The Sun goes off unnoticed through a giant empty bubble, a kind of cavity in space. All the thousands of young stars nearby formed on the edge of that bubble. This is a conclusion from a 3D simulation in which the cosmic history of the Sun’s environment has been traced back in time 17 million years. American astronomers from Harvard University, among others published This week’s results are in the magazine temper nature. They confirm a fifty-year-old theory of American astronomers Christopher Mackie and Jeremiah Osterker.
The Earth revolves around the Sun, and along with hundreds of billions of other stars, the Sun revolves around the center of the Milky Way, a spiral galaxy about 100,000 light-years in diameter. The sun is in the arm of the Orion, which is a small branch of the largest of the spiral arms. Gas and dust float between the stars that make up new stars. Some places have more gas and dust than others. Large regions several light-years wide with little dust and gas are called superbubbles.
These superbubbles were hollowed out by several exploding stars. When a massive star, at least eight times the mass of the Sun, dies, the star’s outer layers rapidly fall into space. This is a supernova. When multiple supernovae occur relatively close together, one after another eruptions sweep away nearly all the nearby gases and dust like brooms. This creates an empty hole with some of the thin hot gas left from the explosion. Scavenging continues, at a decreasing rate, after millions of years. In other words, the super bubbles will continue to grow for a while.
cheese with holes
The first indication that the Solar System was traveling through such a giant bubble appeared at the end of the last century when astronomers using telescopes saw a lot of void around them. Astronomers called it the local bell. Its width is estimated to be about a thousand light-years, and the Sun has been there for about five million years, and it is now in the center. The bell does not affect the sun. It’s just a coincidence that the Sun’s orbit in the Milky Way passed the bubble. However, it was remarkable that almost all nearby stars younger than the Sun (maximum fourteen million years old) are located on the edge of the local bubble.
To explain why there are so many young stars out there, Mackie and Ostereker came up with a theory fifty years ago: that rims have ideal conditions for star formation. One of the researchers in the new study compared that theory in press release With cheese holes. When supernova explosions push the cheese out and create a gap, there is extra cheese on the edge of the cavity. New stars can be formed from this extra cheese, if locally pushed close together. It happens, according to the theory, when another supernova explodes. This creates a shock wave that compresses the extra cheese in some places on the edge.
To confirm this theory, imitative American astronomers have been evolving young stars near the sun over the past 17 million years using 3D technology. “We studied the current locations and velocities of about 1,000 young stars and star-forming regions within 500 light-years,” said Catherine Zucker, one of the participating astronomers. They obtained the data from the database of Gaia: a European space satellite that has mapped billions of stars since 2013. “Then we calculated how far the stars have moved in the past.”
The sun will leave the local bell again in the distant future
Simulations show that all of the nearby young stars have been on the edge of the bubble since their birth. Fourteen million years ago, 15 supernovae removed dust and gas, creating a local bubble, the researchers calculated. This gas and dust moved at a certain speed. Stars arising from this gas and dust were given the same velocity at birth and move outward with the edge of the bubble.
Now the bubble is still growing at a rate of 6.5 kilometers per second. This is slow in cosmic terms. The Sun is orbiting the Milky Way faster than the bubble is growing and will emerge from the bubble again in the distant future.
“Interestingly, astronomers who used the simulations may show a typical stellar cycle for the rest of the universe,” says Ignas Snellen, an astronomer at Leiden University who was not involved in the study. “Some of the stars that formed at the edge of the Local Bubble over the past millions of years will also end up in a supernova. This is how they make new super bubbles. More superbells have been found besides the Local Bell. Very serendipitous if the cycle applies only to the local bubble containing the sun.”
A version of this article also appeared on NRC on the morning of January 13, 2022
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