what is the difference between a nebula and a black hole?
444306
Nebula, in the most basic sense, is any observable cloud of gas.  You have objects like the Orion nebula (a star forming region), the Ring Nebula (a "planetary" nebula that is the result of a low-mass star's death), and the Crab Nebula (gas expelled during the supernoave death of a higher mass star).\n\nA black hole is, at its most basic, a region of space where the local escape velocity exceeds the speed of light.
451952
Gravitational attraction between all the gas and dust in a nebula, and maybe their electrical charges too.\n\nGod should be spelled B-I-G B-A-N-G\nPBrax@netscape.com
252532
A black hole is a super dense hole in space with an extremely powerful gravitational pull (not even light can escape).  The 12 months come from the ancient Romans, and to the best of my knowledge aren't related to constellations.  Life on Earth evolved from a "chemical soup" of elements.  These elements cam together to form amino acids, which formed proteins, which over billions of year multiplied and evolved into the 10 million + species on earth today.
286980
Black holes do not give off any light, so they can't be seen directly.\n\nWhat we can see is the EFFECT of the black hole.  \n\nOne effect is caused by the fact that massive objects will bend light as it passes them - this is called "Gravitational Lensing".  \n\nAs a result, if we detect light from a distant star that is distorted in the specific pattern of gravitational lensing, we can deduce that there is a dark, massive object at the center of the distortion.\n\nAnother effect is produced when matter that is pulled into the black hole.  Once matter or light gets closer to a black hole than the critical distance (the "event horizon") it vanishes into the black hole and is never seen again.  But, matter NEAR the black hole that is falling into it will give off light or other radiation as it is destroyed by the black holes gravitational force.  This radiation includes bursts of X-rays, which we can detect.\n\nThe first black hole that was detected is called Cygnus X-1 (it is an X-ray source in the constellation of Cygnus, the swan).
641573
Black holes have the greatest density. In fact is infinite in a point named "singularity", the black hole`s heart. All this because all the mass of a large star (who died to become a black hole), is condenses in the singularity. Density is mass/volume. And a point have no dimensions...
152097
Different nebula can have different temperatures.  Nebula like the Orion Nebula are really hot because the stars in the center part of the nebula are heating them up to around 10,000 Kelvin.  However, when stars aren't around, nebula can get extremely cold, just a few degrees above absolute zero.\n\nNebula that were formed by exploding stars, such as supernova remnants or planetary nebula, can be even hotter, into the millions of Kelvin.  This is because of the massive amounts of energy that were released in the star's death.
127702
Black holes are full of electrons.They are not capable of any expansion or constriction. Time also does not expand.
74582
ALL STARS HAVE A GRAVITATIONAL PULL FROM THE OUTSIDE IN, WHEN A STAR LOSSES ALL ITD HYDROGEN THE GRAVITY PULLS THE STAR INWARDS(BASICALLY IT IMPLODES) WHNE IT INPLODES IT CAUSES A BLACK HOLE, WICH SUCKS IN THE STAR AND ALL LIGHT AROUND IT. THE INSIDE OF A BLACK HOLE IS CALLED THE EVENT HORIZON, NOTHING CAN EXCAPE THE EVENT HORIZON ONES ITS IN IT. NOT EVEN LIGHT! THATS WHY ITS BLACK! CAUSE ITS SUCKS UP ALL THE LIGHT. KINDA SCARY IF YOU ASK ME!
94500
The gravatational pull from a black hole is so strong that the likelyhood of an object being released is slim at best. The reason it is called a black hole is because gravity is so strong it even absorbs and disburses the waves and particals that make up light. Most scientists believe that even atomic coheasion is lost so that the smallest particals of the nuclious are torn apart.
274083
No.  A black hole is an immensely dense object, like taking all the matter in our solar system plus more, and condensing it to the size of a pea or so.  The moment we could "create" one, the entire earth would be "sucked into" it.
695407
Excellent question! It's got many of us thinking.\n\nThe nature of black holes is such that not everything cannot escape from it, contrary to popular belief.\n\nBlack holes will emit high energy photons in a gamma ray burst.\n\nDavid Cline at UCLA suggests they are the detonation of microscopic black holes formed in the Big Bang, which most astronomers believe was the beginning of the universe. If the idea is right, billions and billions of relatively nearby, primordial black holes are just waiting to explode. \n\nSome may exist just beyond the orbit of Pluto, based on the math.\n\nThere was a recent article in New Scientist regarding a similar topic to this. Another good point for research would be NASA's Chandra telescope pages.\n\nI'll certainly be discussing this one with my team!
84045
A black hole is the collapsed stellar remnant of a supernova (a nova is an entirely different phenomena caused by matter falling onto a white dwarf). Depending on how massive the star is either a white dwarf (lightest) a neutron star (heavier) or a black hole (heaviest) form when a star dies.\n\nType II Supernovas are the catastrophic, yet natural, deaths of massive stars. The star has to be 8 times more massive than the sun to cause a supernova. \n\nOnce a star has used up all of its hydrogen in the fusion processes in the core, there is no more pressure to keep the stars core from collapsing under its own weight. Eventually it gets so hot that the helium begins to fuse which again causes pressure that temporarily halts the collapse. In a star like the sun helium fusion is the end. Once the helium is spent the stars core begins collapsing again while its outer layer puffs out into space leaving a white dwarf. \n\nIn a more massive star carbon fusion, which produces neon and manganese, takes over when the helium is spent because its gravity can cause temperature and pressures great enough. When the carbon is gone the core begins collapsing again. This goes on for several stages of contraction with resulting fusion of increasingly heavier elements. \n\nFinally silicon fuse into iron and the core is the size of earth. The temperature is over 3 billion degrees. No more energy can be produced from fusion as iron is too tightly bound in its nuclei. Instead the iron core collapses with a quarter the speed of light. It shrinks in size from the size of earth to a sphere 100 kilometers across in less then one tenth of a second. This produces gravitational energy 100 times greater than the energy the sun has put out during its entire life. This energy is what blows the outer layers of the star apart. In the expanding envelope neutrons are created that slam into other nuclei to form extremely heavy isotopes. As they decay they form elements heavier than iron. \n\nIn the core, denisty is now so great that protons and electrons can no longer exist. Instead they begin to form neutrons. When that process is complete a neutron star, about 10 to 20 km in diameter, is born. \n\nIf the mass of the star is so great that not even the neutrons can keep it from coallapsing further eventually you end up with an objects so dense its escape velocity becomes greater than the speed of light and a black hole is born.
377533
None. electron hole pairs is simply absence of electron in an atom or molecule. Black hole is a collapsed matter in the Universe due to strong gravity.
727897
Supernovas.  Blackholes don't give much back to the universe other than minute sub atomic partices (and not even many of those); similarly with neutron stars.  The sun makes heavier elements like iron, but not the heaviest.
378154
It is not a star going supernova that creates a blackhole. Its the collapsing of its core that does. Just wanted to clear that up.\n\nA blackhole is created when a star is so massive (at least 20 times that of our Sun) that the bonds between the atoms, or molecules, are no longer strong enough to fight against the force of gravity.  This causes the star to collapse in on itself, and eventualy create a blackhole.\n\nThere are some beliefs that a blackhole could lead to a parallel universe.  But this gets a bit hazy in details, as no one knows for sure, and its currently impossible to prove or disprove.  A blackhole has an "event horizon", that once you have passed through you cannot get back out, nor can you see past it from the outside.  Because of this event horizon, it is very unlikely that you could get out of the blackhole into another universe .....\n\nHowever ..... A theoretical astronomical body called a white hole has been predicted, although its existence has not yet been proved.  It is the opposite of a blackhole, in that instead of "sucking" up all the matter in its path, it spews it out instead.  IF this exists, then there is a chance that a white-black hole pair could be a gateway to another universe, or another part of our universe.  But I can't stress enough, this is purely theoretical, and absolutely NO proof has been found yet.
1145852
Nothing; the "hole" in space isn't like a hole in your shirt, but rather like a giant pit.  What falls in stays in (of course, this is a three-dimensional hole that sucks stuff in from all directions, but we'll stick with the hole-in-the-ground analogy for simplicity)\n\nWhat has been discovered mathematically by people like Hawking and Chandrasekhar is that black holes actually do give off radiation (so-called Hawking radiation) through its effects on local space-time right at the event horizon.  At this specific region of space, charged pairs of virtual particles appear, and every now and then, rather than rejoining and annihilating each other in a tiny flash of light, one particle escapes and goes flying off away from the black hole while the other gets drawn in.  The escaping particle is considered matter, while the one getting drawn in becomes antimatter.  As the antimatter reaches the center of the black hole, it cancels an equal mass of matter and the black hole gets infinitessimally smaller.  An old black hole (one that has consumed all the matter in its vicinity) therefore gradually "evaporates" over a VERY LONG TIME (about 10^61 times the age of the Universe for a 30 solar mass black hole!) until its mass is so small that its gravity is no longer strong enough to hold in light, and it may do any number of things -- explode, fade out and become a really big hunk of red-hot metallic stuff, sit and remain a giant, dark gravity well... depends on what kind of math you like and the current theories at the time you calculate it.
731883
A black hole is a star which has loss most of its mass but retains enough gravity to trap everything including light\n\nA quantum Singularity is close to the same definition of a black hole but it is a point in space that can contain unlimited amounts of mass or things\n\nA wormhole is an unsteady disturbance in the space time continuum that allows for easy journey between two points in space within a reasonable time. Wormholes are sometimes believed to be on the other side of black holes often called white holes for the fact that if they were on the other side of black holes that constantly capture light it would be radiating from the other side