Hollywood megastars need just right the right
conditions to explode onto the scene, a phenomenon shared by rare supermassive
celestial stars.
Two
scientists think they have decoded the gassy recipe to create stars as much as
100 times bigger than the sun, perhaps solving the mystery
of their formation. Mark Krumholz Princeton University in New Jersey and his
colleague Christopher McKee of the University of California Berkeley used
mathematical models to show how small stars can prime
superstar formation.
"Gravity
tends to break interstellar gas clouds into small pieces, preventing massive
star formation," Krumholz said. "But little stars heating up a gas
cloud can smooth it out, forcing gravity to create a huge
star."
Krumholz
and McKee detail their findings in the Feb. 28 issue of the journal Nature.
Star
power
Although
massive stars are about a million times rarer than the most common stars —
those about 80 percent smaller than the sun — they are the movers and shakers
of the universe.
"They're
very rare, but massive stars are the dominant players in galaxies,"
Krumholz said. "They're the things that can push around and heat up
interstellar gas, which is essentially where all stars come from."
He also
explained that big stars seed the cosmos with elements that are required for life.
"They
enrich the universe with metals from their
supernovae," he said, noting that only enormous stars are powerful
enough to fuse together small atoms and create the heavy materials.
Hot
influence
To form a
galactic superpower, Krumholz said an interstellar gas cloud needs to be
thousands of times more dense than average. Problem is, gravity tends to break
dense gas clouds into pieces and thwart massive star formation.
"The
challenge isn't getting enough gas, it's getting the cloud into a small enough
region and preventing its breakup," he said.
If a few
small stars form within the cloud, Krumholz explained, they can heat up the
cloud and increase its "column density," or pressure. The heating
process prevents gravity from taking control of the cloud, breaking it up and
forming only small stars.
"Heating
up the gas helps pressure win over gravity's influence, ultimately forcing the
gas cloud to collapse in a massive star," Krumholz said.
The new
view of star formation highlights the rarity of massive stars — the only kind
astronomers on Earth can see
in distant galaxies — but leads to the possibility that more stars form in
galaxies than previously thought.
"There
may be significant parts of galaxies where massive stars can't form, but
lower-mass stars like the sun can," Krumholz said. "We estimate the
number of stars in a galaxy on the amount of light we see, and if massive stars
are missing, then it's possible that we've dramatically underestimated the rate
of star formation in distant regions of the universe."
advertisement
