Exactly 400 years ago Galileo Galilei aimed a small handheld
telescope at the Milky Way and later wrote: “ The galaxy is nothing else
than a congeries of innumerable stars.”
This was a staggering revelation for his time because the
total number of individual stars that can be seen with the naked eye on a very
dark night is 3,000 to 4,000. Galileo realized there were myraid more. The
universe suddenly got bigger and more complex.
Now if Earth were tipped upside down so that Western Civilization
grew up under the star-bejeweled southern sky that is dominated by the Milky
Way’s hub, modern astronomy may be decades even more advanced than it is today.
Why? Just take a look at this photo from the European Southern Observatory in
Chile. The bright core of the Milky Way is right overhead. From the southern
view it’s clear that we live in a galaxy that we seen edge-on.
For dramatic effect in the photo, a guide star laser was
aimed exactly at the galactic center, which is cloaked behind great dust lanes
and star clouds. Not far from this position a powerful narrowband radio
transmission popped up for little more than a minute on August 15, 1977. Dubbed the “Wow Signal” it may be the
only fleeting hint that we are not alone in the galaxy. But because it has never repeated, the transient
event remains an unresolved mystery.
A view of the galactic center in X-ray light, released by
NASA’s Chandra X-ray space observatory this week, reveals a smoldering graveyard
of white dwarfs, neutron stars, and black holes. But there is also an inferno: million
degree winds of plasma blast into space from a plethora of massive young stars.
Other energy fountains are powered by the galaxy’s
supermassive black hole. Though relatively quiescent, this sleeping giant has
burped out withering X-ray flares 50 and 300 years ago. Even stranger are X-ray
filaments – essentially solar flare-like structures on steroids that are launched
by crushed neutron stars.
We are the first generation ever to behold the Milky Way’s
hub in all its splendor and probe its hidden mysteries. Little might Galileo
have imagined that 400 years later we would come to know our galaxy so intimately.
And the future holds even more intimacy as we estimate the
number of earthlike planets scattered among these stars, as now being sampled by NASA's Kepler space observatory. And who knows, maybe someday the “Wow Signal” will pop up again.