Wednesday, March 27, 2013

ESA Herschel Image: How to Build a Very Large Star

This image does not show any stars because the Herschel Space Observatory’s cameras record far-infrared light instead of visible light. 

Gas is not visible either, even though it makes up most of the 400,000 solar masses of matter in this cloud: dust amounts to only about one percent of the mass. 

Credit: ESA/PACS Array SPIRE consortium, A. Rivera-Ingraham and P. G. Martin, University of Toronto, HOBYS Key Programme (F. Motte)

Stars ten times as massive as the Sun, or more, should not exist: as they grow, they tend to push away the gas they feed on, starving their own growth.

Scientists have been struggling to figure out how some stars overcome this hurdle.

Now, a group of researchers led by two astronomers at the University of Toronto suggests that baby stars may grow to great mass if they happen to be born within a corral of older stars –with these surrounding stars favorably arranged to confine and thus feed gas to the younger ones in their midst.

The astronomers have seen hints of this collective feeding, or technically “convergent constructive feedback,” in a giant cloud of gas and dust called Westerhout 3 (W3), located 6,500 light years from us.

Their results are published in the upcoming month in The Astrophysical Journal.

Alana Rivera-Ingraham
“This observation may lift the veil on the formation of the most massive stars which remains, so far, poorly understood,” says Alana Rivera-Ingraham, who led the study while she was a graduate student in the Department of Astronomy and Astrophysics at the University of Toronto, Canada, and is currently a postdoctoral researcher at the Institut de Recherche en Astrophysique et Planétologie in Toulouse, France.

To study the formation of high-mass stars, Rivera-Ingraham and collaborators used high-quality and high-resolution far-infrared images from a space telescope launched by the European Space Agency in 2009 —the Herschel Space Observatory.

This telescope’s two cameras recorded light that is not visible to the naked eye, spanning a range from infrared radiation partway to the microwave region.

Peter Martin
Exploiting these cameras, scientists including Peter Martin, Professor in the Canadian Institute for Theoretical Astrophysics at the University of Toronto, created the HOBYS Key Programme to study the birth of very massive stars in nearby giant clouds of gas and dust in our own Galaxy, including W3.

Research on HOBYS at the University of Toronto is supported in part by the Canadian Space Agency and the Natural Sciences and Engineering Research Council of Canada.

Scientists track the regions of the gas cloud where stars are about to form by mapping the density of dust and its temperature, looking for the most dense regions where the dust is shielded and cold.

“We can now see where stars are about to be born before it even happens, because we can detect the cold dust condensations,” says Martin. “Until Herschel, we could only dream of doing that.”

Stars are born in the denser parts of gas clouds, where the gas gets compressed enough by gravity to trigger nuclear fusion. The more massive the newborn star, the more visible and ultraviolet light it emits, heating up its surroundings —including the dust studied by Herschel.

“The radiation during the birth of high-mass stars is so intense that it tends to destroy and push away the material from which they need to feed for further growth,” says Rivera-Ingraham.

Scientists have modeled this process and found that stars about eight times the mass of our Sun would stop growing because they run out of gas.

Herschel Observations of the W3 GMC: Clues to the Formation of Clusters of High-Mass Stars. The Astrophysical Journal, 2013

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