A duo of interacting galaxies known as Arp 142 commemorates the second science anniversary of the NASA/ESA/CSA James Webb Space Telescope. Their ongoing interaction was set in motion between 25 and 75 million years ago when the Penguin (individually catalogued as NGC 2937) and the Egg (NGC 2937) completed their first pass. They will go on to shimmy and sway, completing several additional loops before merging into a single galaxy hundreds of millions of years from now.
The James Webb Space Telescope takes constant observations, including images and highly detailed data known as spectra. Its operations have led to a ‘parade’ of discoveries by astronomers around the world. It has never felt more possible to explore every facet of the Universe.
The telescope’s specialisation in capturing infrared light – which is beyond what our own eyes can detect – shows these galaxies, collectively known as Arp 142, locked in a slow cosmic dance. Webb’s observations (which combine near- and mid-infrared light from Webb’s NIRCam [Near-InfraRed Camera] and MIRI [Mid-Infrared Instrument], respectively) clearly show that they are joined by a blue haze that is a mix of stars and gas, a result of their mingling.
Let’s dance
Before their first approach, the Penguin held the shape of a spiral. Today, its galactic centre gleams like an eye, its unwound arms now shaping a beak, head, backbone, and fanned-out tail.
Like all spiral galaxies, the Penguin is still very rich in gas and dust. The galaxies’ ‘dance’ pulled gravitationally on the Penguin’s thinner areas of gas and dust, causing them to crash in waves and form stars. Look for those areas in two places: what looks like a fish in its ‘beak’ and the ‘feathers’ in its “‘tail’.
Surrounding these newer stars is smoke-like material that includes carbon-containing molecules, known as polycyclic aromatic hydrocarbons, which Webb is exceptional at detecting. Dust, seen as fainter, deeper orange arcs also swoops from its beak to tail feathers.
In contrast, the Egg’s compact shape remains largely unchanged. As an elliptical galaxy, it is filled with ageing stars, and has a lot less gas and dust that can be pulled away to form new stars. If both were spiral galaxies, each would end the first ‘twist’ with new star formation and twirling curls, known as tidal tails.
Another reason for the Egg’s undisturbed appearance is that these galaxies have approximately the same mass, which is why the smaller-looking elliptical wasn’t consumed or distorted by the Penguin.
It is estimated that the Penguin and the Egg are about 100,000 light-years apart — quite close in astronomical terms. For context, the Milky Way galaxy and our nearest neighbour, the Andromeda Galaxy, are about 2.5 million light-years apart, about 30 times the distance. They too will interact, but not for about 4 billion years.
In the top right of the image is an edge-on galaxy, catalogued PGC 1237172, which resides 100 million light-years closer to Earth. It’s also quite young, teeming with new, blue stars. In Webb’s mid-infrared-only image, PGC 1237172 practically disappears. Mid-infrared light largely captures cooler, older stars and an incredible amount of dust. Since the galaxy’s stellar population is so young, it ‘vanishes’ in mid-infrared light.
Webb’s image is also overflowing with distant galaxies. Some have spiral and oval shapes, like those threaded throughout the Penguin’s ‘tail feathers’, while others scattered throughout are shapeless dots. This is a testament to the sensitivity and resolution of the telescope’s infrared instruments. (Compare Webb’s view to the 2013 image from the NASA/ESA Hubble Space Telescope here.) Even though these observations only took a few hours, Webb revealed far more distant, redder, and dustier galaxies than previous telescopes — one more reason to expect Webb to continue to expand our understanding of everything in the Universe.
Arp 142 lies 326 million light-years from Earth in the constellation Hydra.
Second year of science operations: in review
Over its second year of operations Webb has advanced its science goals with new discoveries about other worlds, the lifecycle of stars, the early Universe and galaxies over time. Astronomers have learned about what conditions rocky planets can form in and detected icy ingredients for worlds, found tellurium created in star mergers and studied the supernova remnants SN 1987A and the Crab Nebula.
Looking into the distant past, Webb has solved the mysteries of how the Universe was reionised and hydrogen emission from galaxy mergers, and seen the most distant black hole merger and galaxy ever observed. Observations with Webb have also confirmed the long-standing tension between measurements of the Hubble constant, deepening a different mystery around the Universe’s expansion rate.
Webb has continued to produce incredible images of the cosmos, from the detailed beauty of the Ring Nebula, to supernova remnant Cassiopeia A, to a team effort with the the NASA/ESA Hubble Space Telescope and ESA’s Euclid telescope looking at the iconic Horsehead Nebula. Webb imagery was also combined with visible light observations from Hubble to create one of the most comprehensive views of the Universe ever, an image of galaxy cluster MACS 0416.
All images in this article are courtesy of esawebb.org
The main image shows the interacting galaxies Arp 142 (MIRI image).
