The Gravastar: An Alternative to Black Holes?

Colin RobsonMarch 27th 2014

Today, we thought that we would take a look at an alternative model for black holes. Personally, I’m not that fond of the idea in relation to it’s scientific validity, but I do think it is a very interesting hypothesis. Most of the time, we’re quite content to just sit back and follow the popular mindset in relation to scientific hypotheses and theories. Following the crowd and ignoring many of the “stranger” ideas that go against the norm is one way to ensure that you don’t look foolish; however, it is also one way to ensure that you remain stagnant. At the very least, we must be open to questioning. After all, that is what science is all about.

Nonetheless, we often cling to the tried and true. And this isn’t a recent trend; it is the way that we’ve been all through human history. For example, 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.

Which brings us to the Gravastar:

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 “Gravitational Vacuum Condensate Star,” which  is (in theory) an extension of the Bose-Einstein Condensate and put forward as a part of gravitational systems. Ultimately, it is meant to stand as an alternative to black holes.

Artwork by dnb-nOise on deviant art (See a larger image)
Artwork by dnb-nOise on deviant art (See a larger image)

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.

Next-stage Weirdness: 

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 and would require several pages of notes (the linked text can be used to see this information). For the time being, 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 (this isn’t any more dramatic than Stephen Hawking’s latest claim), anything that comes in contact with it becomes a part of it–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 “following” in the grand scheme of things. As I previously mentioned, this isn’t a theory that I personally like as a replacement of the standard black hole theory, but if we are to learn anything from our mistakes all throughout history when it comes to science, we really do need to keep an open mind. What might seem strange today may be a fact tomorrow…

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