* Astronomy

Blobrana · L

RE: Star Formation

Blobrana · L

Title: Star Formation triggered by cloud-cloud collisions
Author: S. K. Balfour, A. P. Whitworth, D. A. Hubber, S. E. Jaffa

We present the results of SPH simulations in which two clouds, each having mass M_o=500 solar masses and radius R_o=2pc, collide head-on at relative velocities of Delta v_o=2.4,2.8,3.2,3.6and4.0kms^-1. There is a clear trend with increasing Delta v_o. At low Delta v_o, star formation starts later, and the shock-compressed layer breaks up into an array of predominantly radial filaments; stars condense out of these filaments and fall, together with residual gas, towards the centre of the layer, to form a single large-N cluster, which then evolves by competitive accretion, producing one or two very massive protostars and a diaspora of ejected (mainly low-mass) protostars; the pattern of filaments is reminiscent of the hub and spokes systems identified recently by observers. At high Delta v_o, star formation occurs sooner and the shock-compressed layer breaks up into a network of filaments; the pattern of filaments here is more like a spider's web, with several small-N clusters forming independently of one another, in cores at the intersections of filaments, and since each core only spawns a small number of protostars, there are fewer ejections of protostars. As the relative velocity is increased, the mean protostellar mass increases, but the {\it maximum} protostellar mass and the width of the mass function both decrease. We use a Minimal Spanning Tree to analyse the spatial distributions of protostars formed at different relative velocities.

Read more (5653kb, PDF)

Blobrana · L

Title: The dangers of being trigger--happy
Author: J. E. Dale, T. J. Haworth, E. Bressert

We examine the evidence offered for triggered star formation against the backdrop provided by recent numerical simulations of feedback from massive stars at or below giant molecular cloud sizescales. We compile a catalogue of sixty--seven observational papers, mostly published over the last decade, and examine the signposts most commonly used to infer the presence of triggered star formation. We then determine how well these signposts perform in a recent suite of hydrodynamic simulations of star formation including feedback from O--type stars performed by Dale et al (2012a, b, 2013a, b, 2014). We find that none of the observational markers improve the chances of correctly identifying a given star as triggered by more than factors of two at most. This limits the fidelity of these techniques in interpreting star formation histories. We therefore urge caution in interpreting observations of star formation near feedback--driven structures in terms of triggering.

Read more (1199kb, PDF)

Blobrana · L

Title: Triggered Star Formation from Bubbles S51, N68, and N131
Authors: Chuan-Peng Zhang, Jun-Jie Wang

We investigated the environment of the infrared dust bubbles S51, N68, and N131 from catalogue of Churchwell et al. (2006), and searched for evidence of triggered star formation.

Read more (2287kb, PDF)

Blobrana · L

Title: The Salpeter Slope of the IMF Explained
Authors: M. S. Oey

If we accept a paradigm that star formation is a self-similar, hierarchical process, then the Salpeter slope of the Initial Mass Function (IMF) for high-mass stars can be simply and elegantly explained as follows. If the instrinsic IMF at the smallest scales follows a simple -2 power-law slope, then the steepening to the -2.35 Salpeter value results when the most massive stars cannot form in the lowest-mass clumps of a cluster. It is stressed that this steepening MUST occur if clusters form hierarchically from clumps, and the lowest-mass clumps can form stars. This model is consistent with a variety of observations as well as theoretical simulations.

Read more (75kb, PDF)

Blobrana · L

How nature shapes the birth of stars

Using state of the art computer simulations, a team of astronomers from the University of Bonn in Germany have found the first evidence that the way in which stars form depends on their birth environment. The team, based at the University of Bonn in Germany, publish their results in the journal Monthly Notices of the Royal Astronomical Society.
The group of scientists now have evidence that the mass distribution of stars does indeed depend on the environment in which they form.
Read more

Blobrana · L

Baby stars born to napping parents

University astronomers believe that a young star's long "napping" could trigger the formation of a second generation of smaller stars and planets orbiting around it.
It has long been suspected that the build up of material onto young stars is not continuous but happens in episodic events, resulting in short outbursts of energy from these stars.
However, this has been largely ignored in models of star formation.
Now, by developing advanced computer models to simulate the behaviour of young stars, University Astrophysicists from the School of Physics and Astronomy Dr Dimitris Stamatellos and Professor Anthony Whitworth, have offered a new insight in star formation.
Read more

Blobrana · L

A Perth astronomer has discovered how thousands of new stars are formed almost simultaneously and why more stars are born in galaxies further from the Milky Way.
International Centre for Radio Astronomy Research astronomer Kenji Bekki used computer simulations to work out how large clusters of galaxies affect the formation of stars.
Galaxies tend to attract each other and form groups from a few dozen to several thousand.
Read more

Blobrana · L

Age of the stars

Blobrana · L

RE: Star Formation