Chandra Release - July 20, 2023

Visual Description: SPT2215  

This release features a composite image of a distant galaxy cluster known as SPT2215. In the main image, the galaxy cluster resembles a blue cloud with a hazy golden light at its core. The cluster is set against the blackness of space, which is dotted with white, orange and blue specks of light. A combination of X-ray, ultraviolet, optical, and infrared light, was used to create the image.

The blue cloud represents X-ray gas observed by Chandra. The cloud is soft, and uniform in texture. Over time, galaxy clusters often merge or collide. These collisions cause disturbances and sharp features in a cluster’s gas. When a cluster takes on a smooth, calm appearance, as found here in SPT2215, it indicates that no such collisions have occurred for a very long time. Astronomers call these galaxy clusters “relaxed”.

The hazy golden light at the heart of the cloud represents a massive central galaxy with a large amount of star formation. This central galaxy is quite isolated within the blue gas cloud. There are relatively few nearby specks of light near the central galaxy, and none are as bright or as large. No other large galaxies have been found within 600,000 light-years of the central galaxy. This implies that SPT2215 has not experienced a galaxy merger in the last billion years.

The universe is about 13.8 billion years old. SPT2215 is located about 8.4 billion light-years from Earth. This means that we are observing the galaxy cluster when the universe was only 5.3 billion years old. This is the first time scientists have discovered a “relaxed” galaxy cluster so far away, when the universe was relatively young and undergoing great turmoil.