The Birth of High-Mass Stars: Accretion and/or Mergers?
By J. Bally, H. Zinnecker. 2005
176 citations recorded by the source corpus.
The observational consequences of the merger scenario for massive star formation are explored and contrasted with the gradual accumulation of mass by accretion. In high-density protostar clusters, envelopes and disks provide a viscous medium that can dissipate the kinetic energy of passing stars, greatly enhancing the probability of capture. Protostellar mergers may produce high-luminosity infrared flares lasting years to centuries followed by a luminosity decline on the Kelvin-Helmholtz timescale of the merger product. Mergers may be surrounded by thick tori of expanding debris, impulsive wide-angle outflows, and shock-induced maser and radio continuum emission. Collision products are expected to have fast stellar rotation and a large multiplicity fraction. Close encounters or mergers will produce circumstellar debris disks with an orientation that differs from that of a preexisting disk. Thus, massive stars growing by a series of mergers may produce eruptive outflows with random orientations; the walls of the resulting outflow cavities may be observable as filaments of dense gas and dust pointing away from the massive star. The extremely rare merger of two stars close to the upper-mass end of the initial mass function may be a possible pathway to hypernova-generated gamma-ray bursts. In contrast with the violence of merging, the gradual growth of massive stars by accretion is likely to produce less infrared variability, relatively thin circumstellar accretion disks that maintain their orientation, and collimated bipolar outflows that are scaled-up versions of those produced by low-mass young stellar objects. While such accretional growth can lead to the formation of massive stars in isolation or in loose clusters, mergers can only occur in high-density cluster environments. It is proposed that the outflow emerging from the OMC-1 core in the Orion molecular cloud was produced by a protostellar merger that released between 1048 and 1049 ergs less than a thousand years ago.
Subfields: Astronomy and Astrophysics
View Paper: https://www.semanticscholar.org/paper/17f40c4b405932298f231739ca758347afdf57ed
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In Astronomy and Astrophysics
Citations in the corpus
- SiO Maser Observations toward Orion-KL with VERA (2008, background): “As described above, there are clearly different interpretations of the dynamical structure of the region around Source I among various authors (e.g., Bally & Zinnecker 2005; Greenhill et al. 2004), with assumed directions of the disk (torus) axis, or the outflow axis being offset by 90ı, although…”
- Toward Understanding Massive Star Formation (2007, background): “…phenomena on short timescales (days to years), such as episodic FU Orionis-like accretion (Chini, private communication) and stellar mergers (Bally & Zinnecker 2005), or η Car-like LBV eruptions (Smith & Owocki 2006) and even infrared supernovae in luminous starburst galaxies (Maiolino et…”
- Theory of Star Formation (2007, background): “Bally & Zinnecker (2005) discuss a number of observational tests of the coalescence model, and suggest that the wide-angle outflow from OMC-1 in the Orion molecular cloud could be due to the merger of two protostars that released 1048 − 1049 erg.”
- The VLT-FLAMES survey of massive stars: observations centered on the Magellanic Cloud clusters NGC 330, NGC 346, NGC 2004, and the N11 region (2006, background): “In their discussion of the competing scenarios of massive-star formation from accretion versus stellar mergers, Bally & Zinnecker (2005) suggest that the multiple star fraction will be larger if merging dominates.”
- Runaway collisions in young star clusters - II. Numerical results (2005, background): “…that a large fraction of clusters may actually be collisional at birth. c© 2005 RAS, MNRAS 000, 1–21 The standard theory of star formation, which assumes spherically symmetric accretion of gas on to the protostar, fails for stars more massive than 10M⊙ (Yorke 2004; Bally & Zinnecker 2005).”
- Disk-mediated accretion burst in a high-mass young stellar object (2016, background): “Here timescale and energetics of the outburst are more consistent with disk fragmentation rather than stellar merger (26) (see Methods).”