Discussion in 'Astronomy, Exobiology, & Cosmology' started by thed, Jan 17, 2002.
a bh has no more gravitational effect than a body of similar mass.
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The actual thing is that for example,the quasars quasars that we see that look so bright are not the black hole, the supermassive black hole, they are the gas and interstellar dust that's just about to fall into the supermassive black hole, that's going around it, shining very brightly just before it disappears down the black hole.The gas rubs against itself essentially and gets extremely hot and extremely hot gas shines very brightly just a second before it falls to a black hole.That's why you see light,X-rays.And they also discovered that 6 or 7 stars near the centre of the Milky Way galaxy were spinning around the dark centre 1000 km/s.Only one thing in the universe is dense enough to speed these stars up-supermassive black hole.
You can't see a black hole directly - that's what makes it a black hole - so what you're looking for is evidence of its gravity, you're looking at how it pulls on the stars that are coming nearby.Pretty simple.
First of all,we don't know enough about light,but what we do know yes,light can be also wave and that it also has mass,since gravity bends the entire universe/space time,and the light travels inside the space,if the space is warped,than the light is warped to.The light can't get out from the black hole,because escape velocity must be greater than the light speed.
Einstein said that closer an object at rest is to a gravitational field, the more time dialates. An example for this is, if I am floating in mid air above earth, the closer I get to the Earth, more time slows down for me. We don't notice this because Earth isn't very massive compare to some other objects, so it has a less gravity. Mass of black hole is enormous, so there is alot more gravity than on earth. Closer an object is to the black hole, more time dialates. Closer the light travels to a black hole, the time dialates more (slows down). If time slows down, but the speed of light stays the same, then its frequency must decrease, and its wavelenght must increase. If light travels so close to this very massive object (black hole) that time dialation increases to the point where it almost stops, then wavelenght would increase to infinity, and frequency would almost be infinitely small. If frequency is shifted to 0 then, there really is no light, which what makes black holes black in the first place.
Can light orbit a black hole just outside its event horizon?
Yes they can, but not for long. The event horizon of a non-rotating black hole is located at a distance, R = 2 G M/c^2. But just outside this horizon at a distance of R = 3 G M/c^2, an incident photon is deflected into a circular 'photon orbit'. These orbits, however, are unstable and after a few orbits, the photon will either spiral inward into the event horizon, or manage to escape to 'infinity' with a very large redshift. Matter can orbit a black hole at distances much greater than the photon orbit radius depending on their velocity, however, for rotating black holes, the so-called Lenz-Tirring 'frame dragging' effect prevents any long-term, stable orbits for matter within about R = 10 G M/c^2.
Why can gravity be 'seen' from a black hole but not light?
Because as seen from a distant observer, all of the mass of the black hole perpetually hangs just outside its event horizon, and from there its gravitational field can reach infinity. Light, however, gets badly redshifted rendering it optically invisible, hence black.
Can black holes really form if it takes an infinite time for matter to fall inside its event horizon?
Imagine a star emitting light, and collapsing to form a black hole. As seen from someone riding the surface of this star, it will only take a few hours for it to fall inside its Event Horizon. As seen from far away, there will come a moment when the last photon emitted by the star has been emitted by the the star's surface when it was just outside the event horizon. When this last photon reaches you at an enormous redshift, the light from the star will have been extinguished. But the amazing thing about the infall process is that you will receive that last photon thousands or even millions of years in the future.
The surface of the star, as seen from your vantage point, may take an enormous amount of time to actually fall inside its horizon, but as seen from the surface of the star, it only takes a few seconds. Black holes, to the external observer, are what physicists call an 'asymptotic' solution to general relativity, which means that they may technically take an eternity to form in our rest frame, but they form nevertheless because the physics of the freely falling observer will see this event as a very well defined and fatal one that takes only a few hours to occur.
Could a galaxy ever collapse into a black hole?
Yes, at least theoretically ( what else!!).
It would take a very long time, however. The stars move in stable 'Keplerian' orbits which could continue as they are for trillions of years...long after the stars themselves have burned out. But objects on elliptical orbits radiate gravitational radiation, and eventually through the very weak leakage of gravitational energy away from the orbiting stars, the orbits around the center of the galaxy begin to slowly drift inwards. Eventually, the cold stellar cinders merge into one vast 'supermassive' black hole and that is the end of stellar matter in galaxies. The time this takes is enormous...something like 10^150 years or more, so this end state is only relevant to galaxy evolution in an infinite universe destined to expand forever. Sadly, this is the kind of universe we seem to be living in!
Can a star clog a black hole that is swallowing it?
No...A black hole is not really like a drain pipe! In fact, if it consumes matter at too ferocious a rate, the radiation pressure generated by the infalling matter provides tremendous resistance to the flow of matter.
The rate at which matter can fall into a black hole is regulated to what is called the Eddington Accretion Rate, which depends on the mass of the black hole. Also, it all depends on whether the star has been captured into orbit or is just passing by. Orbital capture means that the black hole, over the course of millions of years, can leisurely nibble away at the star 'without choking' at the Eddington Accretion Rate.
Also,photons are emitted when electrons in an atom shift from one level to another. They emit a photon and a neutrino. Because of the immense gravity in black holes, there is no distance between electrons and the nucleus of the atom. They are pushed togather into one unit. No space for the electrons to move.
Also:Understandings of black holes is that they rotate; are sperical (but by no means perfectly so), and are extremely massive - the largest individual masses known in the universe.
This combination of; an extremely dense object, that is roughly sperical and is rotating at tremendous velocities will create massive variances of gravitational force vectors emitted from the hole and a whirlpool of directions for them to be applied.
Also, anything spinning must have an axis. Even if a black hole axis wobbles it will still have an astronomically smaller velocity around the poles compared to the particles sitting on its equator and thus super massive variances in the black holes gravitational pull is to be expected.
The jet streams of high energy photons and antiparticles that are emitted (or did they escape?) from black holes is a perfect example of the "Axis of a black hole" or "place of least resistance" that will exist with any rotating object.
The second part concerns lights - Wave Particle Duality. This duality shows that light also behaves like a particle of mass. If light/photons behave as if they have mass is it any suprise that a black holes gravitation can stop or at least diffuse lights quanta.
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