The Penguin and the Egg (Interacting Galaxies Arp 142)

ARP 142 as seen by Hubble vs. Webb

NIRCam + MIRI

This “penguin party” is loud! The distorted spiral galaxy at center, the Penguin, and the compact elliptical galaxy at left, the Egg, are locked in an active embrace. A new near- and mid-infrared image from the James Webb Space Telescope, taken to mark its second year of science, shows that their interaction is marked by a faint upside-down U-shaped blue glow.

The pair, known jointly as Arp 142, made their first pass between 25 and 75 million years ago — causing “fireworks,” or new star formation, in the Penguin. In the most extreme cases, mergers can cause galaxies to form thousands of new stars per year, for a few million years. For the Penguin, research has shown that about 100 to 200 stars have formed per year. By comparison, our Milky Way galaxy (which is not interacting with a galaxy of the same size) forms roughly six to seven new stars per year.

This gravitational shimmy also remade the Penguin’s appearance. Its coiled spiral arms unwound, and gas and dust were pulled in an array of directions, like it was releasing confetti. It is rare for individual stars to collide when galaxies interact (space is vast), but galaxies’ mingling disrupts stars’ orbits.

Today, the Penguin’s galactic center looks like an eye set within a head, and the galaxy has prominent star trails that take the shape of a beak, backbone, and fanned-out tail. A faint, but prominent dust lane extends from its beak down to its tail.

Despite the Penguin appearing far larger than the Egg, these galaxies have approximately the same mass. This is one reason why the smaller-looking Egg hasn’t yet merged with the Penguin. (If one was less massive, it may have merged earlier.)

The oval Egg is filled with old stars, and little gas and dust, which is why it isn’t sending out “streamers” or tidal tails of its own and instead has maintained a compact oval shape. If you look closely, the Egg has four prominent diffraction spikes — the galaxy’s stars are so concentrated that it gleams.

Now, find the bright, edge-on galaxy at top right. It may look like a party crasher, but it’s not nearby. Cataloged PGC 1237172, it lies 100 million light-years closer to Earth. It is relatively young and isn’t overflowing with dust, which is why it practically disappears in Webb’s mid-infrared view.

The background of this image is overflowing with far more distant galaxies. This is a testament to the sensitivity and resolution of Webb’s infrared cameras.

Credits: NASA, ESA, CSA, STScI

MIRI

Webb’s mid-infrared view of interacting galaxies Arp 142 seems to sing in primary colors. The background of space is like a yawning darkness speckled with bright, multi-colored beads.

This image was taken by MIRI, the telescope’s Mid-Infrared Instrument, which astronomers use to study cooler and older objects, dust, and extremely distant galaxies.

Here, the Egg appears as an exceptionally small teal oval with gauzy layers. Mid-infrared light predominantly shows the oldest stars in the elliptical galaxy, which has lost or used up most of its gas and dust. This is why the view is so different from the combined image, which includes near-infrared light.

At right, the Penguin’s shape is relatively unchanged. The MIRI image shows all the gas and dust that has been distorted and stretched, as well as the smoke-like material, in blue, that includes carbon-containing molecules, known as polycyclic aromatic hydrocarbons.

Next, look for the edge-on galaxy cataloged PGC 1237172 at the top right — a dim, hazy line. Find it by looking for the bright blue star with small diffraction spikes positioned over the top of its left edge. This galaxy nearly disappears in mid-infrared light because its stars are very young and the galaxy isn’t overflowing with dust.

Now, scan the full image left to right to spot distant galaxies in the background. The red objects are encased in thick layers of dust. Some are spiral galaxies and others are more distant galaxies that can only be detected as dots or smudges. Green galaxies are laden with dust and are farther away. Bluer galaxies are closer. Zoom in carefully to see if a blue dot has miniscule diffraction spikes — those are stars, not galaxies.

Credits: NASA, ESA, CSA, STScI

NIRCam

The Hubble Space Telescope captured visible light when observing Arp 142, nicknamed the Penguin and the Egg, in 2013. This image is the James Webb Space Telescope’s near-infrared light view of the same region.

The process of applying color to Webb’s images is remarkably similar to the approach used for Hubble: The shortest wavelengths are assigned blue and the longest wavelengths are assigned red. Image processors translate near-infrared light images, in order, to visible colors.

Linger on Webb’s image. A faint upside-down U shape joins the pair of galaxies. This is a combination of stars, gas, and dust that continues to mix as the galaxies mingle. Toward the bottom of the Penguin’s tail are several prominent spiral galaxies. In the Egg, the galaxy shines so brightly that it causes diffraction spikes to slightly extend its gleam.

In the background, many distant galaxies gleam in Webb’s infrared image. This is a testament to the sensitivity and resolution of Webb’s near-infrared camera, and the advantages of infrared light. Light from distant galaxies is stretched as it travels across the universe, so a significant portion of their light can only be detected in longer wavelengths.

Credits: NASA, ESA, CSA, STScI

The Hubble Space Telescope captured visible light when observing Arp 142, nicknamed the Penguin and the Egg, in 2013.

The image is made up of several filters. The shortest wavelengths are assigned blue and the longest wavelengths are assigned red. A dark brown dust lane begins across the Penguin’s “beak” and extends through its body and along its back. Toward the bottom of the Penguin’s tail are several prominent spiral galaxies.