Making a 3D map

Scientists have been studying the 2D projections of Taurus and Perseus in the sky for a century. But how do they make the jump to 3D?

Dust constitutes only a small percentage of the mass of a star-forming cloud. However, it happens to be an excellent tracer of the dominant molecular gas from which stars are born. That’s why, in the new study, astronomers examined the Taurus and Perseus star-forming regions in 3D dust maps published in 2020 by co-author Reimar Leike and collaborators from the Max Planck Institute for Astrophysics in Germany. The maps extend to a distance of 1,300 light-years from the Sun and show details down to features just over 3 light-years in size.

To make such a map, Leike’s team collected information about roughly 5 million stars in the solar neighborhood. They used the stars’ colors, which can be affected by dust sitting between Earth and the stars, to determine how much dust lies in different directions. They then combined this information with accurate distances to the stars, provided by the European Space Agency’s revolutionary Gaia spacecraft.

“Prior to the launch of the Gaia space observatory, we typically knew where star-forming regions are located in a galaxy to the accuracy of 20 to 30 percent, which is a huge [margin of error],” says Catherine Zucker, a postdoc fellow at the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts, and a co-author of the new study. “With Gaia, our distance precision increased by a factor of five.”

Now, Zucker and her collaborators finally got to look at the clouds’ true forms — and they were in for a surprise.




Supernovae and star births

In 2D projections, Taurus and Perseus appear connected by a smooth bridge of material. However, the 3D map revealed they are, in fact, physically separated clouds. Furthermore, both seem to be parts of a near-spherical shell with a radius of about 245 light-years.

Furthermore, the team’s inspection of various images of the region taken at different wavelengths revealed the clouds represent the aftermath of several supernovae that exploded in the central part of the shell in the last 6 million to 22 million years. The blasts rippled outward, compressing gas and dust and creating the conditions necessary to form new stars.

Indeed, astronomers know that supernovae explosions are one of the main regulators of star formation in the Milky Way. “They trigger star formation locally at specific places, while globally they help to suppress star formation,” says Munan Gong, a postdoctoral researcher at Max Planck Institute for Extraterrestrial Physics in Germany, who wasn’t involved in the study. The Perseus-Taurus complex now offers the first 3D observational view of the results of this complex process.

Gong, who simulates star formation in such clouds, looks forward to getting her hands on the 3D maps and compare them to her simulations. So far, she says, astronomers have only looked at how supernovae affect average star-formation properties, such as the rate of star formation or the density of material in such clouds. “But the 3D dust map really allows us to look at the structure,” she says.

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