(music)
(Narrator) I am Stefan Immler, an astrophysicist
at NASA's Goddard Space Flight Center. I'd like to
take you on a tour of two nearby galaxies in our cosmic neighborhood,
the Large and Small Magellanic Clouds, as captured in ultraviolet light
by NASA's Swift satellite. These images are the highest-resolution
wide-field surveys of the galaxies at ultraviolet wavelengths.
Both of these galaxies are less then 200,000 light
years away, and each contains a few hundred million stars
like our sun. If you live or travelled to the Southern Hemisphere, you'll
see both of these galaxies as faint cloudy patches in the night
sky. Both galaxies orbit our own as well as each other.
Of the two, the LMC is physically larger and nearer
to us than the SMC. Their messy shapes are products of gravitational
interactions between them, tidal forces from the much bigger Milky Way, and
internal processes like star formation. In visible light,
we see a mix of sun-like stars, along with pink patches that
mark star-formation regions, where hydrogen gas is set aglow by the light
of young stars. These are especially prominent in the LMC.
Viewed at higher energies, in the UV, the LMC looks
very different. This wavelength blocks out the older stars,
mostly showing those less than 500 million years old.
These galaxies are relatively small, but they're also very
close to us. This means that they appear much larger than the field of view
of Swift's telescope. So we had to take many different observations and
stitch them together. Swift had to image 172 separate
fields in 2,200 short snapshots to take in
the whole galaxy. The LMC's most striking feature
is the dramatic Tarantula Nebula. This is the most active
star factory in any of the dozens of galaxies in
the Local Group, which includes the Milk Way and Andromeda.
Thousands of stars form each year within cool, dark
molecular clouds. Once they start shining, they blow off their
birth cloud with powerful outflows called stellar winds.
These winds, in turn, sculpt the gases into the Tarantula's
spider-like shape. One star here, named R136a1,
is one of the most massive known, weighing more than
260 times the sun. The LMC holds more than
a thousand star clusters formed during previous rounds of star formation.
We mostly see hot, young, luminous stars, plus a few stars
in exotic stages as they near stellar death.
Wherever there are hot, young and massive stars there are also
supernovae. In 1987, the closest stellar explosion
in more than 400 years occurred in the outskirts, of the Tarantula Nebula.
Even 26 years later, the after glow of the explosion
remains detectable in the ultraviolet.
All told, the new Swift mosaics reveal about a million objects
in the LMC and about 250,000 objects in the
smaller, less massive and more distant SMC.
For this mosaic of the SMC, Swift imaged about
50 fields and took 656 snapshots.
One interesting feature is the massive young
star cluster NGC 346. It contains
the SMC's brightest star, HD 5980,
a triple star system where all members among the most luminous
stars known. The intense light and strong outflows from these stars
mold the surrounding gas into a shape resembling a cobweb.
The Swift UV mosaics allow
us to study the evolution of young stars in the LMC and SMC
all in one view. That's impossible for us to do for our own galaxy
because we're inside it. The images
give us a panoramic window into how stars are born, evolve and die
across two complete galaxies. That gives us fresh
insight into the many ways stars transformed the universe
into what we see around us today.
Music
Beeping