Surveying the X-ray Sky

January 11, 2010
This is a false-color X-ray image of a field of galaxies as seen in a survey done by the Chandra X-ray Observatory. The image covers a region of the sky about equal to the size of two full-moons. Red corresponds to low-energy X-ray emitting galaxies, green to intermediate energy X-ray galaxies, and blue to objects emitting high energy X-rays - about ten times more energetic than those seen in red. One result apparent in this image, apart from the fact that so many galaxies emit X-rays, is the wide range of galaxy types. Credit: NASA/Chandra CXO, and B. Wilkes et al.

( -- Astronomers have only modest laboratories to probe the mysteries of the cosmos. Mostly they have to rely on meticulous and clever observations of remote phenomena.

Identifying the most interesting objects for scrutiny has, therefore, always been an important astronomical task. Systematic surveys of regions of the sky at specific wavelengths, for example, turn up lists of expected and unexpected objects for subsequent study. The SWIRE survey (the Spitzer Wide-area Infra-Red Extragalactic survey) scanned a region of the sky as large as 200 full moons in each of the seven infrared cameras on the . The prime goal of SWIRE is the study of the structure, evolution, and environments of galaxies out to distances so far that the light has traveled from them to us for ten billion years, about 70% of the age of the universe.

CfA astronomers Belinda Wilkes and Dong-Woo Kim, along with ten colleagues, used the Chandra X-ray Observatory to observe the best 2% of the large SWIRE region (where "best" is defined here by this region's having no known bright sources and being comparatively free of contaminating emission from our ). Some galaxies are extremely luminous because they have supermassive black holes at their centers. X-rays are a key diagnostic of these (AGN) because the X-rays measure material accreting onto the vicinity of the black hole. X-rays can in this way discriminate AGN from galaxies that are bright for other reasons, for example, because of bursts of .

The astronomers found that nearly every one of the 775 galaxies they found with Chandra were also detected in the SWIRE survey. However, they note significantly that there is no apparent relationship in general between the observed brightnesses at infrared and X-ray wavelengths. This result implies that the have a wide range of internal properties still to be deciphered. On the other hand, the team does find, contrary to conventional methodology, that mid-infrared brightness flux is a much better detector of powerful galactic jet activity than is optical emission. The new results are just the start of a series of more detailed analyses, but already confirm the importance of sensitive, unbiased studies of large regions of the sky at many wavelengths.

Explore further: XMM-Newton 'spare-time' provides impressive sky survey

Related Stories

XMM-Newton 'spare-time' provides impressive sky survey

May 3, 2006

For the past four years, while ESA’s XMM-Newton X-ray observatory has been slewing between different targets ready for the next observation, it has kept its cameras open and used this spare time to quietly look at the heavens. ...

NASA Performs Headcount of Local Black Holes

October 6, 2006

NASA scientists using the Swift satellite have conducted the first complete census of galaxies with active, central black holes, a project that scanned the entire sky several times over a nine-month period.

Active galaxies are different near and far

January 6, 2009

( -- An ongoing X-ray survey undertaken by NASA's Swift spacecraft is revealing differences between nearby active galaxies and those located about halfway across the universe. Understanding these differences will ...

X-Ray Jets from Galaxies

October 19, 2009

( -- Some dramatic galaxies eject gigantic, collimated jets of ionized gas millions of light-years long, powered by the massive black holes at their centers. The ionized jets are detected at radio wavelengths, ...

Galaxy Collision Switches on Black Hole

December 10, 2009

( -- This composite image of data from three different telescopes shows an ongoing collision between two galaxies, NGC 6872 and IC 4970.

Recommended for you

How to prepare for Mars? NASA consults Navy sub force

October 5, 2015

As NASA contemplates a manned voyage to Mars and the effects missions deeper into space could have on astronauts, it's tapping research from another outfit with experience sending people to the deep: the U.S. Navy submarine ...

Researchers find a new way to weigh a star

October 5, 2015

Researchers from the University of Southampton have developed a new method for measuring the mass of pulsars – highly magnetised rotating neutron stars formed from the remains of massive stars after they explode into supernovae.

NASA selects investigations for future key planetary mission

October 1, 2015

NASA has selected five science investigations for refinement during the next year as a first step in choosing one or two missions for flight opportunities as early as 2020. Three of those chosen have ties to NASA's Jet Propulsion ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.