One of the most important questions in cosmology these days is: “What is dark matter?” I’ve brought up dark matter in a previous TC diary. Its existence of dark matter was deduced from the fact that the observed motion of galaxy arms required a vast distribution of invisible matter to be able to correctly describe that motion using Newton’s law of gravity. It’s dark because it does not interact with light in any way; in fact, its only apparent interaction with ordinary matter is through gravity. If dark matter really does exist, there’s approximately five times more dark matter in the universe than there is ordinary visible matter (termed “baryonic matter” by those in the know).
However, that’s not the only question that cosmologists entertain. Another pressing problem, if less sexy than the dark matter problem, was that an awful lot of regular old baryonic matter appeared to be missing as well. Models for the creation and expansion of the universe make fairly definitive predictions regarding the average density of baryonic matter in the universe, and those predictions indicated that we had only observed about half the amount of such matter as there ought to be.
Rest assured that progress is being made. While dark matter remains a mystery, the missing baryonic matter has been found! Details below the fold.
But first, here’s a word from our sponsor:
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So what was wrong with previous estimates of amounts of baryonic matter, and where was the missing matter? Previous estimates concentrated solely on the matter in galaxies and other easily visible cosmic objects. However, these are not the only cosmic-scale objets in the universe made of ordinary matter. Baryonic matter can also be found in so-called “cosmic filaments” that span the space between galaxies to form a cosmic web. While some filaments are hot enough to emit light, and are therefore visible, most of these filaments are too cool to emit light, and are therefore difficult to observe directly. Fortunately, two groups, one in Orsay, France, and one in Edinburgh, Scotland, figured out a way to detect the presence of these filaments. It turns out that the cosmic background radiation, the echo of the Big Bang, is scattered by electrons in these filaments, and thus becomes distorted. High-precision detection of these distortions have revealed that these filaments contain the missing half of the expected baryonic matter in them. If that weren’t enough, the idea of a cosmic web invokes pleasing images, such as the one above, of a complex web spanning the universe. All those galaxies that I always thought were isolated with each other are really not that isolated, as it turns out.
So now the mystery of the missing baryonic matter has been solved. Now if they could just tell me where I left my house key.
Now, on to the comments!
Top Comments (December 13, 2017):
From underwriter505:
iphelgix posted this comment in jmbar2’s recommended post Deepest Gratitude to Alabama’s African-American Voters! I think it's a top comment because it lays out what we need to do better, in fact what we need to start doing so well and consistently that it becomes second nature.
From Holgar:
I have to nominate AverySLC's response to news that Doug Jones has been elected Senator. Somebody KNOWs how to celebrate! From Barbara Morrill’s front page post declaring Doug Jones the winner in the Alabama U. S. Senate election.
Top Mojo (December 12, 2017):
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