The images show X-rays from Chandra, optical data from the Pan-STARRS telescope in Hawaii, and radio data from the LOw Frequency Array in the Netherlands. A region of gas with a curved edge is called a "cold front" and is denser and cooler than the gas it is plowing into. The tail and the cold front all curve in the same direction.
The largest structures held together by gravity crashed into one another, one of the most energetic events in the Universe. Abell 1775 is a system where a smaller galaxy cluster has crashed into a larger one. Astronomers are using data from other telescopes and X-rays from Chandra to piece together the collision.
There are clues in the data, including a curving tail of hot gas and a cold front. The full picture of Abell 1775 will likely need more observations and modeling. There are extraordinary things that can happen when the titans of space collide.
A new study uses NASA's Chandra X-ray Observatory. Hundreds or even thousands of individual galaxies are immersed in giant oceans of superheated gas in the largest structures in the Universe held together by gravity. Normally, the atoms that make up the stars, planets, and everything on Earth are in the form of hot gas and stars.
The normal matter is bound in the cluster by the dark matter. The most energetic events in the Universe are the collisions and mergers of galaxy clusters. The spiral-shaped pattern in Chandra's X-ray data was found in a new study of the galaxy cluster Abell 1775, which is 960 million light-years from Earth.
The results show a turbulent past for the cluster. The smaller cluster will plow through the larger one when they collide. The bigger cluster has the upper hand when it comes to pulling.
The hot gas is stripped off when the smaller cluster moves through. There is a wake behind the cluster. After the center of the smaller cluster passes by the center of the larger one, the gas in the tail starts to encounter less resistance and overshoots the center of its cluster.
This can cause the tail to curve away from the center as it flies to the side. There is evidence for one of the curving tails in the newest Chandra data. There were previous studies of Abell 1775 with Chandra and other telescopes, but they did not confirm that there was an ongoing collision.
X-rays from Chandra, optical data from the Pan-STARRS telescope in Hawaii, and radio data from the LOw Frequency Array in the Netherlands are included in a new image of Abell 1775. The tail is labeled with a region of gas with a curved edge that is denser and cooler than the gas it is plowing into. The tail and the cold front all curve in the same direction.
The field of view of the Chandra data is shown in a separate labeled image. The image of Abell was labeled multiwavelength. Abell 1775 contains an enormous jet and radio source, which is also seen.
The jet is powered by a black hole in a large elliptical galaxy. The radio jet is actually 2.6 million light-years long, according to new data from LOFAR. It's one of the longest ever observed in a galaxy cluster, and it's twice as long as they thought it was before.
The structure of the jet changes abruptly as it crosses into the lower density gas in the upper part of the image, across the edge of the cold front, implying that the collision has affected it. According to the new study, the gas motions inside the cluster could be responsible for other structures detected by observing Abell 1775 in radio waves. The LOFAR and Chandra data allowed the researchers to study the phenomena that contribute to the accelerated electrons in the jet and in the radio emission near the center of the larger cluster.
There is a different explanation for the appearance of the cluster. The dense hot gas of the larger cluster will be attracted to it by gravity when a small cluster approaches it. The direction of motion of the cluster gas reverses after the smaller cluster passes the center of the other cluster.
The cluster gas moves through the center again and "sloshes" back and forth, like wine that was jerked sideways. The gas ends up in a spiral pattern because of the off-center collision between the two clusters. The slingshot tail scenario is favored by the Botteon team, but a separate group of astronomy led by Dan Hu of Shanghai Jiao Tong University in China favors a different explanation.
The scenarios involve a collision between two clusters. The merging of the two clusters will lead to the creation of a larger galaxy cluster. Modeling of Abell 1775 is needed to help decide between the two scenarios.
The paper describing the results was published in the journal Astronomy and Astrophysics. Dan Hu's work on the "sloshing" theory has been accepted for publication. The Chandra program is managed by the Marshall Space Flight Center.
The Chandra X-ray Center is located in Cambridge, Massachusetts.