The Milky Way is shaped like a curvy potato chip

Cepheid stars help scientists trace the galaxy’s warped structure


This new map of the Milky Way reveals the warped shape of the galaxy. The map was made with stars called Cepheids. In this image, the Cepheid stars (green) are overlaid on top of an image of another warped galaxy. That galaxy is NGC 4565. The star icon indicates the sun.

J. Skowron/OGLE/Astronomical Observatory/Univ. of Warsaw

Our home galaxy, the Milky Way, is warped. It looks like a misshapen potato chip. And, there’s a new 3-D map that brings the contorted structure of the Milky Way’s disk into better view.

The Milky Way’s disk is usually depicted as flat. But previous observations had revealed that the galaxy is curved at its edges. The new study shows that the Milky Way is even more warped than scientists had thought, says Dorota Skowron. She is an astronomer at the Astronomical Observatory of the University of Warsaw in Poland. Imagine you took a spaceship into deep space and looked back at our galaxy. “You could see by eye” that it’s misshapen, Skowron says.

To make measurements of the galaxy, scientists have to estimate how far away stars are from Earth. That’s typically a matter of guesswork. This time, the scientists made the map with measurements of stars called Cepheids. Unlike most stars, Cepheids vary in brightness over time. They vary in brightness in a particular way. Scientists can use that brightness to determine a precise distance to each star.

Skowron and colleagues made new observations of Cepheids as part of the Optical Gravitational Lensing Experiment, or OGLE. The team combined those measurements with previously studied Cepheids. That resulted in 2,431 stars charted in the map. The scientists describe the map in the August 2 Science.

The team also used the Cepheids’ brightness variations to estimate the stars’ ages. Younger Cepheids aligned with the Milky Way’s spiral arms. The older stars were more scattered. This is a result of how they move over time as the galaxy rotates. That’s at least according to a computer simulation. The scientists were able to roughly reproduce the stars’ actual distributions. They did it by simulating stars forming in the galaxy’s arms and spreading out over time. That helped scientists understand how the galaxy came to have its current curves.

The Milky Way’s Cepheid stars are plotted in three dimensions. The stars reveal the galaxy’s warped shape. Cepheids are special stars. They vary in brightness in a particular way that helps scientists make more precise estimates of their distances from Earth. Brighter colors represent Cepheids closer to the warped plane of the galaxy. The warped plane of the galaxy is indicated by the grid. The star icon indicates the sun.
J. Skowron/OGLE/Astronomical Observatory/Univ. of Warsaw/Science News/YouTube

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