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Bend your brain around this: the entire galaxy might have buckled under its own weight.

Many disc galaxies, including our own Milky Way, have a central bulge that resembles either a box or an unshelled peanut. This bulge may form when the circular orbits of stars become elongated, creating a “bar” of stars that runs through the centre and tilts out of the disc’s plane. The combined effect makes the once-flat galaxy look like it has buckled under enormous pressure.

There’s just one problem – we’ve never seen this buckling occur. The whole process is thought to take a few hundred million years, so it’s not surprising that we haven’t caught it in action. But it does make the theory difficult to confirm.

“It would be a bit tedious to wait for the whole thing,” says of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.

Now, Erwin and of the University of Central Lancashire in Preston, UK, think they have spotted a couple of galaxies in mid-buckle. “It’s probably what the Milky Way looked like billions of years ago,” Erwin says.

Cosmic fedora

The pair simulated the buckling process and took snapshots of their simulated galaxies from various angles and at various points in time. They noticed that galaxies in mid-buckling form a strange asymmetrical structure that looks a bit like a wide-brimmed fedora tilted at a 45 degree angle.

Looking out into the real universe, they found two galaxies, NGC 4569 and NGC 3227, with a similar shape. “To get this weird asymmetric shape inside the bar, you need to have something like the buckling going on,” says Erwin.

An alternative explanation for these galactic bulges is that they simply form gradually, rather than through the more violent buckling process. But this gradual formation should always be symmetric, which means that the fedora-like structure would not form.

It’s possible that both processes take place in the cosmos, says Erwin, but the pair calculate that in the distant universe – corresponding to 7 billion years in the past – around 40 per cent of galaxies should be in the middle of buckling, which the James Webb Space Telescopemay be able to observe in the future.

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