How could we give boring blobby galaxies a new, exciting shape?

Dead Planets Society is a podcast that takes outlandish ideas about how to tinker with the cosmos – from snapping the moon in half to causing a gravitational wave apocalypse – and subjects them to the laws of physics to see how they fare. Listen on Apple, Spotify or on our podcast page.

For the most part, galaxies only come in two shapes: spirals and blobs. While spirals can be majestic viewed from the right angles, the lack of variety can get boring over the cosmic eons. So in this episode of Dead Planets Society, it’s time to spice things up, galactically.

Our hosts Leah Crane and Chelsea Whyte are joined by Vivian U at the University of California, Irvine, an astronomer who studies how galaxies evolve when they smash together and warp one another. In the real world, galactic collisions can create strange swirls and many-armed behemoths, but over time the chaos from the smash-up results in just another blob. To make a lasting change, we’ll need tools with a bit more precision.

That’s where the supermassive black holes come in. They might be able to carve gaps through the dust and gas of a galaxy, creating more detailed images. But gravity tends to complicate things, and eventually even those black holes would devour too much matter and merge together, resulting in yet another blob. Perhaps dark matter could be used instead to create an invisible scaffold that shapes the distribution of the regular matter that we can see.

Building such a strange-shaped galaxy – especially one unlike anything that a natural galactic collision would create, such as a galaxy with sharp corners or one in a recognisable image like a giraffe – might be a way to signal to aliens or future astronomers that we are here and we have incredible cosmic powers.

In fact, perhaps this has already been done to the Milky Way by some strange alien force – after all, we can’t see our home galaxy from outside of it. We only know its shape by counting the stars that we can see in each direction and building theoretical models, so we can rule out that our galaxy is in the shape of a giraffe or something else wildly out of the ordinary. But if it were, say, a square instead of a spiral, it might be difficult for astronomers to tell the difference.