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Astronomy

Shedding Light on Supermassive Black Holes

An international team of astrophysicists has found evidence of hundreds of hidden, supermassive black holes growing deep inside dusty galaxies billions of light-years away from Earth. The discovery provides crucial new knowledge of how black holes develop.
Scientists had long been convinced of the existence of a large population of supermassive black holes in the distant universe, but were unsure of where to find them.

trou noir

© CEA-CNRS/NASA-Spizer

Rendering of a supermassive black hole at the center of a galaxy. Becoming an active quasar, it emits high-energy X-ray.




Using NASA’s Spitzer and Chandra space telescopes, Emanuele Daddi and his team at the AIM laboratory1 recently found2 black holes present in some 200 dusty galaxies of a similar mass to our own Milky Way, and lying approximately 9-11 billion light-years away.” Thus the light they observed from the galaxies shows what was happening when the universe is believed to have been between just 2.5 and 4.5 billion years old.
The findings provide the first direct evidence that giant galaxies in the distant universe spend their early existence developing massive black holes at their cores. This suggests that there are hundreds of millions of other such holes growing across the young universe.
“Supermassive black holes produce highly energetic structures, called quasars, made up of doughnut-shaped clouds of gas and dust which surround and nourish the evolving black holes,” explains Daddi. “As the gas and dust is consumed, the matter heats up and discharges X-rays.” While the X-rays can be detected as a general glow in space, the surrounding matter of dust and gas hides the quasars themselves from view on Earth. Importantly, these clouds of non-consumed dust emit infrared light, thought to be the result of the heating process.
Working as part of the Great Observatories Origins Deep Survey,3 the most sensitive study to date of the distant universe at multiple wavelengths, Daddi and his colleagues used a technique called “stacking” to analyze X-ray data from Chandra and then targeted specific galaxies with the infrared eyes of Spitzer. This identified the black hole sites by their unusual amounts of surrounding infrared light.
The discoveries show that stars and black holes grow simultaneously in galaxies until the developed black holes begin destroying further formations of stars. They also show that collisions between galaxies are not, as previously believed, fundamental to the creation of quasars which, on the contrary, can be active in undamaged galaxies.
Graham Tearse

Notes :

1. Astrophysique interactions multi-échelles (CNRS / CEA / Université Paris-VII).
2. E. Daddi et al., “Multiwavelength Study of Massive Galaxies at z ~2,” The Astrophysical Journal. 670, 20 November 2007.
3. www.stsci.edu/science/goods

Contacts :

Emanuelle Daddi
CEA, Gif-sur-Yvette.
edaddi@cea.fr


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