JWST Photographs a Fiery Spiral Galaxy With an Unexpectedly Violent Past

JWST Photographs a Fiery Spiral Galaxy With an Unexpectedly Violent Past

The new JWST image of peculiar galaxy NGC 3256, comprising infrared and near-infrared wavelengths. (ESA/Webb, NASA & CSA, L. Armus, A. Evans)

Galaxies come in all shapes and sizes. We have gorgeous, highly structured spirals. We have fuzzy elliptical galaxies and the lenticular blobs in between. 

Amid all these variations are the peculiarities – galaxies that are odd in some way, that have some quirk that give them a little something extra. And one of these peculiar galaxies is the subject of a new galactic portrait from the James Webb Space Telescope.


It's called NGC 3256, and it might look like a fairly standard spiral galaxy. But NGC 3256 betrays evidence of a violent past: a collision and merger between two galaxies that disrupted their interstellar dust and clouds, resulting in an ongoing burst of star formation. 

The full JWST image of NGC 3256. (ESA/Webb, NASA & CSA, L. Armus, A. Evans)

Although there's quite a lot of empty space out there, galaxies are slowly drawn along invisible filaments of the cosmic web, where they collide and merge to form larger galaxies. 

It's a fairly routine part of galactic evolution, and NGC 3256, a Milky-Way-sized galaxy some 120 million light-years away, demonstrates its effects beautifully. 

One of those effects is the long tails of material streaming from the galaxy, pulled out during their gravitational dance as they spiraled in towards each other. 

Another effect is the star formation rate. 

Stars are born
 in immense, dense clouds of dust and gas. When a clump in this material becomes dense enough, it collapses under gravity to form the seed of a star that then grows big and strong by feeding on the cloud around it. 

During a galactic merger, molecular clouds in the two galaxies collide and merge, compressing the gas to produce many, many more clumps than would be there normally. 

These clouds light up with star formation like fireworks, but there's a catch. The clouds around them are very thick and opaque, meaning we can't see them in shorter wavelengths. 

But JWST is an infrared instrument, meaning it can detect longer wavelengths of light that can travel through dust clouds without scattering the way visible light does. So, it can see signs of star formation that instruments like Hubble can't. 

In the new JWST image, these signs are seen in red and orange as dust absorbs light from the stars in infrared. As you can see, there's rather a lot of it, overlapping neatly with the dark filaments of dust lanes seen in Hubble's view. 

This makes NGC 3256 what we classify as a starburst galaxy. Scientists have estimated that it forms around 49 solar masses' worth of new stars a year, compared to the eight or less in the Milky Way. 

NGC 3256 is still in the process of merging. It has two galactic centers, each with its own supermassive black hole, separated by a distance of around 2,770 light-years.

Eventually, they'll merge and form an even bigger supermassive black hole, but that is probably a few million years away yet. 

In the meantime, while we wait for that day, NGC 3256's peculiarity makes it a wonderful laboratory for studying how these colossal mergers evolve. 

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