Our Local Bubble of Near-Nothingness
Teams of scientists reveal that the long mysterious x-ray glow suffusing space is mostly from a bubble our solar system is in which was caused by ancient supernova explosions.
Yes, we live in a bubble. It is called The Local Hot Bubble (or put less thermodynamically, The Local Bubble).
The first hint of that possibility came decades ago at the birth of X-ray astronomy when we noticed a faint but persistent x-ray glow wherever we looked, called the diffuse X-ray background. It seemed certain that these x-rays were produced relatively locally between s few hundred light years away and a few astronomical units away (one unit = earth’s average distance from the sun, 93 million miles). This is because if they were emitted from a much more distant sources, the neutral gas in the Milky Way would have already absorbed them before they got to us.
Some astronomers believed that this radiation was ultimately caused by multiple nearby supernovas over 10 – 20 million years ago when our monkey-like ape ancestors roamed the earth. This tremendous outpouring of debris and radiation tends, of course, to push everything out of the way, even the diffuse hydrogen gas found everywhere within the interstellar medium (ISM). This creates a bubble of low density near-nothingness that is one tenth that found in the general ISM. This amounts to only one atom per liter of space compared to 10. Our Local Bubble is about 300 light years across and our solar system has been cruising through it for 5 – 10 million years. The soft X-rays that we now see inside this bubble are emitted by the hot gases the subsequent supernovas released.
To be anal about this, we are actually in a slightly more dense part of the Local Bubble called the Local Interstellar Cloud
We know how theoretically pugilistic astronomers can be so they had to come up with other theories. The most popular is that the x-rays comes from a process called Solar Wind Charge Exchange. This means that whenever atoms come in contact with the ions (charged particles) of the solar wind, the latter steals electrons from the former causing the production of this radiation. This can be caused by comets, the outer atmospheres of planets or even plain old interstellar gas.
Both scenarios would produce x-rays similar enough in frequency and intensity that it’s been very hard to determine which theory is correct. Hence the controversy and mystery has persisted unabated for years and years.
Various teams of scientists decided to take this bull by the horns and settle the question once and for all. The charge was led by by Massimilliano Galeazzi from the University of Miami. They took x-ray detectors developed in the 1970s and gave them a new lease on life, then they pimped them with serious upgrades. These devices were then launched on sounding rockets to an altitude of 160 miles where they had all of 5 minutes to collect the data needed. That was clearly enough because the mystery was solved, kinda.
It turns out that both theories were correct which is not much of a surprise but the real winner was the supernova/bubble scenario. The pattern of radiation examined reveals that at least 60 percent of the x-rays probably come from the our Local Bubble offering perhaps the best indication yet that this bubble really exists and was caused by a cascade of supernovas millions of years ago.
I can’t help but imagine what our monkey-like ape ancestors saw when this happened. Most likely, all they saw was the monkey butt in front of them as they were running away.
Image Credit: NASA CHIPS