SAO: Stellar Embryos

[bystander]

Stellar Embryos
Smithsonian Astrophysical Observatory
Weekly Science Update | 2012 Jan 20

[i]Infrared image of a cluster of new stars forming in a dark filament of gas and dust in Cygnus. The first detailed observations of one very young, prestellar core in a similar cluster find that stellar development in a clustered environment significantly differs from the isolated case. (Credit: NASA/Spitzer)[/i]

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Stars form as gravity coalesces the gas and dust in interstellar clouds until the material produces clumps dense enough to become stars. But precisely how this happens, and whether or not the processes are the same for all stars, remains very uncertain. Astronomers have been studying very young clumps, called "pre-stellar cores" located deep within stellar wombs, in an attempt to sort out these details. But precisely because the cores have no stars in them yet, or at best only very young stars, they are faint and difficult to observe.

CfA astronomers Tyler Bourke, Phil Myers, and David Wilner, along with three colleagues, used the Submillimeter Array to do the first detailed observational study of the internal structure of a pre-stellar core. Astronomers have come to realize that birth clouds are most often filamentary in shape, not spherical, and so the team examined a suspected embryo embedded within an (even colder) filamentary cloud. They selected a filament that is relatively close by, only about 400 light-years distant, and that was known to contain within it a string of warm spots that might be stellar embryos.

The scientists probed one of these spots using the millimeter wavelength emission from its dust and from two simple, nitrogen-bearing molecules that are known to trace the dense gas expected around a pre-stellar core. The team's results include the first high spatial resolution observations of such a young core. They conclude that the material is apparently collapsing, and that the object's mass is about 0.29 solar-masses (that is, it would make a star smaller than the sun). The core currently extends over about 1000 astronomical units (in the solar system this dimension reaches to the inner zone where comets reside). Overall the new results are notably different from the predictions of simple theory, suggesting that this core has been significantly influenced by fragmentation of the filament and by the presence of other cores in the cluster.

Initial conditions for star formation in clusters: physical and kinematical structure of the starless core Oph A-N6 - Tyler L. Bourke et al

• Astrophysical Journal 745(2) 117 (2012 Feb 01) DOI: 10.1088/0004-637X/745/2/117
  arXiv.org > astro-ph > arXiv:1111.4424 > 18 Nov 2011

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[Ann]

Two things here are interesting and serve as a confirmation of things that were already known.

Click to view full size image

Recent infrared images have shown that star formation very often take place along elongated "strings" of dust. The picture shows an example close to the Omega Nebula, M17.


The second thing that is so interesting here is that the star formation region that is described in today's article has a stellar cocoon that contains only 0.29 solar masses. Such a low mass will give rise to a very cool, very faint, very small star. It will indeed be both hotter and brighter than tiny Proxima Centauri, the most nearby of all stars, whose luminosity of 18,000 times fainter than the Sun in visual light results from a mass only 12% solar. (See http://stars.astro.illinois.edu/sow/rigil-kent.html.)

So the stellar embryo discussed in Smithsonian Astrophysical Observatory Weekly Science Update of 2012 Jan 20, will give rise to a somewhat hotter, larger and brighter star than Proxima Centauri, but the star will still be small, faint and cool compared with the Sun. And that is no surprise. 80% of the stars in the Milky Way are of spectral class M, like this one will be, and our Sun is anything but an average star.

Ann