We've known for a long time that our Sun sits near the center of a vast bubble in space, a growing cavity carved out of ambient gas in the Milky Way. A new study has shown that almost all of the gas clouds that are forming stars sit on the thin edge of the bubble.
The bubble was created. A number of massive stars exploded just a few million years after their birth. The Sun entered the bubble 5 million years ago as it was in the center of the galaxy.
There's a lot going on here, and this is cool.
There is a thin amount of material between the stars. The interstellar medium is made of gas and dust and has a small amount of atoms in it.
Evidence began to come in that we are in a region of the galaxy with a slightly lower density. It has been difficult to pin down the exact size and shape of the Local Bubble. It has been thought that the cause of the bubble was a supernova or three, with material from the exploding stars blowing up and snowplowing up the interstellar medium. A lower density region is surrounded by a thin shell, like a distorted soap bubble.
The Local Bubble was looked at more closely by a team of astronomer to see if they could determine its size, shape, and age. They wanted to see if it would affect the gas clouds surrounding it. Previous studies were too low-resolution to be able to determine any of this.
They were very clever. The positions, motions, and distances of a billion stars around the Sun have been mapped by the European Space Agency mission. The team used the data to find young stars that are less than 20 million years old and within a few hundred light years of the Sun. These are usually in clusters of hundreds or thousands of such stars.
They looked at gas and dust in the space around them, as well as extinction, to see how much light was dimmed by this material. Since we know the distances to so many stars, we can create a 3D volume map of this material.
What they found is amazing. The Local Bubble is 1000 light years across, and contains a cloud of gas and dust that is close to the Sun. The motion of these clusters through space is not the same as it is in the center of the Local Bubble.
This is more than just a coincidence. This supports the idea that the expansion of the bubble triggered the formation of stars. It has been thought that the winds of material expanding away from a supernova can cause star formation, but we've never had evidence of it before. That is very cool.
They have put together an interactive graphic where you can zoom and pan around the structures they found. I suggest playing with it to get a feel for it.
The bubble is expanding at a rate of over 24,000 kilometers per hour. The amount of material swept up and formed the shell of the bubble is more than the mass of the Sun. It would take 15 supernovae to drive that much material to that speed. The bubble started about 14 million years ago, so there would've been about 1.1 million years between the explosions.
That is nightmare fuel. One supernova is frightening. It's fifteen in one volume of space. Enough to blow a hole in the sky.
They found more in the study. There are two star-forming clouds near the Local Bubble. Both are on the edge of a smaller bubble created by supernovae. The cloud of gas is on the far side of the bubble and the cloud of gas is on the near side. This is the closest example of a bubble-bubble collision.
The Gould Belt is a ring of gas and dust that is shaped like a plane of the universe with the Sun inside. The new study shows that this may be a lie, as two different structures are seen in projection. One of the structures is called the Radcliffe wave, a pattern of denser gas that is nearly 9000 light years long on one side of the Local Bubble, and the other is called the Split. It could be that the Gould Belt is what it is and why it exists.
It gets better. The team found that the Radcliffe wave and the Split may have been at the same spot in space roughly 20 million years ago. The Local Bubble may have been triggered by the star formation that created the supernovae. That's not clear, and needs more work.
The Bubble slammed into gas clouds and created waves of star formation 10 million, 6 million, and 2 million years ago. There is more evidence for star formation.
This is very exciting. It's difficult to put together a picture of local space around the Sun because we're inside the Bubble and it's all around us. The new study puts it in a new light. It's like moving into a house and finding a photo album of its history on one of the walls. It's very informative about the place where you live when you see all this structure from a different perspective.
We are all on this planet and we are all in the same place, but we are starting to understand what the neighborhood looks like and how it got that way.
The Astrometrics lab!