How Vast is the Universe
APRIL 22, 2010: NASA's best-recognized,
longest-lived, and most prolific space observatory zooms past a threshold of 20 years of operation this month.
On April 24, 1990, the space shuttle and crew of STS-31 were launched to deploy the Hubble Space Telescope into
a low Earth orbit. What followed was one of the most remarkable sagas of the space age. Hubble's unprecedented
capabilities made it one of the most powerful science instruments ever conceived by humans, and certainly the
one most embraced by the public.
Hubble discoveries revolutionized
nearly all areas of current astronomical research, from planetary science to cosmology. And, its pictures were
unmistakably out of this world. This brand new Hubble photo is of a small portion of one of the largest seen
star-birth regions in the galaxy, the Carina Nebula. Towers of cool hydrogen laced with dust rise from the wall
of the nebula. The scene is reminiscent of Hubble's classic "Pillars of Creation" photo from 1995, but is even
more striking in appearance. The image captures the top of a three-light-year-tall pillar of gas and dust that
is being eaten away by the brilliant light from nearby bright stars. The pillar is also being pushed apart from
within, as infant stars buried inside it fire off jets of gas that can be seen streaming from towering peaks
like arrows sailing through the air.
Giant galaxies weren’t assembled in a day. Neither was
this Hubble Space Telescope image of the face-on spiral galaxy Messier 101 (M101). It is the largest and most
detailed photo of a spiral galaxy that has ever been released. The galaxy’s portrait is actually composed of 51
individual Hubble exposures, in addition to elements from images from ground-based photos. The final composite
image measures a whopping 16,000 by 12,000 pixels.
The Hubble archived observations that went into
assembling this image were originally acquired for a range of Hubble projects: determining the expansion rate of
the universe, studying the formation of star clusters in the giant star birth regions, finding the stars
responsible for intense X-ray emission, and discovering blue supergiant stars.
The giant spiral disk of stars, dust, and gas is
170,000 light-years across or nearly twice the diameter of our galaxy, the Milky Way. M101 is estimated to
contain at least one trillion stars. Approximately 100 billion of these stars could be like our Sun in terms of
temperature and lifetime.
The galaxy's spiral arms are sprinkled with large
regions of star-forming nebulae. These nebulae are areas of intense star formation within giant molecular
hydrogen clouds. Brilliant young clusters of hot, blue, newborn stars trace out the spiral arms. The disk of
M101 is so thin that Hubble easily sees many more distant galaxies lying behind the galaxy.
All the Ovals in this picture are Galaxies. How big then
is the Universe?