Interstellar Gas Clouds
Simulation of the collapse of an interstellar gas cloud into a massive star. The left side shows the whole cloud, and the right side shows a zoom-in around the massive star in the center. Credit: Mark Krumholz
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, and detail their findings in the Feb. 28 issue of the journal Nature.
Gravity tends to break interstellar gas clouds into small pieces, preventing massive star formation, but little stars heating up a gas cloud can smooth it out, forcing gravity to create a huge star.
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 - 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.
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Massive Stars Need Their Smaller Siblings To Grow @ Universe Today
The Dragon - Beijing's New Monster Airport from The Daily Galaxy
X marks the spot in dark matter web from Space New Scientist
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Labels: Astro Physics, Star formation, Theoretical Physics
posted by QUASAR9 at 9:30 am
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Outer cocoon
At this very early stage, an outer cocoon of gas and dust called an envelope still surrounds the star and its swirling disc. Previous observations in the microwave portion of the spectrum suggested that this large cocoon is contracting and sending material onto the disc. But the inner region, where the disc meets the cocoon, could not be seen at these wavelengths.
The Spitzer observations probe this inner region and reveal infrared light emitted by massive amounts of water vapour – the equivalent of five times the content of the Earth's oceans.
The vapour is too hot to be explained by the embryonic star's radiation alone, suggesting another process must be heating it up.
Sonic boom
The team believes ice from the cocoon is pelting the disc at a rate faster than the speed of sound there, creating a shock front. "The sonic boom that it endures when it lands on the disc heats it up very efficiently" and vaporises it.
This supersonic shock "has been searched for and theorised about for decades", Watson says. It is a short-lived phenomenon that only occurs during the first few hundred thousand years of the star and disc formation, while the envelope is still feeding the disc.
The light emitted as the icy particles hit the disc can be used to learn more about the disc itself at this early stage, which could shed light on how planets form.
Turbulent birth
Most astronomers believe planets form according to a model known as "core accretion", in which small particles snowball into larger and larger objects over millions of years.
A competing idea, called "disc instability", is that turbulence in the disc can cause matter to collapse into planets extremely quickly, producing gas giants such as Jupiter in just a few thousand years.
"If you wanted to test between those scenarios, one of the most important places to look would be the stage we're looking at now." Future observations of such young discs could reveal how turbulent the discs are, and thus whether they boast the conditions required for disc instability. "The whole subject of the very beginnings of the development of solar systems is open to study now," Watson says.
Source: The development of a protoplanetary disk from its natal envelope