Original | Evan Gough
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The Sun is not the only star in a nearby galaxy, and other stars have called this area home. But what about the history of the area? What triggered the birth of these stars?
A group of astronomers say they have stitched together pieces of history and identified the trigger: a series of supernova explosions that began about 14 million years ago.
About 14 million years ago, a series of stars around us exploded into supernovae. They create a giant bubble of gas about 1,000 light-years in diameter, known as a "local bubble." The sun is currently in the center of the bubble. Stars near the Sun formed at the edge of this bubble, and previous supernova explosions were catalysts for their formation.
A new study published in the journal Nature demonstrates these findings. The title is "Star formation near the Sun is driven by the expansion of local bubbles." Lead author Catherine Zucker, an astronomer and data visualization expert.
"We calculated that over millions of years, about 15 supernovae disappeared, forming the local bubble we see today."
Stars are formed by clouds of hydrogen known as giant molecular clouds (GMC). To form a star, there must be enough gas to accumulate at a point. This happens when the density of the gas changes. The density becomes larger and larger due to gravity, and if the time is long enough and the conditions are right, enough gas gathers together to trigger fusion, and a star is born.
But supernova explosions can also form stars. Supernova explosions release enormous amounts of energy that travel outward in the form of shock waves. Shock waves squeeze gases together to form clouds and create greater densities. This can bring new stars.
That's what's happening around us, it forms stars at the edge of the local bubble, which is also the edge of the supernova blast. Inside the local bubble, the density of the interstellar medium (ISM) is much lower than that of ISM throughout the Milky Way. This series of supernova explosions pushed the gas to the side, forming dense edges and pushing the star formation there.
Over time, the edges of the bubbles have broken and collapsed into a cloud of star formation. The once smooth edges of it were gone. The team reports that there are seven star-forming regions on the surface of the bubble that form in the form of molecular clouds. These include Orion A and Orion B, both of which are important components of the Orion Molecular Cloud Complex. "Remarkably, we found that every famous molecular cloud within 200 parsecs from the Sun is located on the surface of the local bubble," the paper said. The Perseus molecular cloud may be an exception.
Star formation doesn't happen all at once. In their paper, the authors note that it occurred in four different eras: 10 million years ago, 6 million years ago, 4 million years ago, and now. They don't know exactly how many supernova explosions formed the bubble, but they limited it to between 8 and 26, determining that the most likely number was 15. "We've calculated that about 15 supernovae formed the local bubbles we see today over a few million years," said Zucker, who is now a Hubble Researcher at NASA's Space Telescope Science Institute.
This diagram shows the evolution of the local bubble and the continuous process of star formation on the surface of its expanding shell.
"It's really a story about origins: for the first time we can explain how all the nearby star formation began," said Zach, who completed the work while working as a researcher at cfA.
Zach is an expert at data visualization, and visualization stands out in particular in this study. Zucker and her colleagues created an interactive tool to explore the local bubble and its surroundings.
Here's a static screenshot of an interactive tool created by Zach and her colleagues.
You may recognize some stars at the edge of the local bubble. For example, the red supergiant Star Cephalodo ii is the brightest and most massive star in the Scorpio-Centauri combination. It is the 15th brightest star in the sky and one of the largest stars visible to the naked eye.
The local bubble isn't a static object: it's still growing slowly, like a car after you release the throttle. "It's gliding at 4 miles per second," Zucker said. "However, it has lost most of its momentum and has almost stagnated in speed."
Like many other discoveries about our proximity to the Milky Way, this work relies heavily on data from the European Space Agency's Gaia spacecraft. Gaia created a magnificent 3D model of the Milky Way based on position and velocity measurements of about 1 billion stars.
The team traced the movement of the stars to map the formation of bubbles. The observed geometric motion means that all of the sun's famous star-forming regions within the 200-parsec range are formed by gas engulfed by the expansion of local bubbles," they explain in the paper.
"It's an incredible detective story, driven by data and theory," said Alyssa Goodman, an astroomer at harvard professor and astronomer at the Center for Astrophysics, a collaborator on the study and the founder of green, the data visualization software that made this discovery possible. "We can use a wide variety of independent clues to piece together the history of star formation around us: supernova models, stellar motion, and a new 3D map of the material around the delicate local bubble."
The sun is at the center of a local bubble, but not always. As the sun travels through space, it enters the bubble. Now we find ourselves in it, even at the beginning of humanity, we were inside.
This is a local bubble map drawn by the artist, and new stars are forming on the surface of the bubble.
"When the first supernova that produced local bubbles exploded, our sun was still far from that activity," said co-author Jo o Alves, a professor at the University of Vienna. "But about 5 million years ago, the sun's path through the Milky Way brought it into the bubble, and now the sun (with luck) is almost right in the center of the bubble."
What does it mean that we find ourselves in the center of a bubble? This is statistically impossible, so this means that such bubbles are not uncommon. In fact, astronomers have believed for 50 years that these bubbles exist. "Now, we have proof — what's the chances that we're right in the middle of these things?" Goodman asked.
What happened after the supernova exploded? When supernovae exploded, the stars weren't completely destroyed, leaving them with remnants. In their paper, the authors say survivors of all these supernovae may be included in UCL and Crux (LCC) clusters. "We found that 15-16 years ago, the interval between the birth of UCL and Crux (LCC) clusters was about 15 parsecs, and the bubbles themselves were most likely created by the surviving supernova members of these clusters."
If we zoom in on the famous star-forming regions on the surface of local bubbles, what do we see?
The discovery suggests that the Milky Way has the form of a Swiss cheese, where thin ISM bubbles are everywhere. Now that the team has found a bubble, they want to discover more. Will our local bubble be different or generic in some way?
There are other issues that need to be resolved. "Where do these bubbles come into contact?" Zach asked in a press release. "How do they interact with each other?" How did superbubbles propel the birth of stars like our sun in the Milky Way? ”
To answer these questions, the team will have to wait for Gaia's phase iii data release (Gaia DR3). The European Space Agency has published some data, but not all.
The team looks to the future at the end of the paper: "The vast amount of new star radial velocity data in Gaia DR3 not only provides more precise estimates of the evolution of local bubbles, but can also perform similar studies farther away, providing further observational constraints for supernova-driven star formation near the Milky Way." ”
original:
https://www.universetoday.com/154047/nearby-supernovae-exploded-just-a-few-million-years-ago-leading-to-a-wave-of-star-formation-around-the-sun/