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.

2018 January 2
See Explanation.  Clicking on the picture will download
 the highest resolution version available.

Unexpected X-Rays from Perseus Galaxy Cluster
Image Credit: X-ray: NASA/CXO/Oxford University/J. Conlon et al.; Radio: NRAO/AUI/NSF/Univ. of Montreal/Gendron-Marsolais et al.; Optical: NASA/ESA/IoA/A. Fabian et al.; DSS

Explanation: Why does the Perseus galaxy cluster shine so strangely in one specific colour of X-rays? No one is sure, but a much-debated hypothesis holds that these X-rays are a clue to the long-sought identity of dark matter. At the centre of this mystery is a 3.5 Kilo-electronvolt (KeV) X-ray colour that appears to glow excessively only when regions well outside the cluster centre are observed, whereas the area directly surrounding a likely central supermassive black hole is actually deficient in 3.5 keV X-rays. One proposed resolution -- quite controversial -- is that something never seen before might be present: fluorescent dark matter (FDM). This form of particle dark matter might be able to absorb 3.5 keV X-radiation. If operating, FDM, after absorption, might later emit these X-rays from all over the cluster, creating an emission line. However, when seen superposed in front of the central region surrounding the black hole, FDM's absorption would be more prominent, creating an absorption line. Pictured, a composite image of the Perseus galaxy cluster shows visible and radio light in red, and X-ray light from the Earth-orbiting Chandra Observatory in blue.

Free APOD Lectures: January 5 in NYC & January 9 in DC
Tomorrow's picture: helical space


< | Archive | Submissions | Index | Search | Calendar | RSS | Education | About APOD | Discuss | >

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
NASA Web Privacy Policy and Important Notices
A service of: ASD at NASA / GSFC
& Michigan Tech. U.