Is This the Biggest Spiral Galaxy in the Universe?

Feb 5, 2016

Photo credit: Galaz et al., 2016

By Phil Plait

From the cream floating in your coffee cup to hurricanes to galaxies themselves, spirals form on a vast range of scales. They may be for different reasons (coffee and hurricanes have faster rotation in the center, winding up the arms, whereas galaxies form spirals from a more subtle and complex effect that acts like an interstellar traffic jam), but when you have stuff that spins, spirals can arise naturally.

But how big a spiral can you get? Our Milky Way galaxy is pretty beefy, one of the bigger spiral galaxies in the Universe. It’s roughly 100,000 light-years across, or a quintillion kilometers. That’s a lot of kilometers.

Don’t go bragging to your friends just yet though. It turns out spirals can get bigger. Way, way bigger.

The galaxy pictured at the top of this post is called Malin 1. It’s faint; so dim it was only discovered in 1986, and was the first discovered in a class of galaxies called low-surface brightness spiral galaxies. Most spirals are pretty bright and easy to see, but LSBs are much fainter. Despite that, they can grow to huge sizes.

I’ve known about Malin 1 for a while, but it hadn’t really registered with me one way or another. That changed instantly when I saw a new paper about it, which was featured on the American Astronomical Society’s Nova site, where notable discoveries are highlighted.

I saw the photo of it and nodded in admiration; it’s a very pretty and interesting spiral. But then I saw the distance, and my brain did a double take. Malin 1 is 1.2 billion light-years away.

“Wait,” my brain said, shaking itself. “What? That can’t be right!”

But it is: 1.2 billion light-years is a tremendous distance. If it’s that far, and that big in the image, it must be huge. Freaking huge.

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