Monday, August 2, 2010

10) Dark Matter: Odd Galactic Neighborhoods

If there isn't enough observable matter within a given galaxy to account for the fact that it does not simply fall apart, then what explanation (other than Dark Matter) is there for its formation? Is it possible that the galaxies formed in place, at their relative positions within the Universe, rather than being part of the debris field of some enormous explosion (the Big Bang)? It seems worth considering. Of course, if we do consider it, we must then ask where all the matter did come from.

Indeed we do.

For some, this question is enough in itself to dismiss any argument against the Big Bang altogether. Yet, I must hold out that to the open-minded, considering this question is no less sensible than believing that all the matter in the Universe originated from a singularity.

Speculation like this leads to many valid questions, not the least of which being, "What about all the other supporting evidence for the Big Bang?" A fair question to be sure, but that's what we're doing here; we're attempting to see if another hypothesis matches that evidence as well, or even better. Maybe there isn't one, but maybe there is. So, let us state the question a little more clearly: If there was no Big Bang, where did all the matter in the Universe come from?

Let us begin by considering the Hubble Ultra Deep Field Image, which shows thousands of distant galaxies glowing faintly against a deep-black backdrop. Oddly, the image seems rather unremarkable until you realize that these aren't just any galaxies - they are the most distant galaxies we have been able to photograph to date. In fact, if you haven't looked into it, click on the link above to learn more - it is well worth the time.

The actual distance to the galaxies in this image is not entirely straightforward. Yes, it took 13.2 billion years for the light we are now receiving from them to reach us, but the Universe has been expanding all along too. What's more, that expansion has, as far as we can tell, been accelerating the whole time as well. So, rather than attempt to establish an actual distance (which would add only marginal value to our discussion anyway), let's settle on the fact that they are ancient, and that we have yet to glimpse anything farther away. Perhaps even more importantly with respect to this discussion, is that this photograph is believed by many to show the galaxies as they were when the entire Universe was less than one billion years old (about 800 million years). I happen, not to agree, but won't expound upon the reasons until later.

In light of this, a couple things immediately leap out. First, as expected, this image appears to contain hundreds of young galaxies - that is, galaxies with shapes, colors and sizes to indicate that they were indeed captured during the early years of their formation. No surprise there. But, there are also what appear to be very mature galaxies, such as, HUDF-JD2 and others in the same region. This is odd indeed. Why would galaxies from largely the same region, and such an early period in the history of the Universe differ so greatly?

One possibility is that the more mature galaxies aren't as far away as they seem. We are not able to know for sure as yet, but astronomers believe they are. There is also the possibility that these galaxies just happened to have a larger starting mass than their neighbors, which could have accelerated their formation, in which case they are not older, but only further developed. This actually strikes me as quite plausible too.

But, what if they are older? How could galaxies from what appears to be the same region of space be of such vastly different ages? Are they drifters, just passing through the neighborhood? The evidence seems to suggest otherwise. Their redshifts, for instance, suggest that they are native to the regions where they appear.

The only explanation for this phenomenon having any degree of elegance is that they formed in place, but at different times. The only difficulty with this otherwise simple solution is the Big Bang. If all of these galaxies, old and new, are products of the same Big Bang event, then we have a disconnect - since we would naturally and quite reasonably expect all of them to be about the same age. On the other hand, if the galaxies formed place (at their relative positions) as a result of some other cause, then the mystery becomes....less mysterious - we need only discover what triggered their formation. And, fortunately, this may not be a difficult puzzle to solve at all.