Images






Abell 520: a system where at least two massive galaxy clusters have collided
This multi-wavelength image shows the chaotic aftermath of the collision of at least two galaxy clusters, some of the most massive objects in the Universe. 
The individual galaxies appear in the CFHT MegaCam visible-light observations (yellow and orange), which also reveal the presence of dark matter (blue) by the subtle distortions of the distant objects. X-rays from Chandra (red) show the hot gas the envelopes the clusters. 
The behavior of the dark matter with respect to the galaxies and hot gas in Abell 520 is very unusual.  These data can be explained by changes to the current understanding of dark matter or how galaxy clusters interact when merging.
High Resolution Images: format jpg (~0.5MB) or tif (~4.2MB)

Credit: X-ray: NASA/CXC/UVic./A.Mahdavi et al. Optical/Lensing: CFHT/UVic./A.Mahdavi et al.




A closer look at the dark matter distribution

The five concentrations (or peaks) in the dark matter distribution around Abell 520 are identified as circles numbered 1 to 5 on this image, similar to the one shown above, but where only the galaxies member of the cluster are shown together with the hot gas seen by Chandra.

While four of these peaks correspond to regions of the cluster where many galaxies are visible, peak number 3, in the middle of the hot gas cloud, does not seem to be associated to galaxies. What could have made a significant amount of dark matter stay in the middle of the cluster? An exciting question which will require many more follow-up observations to be answered!


Click on the image for a larger version.
Credit: X-ray: NASA/CXC/UVic./A.Mahdavi et al. Optical/Lensing: CFHT/UVic./A.Mahdavi et al.



A peculiar dark matter distribution indeed!

In this image of the "Bullet Cluster", known as 1E 0657-56, the hot gas is slowed down during the collision but the galaxies and dark matter (in blue) appear to continue on unimpeded, unlike in Abell 520.

Click on the picture for a larger one showing the two clusters side by side.

Credit for the 1E 0657-56 image: X-ray: NASA/CXC/CfA/M.Markevitch et al.;Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.;
Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.




CFHT - The telescope with MegaPrime/MegaCam

The Canada-France-Hawaii telescope structure is based on an equatorial mount design, with one of the axis of rotation set parallel to the axis of the Earth¹s rotation. The mirror cell (the white circular structure at the bottom of the telescope, seen just above the person giving the scale on this photograph) holds and protects the most precious element: the 3.6-meter diameter mirror.
Light from distant objects enters the dome through the slit, bounces back from the mirror such that it will focus, and create a crisp image at the prime focus, MegaPrime, where the image is captured by MegaCam, CFHT's wide-field digital camera (340 MegaPixels!) .
By today's standards, the CFHT telescope is a heavy structure compared to the diameter of its mirror: the total mass of the telescope is 325 tons, with 250 tons for the mobile section alone. Yet the telescope can point to any location in the sky with an accuracy of 3 thousandths of a degree - and can follow astronomical objects with an even better accuracy, thanks to an automated guiding mechanism that compensates for the apparent motion of the sky due to the Earth's rotation.

High Resolution image

© Canada-France-Hawaii Telescope Corporation 2006



The MegaCam CCD mosaic

At the focal plane of  MeagCam seen in this photograph, there are 40 CCDs. Each of them, known as the 'e2v 'CCD42-90'',  account for more than 9.5 megapixels. 36 of them are used to image the sky, bringing the total number of pixels for the MegaCam mosaic to a staggering 340 million!

Want to know more about MegaPrime/MegaCam? You can go here (first light of the camera) or here for more technical information.

Various resolution downloads:
[Full scale - 954x805 - JPEG - 84Kb] 
[Scaled 1/2th - 476x402 - JPEG - 19Kb]


© Canada-France-Hawaii Telescope Corporation 2006





Copyright policy and credits related to all press release materials

All images on this page are to be used exclusively for the purpose of media announcements
related to the " Dark matter mystery deepens in cosmic "train wreck" (August 2007)" press release.
For any other use, please seek authorization from CFHT's PR officer .