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CB244 Coreshine Unravels Stellar Formation Mystery

29/10/2010

Opaque to light and obscured by dust and gas, astronomers find it very difficult to probe deep inside stellar nurseries, the birthplace of stars. A recent study, published in September this year, outlines a new phenomenon that appears to occur deep within these dust clouds and enables greater understanding on the formation of stars. The research suggest that infra-red light that is scattered by unexpectedly large grains of dust, now known as “coreshine”, allowing astronomers to probe the densest regions of the star birth (Bonnel et al. 2006).

Fig.1: The molecular cloud CB 244 in the constellation Cepheus, 650 light-years from Earth. In such clouds, the Milky Way's light is scattered in different ways: Visible light is predominantly scattered by small grains of dust in the cloud's outer regions ("cloudshine"). The false-colour image shows mid-infrared light scattered by larger grains of dust in the interior of the cloud, the newly discovered "coreshine". (Credit: MPIA)

The basic mechanism for how stars are formed is when dense regions of molecular clouds, comprising of dust and gas (usually hydrogen and slight amounts of helium), gravitationally collapse in areas where the density is higher than average. Over time, this collapsing material grows and grows until, due to frictional forces, the heat is high enough to ignite nuclear fusion of hydrogen.

Until this recent study, astrophysicists had little knowledge of what happens at the earliest phases of star formation. The team responsible for this latest study was led by Laurent Pagani (LERMA linked with the Observatoire de Paris) and Jürgen Steinacker (Max Planck Institute for Astronomy in Heidelberg, Germany). The team’s study is based on observations via the NASA SPITZER Space Telescope.

The study outlines a new phenomenon which promises greater information about the crucial earliest phase of the formation of stars and their subsequent planetary systems. The team has coined the phrase “coreshine” to relate to the scattering of infra-red light by dust grains (usually chondrites rich in the silicate minerals olivine and pyroxene) in such dense clouds (Henyey et al. 1955). The scattered light carries information about the size and density of the dust particles, about the age of the core region, the spatial distribution of the gas, the prehistory of the material that will end up in planets, and about chemical processes in the interior of the cloud, given the most detailed picture of inside these colossal star factories.

The discovery of coreshine suggests a host of follow-on projects, for the SPITZER Space Telescope as well as for the James Webb Space Telescope, which is due to be launched in 2014. The first coreshine observations have yielded promising results: The unexpected presence of larger grains of dust (diameters of around a millionth of a metre) shows that these grains begin their growth even before cloud collapse commences. An observation of particular interest concerns clouds in the Southern constellation Vela, in which no coreshine is present (Bonnel et al. 1998). It is known that this region was disturbed by several stellar (supernova) explosions. Steinacker and his colleagues hypothesize that these explosions have destroyed whatever larger dust grains had been present in this region.

Journal References:

  • Henyey, L.G.; Lelevier, R.; Levée, R.D. (1955). The Early Phases Of Stellar Evolution. Publications Pacific Astronomical Society, 67 (396) pp.154.
  • Bonnell, I.A.; Bate, M.R.; Zinnecker, H. (1998). On The Formation of Massive Stars. Monthly Notices Royal Astronomical Society, 298 (1) pp.93–102.
  • Bonnell, I.A.;  Bate, M.R. (2006). Star Formation Through Gravitational Collapse & Competitive Accretion Monthly Notices Royal Astronomical Society, 370 (1) pp.488–494.
  • Steinacker, J. et al., (2010)  The Ubiquity of Micrometer-Sized Dust Grains in the Dense Interstellar Medium. Science, 329 (5999) pp.1622-1624.

Further Reading:

  • Prialnik, D. (2000). An Introduction to the Theory of Stellar Structure and Evolution Cambridge: Cambridge University Press.
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