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Tea Talk Tuesday: The Search for Dark Matter

When pondering the universe, we can think of it as an iceberg floating in the ocean. All that we can see – the planets, the stars, the galaxies – is within the tip. Roughly one-tenth of the volume of an iceberg is above the water. Similarly, what we can “see” of the universe makes up only around 15% of the matter in the universe. The rest is something called “dark matter.” It is invisible to our telescopes and other methods of direct detection. How, then, do we study what makes up so much of the universe?

On, April 7, our Tea Talk Tuesday speaker Emma Storm presented her contribution to the answer to that question. A physics PhD student, Emma studies massive conglomerates of galaxies, or “galaxy clusters,” in radio wavelengths to look for signs of dark matter.

nasa_pic
Credit: NASA. The “Bullet Cluster” contains two colliding clusters of galaxies. In the colliding process, high-energy X-rays are emitted as a result, and they are colored pink in the figure. The purple hues represent the inferred presence of dark matter.

Many theories predict that dark matter annihilates with itself, producing less exotic particles such as electrons. These electrons can be accelerated in the magnetic fields of space and produce radiation in the form of radio waves. Galaxy clusters have two of the key ingredients for this chain of events: they are made up of large amounts of dark matter and are permeated by magnetic fields. Emma’s observations of galaxy clusters in radio aim to tease out this signal and separate it from other astrophysical processes.

While she hasn’t unlocked the secrets of dark matter quite yet, even non-detections are important. If she doesn’t see anything, she knows that the rate at which dark matter is annihilating (its cross section) must be small enough not to produce anything observable. She can set upper limits on the dark matter annihilation cross section. Her observations are some of the most constraining limits published, and future instruments are expected to push them even further.

Join us on April 21 for the third Tea Talk Tuesday. Nathaniel Ober from the Department of Digital Arts and New Media will be talking about how he combines art and science through sound!

— Kat Feng & Caitlin Johnson (grad students and organizers of the Tea Talk)

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