A 3-D map of stars reveals the Milky Way’s warped shape

Scientists used thousands of stars called Cepheids to trace the galaxy’s structure

Milky Way

BENT OUT OF SHAPE  A new map of the Milky Way made with Cepheid stars reveals the warped shape of the galaxy. In this image, those stars (green) are overlaid on top of an image of another warped galaxy, NGC 4565. The star icon indicates the sun.

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

Like a misshapen potato chip, our home galaxy is warped. A new 3-D map brings the contorted structure of the Milky Way’s disk into better view, thanks to measurements of special stars called Cepheids, scientists report in the Aug. 2 Science.

Making 3-D measurements of the galaxy requires estimating how far away stars are from Earth, typically a matter of guesswork. But unlike other stars, Cepheids vary in brightness over time in a particular way that can be used to determine a precise distance to each star.

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

Skowron and colleagues made new observations of Cepheids as part of the Optical Gravitational Lensing Experiment, or OGLE. Combining those measurements with previously studied Cepheids resulted in 2,431 stars charted in the map.

The team also used the Cepheids’ regular brightness variations to estimate the stars’ ages. Younger Cepheids aligned with the Milky Way’s four main spiral arms, while the older stars were more scattered, a result of their dispersal over time as the galaxy rotates, a computer simulation suggests. The scientists were able to roughly reproduce the stars’ actual distributions by simulating stars forming in the galaxy’s arms and spreading out over time, helping scientists understand how the galaxy came to have its current structure.

The Milky Way’s Cepheid stars are plotted in three dimensions, revealing the galaxy’s warped shape. Unlike other stars, Cepheids 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, indicated by the grid. The star icon indicates the sun.

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