Wednesday, June 15, 2011

Chandra Deep Field South : NASA's Chandra Finds Massive Black Holes Common in Early Universe

Credit: X-ray: NASA/CXC/U.Hawaii/E.Treister et al;
Infrared: NASA/STScI/UC Santa Cruz/G.Illingworth et al;
Optical: NASA/STScI/S.Beckwith et al


This composite image from NASA's Chandra X-ray Observatory and Hubble Space Telescope (HST) combines the deepest X-ray, optical and infrared views of the sky. Using these images, astronomers have obtained the first direct evidence that black holes are common in the early Universe and shown that very young black holes grew more aggressively than previously thought.

Astronomers obtained what is known as the Chandra Deep Field South (CDFS) by pointing the telescope at the same patch of sky for over six weeks of time. The composite image shows a small section of the CDFS, where the Chandra sources are blue, the optical HST data are shown in green and blue, and the infrared data from Hubble are in red and green.

The new Chandra data allowed astronomers to search for black holes in 200 distant galaxies, from when the Universe was between about 800 million and 950 million years old. These distant galaxies were detected using the HST data and the positions of a subset of them are marked with the yellow circles (roll your mouse over the image above).

The rest of the 200 galaxies were found in other deep HST observations located either elsewhere in the CDFS or the Chandra Deep Field North, a second ultra- deep Chandra field in a different part of the sky.

None of the galaxies was individually detected with Chandra, so the team used a technique that relied on Chandra's ability to very accurately determine the direction from which the X-rays came to add up all the X-ray counts near the positions of these distant galaxies. The two "stacked" images resulting from this analysis are on the right side of the graphic, where the bottom image shows the low-energy X- rays and the top image has the high-energy X-rays. Statistically significant signals are found in both images.

These results imply that between 30% and 100% of the distant galaxies contain growing supermassive black holes. Extrapolating these results from the relatively small field of view that was observed to the full sky, there are at least 30 million supermassive black holes in the early Universe. This is a factor of 10,000 larger than the estimated number of quasars in the early Universe.

Illustration of Baby Black Hole

The stronger signal in high-energy X-rays implies that the black holes are nearly all enshrouded in thick clouds of gas and dust. Although copious amounts of optical light are generated by material falling onto the black holes, this light is blocked within the core of the black hole's host galaxy and is undetectable by optical telescopes. However, the high energies of X-ray light can penetrate these veils, allowing the black holes inside to be studied.

Fast Facts for Chandra Deep Field South :

Scale: Main image is 19.6 arcmin across. (about 6.6 million light years across)
Category: Cosmology/Deep Fields/X-ray Background, Black Holes
Coordinates: (J2000) RA 03h 32m 28s | Dec -27° 48' 30.00
Constellation: Fornax
Observation Date: 54 pointings between Oct 15, 1999 to Jul 22, 2010
Observation Time: 1111 hours 6 min (46 days 7 hours 6 min) Obs. ID: 441, 581-582, 1431, 1672, 2239, 2312-2313, 2405-2406, 2409, 8591-8597, 9575, 9578, 9593, 9596, 9718, 12043-12055, 12123, 12128-12129, 12135, 12137-12138, 12213, 12218-12220, 12222-12223, 12227, 12230-12234
Color Code: X-ray (Blue); IR (Red, Green); Optical (Green, Dark Blue)
Instrument: ACIS
References: Treister et al., (2011), Nature, in press Distance Estimate: 12.7 to 12.9 billion light years (redshift 6 to 7)

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