Tuesday, August 29, 2017

Look! Up in the sky! Dark awesomeness.

My most recent post having been about the awesomeness of last week's total solar eclipse, why not post more generally about astronomy/cosmology news? Exciting things are happening in the broader (heh!) field -- as these four recent articles from Cosmos attest.

Pink: most normal/visible mass. Blue: where most mass seems to be.
What we (think we) understand about the distribution of dark matter is inferred from observations of the motions of stars. A small fraction of stars move much faster than expected. So: what's that about? It's hard to know when so few stars are anomalous speed demons. If we had a bigger population to analyze, maybe we'd understand better. And -- leveraging a quite non-astronomical discipline -- perhaps soon we will. See "Artificial brain scans the galaxy for speeding stars: Neural networks come to astronomy as a self-adapting algorithm digs through star maps to find rogue fast-moving stars."

Is it possible that some dark matter -- whatever that is, because we simply don't know -- could take the form of failed stars? (A failed star is a large mass -- massier than Jupiter -- that failed to ignite fusion, and so is hard to see at a distance.) Probably not all dark matter, and yet perhaps a larger fraction than was originally suspected. See "100 billion brown dwarfs may populate our galaxy: New survey dramatically increases estimated number of failed stars throughout the Milky Way."

Dark energy, like dark matter, is a label for our ignorance rather than a known thing. Astrophysicists invoke dark energy to explain otherwise inexplicable observations regarding the inferred rate of expansion of the universe. So it is more than a little intriguing to read, "Can we ditch dark energy by better understanding general relativity? A new understanding of Einstein’s century-old theory may let us do away with the idea of dark energy." The basic idea: a heretofore little-questioned simplifying assumption used to apply the fiendishly challenging math of general relativity (for the mathematically inclined: ten nonlinear partial-differential equations!) may sometimes have led physicists astray.

Gravitational lensing
Emphasis on may and sometimes. Certainly general relativity has had many successes. Consider this very recent -- and very eye-catching -- example: "Supernova déjà vu, all over again: When astronomers saw a star explode they knew – thanks to Einstein – that they could watch it again a year later."

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