Stars forming in the Rosette Nebula

Original image download(11 Mb jpeg). I think this is probably the best image from Herschel where the forming stars are truly pinpointed:

The Rosette Nebula resides some 5000 light-years from Earth and is associated with a larger cloud that contains enough dust and gas to make the equivalent of 10 000 Sun-like stars. The Herschel image shows half of the nebula and most of the Rosette cloud. The massive stars powering the nebula lie to the right of the image but are invisible at these wavelengths. Each colour represents a different temperature of dust, from –263ºC (only 10ºC above absolute zero) in the red emission to –233ºC in the blue. The bright smudges are dusty cocoons hiding massive protostars. These will eventually become stars containing around ten times the mass of the Sun. The small spots near the centre and in the redder regions of the image are lower mass protostars, similar in mass to the Sun.

A new paper today by Gahm et al. ( pdf) addresses the question of brown dwarf formation in the region. From the abstract:

We conclude that the entire complex of shells, elephant trunks, and globulettes in the northern part of the nebula is expanding with nearly the same velocity of ~22 km/s, and with a very small spread in velocity among the globulettes. Some globulettes are in the process of detaching from elephant trunks and shells, while other more isolated objects must have detached long ago and are lagging behind in the general expansion of the molecular shell. The suggestion that some globulettes might collapse to form planetary-mass objects or brown dwarfs is strengthened by our finding of dense cores in several objects.

“Baby stars in the Rosette Cloud” (ESA)

Update: The results from the Herschel mission have shown us a pre-picture of star formation, as material flows under the influence of magnetic fields into and along streams, or filaments, which lead to condensation under self-gravitation and all the accretion phenomena of star formation – disks – which have been observed in the near-infrared. Now, in a new paper by P. Hennebelle, “On the origin of non-self-gravitating filaments in the ISM”, Astronomy & Astrophysics 556, A153, the physical origins of the filaments themselves, as they exist in the interstellar medium before any onset of self-gravitation and star formation, have been investigated thoroughly by supercomputer simulations of the underlying magnetohydrodynamic processes within the material. The formation of the filaments themselves is thought to be simply driven by energy dissipation.

Filaments are ubiquitous in the interstellar medium, as recently emphasized by Herschel observations, but their physical origin remains elusive. In this paper, the author uses ideal MHD simulations to study the formation of non-gravitating clumps in various conditions, including different setups, magnetization, and Mach numbers. On average, clumps in MHD simulations are more filamentary than clumps in hydrodynamic simulations. Detailed analyses reveal that the filaments are in general preferentially aligned with the strain, indicating that they simply result from the stretch induced by turbulence. Moreover, filaments tend to be confined by the Lorentz forces, which therefore lead them to survive longer in magnetized flows. The author concludes that filaments are ubiquitous because they are the results of the very generic turbulent strain, and because the magnetic field helps to keep them coherent. Energy dissipation appears to play a fundamental role in filament formation.


One Response to “Stars forming in the Rosette Nebula”

  1. […] paper of this research is now published; I have linked the preprint in an earlier post. The paper is “Mass and motion of globulettes in the Rosette Nebula”, G.F. Gahm et al., […]

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