We’re a nation of science dummies. No more than 25 percent
of Americans are “scientifically savvy and alert,” says public opinion researcher
Jon Miller. Most of the rest of us “don’t have a clue.”
Prime time TV dramas like the upcoming miniseries, Impact,
which will air on ABC-TV the next two Sunday evenings (June 21st and 28th) underscores this
sad state of science cluelessness. The scriptwriter Michael Vickerman (author
of several B-grade sci-fi flicks) is a total ASTRO-101 flunky.
After two weeks on the road in support of the Hubble Space
Telescope servicing mission I finally got around to seeing the latest Star Trek
film. Great story, but once again, the astronomy is utterly "illogical."
A titanic battle of the giants is looming in intergalactic
space. The neighboring spiral galaxy in the constellation Andromeda is falling
toward us at a speed of one million miles per hour. At that velocity it will
plow into our Milky Way only a few billion years from now.
This close-to-home galaxy mergers ranks among the biggest
big bang-ups in the universe, and it's dramatically illustrated in
the Discovery Channel's upcoming TV series -- Cosmic Collisions.
Wait -- galaxies collide? At first glance this may sound counterintuitive; after all, Andromeda is more than a million times farther away than the nearest star to
our sun, so it seems there would be no chance of them ever colliding.
But consider that our Milky Way galaxy is 100,000 light
years across, and is separated from Andromeda by 22 galaxy diameters (2.2
million light years). By comparison, the sun is nearly a million miles across.
The nearest star, Proxima Centauri, is 100 million solar diameters away (24
trillion miles).
Put another way, if the sun were the size of a hockey puck,
the nearest star would be -- to scale -- 4,700 miles away! But if the Milky Way were the size of a hockey puck,
the Andromeda galaxy would be another hockey puck located a little less than
six feet away. That's within gravity's striking distance for a pair of galaxies
that each weigh a few trillion solar masses.
Supercomputer simulations that model the galaxies'
gravitational pull on each other give us a preview of the close encounter
that's coming (the actual collision will span one billion years). It looks sort
of like what happens in the children's poem the Gingham Dog and the Calico Cat, who
rip each other apart. The stars are scatted like a fallen box of marbles and
the galaxies lose their trademark spiral shape and finally morph into a giant
elliptical galaxy.
This is more than theory though. Over the past few decades
astronomers have collected dramatic snapshots of pairs of galaxies colliding,
or more politely put, interacting.
Sometimes more than two galaxies get into the act. One of
the most spectacular examples is the mosh pit called Stephan's quintet of five
galaxies mixing it up. Hubble Space Telescopes has shown that this was more the
case in the early universe because it was smaller, and galaxies bumped intro
each other more often.
When you view computer simulations, it looks like the end of
the line for anyone living in a colliding pair of galaxies. But this couldn't
be further from the truth.
Remember how comparatively far apart stars are? Even if another galaxy passed through the
Milky Way the sun would never collide with another star.
But what other bad things might happen to our solar system
in a galaxy collision? On closer
inspection it's sort of like the aftermath of a Roadrunner vs. Coyote cartoon. Despite all hell breaking
loose in the dynamics of the collision, the vast majority of earthlike planets
would go on with life as usual.
The biggest consequence of a galaxy collision is that stars
are tossed along gravitational tidal arms that stretch out each galaxy to
resemble an s-shaped fan blade. During the bang-up our solar system may find
itself rapidly relocated in one of these long arms. Our distant descendants
would have a truly bird's-eye view of the galaxy makeover in progress.
Billions of new stars would be born is a firestorm of
star birth triggered by the impact's compression of cold hydrogen in each
galaxy. Five billion years from now the sky will be ablaze with gem-like
clusters of brilliant hot blue stars and glowing nebulae. It will be a great
time to be an astronomer.
The downside of a having a beautiful faux Van Gogh Starry
Night sky is that there will be many more massive stars that explode as
supernovae and belch out lethal radiation. Mergers of double stars may cause
gamma ray bursts that would barbecue planets caught in their death-ray beam
within a few hundred light-years. But given the vastness of the galaxy this is not
as doomsday-ish as it sounds. The large majority of stars and planets will go
on unscathed.
Another scary consequence is that the 3 billion-solar-mass
black hole in the core of the Milky Way would merge with the 4 billion-solar-mass black hole in Andromeda. This would send gravitational waves rippling
across the galaxy that would monetarily pinch Earth's diameter by one-inch,
like squeezing a soccer ball.
Gas falling toward the monster black hole would be heated
and expelled along a blowtorch-like beam of high-speed particles and radiation
called an extragalactic jet. Any unlucky planet caught in the beam could see
much of its atmosphere stripped away.
However, a huge teardrop shaped solar wind “bubble” around
our sun could serve as a buffer to deflect the jet particles, depending on the
sun's distance and beam intensity. Also, a laser-narrow jet would only affect a
small fraction of the stars in the Milky Way.
Probably the biggest risk to Earth would come from having a
near-passing star gravitationally perturb the Oort cloud of comets. Like
shaking apples out of a tree, the dislodged comets would fall into the inner
solar system. A shower of wayward comets would bombard Earth, causing global
mass extinctions.
Now, to avoid any more melodrama, all of this could very well be a moot
point -- the sun is scheduled to burn out in 5 billion years, just when the
intergalactic fun is beginning.
The other unknown is that we won't know if the galaxy close-encounter
will be a head-on collision or glancing blow. Astronomers do not precisely know
if the Andromeda galaxy is on a trajectory causing it to swing wide of us. In
fact the Milky Way and Andromeda may simply orbit each other for quite some
time, like two Sumo wrestlers sizing each other up.
The bottom line is that the universe is indifferent to our
fate. Trillions of new planets could be born out of such a galactic close
encounter, even if it did mean demolishing old homesteaders like Earth.
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