Using data from NASA’s Chandra X-ray Observatory and infrared telescopes, astronomers have made an important advance in the understanding of how clusters of stars come into being.
The data show early notions of how star clusters form cannot be correct. The simplest idea is stars form into clusters when a giant cloud of gas and dust condenses. The center of the cloud pulls in material from its surroundings until it becomes dense enough to trigger star formation. This process occurs in the center of the cloud first, implying that the stars in the middle of the cluster form first and, therefore, are the oldest.
However, the latest data from Chandra suggest something else is happening. Researchers studied two clusters where Sun-like stars currently are forming — NGC 2024, located in the center of the Flame Nebula, and the Orion Nebula Cluster. From this study, they discovered the stars on the outskirts of the clusters actually are the oldest.
Galaxy Cluster in Cosmic Free-for-All (NASA, Chandra, 4/28/09)
Originally uploaded by nasa1fan.
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, where the coolest gas is 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.
Credits: X-ray: NASA/CXC/IfA/C. Ma et al. Optical: NASA/STScI/IfA/C. Ma et al.
p.s. You can see all of our Chandra photos in the Chandra Group in Flickr at: www.flickr.com/groups/chandranasa/ We’d love to have you as a member!