Astronomers say they've cracked a 50-year puzzle of the origin of a glowing low-energy X-ray "fog" they see wherever they look into space around us.
Scientist have debated the origins of this glow for 50 years, but researchers say new studies suggest it comes from both inside and outside our Solar System.
Using a refurbished detector that first flew on a NASA rocket in the 1970s, they've confirmed that the majority of the glow comes from an area of interstellar plasma dubbed the local hot bubble, or LHB.
That bubble could be a remnant of a nearby supernova explosion that occurred sometime during the past 20 million years, they reported in their work in the journal Nature.
This million-degree plasma accounts for most of the X-rays, but the study also identified the presence of low-energy or "soft" X-rays produced within our solar system by the solar wind of charged particles emitted by the sun colliding with diffuse interplanetary gas, they said.
Finding which sources were responsible for what portions of the X-ray glow was important, says research astrophysicist Steve Snowden at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
"Interactions between the solar wind and neutral atoms in comets, the outer atmospheres of planets, and even interstellar gas produce soft X-rays," he explained. "We need to account for these processes because the X-rays they produce complicate our observations of the wider universe."
The X-ray glow is surprisingly intense in the gas-heavy region of our Milky Way galaxy's central plane, where it ought to be mostly absorbed, suggesting the fog seen from Earth emanates in the local hot bubble of gas that extends just a few hundred light years out from our solar system.
"We now know that the emission comes from both sources but is dominated by the local hot bubble," says researcher Massamiliano Galeazzi.
"This is a significant discovery," he says. "Specifically, the existence or nonexistence of the local bubble affects our understanding of the area of the galaxy close to the sun, and can, therefore, be used as a foundation for future models of the galaxy structure."
To gather the data, the refurbished 1970s detector was launched in 2012 from the White Sands Missile Range in New Mexico on a NASA sounding rocket.
Reaching a peak altitude of 160 miles, the detector spent around 5 minutes above the Earth's atmosphere, making recordings of the cosmic X-ray glow.
Its data shows the X-ray fog is dominated by the local hot bubble, with at most 40 percent being created within the Solar System, the researchers said.
