- Chandra and other telescopes observed a gigantic combination of four galaxy clusters in Abell 1758.
- Abell 1758 contains two pairs of galaxy clusters, each with hundreds of galaxies submerged in large amounts of hot gas and invisible dark matter.
- Eventually, these two pairs of clusters will collide, forming one of the most massive objects in the Universe.
- Chandra's x-rays have helped astronomers estimate how fast one pair of clusters is approaching each other.
Astronomers using data from the Chandra X-ray Observatory and other NASA telescopes have prepared a detailed map of the rare collision of four galaxy clusters. After all, all four clusters – each weighing at least several hundred trillion times greater than the Sun – will merge to form one of the most massive objects in the universe.
Galaxy clusters are the largest structures in space that are held together by gravity. Clusters are made up of hundreds or even thousands of galaxies embedded in hot gas and contain even more invisible dark matter. Sometimes two galaxy clusters collide, as in the case of Missile Clusters, and sometimes more than two clusters collide simultaneously.
New observations show that the mega-structure is assembled in a system called Abell 1758, located about 3 billion light years from Earth. It contains two pairs of colliding galaxy clusters that are moving toward each other. Researchers first recognized Abell 1758 as a quadruple system of galaxy clusters in 2004, using data from Chandra and XMM-Newton, a satellite operated by the European Space Agency (ESA).
Each pair in the system contains two galaxy clusters that are well on their way to merging. In the northern (upper) pair seen in the composite image, the centers of each cluster have already passed once, about 300 to 400 million years ago, and will eventually turn back. The southern pair at the bottom of the image has two clusters that are close to approaching each other for the first time.
Chandra X-rays are shown as blue and white, representing weaker and lighter diffuse emissions respectively. This new composite image also includes an optical image from the Sloan Digital Sky Survey. Chandra data for the first time revealed a shockwave – similar to a sonic bang from a supersonic aircraft – in the hot gas visible from Chandra in the collision of a northern steam. Based on this shockwave, scientists estimate that two clusters travel approximately 2 million to 3 million miles per hour (3 million to 5 million kilometers per hour).
Chandra data also provides information on how elements heavier than helium, "heavy elements" in galaxy clusters, mix and redistribute after clusters collide and merge. Because this process depends on how far the fusion has taken place, Abell 1758 offers valuable case studies because the northern and southern pair of clusters are at different stages of merging.
In the southern pair, heavy elements occur most frequently in the centers of two colliding clusters, which shows that the ongoing collision did not have a strong impact on the original position of the elements. However, in the northern pair, where collision and fusion continued, the collision strongly affected the location of heavy elements. The highest numbers occur between the two cluster centers and on the left side of the cluster pair, and the lowest numbers are in the center of the cluster on the left side of the image.
Clusters between clusters affect their constituent galaxies, as well as the hot gas that surrounds them. Data from the 6.5-meter MMT Arizona telescope obtained from the Redshift Survey Arizona Cluster show that some galaxies are moving much faster than others, probably because they were ejected from other galaxies in their cluster by gravitational collision forces .
The team also used radio data from the Giant Metrewave Radio Telescope (GMRT) and X-ray data from the XMM-Newton ESA mission.
The article describing the last results by Gerrit Schellenberger, Larry & # 39; ego David, Ewan O & # 39; Sullivan, Jan Vrtilek (all from Center for Astrophysics | Harvard & Smithsonian) and Christopher Haines (Universidad de Atacama, Chile) was published in the issue of September 1, 2019, The Astrophysical Journal and is available online.
NASA Marshall Space Flight Center manages the Chandra program. The Chandra X-ray Center at the Smithsonian Astrophysical Observatory controls science and flight operations from Cambridge, Massachusetts.