28th October 2007 - 04:24 PM
I appreciate the Wikipedia ideas from Mr. Robin Parsons but they are not really entirely tallying with actual observations that can be made though it is a popular interpretation of the way things could be. Obviously the "surface of Black Holes" do not radiate light. No surface radiates light unless it has internal sources of energy or is reflecting. It is doubtful there is a surface there at all. This does not mean that the object does not emit light. It is indeed absorbing "stuff". It is true that if "Black Holes" were truly black then we could not see them at all with our telescopes. In fact we can see some of these objects with relative clarity in some HST pictures. The interpretation of these images can be pretty confusing when there is some commentary that emphasizes how "black" they are. Actually this blackness is usually just a cleared zone in the vicinity of the "Black Hole" where most of the matter has "gone down the drain". If nothing is currently "going down the drain" perhaps they do look black.
I still maintain that we really do not understand Black Holes yet. Hawking Radiation is not as easy to explain as all that and while the idea that a Black Hole can radiate completely away to nothing by only absorbing 1/2 the mass of matter falling into it sounds a little "strained". There is a real problem about the information
contained in this influx... theory suggests that it cannot actually be destroyed, this has "implications" regarding its "blackness". The latest theories are a lot more complex than "simple Black Holes" of a few years ago. "Black holes" must radiate.... and eventually must completely radiate away returning all the "information" swallowed in the process. This foils many of the original theories including some of those of Stephen Hawking.
It really does not matter where the energy is escaping from though... Black Holes emit light and one example of it is M87 where the Jet of matter is very visible and pointed generally toward the Earth where it is moving in our direction at nearly the speed of light. The light from the central object is still red shifted since it must climb out of the gravity well while the light from the Jet is blue shifted and moving toward us. If you classify objects just on red shift then they "look" much older and further away than Hubble Shift alone would suggest if we could separate them accurately.
Many objects in our Universe are "older" than the theoretical age of the Universe itself by that reckoning... Naturally this is "impossible" and gravitational red shift accounts for some of these difficulties. Due to relativistic effects this Jet in M87 appears to us to be traveling at six times the speed of light in our general direction while the distance to the Black Hole is artificially exhibiting a larger than normal red shift..
Here is a picture of that Black Hole M87 (quite visible) and note the red shift in the core and the blue shift in the plume...
... Click to enlarge...
The light is still Doppler shifted and there are complex ways to look at this problem.http://en.wikipedia.org/wiki/Fuzzballs
These fuzzball objects are more probably what Black Holes are really like. I really do not like stories about rents in the spacetime continuum and their "infinities" without a description of "what lies beneath" the carpet of that spacetime and the subsequent stories about breaking the Laws of Physics. These "mystical" descriptions which are meant to impress may lead to awe and also to complex tricky answers that provide no real answers. The laws of physics are not "broken"... its our simplistic theories that are "broken" and are in need of repair. I don't know why some physicists prefer these "mystical" descriptions rather than calling a spade a spade.
Here are some very recent images of Black Holes in context showing an image seen by the HST (including M87).http://www.damtp.cam.ac.uk/user/gr/public/bh_obsv.html
The event horizon is not normally seen and many pictures are showing a cleared space near to the Black Hole and identifying this with the event horizon. I doubt that that is true. The observation of an event horizon is dependent on a number of factors depending on how the Black Hole is rotating. Note that these Black Holes are certainly not "black" and are visible as bright areas at the core that are red shifted. Claims to having seen actual event horizons are a bit far fetched when you consider how small these objects are and how far away they are supposed to be despite the false Hubble Shift. Only very bright objects can be seen with the HST and I discount event horizon sightings reported in the popular lore.