National Aeronautics and Space Administration

Questions (and Answers) About Cosmic High-Energy (X-ray & Gamma-Ray) Astronomy

How many individual X-ray sources are known currently?
How has the number grown since the first cosmic X-ray astronomical observations in 1962?

How do the sensitivity & angular resolution of current X-ray telescopes compare with previous ones?

What kinds of cosmic objects are X-ray emitters?

What are the brightest objects in the X-ray sky?

How many individual gamma-ray sources are known currently?
How has their number grown since the first gamma-ray astronomical observations in 1970?

How do the numbers of catalogued X-ray & gamma-ray sources compare with other energies?

How much X-ray and gamma-ray data are in the HEASARC's archive?

How much X-ray and gamma-ray data are being archived by the HEASARC every day? How much X-ray and gamma-ray data are downloaded by HEASARC users every day?

Please send information concerning dates/deadlines not currently included on this page and/or corrections to: