Scientists released the latest images from NASA’s triumphant James Webb Space Telescope on Tuesday. The latest release documents the Cartheel galaxy, which is about 500 million light-years from our planet and is aptly named for its wheel-like appearance, complete with a central hub, rubber and even wavy fluorescent spokes. Webb also recorded two smaller satellite galaxies along with Cartwheel.
The new images follow NASA’s July 12 unveiling of five initial scenes captured by the Webb Space Telescope, the most powerful space observatory yet built. Since they were launched on December 25, Webb’s 18 hexagonal gold mirrors have been aligned to pick up other targets in space, although not all images have been released. Snapshots include the South Ring Nebula, which looks like a soap bubble expanding from a dead star, and the striking Carina Nebula, made up of swirling dust that looks like jagged rocks.
Astronomers have been studying the Wheel galaxy for decades. It was initially inspected by two ground-based observatories in Australia, first the British Schmidt Telescope and later the Anglo-Australian Telescope. But it’s best known from the Hubble Space Telescope, which produced images in the 1990s with more detail about the galaxy’s structure. And just as Webb in July revealed the presence of even more distant galaxies that hide from our view, his Cartwheel images zoomed in on the detailed star formation in the galaxy’s rings and the dozens of other star systems beyond.
The appearance of the Cartwheel comes from a collision of two galaxies that happened hundreds of millions of years ago. “We think the Wheel probably started out looking like the Milky Way, and then this other galaxy moved through it,” said Marcia Riecke, principal investigator of the Near Infrared Camera, or NIRCam, one of the Webb telescope’s science instruments. However, the smaller galaxy, instead of getting stuck in the large spiral it entered, continued to move away from the larger one. Not visible in the photo released by NASA.
Galactic collisions are not uncommon in deep space, although they rarely result in such a perfect shape as to pique human curiosity. Kirk Bourne, who was Hubble’s principal investigator for the Cartwheel observation but was not involved with Webb, said the galaxy’s strange shape, which formed by chance during the merger, has motivated astronomers to study it for decades .
Because a smaller galaxy crashed into a larger one—and right through the middle of it—it was less disruptive to the shape of each galaxy, and the two relatively managed to retain their individuality. “What changed the shape of the Cartwheel was the influence of the gravitational field of this other galaxy, which changed the orbits of the stars in the original Cartwheel galaxy,” Dr Riecke said.
Dr Born, who has studied other galaxy collisions, described the smaller galaxy as a bullet that had shot through the larger one. After observing the space object in the 1990s, scientists noticed a trail of hydrogen gas left behind that followed the smaller galaxy, which Dr Bourne called the “smoking gun”, indicating that it had continued to move after creating the new Cartwheel formation.
Now 1.5 times the size of the Milky Way, the Cartwheel is still expanding and new stars are forming both in its outer ring and along its rim. However, there is no concrete answer to how big Cartwheel will get, when it will stop growing, or what form it will take when it does.
Cartwheel images were already in hand on July 12, but weren’t available to the public until this week. They have been filtered to make them more visually accessible, highlighting bright, blue-tinged young stars and red molecules from older stars and cosmic dust floating between the rings. Although colorful, Joseph DePasquale, senior science visuals developer at the Space Telescope Science Institute, which operates the Webb and Hubble spacecraft, emphasized that the stars and dust are actually detected as infrared light instead of colors.
The new technology to detect this light in such detail is what sets Webb’s images apart from those taken by Hubble and the Anglo-Australian Telescope. While Hubble had some capabilities to record light in the infrared spectrum, Webb’s is more advanced and produces more vivid pictures. The NIRCam, for example, which was created by about 25 people working with Dr. Rieke over 11 years, distinguishes the infrared colors of stars that are invisible to the human eye from one another.
When Hubble photographed the Wheel in the 1990s, the galaxy’s “spokes” were obscured by gas clouds that scattered light, making it difficult to see the thousands of stars forming inside. Now, because Webb can study mid-infrared and near-infrared wavelengths, it is able to filter out cosmic dust. This helps confirm some of the theories about the Cartwheel’s composition that have been formed using Hubble technology and reveal new information, such as the lack of star formation in some areas between the wheel’s spokes.
“I think the combination of the two telescopes, far from making one of them obsolete, it actually just adds to the advantages and the power of Hubble because now we can make these comparisons,” Dr Bourne said.