A pair of molecular clouds known as Taurus and Perseus are famous among astronomers. These star-forming regions are only 400 and 1,000 light-years from Earth, respectively, offering a glimpse of how stars come to be in the galaxy. We now know a little more about the origin of these clouds from ESA’s Gaia spacecraft. Using Gaia’s incredibly accurate mapping data, scientists have discovered a spherical void between the clouds, which points to an explosive formation.
From our perspective on Earth, Taurus and Perseus overlap. We knew that Taurus was closer to Earth, but we did not know what was between him and Perseus. It turns out that there is nothing, which is a remarkable thing in itself, as it helps confirm long-held beliefs about star formation in the astronomical community. Essentially, supernovae that signal the death of a star can trigger the formation of molecular clouds like Taurus and Perseus that become stellar nurseries, starting the cycle all over again.
If the supernova hypothesis of molecular cloud formation is correct, you would expect to find a large empty space between Taurus and Perseus, and indeed that is what we see. It was difficult to know the arrangement 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 study of the galaxy to date, reducing the margin of error to just 1 percent. Using the most recent Gaia data release from late 2020, Harvard astronomers mapped the spherical gap between Taurus and Perseus, which they called the Per-Tau layer.
With this new data, we have a better idea of how this little corner of the galaxy evolved. It began 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 where it eventually cooled to form the molecular clouds of Taurus and Perseus. Meanwhile, Per-Tau’s shell is still relatively devoid of matter. You can even view the new Per-Tau shell map in 3D, courtesy of the Harvard team.
The next step in the study will be to try to identify the star cluster that contained the supernova. That will require data from Gaia’s next launch (technically, the second half of the third data set), which is expected in 2022. Then astronomers should be able to detect 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 the surrounding space.