Over 4000 free audio and video lectures, seminars and teaching resources from Oxford University.
Skip to Content Skip to Navigation

Thank you for visiting! Please consider filling out our questionnaire. This will help us improve our service providing free educational media recorded from the University of Oxford. Many thanks!

Click here to access the survey (3 minutes to complete).

Black Holes, Axions and the Gravitational Atom in the Sky

Loading Video...
Duration: 0:46:28 | Added: 17 Dec 2014
Physics Colloquium 5th December 2014 delivered by Dr Asimina Arvanitak

The QCD axion was proposed more than thirty years ago to explain the smallness of the electric dipole moment of the neutron and has been looked for ever since. It is an excellent dark matter candidate and its size is significantly larger compared to the elementary particles of the Standard Model: it can easily vary from tens of microns to thousands of kilometers. When its size is similar to that of astrophysical black holes, it binds to them forming a gravitational atom in the sky. The number of axions occupying the levels of this gravitational atom can grow exponentially around rapidly rotating black holes through an effect that is known as super-radiance. This growth slows the black hole down and a Bose Einstein Condensate of axions is formed orbiting the black hole. Just like a laser, this BEC emits gravitational waves as axions can annihilate or transition to different levels of this gravitational atom. These gravitational waves fall within the frequency range of the upcoming Advanced LIGO experiment. Through super-radiance, black holes are thus turned into cosmic particle detectors through the only universal force: gravity.

Oxford Unit:
Copy and paste this HTML snippet to embed the audio or video on your site: