James Webb Captures Stunning Dance of Dwarf Galaxies NGC 4490 & NGC 4485

JWST Discovery Today - James Webb Captures Stunning Dance of Dwarf Galaxies NGC 4490 & NGC 4485

James Webb 2025 image of dwarf galaxies NGC 4490 and NGC 4485 connected by red tidal bridge of stars and gas – Arp 269

James Webb Space Telescope’s stunning 2025 image of interacting dwarf galaxies NGC 4490 and NGC 4485 (Arp 269), connected by a glowing red tidal bridge of gas and newborn stars – the closest dwarf-dwarf merger ever seen in such detail. Credit: ESA/Webb, NASA & CSA, A. Adamo, FEAST JWST team

Updated on: December 02, 2025 | By: Jameswebb Discovery Editorial Team

James Webb Telescope Captures Stunning “Dance of Dwarf Galaxies” NGC 4490 & NGC 4485 – Closest Dwarf-Dwarf Merger Ever Seen (December 2025)

ESA has just dropped the December 2025 Picture of the Month, and it is already one of the most talked-about James Webb images of the year. For the first time, the NASA/ESA/CSA James Webb Space Telescope has revealed the full dramatic story of NGC 4490 and NGC 4485 – two dwarf galaxies locked in a gravitational “dance” only 24 million light-years from Earth in the northern constellation Canes Venatici (the Hunting Dogs). Together known as Arp 269 in the famous Atlas of Peculiar Galaxies, this pair is officially the closest interacting dwarf-dwarf system where astronomers can see both a clear tidal gas bridge and thousands of individually resolved stars – second only to our own Large and Small Magellanic Clouds orbiting the Milky Way.

The Full Timeline of This Cosmic Ballet

~200 million years ago – First close encounter. The larger galaxy, NGC 4490 (nicknamed the Cocoon Galaxy because of its dusty appearance), swung past tiny NGC 4485 and tore out a gigantic stream of hydrogen gas.
~30 million years ago – The stolen gas mixed with NGC 4490’s own reservoir, compressed, and collapsed, triggering a second, ferocious wave of star formation that lit up the entire system.
Today – Webb shows us the glowing aftermath: a spectacular red tidal bridge packed with warm dust, newborn stars, and super star clusters just a few million years old.

What the New James Webb 2025 Image Actually Shows

Left half of the image – NGC 4490, the bigger and more chaotic galaxy, filled with pinkish star-forming regions and dark dust lanes.
Top-right corner – NGC 4485, the smaller companion, appearing almost pure white in mid-infrared because of intense heating from young stars.
The dramatic red “river” – A 50,000-light-year-long tidal bridge made of warm dust and polycyclic aromatic hydrocarbons (PAHs) glowing brightly in Webb’s MIRI instrument.
Bright blue-white dots – Hundreds of super star clusters, some containing thousands of massive O- and B-type stars, lighting up bubbles of ionized hydrogen.

No previous telescope – not Hubble, not Spitzer, not ground-based observatories – could see this level of detail through the thick dust.

Why NGC 4490 and NGC 4485 Are “Living Fossils” of the Early Universe

These dwarf galaxies look almost exactly like the building blocks of the cosmos 10–13 billion years ago:

Total stellar mass: only about 3–5 billion solar masses (the Milky Way has roughly 60 billion solar masses).
Metallicity (abundance of elements heavier than helium): just 1/5 of the Sun’s value, compared to the Milky Way’s near-solar level.
Gas fraction: more than 50% of their total mass is still pristine hydrogen and helium (the Milky Way has less than 10%).
Current star-formation rate: 5–10 times higher than typical nearby dwarf galaxies and far more bursty than the steady, moderate pace in the Milky Way.

These extreme properties make Arp 269 one of the best local analogs we have for the thousands of small, gas-rich galaxies that merged together in the early Universe to create today’s giants.

Groundbreaking Science from the FEAST Program

These observations come from the FEAST survey (Feedback in Emerging extrAgalactic Star clusTers), JWST program #1783 led by Prof. Angela Adamo (Stockholm University). Major new findings already published or in press:

Confirmation of two distinct starburst phases exactly as predicted by simulations
The first direct measurement of feedback strength from super star clusters in a dwarf-dwarf interaction
Precise ages for more than 2,000 individual star clusters across the system
Evidence that tidal bridges are among the most efficient star-forming environments in the local Universe

Detailed FAQ – Everything You Want to Know

How far away are NGC 4490 and NGC 4485? - Approximately 24–25 million light-years (7.4–7.8 Mpc). That’s close enough that Webb can resolve individual stars across the entire system.

Will these galaxies fully merge? - Yes. Current models predict a final merger in roughly 500–800 million years, creating a single, more massive dwarf elliptical or irregular galaxy.

Why does the tidal bridge look red in the Webb image? - The red color comes primarily from Webb’s MIRI instrument detecting warm dust (50–300 K) and large organic molecules (PAHs) that glow brightly at 7.7–18 microns.

Is NGC 4490 the same as the Cocoon Galaxy? - Yes – NGC 4490 earned the nickname “Cocoon Galaxy” because of its dusty, cocoon-like appearance in optical images.

Can amateur astronomers observe this pair? - Absolutely!

NGC 4490 is magnitude ~9.8 and easily visible in 8–10 inch telescopes as an elongated glow.
NGC 4485 is magnitude ~11.8 and requires 12–16 inch scopes under dark skies.
The tidal bridge itself is only visible in professional infrared images.

What filters were used to create this image?