The Milky Way is shaped like a curvy potato chip | Science News for Students

The Milky Way is shaped like a curvy potato chip

Cepheid stars help scientists trace the galaxy’s warped structure
Aug 21, 2019 — 6:45 am EST
a map of the Milky Way showing the warped curvature of the galaxy

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.
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Power Words

(more about Power Words)

3-D     Short for three-dimensional. This term is an adjective for something that has features that can be described in three dimensions — height, width and length. 

astronomy     The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.

colleague     Someone who works with another; a co-worker or team member.

galaxy     A massive group of stars bound together by gravity. Galaxies, which each typically include between 10 million and 100 trillion stars, also include clouds of gas, dust and the remnants of exploded stars.

gravitational lensing     The distortion of light by an intense gravitational force, such as what can be exerted by clusters of galaxies — the most massive things in the universe. The gravity can bend or focus light, making it appear brighter and in one or more different places in the sky.

Milky Way     The galaxy in which Earth’s solar system resides.

observatory     (in astronomy) The building or structure (such as a satellite) that houses one or more telescopes.

optical     An adjective that refers to light or vision.

simulation     (v. simulate) An analysis, often made using a computer, of some conditions, functions or appearance of a physical system. A computer program would do this by using mathematical operations that can describe the system and how it might change over time or in response to different anticipated situations.

star     The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

Citation

Journal:​ ​​ D.M. Skowron et al. A three-dimensional map of the Milky Way using classical Cepheid variable stars. Science. Vol 365, August 2, 2019, p. 479. doi: 10.1126/science.aau3181.