Our Dangerous Galactic Passage
We’re only a little more than three months away from the imaginary 2012 End of Times (based on silly misinterpretations of the ancient Mayan calendar). The 2012 doom and gloom folks have glommed onto all kinds of nonsensical predictions where the Milky Way galaxy disrupts us: the passage of the solar system across the galactic plane, or a supposed “grand alignment” with the galactic center will trigger a mysterious and nondescript celestial ‘force.’
In reality, our Milky Way really does pose numerous hazards to Earth during the sun’s orbital journey around the galactic center. But no future space disaster can be circled on a calendar on Dec. 21 or any other date.
The sun has completed 20 orbits of the galactic hub since Earth formed. Each orbit is called a galactic year — a vast stretch of time (220 million Earth years) that the Mayans could have never imagined. Whatever cosmic catastrophes might have happened along the way, it has not prevented complex life from arising and evolving on Earth over roughly the past three galactic years. There have been attempts at statistically linking mysterious mass extinctions to cosmic disasters, but we simply don’t have enough data, says Colin Norman the Johns Hopkins University in Baltimore, Md.
The reality is that the potential of navigational hazards along our galactic journey lie far into the future over many millions or billions of years. Our distant descendants could come up with strategies to guard against some of these mishaps. However, the biggest threat is from extremely rare energetic events in the galaxy, says Norman.
Killer catastrophes were much more frequent in the Milky Way’s formative period, billions of years before Earth was born. Stars were being made at such a voracious rate — and then quickly exploding — that the galaxy would have been made uninhabitable by the radiation saturation, says Norman.
This is sobering because we suspect there could be ancient Methuselah planets in the galaxy that might have formed 12 billion years ago (as opposed to Earth’s 4.5 billion year birthday). But they would have been sterilized of life by radiation from multiple supernova and hot stellar winds from giant stars.
Over time there have been 1 billion supernovae in our galaxy. They accelerate cosmic rays that irradiate any nearby star systems. Even more devastating are so-called Quimby events. These are an unusual class of extraordinarily powerful supernova that defy conventional explanations for their power generation. It’s hypothesized that these super-blasts only happen in very rare stars that are over 100 times the mass of our sun. There could have been 10 million of these popping off in our galaxy to date.
Gamma ray bursts (GRBs) ratchet up the killer potential. It’s estimated there have been 100,000 gamma-ray bursts over our galaxy’s lifetime. These are produced by the biggest bangs since the Big Bang: hypernovae. These titanic stellar detonations unleash 1,000 times the energy of a supernova. It is concentrated in a narrow Death Star-like beam. The GRB beam evaporates anything that is nearby and along its path. The radiation would catastrophically damage DNA even over interstellar distances.
When the Milky Way and Andromeda galaxies collide in about another 10 galactic years there will be supersonic collisions between gas clouds that generate shockwaves. There will also be gravitational tidal torques on the stellar distribution.
Planetary systems will survive the fireworks, but the clouds of cometary embryos surrounding these systems (known as the Oort cloud for our solar system) could be disrupted. The planets could then be subjected to devastating comet showers. However, advanced civilizations would have the technological prowess to set up a planetary protection system to deflect space invaders, like the classic Atari arcade game Asteroids.
The frequency of supernova blasts will go up as a firestorm of new star birth sweeps across the merging galaxies. But advanced civilizations might set up radiation storm cellars by burrowing underground, or even hollowing out asteroids.
When the supermassive black holes in the cores of the Milky Way and Andromeda merge, they will send out a gravitational wave that will momentarily distort the shape of every object in the galaxy. But not to worry. Earth’s diameter would briefly “squish” by merely one-millionth of an inch.
There will not be any residual dust and gas in space to feed the 10 million solar mass newly merged black hole. All the Milky Way’s nebulosity will have all been blown away by the star formation firestorm. Therefore the elliptical galaxy formed from the Milky Way-Andromeda merger will not have a blazing active galactic nucleus powered by a well-fed black hole.
This is very good news. Otherwise the blast of radiation from an active black hole would increase the pressure of the tenuous interstellar medium by a factor of as much as one million. This would crush the heliosphere around the sun, a roughly 25 billion-mile diameter bubble of solar charged particles and plasma that protects our planet from low energy cosmic rays from interstellar space and solar wind particles.
However, Norman predicts that at least once during the sun’s orbit, the solar system will make a bull’s eye passed through the core of a dense molecular cloud that contains the raw material for new star formation. The space densities will also collapse the heliosphere allowing Earth to be irradiated. “We’ll be in big trouble without shielding,” says Norman.
The 2012 doomsayers can reset their end-of-world calendar. In the evolving universe the future is always uncertain and fraught with unpredictable danger. But as measure in galactic years, doomsday is never right around the corner.
Image credit: NASA