Surveying the X-ray Sky

Jan 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.

(PhysOrg.com) -- 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: Planets with oddball orbits like Mercury could host life

Related Stories

Galaxy Collision Switches on Black Hole

Dec 10, 2009

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

NASA Performs Headcount of Local Black Holes

Oct 06, 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

Jan 06, 2009

(PhysOrg.com) -- 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 ...

X-Ray Jets from Galaxies

Oct 19, 2009

(PhysOrg.com) -- 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 ...

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

May 03, 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 ...

Recommended for you

The entropy of black holes

Sep 12, 2014

Yesterday I talked about black hole thermodynamics, specifically how you can write the laws of thermodynamics as laws about black holes. Central to the idea of thermodynamics is the property of entropy, which c ...

Modified theory of dark matter

Sep 12, 2014

Dark matter is an aspect of the universe we still don't fully understand. We have lots of evidence pointing to its existence (as I outlined in a series of posts a while back), and the best evidence we have point ...

Gaia discovers its first supernova

Sep 12, 2014

(Phys.org) —While scanning the sky to measure the positions and movements of stars in our Galaxy, Gaia has discovered its first stellar explosion in another galaxy far, far away.

User comments : 0