credit: modification of work by NASA
Orbit X-ray observatories have shown that the galaxy is filled with bubbles of hot gas, X ray emitting gas. They also showed a diffuse X-ray background that, from our perspective, appears to fill the entire sky.
While part of this emission comes from the interaction of the solar wind with the interstellar medium, most of them come from beyond the solar system. The natural explanation for why X-rays are emitted gas around us is that the sun itself is in one of the bubbles. Hence we call our “neighborhood” the local hot bubble, or the local bubble for short.
The local bubble is much less dense (about 0.01 atoms per cm3 on average) than the average interstellar density of about 1 atom per cm3. This local gas has a temperature of around a million degrees, like the gas of the other super-bubbles that are spreading in our Galaxy, but since there is very little hot material, this high temperature does not affect the stars or planets in the area in any way.
What caused the local bubble to form? Scientists aren’t entirely sure, but the main candidate is winds from stars & supernova explosions. In a nearby region towards the constellations Scorpio and Centaurus, a large amount of star formation occurred about 15 million years ago.
The most massive of these stellars evolved very quickly until they generated strong winds & Some people ended their lives in the explosion. These processes fill the area around the sun with hot gas, replacing the colder, denser gas. The rim of this expanding super-bubble reached the Sun about 7.6 million years ago and is now more than 200 light-years from the Sun towards the constellations Orion, Perseus, and Auriga.
There are some clouds of interstellar matter inside the local bubble. The sun itself appears to have entered a cloud about 10,000 years ago. This cloud is warm (with a temperature of approx. 7000 K) and has a density of 0.3 hydrogen atom per cm3. —Higher than most of the local bubble, but still so weak it’s also known as the local fluff.
While this is a fairly thin cloud, we estimate that it helps 50-100 times more particles than the solar wind to diffuse material between planets in our solar system. These interstellar particles were discovered by spaceships traveling between planets and their numbers were counted. Perhaps one day scientists will find a way to collect them without destroying them and bringing them back to Earth so that we can touch them, or at least study them in our laboratories. “Those messengers from distant stars.”
