Over the last few months, I wrote a three-part series of longer articles on dark matter, covering three different aspects. The third and final installment ran today. Though I could hardly be comprehensive in just three articles, I tried to cover three major aspects of dark matter science: direct-detection experiments, mapping the location of dark matter in galaxy surveys, and finally some alternative theoretical ideas about dark matter identity. This was a fun series to write, and I learned a lot by writing it — not to mention having the chance to visit the LUX experiment in South Dakota.
Scientists are explorers by nature, and when the edges of their maps are terra incognita, researchers sometimes must give names to phenomena for which we have little knowledge. Sometimes those names linger after we know exactly what an unknown quantity is; X-rays are a classic example. The “X” initially referred to mystery, but by the time physicists determined they were simply a high-energy form of light, the name had stuck.
Dark matter, however, is still a placeholder term. Over the decades since astronomers determined that most of the mass in the cosmos is invisible, researchers have done a much better job of figuring out what dark matter isn’t than what it actually is. [read more…]
And of course a lot more can be said! In this piece, I only touched on a few prominent ideas about non-WIMPy dark matter. (WIMP stands for “weakly interacting massive particle”, which is a fairly broad category of possibilities. It’s also the most popular idea, for reasons I go into in both part 1 and part 3 of the series.) From the particle physics side, we could talk about interactions in supersymmetry, dark forces, and the birth of dark matter particles in the very early Universe. From the astronomy and cosmology side, we could talk about the creation of dark matter in the atmospheres of neutron stars, the annihilation at the centers of galaxies, and the effects of dark matter particles on sound waves appearing in the cosmic microwave background. That’s why I love writing about dark matter: it’s the biggest mystery in modern cosmology, and one that will likely take our most creative minds to solve.
One response to “The dark matter at the edge of the map”
Many thanks for mentioning Hartle’s “Gravity” book on a previous blog post. It’s perfect! I have a question regarding the interesting “dimensionless ratio” GM/Rc² (eqn 1.3), which equals 0.5 at the Schwarzschild radius. Has anyone else noted or investigated the meaning of this ratio, do you know?