Scientists recreate what the Milky Way might look like to alien astronomers

What would an alien astronomer in a distant galaxy see if they looked up at the Milky Way in the night sky with a telescope?
John Loeffler

We see alien galaxies every time we look up into the night sky with a telescope, but what might aliens on those galaxies see when they look at us? New research has just painted a new picture of what our home galaxy might look like to anyone looking in from the outside.

“Finding ways to compare our home galaxy with more distant galaxies is what we need if we want to know whether the Milky Way is special or not," Jianhui Lian, an astronomer at the Max Planck Institute for Astronomy and Yunnan University, said in a statement. "This has been an open question since astronomers realized a hundred years ago that the Milky Way is not the only galaxy in the universe.”

Determining what our galaxy looks like from the outside is hard work, especially since no one alive has ever seen it, but we have some clues based on what we know about our own galaxy and our place in it. We also have thousands of distant galaxies that we can study to get a sense of what a galaxy like ours might look like.

Specifically, Lian, Maria Bergemann, and other astronomers at the Max Planck Institute for Astronomy set out to use comprehensive data about the chemical composition of our galaxy and the chemical spectra compositions of other spiral galaxies to pull together a chemical picture of what an alien astronomer in the Andromeda galaxy might see when looking over at its smaller neighbor, the Milky Way.

While there's no way to know what exactly our galaxy looks like from the outside, we can at least paint a picture of its chemical composition similar to what other galaxies look like to us. Specifically, the astronomers at the Max Planck Institute for Astronomy looked at how elements heavier than helium (any element heavier than helium is considered a 'metal' in astronomy) distributed through our galaxy's disk.

What they found is that there is a 'metallic belt' starting at around 23,000 light-years from the galaxy's center where the metal content of the stars rises to roughly the same level as our sun, before slowly declining to about a third of the sun's metallicity at about 50,000 light-years from the galaxy center.

Compared to simulations and other data from observations of other galaxies, about 1% to 11% of galaxies have a similar metallic belt, and the drop off of metallicity toward the Milky Way's edge appears to be more severe than in similar galaxies. If nothing else, it would appear that we would be an interesting galaxy to study for alien astronomers due to our somewhat outlier status.

“The findings are very exciting!" Bergemann said. "This is the first time that we can meaningfully compare the detailed chemical content of our Galaxy with the measurements of many other galaxies. The results are important for the next generation of comprehensive studies of galaxy formation. Those studies will use data from upcoming large-scale observational programs targeting the Milky Way or targeting distant galaxies. Our research shows how to sensibly combine the two kinds of data set.”