(CN) — The James Webb Space Telescope has peered back 500 million years to reveal new images of the aptly named Cartwheel Galaxy. The images released Tuesday shed light on the rare circumstance that created the galaxy's striking spoked-wheel shape.
That is, a head-on galactic collision.
"Its appearance, much like that of the wheel of a wagon, is the result of an intense event – a high-speed collision between a large spiral galaxy and a smaller galaxy not visible in this image," NASA said in a press release accompanying the image. "Collisions of galactic proportions cause a cascade of different, smaller events between the galaxies involved; the Cartwheel is no exception."
The Cartwheel Galaxy is located some 500 million light years from Earth, in the Sculptor constellation. It is thought to have once been a typical spiral galaxy similar to our own Milky Way, before the galactic collision disrupted its shape some 940 million years ago. The vast distances between star systems even in a single galaxy means direct collisions between stars or planets in such an event would be rare, but the gravitational shockwaves nevertheless ripped apart Cartwheel's spiral arms and forced them into two concentric rings that continue to expand.
"These two rings expand outwards from the center of the collision, like ripples in a pond after a stone is tossed into it," NASA said.
Similar collision events are believed to be behind the shape of other so-called ring galaxies, said astronomer Christine Pulliam of the Space Telescope Science Institute in Baltimore.
"We're seeing the aftermath [of the collision]," Pulliam said. "Galaxies don't naturally form this way."
While Hubble and other telescopes have imaged Cartwheel's expanding rings before, the James Webb Space Telescope's infrared cameras were able to see more clearly through the layers of interstellar dust than ever. The infrared observations revealed that the inner ring is filled with large star clusters and "tremendous amounts" of hot dust, evenly distributed around the galactic nucleus.
The outer ring, by contrast, is more chaotic. Webb's infrared cameras found it was dominated by supernovas and new star formation spread out in uneven clumps. As the ring expands, it plows into surrounding areas of gas and dust, triggering the birth of yet more stars.
But the two rings are not the only notable features in the Cartwheel Galaxy. The gap between the rings is bridged by several spokes of gas, theorized to be Cartwheel's ancient spiral arms beginning to reassert themselves. These spokes show signs of being rich in hydrocarbons and silicate dust, chemical compounds that are abundant on Earth. They also indicate the Cartwheel Galaxy is in a transitory stage of its lifetime, and will continue to change shape as time goes by.
"The galaxy, which was presumably a normal spiral galaxy like the Milky Way before its collision, will continue to transform," NASA said. "While Webb gives us a snapshot of the current state of the Cartwheel, it also provides insight into what happened to this galaxy in the past and how it will evolve in the future."
Several smaller galaxies are also visible in the new images, which are all considered part of the larger Cartwheel Galaxy group. Pulliam said these companion galaxies may or may not eventually collide with Cartwheel, depending on how far away they are.
Our own Milky Way is also due for a collision. Astronomers predict that it will crash into the neighboring Andromeda Galaxy in about 5 billion years. The elliptical super-galaxy that would result from such a merger has been nicknamed "Milkdromeda."
As the James Webb Space Telescope continues to explore deep space, Pulliam said there are "various targets" besides Cartwheel that are being prioritized for the scientific community. The telescope has already amassed a large number of images, she added, some of which the public will be able to view in the coming weeks.
"We already have several images that we couldn't release all at once," Pulliam said. "There should be a few more in about two weeks, but I don't want to spoil the surprise."
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