Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2021 April 13
A picture of the center of the Flame Nebula is shown, with the 
bright star Alnitak off on the left. For more details, please read
the explanation.

Confirmed Muon Wobble Remains Unexplained
Image Credit: Fermi National Accelerator Laboratory; Photographer: Reidar Hahn

Explanation: How fast do elementary particles wobble? A surprising answer to this seemingly inconsequential question came out of Brookhaven National Laboratory in New York, USA in 2001, and indicated that the Standard Model of Particle Physics, adopted widely in physics, is incomplete. Specifically, the muon, a particle with similarities to a heavy electron, has had its relatively large wobble under scrutiny in a series of experiments known as g-2 (gee-minus-two). The Brookhaven result galvanized other experimental groups around the world to confirm it, and pressured theorists to better understand it. Reporting in last week, the most sensitive muon wobble experiment yet, conducted at Fermi National Accelerator Laboratory (Fermilab) in Illinois and pictured here, agreed with the Brookhaven result. The unexpected wobble rate may indicate that an ever-present sea of virtual particles includes types not currently known. Alternatively, it may indicate that flaws exist in difficult theoretical prediction calculations. Future runs at Fermilab's g-2 experiment will further increase precision and, possibly, the statistical difference between the universe we measure and the universe we understand.

Tomorrow's picture: supernova shock wave

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