Astronomers Peek Inside the Nursery of a Monster Star
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Thursday, Aug. 15, 2013, at 8:00 AM
A monster lurks in the heart of this glowing cloud of dust and gas.
Photo by ALMA (ESO/NRAJ/NRAO)/NASA/Spitzer/JPL-Caltech/GLIMPSE
Photo by ALMA (ESO/NRAJ/NRAO)/NASA/Spitzer/JPL-Caltech/GLIMPSE
Massive stars in the galaxy are pretty rare. The Sun is a big star,
comparatively, bigger and brighter than about 80-90 percent of all the
stars in the Milky Way. But the true monsters, stars with a whopping 100
times the Sun’s mass, are far more rare; maybe one in 10,000 stars is
that big. They’re super bright, and generally unstable—they undergo
pretty violent paroxysms during their short lives before exploding as a
supernova.
Despite being so obvious, we know very little about how they’re born.
It’s actually hard to pile that much material onto a forming star
before it heats up and starts blasting out light and matter, blowing
away the cocoon from which it formed. Plus the formation time is pretty
short, so you have to catch it at just the right moment. Not only that,
but the clouds of material from which they’re born are pretty thick,
choked with dark material, making it hard to see what’s going on.
But sometimes we catch a break: Astronomers have found just such a beast.
About 10,000 light years from Earth (a pretty fair distance, actually)
is a dark cloud of material called SDC 335.579-0.292. The cloud is about
10 light years across, and has enough material to make well over 5000
stars like the Sun. Although the cloud is dense, the radio waves
generated by the stars forming inside it can travel right through the
surrounding material, where it can be detected on Earth by powerful
telescopes.
In this infrared image, the tendrils of the cloud (seen as being dark
here) are labeled. The scale bar is one parsec, about 3.25 light years.
Photo by Peretto et al., from their paper.
Photo by Peretto et al., from their paper.
One such telescope is the brand spanking new Atacama Large
Millimeter/submillimeter Array, and its view of the cloud is pretty
good. Pictured above (combined with images from other telescopes), you
can see the cloud has several filaments, or tendrils, that meet near the
center. And right in the middle of this mess are two dense knots of
material (they’re pictured in yellow in the image).
Those knots are where new stars are being born. The brighter of those
two knots has a mass of well over 500 times the mass of the Sun, which
is a lot. It seems likely that right in the heart of that knot a
star is forming that may wind up as one of the galaxy’s most massive,
tipping the cosmic scale at about 100 times the mass of the Sun!
Having read the journal paper associated with this discovery,
I’ll admit I’m not 100 percent convinced this knot of material is
forming a single star. It’s more of a statistical argument—given a
certain amount of material you’ll get a certain number of stars of a
given mass. But in this case, there’s so much material that a single
star that ginormous isn’t out of the question, and is even likely.
So we may very well have a front-row seat to a massive star being
born. And these observations may also just cut through an old problem in
massive star formation. There are two possible scenarios to make a big
star: one in which the cloud fragments as it collapses, forming several
distinct regions where stars form after the fragmentation, and another
in which the cloud collapses globally, all of the material forming stars
at the same time as the collapse.
The new observations show the filaments appear to be streaming into
the bright knots, which would seem to indicate the cloud itself is
collapsing globally, feeding scads of material into the center. That’s
actually a pretty big deal; I remember studying this issue in graduate
school, and even simplifying the situation as much as possible it’s a
tough problem to solve. When you add real-Universe physics (magnetic
fields, turbulence, chemical composition of the material screwing up how
it absorbs and radiates energy) this gets hair-pulling-outingly
complex.
The ridiculously photogenic Orion Nebula, seen in the infrared by Spitzer Space Telescope.Photo by NASA/JPL-Caltech/J. Stauffer (SSC/Caltech)
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