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Rob WaughBlast from exploding stars trapped Earth in “space bubble”, NASA says
NASA has found evidence that a nearby cluster of the explosions “went off like popcorn”, blowing an enormous bubble into space - which we are still inside.
Supernova explosions are terrifyingly powerful - in a split second, a star tears itself apart, and more energy is released than the sun shines out in a million years.
Supernova explosions happen on average once every 50 years in our galaxy - making the exploding star outshine the entire Milky Way for a brief moment. A new NASA X-ray experiment has found evidence of a barrage of relatively recent explosions near Earth - and a strange "bubble" created around us.
Astronomers today scan for nearby stars likely to explode: were a Type II supernova to occur within 26 light years of Earth, the blast of gamma rays would shred the ozone layer, leaving creatures on Earth exposed to deadly cosmic rays.
The cluster of supernovas which NASA thinks exploded near Earth did so 10 million years ago - at which point, human beings did not exist, but Great Apes, our ancestors, did.
The explosions weren’t close enough to wipe out life - but DID have a mysterious effect on our solar system, which still remains today.
The evidence is “the Local Bubble” - a searingly hot, peanut-shaped bubble around 300 light years long, and with almost nothing inside.
The Local Bubble was discovered gradually in the 1970s and 1980s.
Optical and radio astronomers looked carefully for interstellar gas in our part of the galaxy, but couldn't find much in Earth's neighborhood.
Meanwhile, x-ray astronomers were getting their first look at the sky using sounding rockets and orbiting satellites, which revealed a million-degree x-ray glow coming from all directions. It all added up to Earth being inside a bubble of hot gas blown by exploding stars.
"Within the last decade, some scientists have been challenging the [supernova] interpretation, suggesting that much or all of the soft X-ray diffuse background is instead a result of charge exchange," says F. Scott Porter of the Goddard Space Flight Center.
"Charge exchange": Basically, it happens when the electrically-charged solar wind comes into contact with a neutral gas.
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The solar wind can steal electrons from the neutral gas, resulting in an X-ray glow that looks a lot like the glow from an old supernova. Charge exchange has been observed many times in comets.
So, is the X-ray glow that fills the sky a sign of peaceful "charge exchange" in the solar system or evidence of terrifying explosions in the distant past?
To find out, an international team researchers including Porter and led by physics professor Massimiliano Galeazzi at the University of Miami in Coral Gables, developed an X-ray detector that could distinguish between the two possibilities. The device was named DXL, for Diffuse X-ray emission from the Local Galaxy.
On Dec. 12, 2012, DXL launched from White Sands Missile Range in New Mexico atop a NASA Black Brant IX sounding rocket, reaching a peak altitude of 160 miles and spending five minutes above Earth's atmosphere.
That was all the time they needed to measure the amount of "charge exchange" X-rays inside the solar system.
The results, published online in the journal Nature on July 27, indicate that only about 40 percent of the soft X-ray background originates within the solar system. The rest must come from a Local Bubble of hot gas, the relic of ancient supernovae outside the solar system.
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Obviously, those supernovas were not close enough to exterminate life on Earth—but they were close enough to wrap our solar system in a bubble of hot gas that persists millions of years later.
"This is a significant discovery,' said Galeazzi. "[It] 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."
