A cosmic riddle for you: When does not finding something where you expect to it to be tell you that it exists?
In the 1960s and 70s, astronomers measured the speed of stars and gas clouds orbiting at the edge of our galaxy, and discovered something strange: their rotational velocities were too fast. Way too fast. So fast, there’s no way the gravity from the visible mass in the galaxy could possibly keep them in orbit.
There was clearly some mass out there across the galaxy that astronomers couldn’t see. Like, more than three quarters of it. Awkward!
Astronomers call this invisible stuff Dark Matter, and fro decades the evidence has mounted for its existence across the universe. But in March 2018 astronomers found a galaxy with no Dark Matter at all … which, in a wonderful leap of logic, gives them even more confidence that this mysterious material exists.
Emily at the University of York: www.york.ac.uk/physics/people/brunsden/
Chris online: kipstewart.com
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Some of the things we talk about in this episode:
- Dark Matter in the news: https://arstechnica.com/science/2018/03/galaxy-seems-to-lack-dark-matter-stumping-astronomers/
Hubble picture of the deficient galaxy: http://www.spacetelescope.org/images/heic1806a/
Nature Paper: https://www.nature.com/articles/nature25767
PDF of the paper: http://www.astro.yale.edu/dokkum/papers/mass.pdf
- Galaxy Rotation Curve: https://en.wikipedia.org/wiki/Galaxy_rotation_curve
- MACHOs, WIMPS & other weirdness: https://theconversation.com/from-machos-to-wimps-meet-the-top-five-candidates-for-dark-matter-51516
- Dark matter and galaxy clusters: https://www.nasa.gov/feature/jpl/galaxy-clusters-reveal-new-dark-matter-insights
- Galaxies in collision: https://phys.org/news/2016-10-galaxies-collide.html
- The Bullet Cluster: https://apod.nasa.gov/apod/ap060824.html
Syzygy is produced by Dr Chris Stewart and co-hosted by Dr Emily Brunsden from the Department of Physics at the University of York.