurred early in Earth's history due to the planet's heat and pressure. The heavier elements sinking towards the core created the dense metallic core, while the lighter silicate minerals rose to form the Earth's crust and mantle. This differentiation is responsible for the layered structure of Earth.

Large Spiral Galaxy. This is because they contain more of the OB stars that are required for a supernova event.

Elliptical galaxies tend to be older and have more low mass stars and are not as common as spiral galaxies.

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To calculate the density of the white dwarf, we first need to determine its volume using the volume of the Earth. The volume of the Earth is about 1 trillion cubic kilometers. If we assume the white dwarf is roughly the same size as the Earth, its density would be the mass (1.3 Msun) divided by the volume of the Earth. This calculation would yield a rough estimate of the white dwarf's density.

Whether a star will become a neutron star is determined by its mass. Generally, stars that are more than 8 solar masses (have a mass that is more than 8 times that of our Sun), but are less than 15 solar masses will become neutron stars when they die.

Because it IS a supernova remnant.

It's the visial remains of a star that expolded and was seen in 1054. Designated SN 1054.

Not much, really. Our Universe MIGHT be significantly larger than what we can see -- that portion of our Universe we call the "observable Universe" -- or it might be infinite. No conclusion can be made about the size of our Universe based on the fact of the Big Bang.

The first recorded supernova was observed by Chinese astronomers in 185 AD, which is known as SN 185. However, the discovery of the first modern supernova, SN 1572, was made by the astronomer Tycho Brahe in 1572.

According to the Book on Astronomy written by Susan Douglas and Ryan Smith, they must be anything taller than a minimun of 1,200 m (meters)

The most massive ones. The exact amount of mass requires varies, depending on the type of supernova, and on the element mix of the initial star.

The mass of a star determines how it ends its life cycle. Less massive stars become white dwarfs, shedding their outer layers as glowing shells of ionized gas (planetary nebulae). Stars 10+ times more massive than the Sun can be rendered as supernovae, as their cores collapse into black holes.

clouds of dust and gas

That will happen to stars that are very massive.

It was first observed by Chinese astronomers in 1054 AD, but given it's (estimated) distance from earth of 3,600 light years, the actual explosion would have taken place 3,600 years earlier, or around 2,500 BC.

yeah

Depending on your version of Google Earth. Go View --> Switch to sky --> search for Crab Nebula or M1

It will destroy it in a cataclysmic explosion.

A white dwarf is the remnant of a star that has lost most of it mass. When it is formed it is very hot indeed but, as it now has insufficient mas to carry on fusion, it begins to cool down. For objects as massive as stars, even dwarfs, this cooling down takes a long time but eventually a white dwarf will cool down completely and become a black dwarf. Red dwarfs are never very hot as they have barely sufficient mass to effect fusion so don't do it very vigorously. However the fact that they go about their fusion slowly means they can maintain their meager temperatures for a long long time indeed. Some red dwarfs are older than the calculated age of the universe. (which is an interesting paradox) a

nova

What this person^^^^^ is really trying to say is that : The hottest star is white dwarf.

Xibalba is the name of the Mayan underworld ... essentially the equivalent of the Greek Hades (the place, not the god). Also, the Mayans appear to have regarded a dark rift in the Orion Constellation as being the road to Xibalba. On Ganymede, one of Jupiter's moons, there is a feature (a sulcus, which is basically a kind of ditch) named after it; that's the only modern non-fictional astronomical reference to it that I know of The nebula in the movie, The Fountain, is referred to as Xibalba, which the Mayans believed to be the Orion Nebula. There is no star or nebula technically referred to as Xibalba, but as you can see throughout the movie, it is shown to be within the constellation Orion and specifically the location of the Orion Nebula. According to Wikipedia: "The Maya of Central America had a folk tale which dealt with Orion's part of the sky, known as Xibalba. Their traditional hearths included in their middle a smudge of glowing fire that corresponded with the Orion nebula. This is clear pre-telescope evidence that the Maya detected a diffuse area of the sky contrary to the pin points of stars."

During the main life cycle of a star, no elements heavier than iron can be created, and that's only in very massive stars (our sun is only massive enough to fuse hydrogen into helium). Your question is a very good one, and if you thought of it on your own, you should be proud. Every element heavier than iron is created when the star dies. Specifically, when it becomes a super-nova. When all the lighter elements have been fused, the star can't generate enough energy to resist its own gravity, so it collapses in on itself. The result is a sudden gigantic spike in pressure that creates all the heavier elements. As if it weren't cool enough that we're all made from star-stuff, a good bit of us is made from supernovae, too!

Ok, a bunch of interstellar dust began to collect in a slightly hotter region of the solar system. The gravitational attraction between these particles began to draw them closer and closer to each other. Since the density near the center of the cloud was constantly increasing, the kinetic energy of the cloud also increased. The outer parts of the dust cloud began to spiral around the center. Eventually, the gas in the center became so hot and dense that it condensed to form our sun, fusing its hydrogen particles into helium. The outer rings of space dust then began to condense at other key points around the sun, maintaining their orbital velocity but being held at a constant distance by the star's gravitational pull. These clouds of dust eventually condensed to form the planets and the asteroid belt. This explains why all the orbital paths of the planets are within a few degrees of the same plane. As for galaxies, just extrapolate that explanation to the next level, replacing the dust particles with stars. Mind-blowingly simple, right?