interesting suff ont he universe

[Icefrisco]

i would like to know some interesting facts on the universe. the only one i no is that the stars in the sky are millions of years old(light take sa while to travel). any others?

[Time Commander Bob]

Here's a few facts:

-Most of the universe consists of dark energy and dark matter. Scientists do not yet know what they are. Only 0.5% of the universe consists of stars.
-At the centre of the Milky Way there is probably a supermassive black hole that has a mass 3.7 million times greater than the Sun. Most galaxies are believed to contain supermassive black holes in their centre.
-The nearest star to the Earth (apart from the Sun) is Proxima Centauri which is 4.24 light years away.

[Shatterer]

-At the centre of the Milky Way there is probably a supermassive black hole that has a mass 3.7 million times greater than the Sun. Most galaxies are believed to contain supermassive black holes in their centre.

Sounds interesting...why do such things happen?

[eventhorizen]

Because there is a force called gravity where matter is attracted to matter, and a non uniform spread of matter after the big bang. These two properties result in matter forming 'clumps', ultimatly leading to the all the matter in a given locality being attracted to some central focus point of the gravitational pull of all the nearby matter.

If the density of matter at one of these focal points reaches a certain level, gravitational attraction overcomes different forces such as nuclear forces, electromagnetism etc. and these 'clumps' will continue to contract and increase in density. This leads to a singularity.

At the same time, a certain density is reached whereby any light that gets within a certain distance to this 'clump' does not have the velocity required to 'escape' and will either orbit the clump at a specific distance, or be 'pulled' into this clump due to the curvature of spacetime due to the density of the clump.

The area around the 'clump' where light cannot escape, but only orbit the 'clump' is called the event horizon. This is the 'black' bit. Combine a singularity and an event horizon and you have a (true) blackhole.

The exact density of the 'clump' required to eventually become a singularity is something I do not know offhand, but any Star that has 2.5 times the mass of our own Star will have enough material left over when it goes supernova to eventually form a blackhole.

Now galaxies are full of billions of stars, and all these stars are close enough to be gravitationally attracted to each other. Infact gravitational attraction has no limit, only strength, so infact all matter is gravitational attracted to all other matter, throughout the entire universe.
However the proximity and strength of the gravitational forces of all the matter in our galaxy is enough so that all the stars in our galaxy are slowly being attracted to the centre of the galaxy, and if a blackhole is not already present, eventually a blackhole will form at the centre of the galaxy, and eventually all the stars and matter in the galaxy will end up inside the blackhole.

[chris_uk_83]

And did you know that when you get particularly close to a black hole, the gravitational field causes spacetime (the universe) to bend in odd ways and makes time slow down for you?

However the proximity and strength of the gravitational forces of all the matter in our galaxy is enough so that all the stars in our galaxy are slowly being attracted to the centre of the galaxy, and if a blackhole is not already present, eventually a blackhole will form at the centre of the galaxy, and eventually all the stars and matter in the galaxy will end up inside the blackhole.

I don't think this is actually true, all the stars just orbit the supermassive black hole in the centre of the galaxy, in the same way that the planets in our solar system orbit our sun without falling into the sun.

[eventhorizen]

And did you know that when you get particularly close to a black hole, the gravitational field causes spacetime (the universe) to bend in odd ways and makes time slow down for you?

Yes, and did you know that the closer an observer gets to an event horizon, the further away it appears, and did you also know that it is impossible for an observer to observe an event where an object actually crosses the event horizon?

I don't think this is actually true, all the stars just orbit the supermassive black hole in the centre of the galaxy, in the same way that the planets in our solar system orbit our sun without falling into the sun.

See now given enough time, all the planets in our solar system would fall into the sun, or they would eventually escape from being in orbit around the sun. There are a great many forces at work between a massive orbiting object and the massive object it orbits, that work to slowly 'bleed away' orbital energy.

An example of this would be tides on Earth. This energy is not 'free', but is taken directly from the energy within the moons orbit. This is not the only force exchanging energy between the Earth and Moon and vice versa, but it does mean it may be realistically impossible to have a perfectly stable gravitational orbit.

However Star formation is different to planetary formation. Star Formation is always the result of a coalescing of matter and an implosion/ignition. Planetary formation is, in our solar system anyway, the result of the blast following the ignition of the fusion processes in the star.

Stars do not orbit this central blackhole like planets orbit a star.
The entire galaxy rotates like a huge disk, because over 95% of the galaxy is made up dark matter that we cannot detect easilly. It is almost as if Stars themselves in a galaxy are imbedded in a huge invisible thick fluid that is slowly rotating and draining away into the central unplugged hole that is the galactic centre blackhole.

There is no mechanism or force from within a galaxy itself, barring some kind of intelligent life anti-galactic-death-ray of life, that we know of, that can prevent the slow attempted but futile, accumulation or 'rain' of matter onto the surface of the quantum singularity, which will be accelerating and collapsing and so becoming more dense and increasing the external size of the blackhole via its eventhorizen and strength of its gravitational fields.

The singularity will accelerate its implosion or collapse and so get further and further away from all objects, inside 4 dimensional space. Matter will approach the event horizon and be torn apart, never actually being able to see beyond the external edge of the event horizon, even as the forces beyond the event horizon tear them apart. This matter, its constituent parts, will never, ever reach the singularity, because the singularity is collapsing to infinity and continuing to accelerate, and it had a head start. The distance between the quantum singularity, and any object that falls into the blackhole, will only ever increase and increase, even as the object moves further into the blackhole.

Consider this. A blackhole with an event horizon of a diameter of the one at our galactic centre has an event horizon with the same radius roughly as our planetary system, including Pluto.

From one edge of the event horizon, across its diameter, to the opposite edge, is the same diameter as the orbit of Pluto.

The distance from the internal edge of the event horizon to the quantum singularity, the internal radius of this object, will be approaching infinite.

Consider a volume of space, such as say a volume of space in your bedroom. Imagine inside this volume of space is a small sphere, now imagine that the edges of this sphere continue to contract inwards, moving away inwards in each direction, and moving further away from every object in the Universe in all directions.

The expansion of space is an inwards expansion. Distances between galaxies that are far apart increase, because each region of space which holds these galaxies is expanding inwards.

The two dimensional representation of relativity, the heavy balls on a trampoline surface, show that space stretches and expands in a third dimension. When you apply this to a three dimensional enviroment, you have the expansion of space, due to gravity, being at a tangent to all two dimensional co-ordinates. In the presence of gravity, space expands inwards.

This is my interpretation of the interaction between gravity and spacetime, and ofcourse people are free to disagree with it, but I dont see any inconsistancies, and indeed this interpretation, to me atleast, seems entireally accurate.

[Semi Skimmed]

This song always impresses me...

Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour,
That's orbiting at nineteen miles a second, so it's reckoned,
A sun that is the source of all our power.
The sun and you and me and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm, at forty thousand miles an hour,
Of the galaxy we call the 'Milky Way'.
Our galaxy itself contains a hundred billion stars.
It's a hundred thousand light years side to side.
It bulges in the middle, sixteen thousand light years thick,
But out by us, it's just three thousand light years wide.
We're thirty thousand light years from galactic central point.
We go 'round every two hundred million years,
And our galaxy is only one of millions of billions
In this amazing and expanding universe.

The universe itself keeps on expanding and expanding
In all of the directions it can whizz
As fast as it can go, at the speed of light, you know,
Twelve million miles a minute, and that's the fastest speed there is.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger all down here on Earth.

Might not be terribly accurate, but it serves a good purpose - it reminds me how utterly insignificant we all are.

[chris_uk_83]

Did you know that Black holes eventually reach a state of equillibrium where any matter they 'suck in' is converted to energy and re-radiated by them? It's called Hawking Radiation and it does exist (at least the theory is sound)
http://en.wikipedia.org/wiki/Hawking_radiation.

It's not really accurate to talk about black holes as 'giant intergalactic plugholes' because they don't actively suck everything in. If anything gets too close then yes, it will fall in, but it's only like things crashing into stars. It is quite possible to orbit a black hole and not fall in, just as it is quite possible to orbit a star without crashing into it.

For more on black holes click here

The planets won't eventually 'fall into the sun' because there is no force to cause them to do this. Kepler's third law of planetary motion states that the orbital radius of a planet will remain constant as long as its velocity, mass and the gravitational field it is moving through remain constant.
http://hypertextbook.com/physics/mec...l-mechanics-1/
Therefore, the only way for the planet to 'fall into the sun' is for its mass to change (unlikely, unless we blow part of a planet away), the gravitational field of the Sun to change (again, unlikely unless the Sun's mass were to change) or the velocity of a planet to change (impossible unless acted on by an outside force, of which there are very few. Gravity from other stars and planets will have an effect, but it is minute and will cause no noticable difference).
The orbit of the Earth has been constant enough for over 200 million years (we know this because if it had changed much, it would not be able to support life and we have evidence that dinosaurs roamed the Earth around 200 million years ago). That's pretty good evidence that the orbit is constant.

It should also be noted that dark matter is only a theory and the only reason anybody thinks it exists is becasue the expansion of the universe is accelerating when it should be slowing down. This observation itself could yet turn out to be flawed. The other alternative is that we just don't know enough about gravity yet to explain the expansion properly, though we're still working our way there.