An over-massive black hole in a typical star-forming galaxy, 2 billion years after the Big Bang

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Science  10 Jul 2015:
Vol. 349, Issue 6244, pp. 168-171
DOI: 10.1126/science.aaa4506

Black hole out of kilter with theory

It is believed that black holes and their host galaxies coevolve, with the feedback from the black hole inducing star formation. Such a scenario requires certain timing and mass constraints for the black hole and the star-forming gas. Trakhtenbrot et al. looked at high–red shift galaxies, when the universe was only about 2 billion years old. They found a black hole that developed to maturity much earlier than would be expected and was about 10% of the total galactic mass—much more than expected. Moreover, star formation continued after it would have been expected to stop.

Science, this issue p. 168


Supermassive black holes (SMBHs) and their host galaxies are generally thought to coevolve, so that the SMBH achieves up to about 0.2 to 0.5% of the host galaxy mass in the present day. The radiation emitted from the growing SMBH is expected to affect star formation throughout the host galaxy. The relevance of this scenario at early cosmic epochs is not yet established. We present spectroscopic observations of a galaxy at redshift z = 3.328, which hosts an actively accreting, extremely massive BH, in its final stages of growth. The SMBH mass is roughly one-tenth the mass of the entire host galaxy, suggesting that it has grown much more efficiently than the host, contrary to models of synchronized coevolution. The host galaxy is forming stars at an intense rate, despite the presence of a SMBH-driven gas outflow.

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