The James Webb Space Telescope has observed the dwarf galaxies NGC 4490 and NGC 4485 engaged in a gravitational dance, seen in unprecedented detail and revealing the connective features that hold the pair together.
This cosmic rendezvous is occurring at a distance of 24 million light-years from Earth, in the constellation Canes Venatici. The system is peculiar enough that astronomer Halton Arp included it in his landmark 1966 work, The Atlas of Peculiar Galaxies, under the name Arp 269, long before the recent Webb Telescope images.
Dwarf Companions
Astronomers have previously observed dwarf companions even closer to home, such as with the Milky Way’s Large and Small Magellanic Clouds. Outside of our local cosmic neighborhood, this is the closest dwarf-dwarf system for which astronomers have been able to resolve a gas bridge and stellar populations.
That was accomplished not just as a result of the galaxies’ close proximity to Earth, but by the James Webb Space Telescope’s impressive ability to pierce through dust clouds to capture remarkably clear imagery of distant objects.
It was almost 30 years ago that scientists first spied the gas bridge connecting NGC 4490 and NGC 4485. Still, years of Hubble Space Telescope observations proved insufficient to adequately trace the history of their interactions.
The Early Universe
The interactions between the two dwarf galaxies today are similar to those that were much more common across the universe billions of years ago, allowing astronomers a rare view into the processes that shaped the present universe.
Astronomers believe that dwarf galaxies bear many resemblances to the early universe’s young galaxies. These include their low masses, high gas content, and few stars. Additionally, dwarf galaxies tend to contain mostly light elements rather than heavier elements such as metals, which form later in the evolution of complex galaxies. Watching interactions between two dwarf galaxies allows researchers the ability to observe the processes that may have shaped regions of the cosmos as they appear today, as they collide, merge, or exchange gas.
James Webb Space Telescope Image
The two galaxies were only recently imaged correctly in context, with the James Webb Space Telescope’s Feedback in Emerging extrAgalactic Star clusTers (FEAST) program. FEAST’s objective is to utilize Webb’s infrared instruments to observe new star formations in nearby galaxies.
The new image captured by the James Webb Space Telescope shows NGC 4490 to the left, while NGC 4485 appears as a white glow in the upper right. The gas bridge bringing the two dwarf galaxies together is the red streak that crosses the image, beginning in the top left and extending to the right side, connecting to the bottom of NGC 4485. The bright blue spots in the image reveal concentrations of ionized gas, while other galaxies and the blackness of space peak out from the background.
James Webb Space Telescope Instruments
The specific instruments used to capture the image were the James Webb Space Telescope’s Near-InfraRed Camera (NIRCam) and Mid-InfraRed Instrument (MIRI), composited with a narrow band filter from the Hubble Space Telescope.
The high resolution of the new image allows astronomers to pick out individual stars. The team used that ability to identify regions composed of young, middle-aged, or old stars, from which they constructed a timeline of galaxy interactions. According to the timeline established by astronomers, the two dwarf galaxies in the image came together for a time before eventually moving apart again.
The wispy gas belt connecting the two developed during this time as the larger NGC 4490 captured a stream of gas from NGC 4485. That bridge wasn’t the only outcome of the interaction, as the collision also produced many new stars. Stars formed from interactions between galaxies are creating the blue, ionized gas regions seen in the image. They formed about 30 million years ago, when the two dwarf galaxies’ gases mixed together in the collision.
With a new understanding of these dwarf galaxies’ histories, astronomers have gained important new context for the processes at play in the early evolution of our universe.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.