A pair of molecular clouds known as Taurus and Perseus are famous among astronomers. These star-forming regions are just 400 and 1,000 light-years from Earth, respectively, offering a glimpse of how stars come to be in the galaxy. Now we know a bit more about the origin of these clouds thanks to the ESA’s Gaia spacecraft. Using the incredibly precise mapping data from Gaia, scientists have discovered a spherical void between the clouds, which points to an explosive formation.
From our perspective on Earth, Taurus and Perseus overlap each other. We knew Taurus was closer to Earth, but we didn’t know what was between it and Perseus. It turns out there’s nothing, which is something notable in itself as it helps confirm long-held beliefs about star formation in the astronomical community. Essentially, supernovae that signal the death of one star can trigger the formation of molecular clouds like Taurus and Perseus that become stellar nurseries, beginning the cycle all over again.
If the supernova hypothesis of molecular cloud formation is right, you’d expect to find a large empty space between Taurus and Perseus, and indeed that’s what we see. It was difficult to know the layout of objects hundreds of light-years away before Gaia. Our estimates could easily vary by as much as 30 percent. When Gaia launched in 2013, it began the most detailed survey of the galaxy ever, lowering the margin of error to just 1 percent. Using the most recent Gaia data release from late 2020, astronomers at Harvard mapped out the spherical gap between Taurus and Perseus, which they’ve named the Per-Tau shell.
With this new data, we have a better picture of how this little corner of the galaxy evolved. It started about 10 million years ago when a star reached the end of its natural life. It exploded in a supernova, pushing nearby gas and dust away where it eventually cooled to form the Taurus and Perseus molecular clouds. Meanwhile, the Per-Tau shell is still relatively devoid of matter. You can even see the new map of the Per-Tau shell in 3D, courtesy of the Harvard team.
The next step in the study will be to try and identify the star cluster that contained the supernova. That will require data from the next Gaia release (technically, the second half of the third data set), which is expected in 2022. Then, astronomers should be able to spot a group of stars that were in the right place at the right time to create the Per-Tau shell. That could help us learn even more about how cataclysmic events can affect surrounding space.
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