For the first time, researchers have studied a series of events beginning 14 million years ago that caused a still-expanding cosmic bubble to envelop Earth's galactic neighborhood, forming all the nearby stars, a statement explains. Called the Local Bubble, the expanse stretches 1,000-light-years-wide. Within 500-light-years of Earth, all stars and star-forming regions sit on the surface of the Local Bubble, but not inside, giving clues to why Earth sits in a part of the Milky Way Galaxy that is mostly empty, reports Denise Chow for NBC News.
Scientists have suspected the giant bubble's existence for decades. However, astronomers only recently have observed the net, its shape, and how far it reaches. Astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) and the Space Telescope Science Institute (STScI) published the study this week in Nature.
The Local Bubble formed from a series of supernovae, or powerful explosions that take place when stars collapse at the end of their life span, reports NBC News. These explosions occurred near the void's center and blasted gas across space over the last 14 million years. The shockwave gathered clouds of gas and dust into a thick frigid, hollow shell that formed the surface of the Local Bubble, explains Catherine Zucker, the study's lead author and astronomer at the Center for Astrophysics, to Isaac Shultz for Gizmodo. The clouds of gas and dust provided enough fuel for star-forming regions on the bubble's surface.
Using data visualization software, the team mapped the asymmetrical bubble. Over millions of years, at least 15 supernovae have burst and pushed gas outward, creating a bubble where seven star-forming regions are found on the surface. The astronomers also created gorgeous 3-D maps of the Local Bubble's celestial material.
When the bubble first formed, it was moving at about 60 miles per second, according to data collected by Gaia, a space-based observatory belonging to the European Space Agency. Currently, the bubble is still expanding at four miles per second, Gizmodo reports.
Astronomers suspect that the solar system is situated in the middle of the bubble because it is much older than 14 million years, per Gizmodo. When the first supernovae went off that created the Local Bubble, the sun was far away from it, explains João Alves, a University of Vienna astrophysicist, in a statement. About five million years ago, the sun crossed into the Local Bubble, where it currently sits near the middle.
"When the Local Bubble first started forming, the Earth was over 1,000 light-years away," Zucker tells Gizmodo. "We think the Earth entered the bubble about 5 million years ago, which is consistent with estimates of radioactive iron isotope deposits from supernova in the Earth's crust from other studies."
Researchers suggest more star-forming bubbles are likely common throughout the Milky Way. Study author and CfA astronomer Alyssa Goodman—who founded Glue, the data visualization software that helped piece together the study's maps—explains in a statement that statistically, the sun wouldn't be near the middle of a vast bubble if they were not common throughout the galaxy.
"The Local Bubble is just the one that we happen to be inside of at the moment," Zucker tells NBC News. "We think that the sun in its history has likely passed through many, many super bubbles."
The team plans on mapping more cosmic bubbles to get a full 3-D view of their shape, locations and size. By charting out where the bubbles lay in the vast expanse of space, astronomers can piece together how these bubbles act like nurseries for stars, how the bubbles interact with each other, and how galaxies like the Milky Way evolved over time, per a statement.