Images by Date
Images by Category
Solar System
White Dwarfs
Neutron Stars
Black Holes
Milky Way Galaxy
Normal Galaxies
Galaxy Clusters
Cosmology/Deep Field
Images by Interest
Space Scoop for Kids
Sky Map
Photo Blog
Top Rated Images
Image Handouts
Fits Files
Image Tutorials
Photo Album Tutorial
False Color
Cosmic Distance
Look-Back Time
Scale & Distance
Angular Measurement
Images & Processing
Image Use Policy
Web Shortcuts
Chandra Blog
RSS Feed
Email Newsletter
News & Noteworthy
Image Use Policy
Questions & Answers
Glossary of Terms
Download Guide
Get Adobe Reader
MACSJ0717.5+3745: Cosmic Heavyweights in Free-For-All

This composite image shows the massive galaxy cluster MACSJ0717.5+3745 (MACSJ0717, for short), where four separate galaxy clusters have been involved in a collision, the first time such a phenomenon has been documented. Hot gas is shown in an image from NASA's Chandra X-ray Observatory and galaxies are shown in an optical image from NASA's Hubble Space Telescope. The hot gas is color-coded to show temperature, similar to a temperature map of the Earth given in a weather forecast. In MACSJ0717 the coolest gas is shown as reddish purple, the hottest gas is blue and the temperatures in between are purple.

The repeated collisions in MACSJ0717 are caused by a 13-million-light-year-long stream of galaxies, gas, and dark matter — known as a filament — pouring into a region already full of matter. A collision between gas in two or more clusters causes the hot gas to slow down. However, the galaxies, which are mainly empty space, do not slow down as much and so they move ahead of the gas. Therefore, the speed and direction of each cluster's motion — perpendicular to the line of sight — can be estimated by studying the offset between the average position of the galaxies and the peak in the hot gas.

A labeled version of the MACSJ0717 image (roll your mouse over the image above) shows the galaxies in the four different clusters — identified by the letters "A," "B," "C," and "D" — involved in the collision, plus the direction of motion for the three fastest moving clusters. The length of the arrow shows the approximate speed in a direction perpendicular to the line of sight. Note that the direction of motion of the clusters is roughly parallel to the direction of the filament. Data from Keck Observatory was used to derive the speed of the clusters along the line of sight, allowing the three-dimensional geometry and dynamics of MACSJ0717 to be derived.

The cooler (redder) region of gas towards the lower left of the cluster labeled "D" has likely survived from before the collision. Cluster A is likely falling back into the main cluster after already having passed through once in the opposite direction. Both of these clusters probably originated from the filament. Cluster B, however, has a much higher speed than the other clusters along the line of sight and its origin is unclear. It may have fallen along the outer edge of the filament, causing its infall trajectory to curve, or it may be falling in along another, smaller filament. The good alignment between the galaxies and hot gas for cluster C, along with its motion compared to MACSJ0717 as a whole, makes this system a good candidate for the core of the main cluster.

The large region of relatively hot gas (shown in blue) that extends from the left side of cluster C to the right side of region D may be caused by heating as significant quantities of gas from the filament plough into the main cluster.

MACSJ0717 is located about 5.4 billion light years from Earth. It is one of the most complex galaxy clusters ever seen. Other well-known clusters like the Bullet Cluster and MACSJ0025.4-1222 involve the collision of only two galaxy clusters and show much simpler geometry.

Fast Facts for MACSJ0717.5+3745:
Credit  X-ray (NASA/CXC/IfA/C. Ma et al.); Optical (NASA/STScI/IfA/C. Ma et al.)
Release Date  April 16, 2009
Scale  Image is 4.5 arcmin across
Category  Groups & Clusters of Galaxies
Coordinates (J2000)  RA 07h 17m 31.00s | Dec +37° 45´ 39.60"
Constellation  Aurigae
Observation Date  January 10, 2003
Observation Time  16 hours 40 minutes
Obs. ID  4200
Instrument  ACIS
References Ma C. et al 2009he Astrophysical Journal Letters, Volume 693, Issue 2, pp. L56-L60 (2009)
Color Code  X-ray (Blue, Violet); Optical (Cyan, Yellow)
Distance Estimate  About 5.4 billion light years
distance arrow
Visitor Comments (2)

The purple colors are very powerful, as you can see in the image, is it possible that purple hydrogen can form on the surface of each galactic star, so each galactic star can deviate stress, cure humans and help control every occurrence? This is one of the best images I have ever seen.

Posted by Martin Savoie on Friday, 05.18.18 @ 01:04am

What is the 2 facts?

Posted by emme on Wednesday, 03.11.15 @ 13:32pm

Rate This Image

Rating: 3.8/5
(626 votes cast)
Download & Share


1024x768 - 780.4 kb
1280x1024 - 1.2 MB
1680x1050 - 1.6 MB
More Information
More Images
Chandra X-ray Image
of MACSJ0717.5+3745
Jpg, Tif

More Images
Animation & Video
Images of MACSJ0717

More Animations
More Releases


Related Images
Bullet Cluster
Bullet Cluster
(30 Oct 08)

(07 Aug 08)

Abell 520
Abell 520
(16 Aug 07)

1E 0657-56
1E 0657-56
(21 Aug 06)

Related Information
Related Podcast
Top Rated Images
Chandra Releases 3D Instagram Experiences

Timelapses: Crab Nebula and Cassiopeia A

Brightest Cluster Galaxies