Differences

This shows you the differences between the selected revision and the current version of the page.

how_can_x-rays_escape_the_gravity_of_black_holes 2009/01/16 11:10 current
Line 1: Line 1:
+**Since Black holes are basically a type of gravitational well absorbing matter at varying rates,  since itâ€™s taught that  matter cannot escape the gravity of a black hole, why then X-rays escape the gravity effects of a black hole?**
+----
+{{ :750px-accretion_disk.jpg?200x100|}}
+Good questions.  X-rays don't escape from _inside_ the black hole, but
+rather come from hot material right _next to_ the black hole.  Once
+that hot material goes inside the black hole, no X-rays or anything
+else ever come out again.
+
+Why does stuff get hot when it falls into a black hole?  Basically, as
+stuff starts falling toward a black hole, it moves faster and faster
+(just like if you drop something, it falls toward the Earth faster and
+faster).  However, the stuff falling toward the black hole hits
+_other_ stuff that's also falling toward the black hole.  The effect
+of this is to heat everything up.  This is just like what happens when
+your hand heats up if you rub it back and forth on your desk.
+Finally, why does hot stuff emit X-rays?  Well, we know that hot
+things glow--if you put an iron rod into a fire, it will eventually
+glow red, and then white.  If something gets _extremely_ hot (several
+million degrees) it emits not visible light, but X-rays.
+
+So that's the story.  Here's a nice artist's impression of the whole thing:
+http://en.wikipedia.org/wiki/Image:Accretion_disk.jpg
+
+The X-rays are coming from the disk of material around the black hole.
+
+Take care,
+Greg
+
+<sub>Image source: Wikipedia</sub>
+

how_can_x-rays_escape_the_gravity_of_black_holes.txt · Last modified: 2009/01/16 11:10 by czars · [Old revisions]