The Mass and Growth of Black Holes
Xue-Bing Wu, Department of Astronomy, Peking University, Beijing 100871, China

Since black holes do not emit light, detecting them is a big challenge to us. However, nowadays black holes with different masses and scales are widely believed to exist in our universe. Using the huge ground-based and space telescopes astronomers have discovered numerous black holes, especially those with mass of a few solar masses existed in our Galaxy and those with mass of a few million to billion solar masses existed in the center of nearby and distant galaxies. Although we can not see the black holes directly, we can probe the strong gravity of black holes by observing the stars and gas near to them. Various dynamical methods and empirical relations have been adopted by astronomers to reliably estimate the masses of supermassive black holes in both inactive and active, nearby and distant galaxies. There are clear evidences for the existence of supermassive black holes with several billion solar masses in the very early universe. But how these masive black holes can form and grow in a relatively short time is still under debate. How massive are the seed black holes for them? How to form the seed black holes? Can they rapidly grow by continuous mass accretion or galaxy-galaxy merge? Future studies with more giant telescopes will help us to answer these questions.

Further reading:
(1) Black Holes FAQ (Frequently Asked Questions) List by Ted Bunn (

(2) "Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research" by Laura Ferrarese & Holland Ford, 2005, Space Science Reviews, Volume 116, Issue 3-4, pp. 523-624 (

(3) "Supermassive Black Holes in Nuclei of Galaxies" by John Kormendy & Karl Gebhardt, 2001, AIP conference proceedings, Vol. 586. Edited by J. Craig Wheeler and Hugo Martel, p.363

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