For many years, we believed that the Earth was flat and that one could eventually fall off of the globe. We also believed that the Earth was the center of the universe (some people still do). And several ancient civilizations even used to use mercury as a medicine. Fortunately, we tested these ideas and came up with better ones.
Since Sir Isaac Newton described gravity in his publication, "Principia." in 1687, to John Michell conjectured that there might be an object massive enough to have an escape velocity greater than the speed of light, to 1970 when Stephen Hawking defined modern theory of black holes, which describes the final fate of black holes, we have always been fascinated about the nature of black holes. But what if I tell you thatâ€™s not it. You don't believe me? Well thatâ€™s okay. To those that do not believe me, leave now or just shut up and don't comment. To those that are interested, prepare to have your mind blown.
What is it? This is an unconventional idea that is as interesting as it is odd. This hypothesis was originally put forward by Mazur and Mottola in 2004. Gravastar literally means â€œGravitational Vacuum Condensate Star,â€ which is (in theory) an extension of theBose-Einstein Condensate and put forward as a part of gravitational systems. Ultimately, it is meant to stand as an alternative to black holes.
One of the benefits of the Gravastar over that if an ordinary black hole is that of entropy, the current accepted models of black holes have them having a very large entropy value. Gravastars, on the other hand, have quite a low entropy. The theory goes that, as a star collapses further [past the point of neutron degeneracy] the particles fall into a Bose-Einstein state where the entire star [all of the collapsing material] nears absolute zero and is able to get very compact. As a result, it acts as a giant atom composed of bosons.
The interior of these Gravastars is thought that it might be within a de Sitter Spacetime, which means that it has a positive vacuum energy which could give rise to an internal negative pressure. Most of the math that goes into explaining this new model for a black hole is extremely complex. It suffices to say that this theoretical model consists of 5 different layers that construct the Gravastar, with de sitter spacetime effectively creating the negative pressure that keeps the Gravastar from collapsing along with some other mathematical constructs. Instead of using the Einstein field equations to calculate the event horizon of a black hole, Mazur & Mottola put forward that the event horizon (as we know it) is actually the outer shell of the Bose-Einstein matter, anything that comes in contact with it becomes a part of itâ€“similar to matter hitting a neutron star and being broken down into neutrons due to the environment.
Over the past few years this model has been getting more and more attention as a contender of the current black hole model; however, it still only has a small â€œfollowingâ€ in the grand scheme of things.