In a study published today in Nature, they describe an amorphous, 1,000-light-year-wide bubble ensconcing Earth that is responsible for those stars.
Called the Local Bubble, the researchers believe it formed from a series of large explosions that blasted energy into space over the last 14 million years. Those explosions were supernovae—spectacular collapses of stars that sometimes leave behind beautiful nebulae. In this case, the supernovae also shaped our galactic neighborhood, 500 light-years in any direction from Earth.
“We find that all nearby, young stars formed as powerful supernova explosions triggered an expanding shockwave, sweeping up interstellar clouds of gas and dust into a cold dense shell that now forms the surface of the Local Bubble,” said study co-author Catherine Zucker in an email to Gizmodo.
“Astronomers have theorized for many decades that supernovae can ‘sweep up’ gas into dense clouds that ultimately form new stars, but our work provides the strongest observational evidence to date in support of this theory,” added Zucker, an astronomer at the Center for Astrophysics | Harvard & Smithsonian.
The team modeled how the explosions likely took place over millions of years, pushing gas outward like a broom sweeping up dust. At its genesis, the bubble was probably moving outward at about 60 miles per second, Zucker said. It’s still expanding today, but at a more leisurely 4 miles per second. Interactive figures of the bubble can be seen here.
Our Solar System is at the center of the bubble, rather than at its edge. That’s because, unlike the stars on the Local Bubble’s periphery, our solar system was born much longer ago than the last 14 million years.
NGC2392, a nebula left by a supernovae some 5,000 light-years from Earth, taken by the Hubble Space Telescope in 2002.
“When the Local Bubble first started forming, the Earth was over 1,000 light-years away,” Zucker said. “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.”
