This post by Gregg Easterbrook is shown below.
Cosmic Thoughts -- Bummer Edition: Recently, I was creeped out by this supernova. Detected Feb. 18 by Swift, a satellite launched to look for gamma-ray bursts, the exploding star already was the 24th supernova discovered at that early point in 2006. As instruments improve, exploding stars appear more common than cosmologists had expected, and that's not the best news we might have heard. Coded GRB 060218, this star detonation began as a gamma-ray burst that lasted 33 minutes -- absolutely stunning because previous gamma-ray bursts from space have lasted a few seconds at the most. The gamma rays came from 470 million light-years away. That was discomfiting because strong gamma-ray bursts usually emanate from what astronomers call the "deep field," billions of light-years distant and thus billions of years back in the past. A distance of 470 million light-years means the GRB 060218 supernova happened 470 million years ago. That is ancient by human reckoning, but many cosmologists had been assuming the kind of extremely massive detonations thought to cause strong gamma-ray busts occurred only in the misty eons immediately after the Big Bang. The working assumption was that since life appeared on Earth, there had been no stellar mega-explosion. Now we know there has.
For several days as the giant dying star GRB 060218 collapsed, this single supernova shined brighter than all 100 billion other suns in its galaxy combined. The detonation was so inexpressibly luminous that, though 470 million light-years distant, it could be seen by telescopes on Earth. And not just fancy telescopes at the tops of mountains: A few days after the Swift satellite detected the gamma-ray surge, an amateur astronomer in the Netherlands sighted the forming supernova through a backyard telescope. The stellar coordinates hit the Web -- it was at RA: 03:21:39.71 Dec: +16:52:02.6 -- and soon amateur astronomers the world over were marveling at the glistening beacon from the cosmic past. This explosion released so much energy that it happened 470 million years ago yet the light could travel for that protracted period, plus pass through the gas and dust of roughly a hundred galaxies along the way, and still illuminate mirrors of backyard telescopes on Earth.
Now here's what creeped me out: had GRB 060218 happened in our galaxy, life on Earth would have ended Feb. 18.
Gamma rays are a deadly form of radiation. Routine gamma-ray bursts course through the Milky Way, our galaxy, all the time, and the threat from them appears small. Recently Krzysztof Stanek, a professor of astronomy at Ohio State and one of the hot names in astronomy -- reader Jim Yrkoski of Warsaw, Poland, notes I missed one "z" in Stanek's name the last time I cited him -- calculates that a regular supernova causing a routine gamma-ray burst would need to detonate within about 3,000 light-years of Earth to expose our world to enough radiation to cause a calamity. Only a small portion of the Milky Way, and none of the larger universe beyond, is within 3,000 light-years of our world.
This does not rule out "nearby" gamma-ray bursts as causes of past extinctions. About 340,000 years ago, a supernova called Geminga exploded 180 light-years from Earth, which is much too close. Calculations suggest Geminga was bright enough to rival the full moon; our Homo erectus ancestors must have looked up on it in wonder. The Geminga supernova is believed to have blown off much of the ozone layer, exposing Earth to solar and cosmic radiation that killed many mammals, including many of those ancestors. Another supernova, Vela, about 1,500 light-years away, detonated 11,300 years ago. About the same time, several large mammals of North America and Eurasia fell extinct: among them, the woolly mammoth, the giant sloth and the glyptodon, an armadillo larger than a bear. There's a lively archeological debate about whether these extinctions were triggered by climate change or by people armed with new hunting tools such as bow and arrow. Maybe the extinctions were caused by the supernova bathing Earth in gamma rays.
At any rate, Vela and Geminga were normal supernovas that caused relatively mild gamma bombardments lasting just seconds. If a 33-minute, incredibly powerful gamma-ray burst similar to the one associated with GRB 060218 happened anywhere in the Milky Way or any nearby galaxy, Earth would be sterilized; any life that might exist on other planets in our galaxy and nearby galaxies also would end. Most likely, the gamma radiation from GRB 060218 ended all life in numerous galaxies near the explosion. After GRB 060218, a team of astronomers led by Andrew Fruchter of the Space Telescope Science Institute calculated that the class of extremely massive blue star that caused this mega-supernova probably is not found in the Milky Way. That's some consolation. But February's ultimate supernova tells us nature has a doomsday weapon -- and that creeps me out.
