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.

January 15, 1997
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.

Black Holes Signature From Advective Disks
Research Credit:
R. Narayan et al. (CfA), ASCA, ISAS, NASA

Explanation: What does a black hole look like? If alone, a black hole would indeed appear quite black, but many black hole candidates are part of binary star systems. So how does a black hole binary system look different from a neutron star binary system? The above drawings indicate it is difficult to tell! Recent theoretical work, however, has provided a new way to tell them apart: advective accretion flows (ADAFs). A black hole system so equipped would appear much darker than a similar neutron star system. The difference is caused by the hot gas from the ADAF disk falling through the event horizon of the black hole and disappearing - gas that would have emitted much light were the central object only a neutron star. Recent observations of the soft X-ray transient V404 Cyg has yielded a spectrum much like an ADAF onto a black hole - and perhaps brighter than allowable from an ADAF onto a neutron star.

Tomorrow's picture: Trapezium: Teardrops in My Skies

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