EIU Astro

Cosmic Holes July 26, 2012

An artist rendering of a white hole
http://www.unsolvedrealm.com/wp-content/uploads/2010/12/white-hole.jpeg

We have gazed out into the sky for thousands of years, with each passing generation developing a deeper understanding how the universe functions.  In the last 100 years, developments in physics have lead to a greater understanding of the actual makeup of the cosmos than ever before.

Albert Einstein, the famous German-American physicist, helped to pioneer this deeper understanding.  Under the postulates of the Special Theory of Relativity, Einstein found that space and time were connected.  Through this connection, variation in space must be accompanied by a variation in time.  Under Newtonian physics, any object with mass has its own gravity, but space itself is “flat”.  Under general relativity, any object with mass will cause curvature in space and time.  This curvature is what we experience as the force of gravity.   As the mass increases, so does the curvature of space and the gravitational force. 

http://www.cosmosmagazine.com/files/imagecache/news/files/news/Black%20hole%20eats%20star.jpg

In the life cycles of stars, the more massive the star is, the more interesting its life will be.  Stars that have a mass over eight times the mass of our sun put on one of the most spectacular shows the universe can put on.   For stars greater than this, their end comes with a tremendous bang, in which much of the stars mass is ejected into space.  This phenomena, which can be seen from distant galaxies is referred to as a supernova.  The remnant for a star of such mass leads to high density neutron stars. For more massive neutron stars, the escape velocity becomes begins to approach levels nearing the speed of light.  For a neutron star with a mass high enough, the escape velocity will become so great that a photon will no longer be able to escape.  This stellar fragment is left with a highly dense core referred to as a singularity.  As you approach the singularity, there is a point called the event horizon.  This is the last chance for any particle or photon of light to turn back.  Should one dare to cross into this horizon, no matter your speed, there will be no journey back.

Early on into the history of general relativity, the very concept of this “black hole” was met with skepticism.  In their very nature, black holes are difficult to detect.  Due to a black hole’s possession of greater than the speed of light escape velocity, light itself finds itself helplessly ensnared in the cosmic hole’s grasp.  Thankfully direct detection of these phenomena is not the only way of detecting black holes in the universe.  Our best hope for detection of a black hole comes from the study of the effects black holes have upon other stellar phenomena. They can even lead to other death of nearby stars, flattening the star out as it is pulled towards the more massive objects gravitational well.  The result are X-rays as the doomed star is pulled into the black hole, which can be detected on Earth.

Cosmologists need not only rely of the detection of doomed stars to detect black holes.  We can look for deviations of a star from a predicted orbit of its type.  Another method is to observe stars that seem to periodically “disappear”.  In this case, its light can be seen to periodically disappear from sight of our planet, lending evidence towards the existence of a black hole.

Black holes may only come in one shape, however, there seems to be little limit to the size.  It has been postulated that at the center of our galaxy exists a super massive black hole, one which is thought to measure close to 4.5 x 10⁶ times larger than our own star, the sun. 

Penrose–Hawking singularity theorems

To form a singularity, it was postulated by Roger Penrose and Stephen Hawking potential black holes must qualify for one of these stipulations as solutions to Einstein’s field Equations:

1. A situation where matter is forced to be compressed to a point (a space-like singularity)
2. A situation where certain light rays comes from a region with infinite curvature.

http://www.inquisitr.com/wp-content/2012/01/black-hole.jpg

One great explanation by Karen Masters, an astronomer at the University of Portsmouth, of the phenomena is:
“In the full and most simple General Relativistic solution for a space-time which has a Black Hole (in a vacuum), there are two singularities. One is in what we call the ‘future-light cone’ and this is the Black Hole. The other is in the ‘past-light cone’, and is called a white hole. This solution is however completely unphysical in many ways and in a real black hole (formed from the collapse of a star for example) we cannot use the vacuum solution as there is matter present, in addition to the fact that the white hole singularity disappears.”

White holes now reside in the undetectable category that black holes were resided sixty years ago.  The history of white holes starts with the study of Quasars, which for many years were postulated much elusive “white holes”.  However, this has proven to be an ineffective description.  Quasars are themselves “powered” by gravitational forces caused by accretion disks.  The ejection of electromagnetic radiation is caused by compression of the matter from the circular motion inside the black holes.

http://www.eso.org/public/images/eso1122a/

In the mathematical theory of general relativity, there is a component which has lead scientists to the possibility of a time-inverted black hole, dubbed a white hole.  The idea behind a white hole is an “action-reaction” connection between black holes and their white hole counterparts.  For each particle that enters a black hole past the event horizon, there is corresponding emission of a particle from the white hole. From this it is postulated that each of these particles would exist in their own universe, one particle on “each side”.  It has been postulated Schwarzschild wormholes or Einstein-Rosen bridges could be theoretically formed connecting these to particles.  These would allow some object, for example a photon, to try to cross in the center at which the event horizons meet.  At this point, it could be possible to travel to the other corresponding hole.  The concept of such a bridge was approached by John A. Wheeler and Robert W. Fuller in 1962.  They found that such a path, such a wormhole would be too quickly pinched off, so much so as to not allow light from one exterior region (universe) to travel to another.

http://www-users.york.ac.uk/~mijp1/transaction/figs/fig02_h.gif

Sources

Karen Masters January 2002 http://curious.astro.cornell.edu/question.php?number=108

Hawking, Stephen & Penrose, Roger (1996). The Nature of Space and Time. Princeton: Princeton University Press. ISBN 0-691-03791-4.

John Roach  November 2, 2005 http://news.nationalgeographic.com/news/2005/11/1102_051102_black_hole.html