![This contour map shows the location of dark matter near galaxies, as determined using gravitational lensing. [Credit: Richard Massey/Nature]](https://sciencevspseudoscience.files.wordpress.com/2014/07/massey2008_fig3_small.png?w=1024&h=760)
- The second part of my series on dark matter is up over at Ars Technica: how do we map the location of dark matter relative to ordinary matter?
Unlike ordinary matter, we can’t see where dark matter is by using the light it emits or absorbs. Astronomers can only map dark matter’s distribution using its gravitational effects. That’s especially complicated in the denser parts of galaxies, where the chaotic stew of gas, stars, and other forms of ordinary matter can mask or mimic the presence of dark matter. Even in the galactic suburbs or intergalactic space, dark matter’s transparency to all forms of light makes it hard to locate with precision.
Despite that difficulty, astronomers are making significant progress. While individual galaxies are messy, analyzing surveys of huge numbers of them can provide a gravitational map of the cosmos. [read more…]
- This week’s column for The Daily Beast covers a new method called SAMI for surveying galaxies that provides both the ability to study multiple galaxies quickly, but also obtain details about each one. The result is a kind of “Google Earth” for galaxies (though without the sometimes creepy surveillance feel of the Earth version).
SAMI consists of 13 bundles of fiber-optic cables, each containing 60 or more fibers in what the researchers call “hexabundles.” Each hexabundle is kind of like a bug’s compound eye, but instead of images from each eye facet, each fiber measures a spectrum. Whereas a typical galactic survey telescope would dedicate one fiber to each galaxy, SAMI can point one hexabundle at the same galaxy. The result is a mosaic of spectra, covering up to 60 different regions. [read more…]
Galileo's Pendulum 