Galactic winds slow new star formation

May 8, 2017, University of Edinburgh
This is an artist's concept of the metric expansion of space, where space (including hypothetical non-observable portions of the universe) is represented at each time by the circular sections. Note on the left the dramatic expansion (not to scale) occurring in the inflationary epoch, and at the center the expansion acceleration. The scheme is decorated with WMAP images on the left and with the representation of stars at the appropriate level of development. Credit: NASA

Scientists have created computer simulations of events soon after the Big Bang to better understand how stars today are being formed.

Researchers have formed the clearest picture yet of massive explosions that controlled the creation of galaxies, including our own, and continue to influence today.

The findings confirm a long-held theory about the after-effects of these spectacular explosions called supernovae, and how they slow down the formation process.

Blast waves

Scientists at Edinburgh say supernovae trigger powerful gusts of wind that slow the rate at which gas for new stars pours into developing galaxies.

The team used a supercomputer to create simulations of the , hydrogen and helium formed post Big Bang – all key elements of galaxy formation. They compared these with measurements of the amount of hydrogen that surrounds galaxies.

Researchers found higher levels of hydrogen outside galaxies than expected, suggesting that violent winds produced by supernovae slow down the flow of gas into galaxies.

Black hole impact

However, the simulations were unable to reproduce the hydrogen around the most , which contain quasars – the most energetic objects in the Universe.

The team suggests that quasars may have an even greater influence than supernovae on star formation, by producing enormous jets of gas fuelled by black holes.

The study is published in the journal Monthly Notices of the Royal Astronomical Society by Oxford University Press. The research was carried out in collaboration with scientists at the Universities of Cambridge and Nottingham.

"Our simulations provide highly accurate descriptions of the properties of dark matter and gas found between galaxies. Understanding how form presents new challenges because the physical processes involved are much more complex. Our results suggest we are on the right track," says Professor Avery Meiksin.

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4.4 / 5 (7) May 08, 2017
An open access copy of paper can be found here:
not rated yet May 08, 2017
I can see how the different shock shells of star forming regions would have the effect of funneling the mass of dust and gases into what we now call 'dust lanes'. If gas and dust is thrown from the central black hole in the jets both 'above' and 'below' the galaxy it would fall back towards the disc plane and the slight shock effects at the edges of the supernovae zones, which seem to form bands to either side of the areas with heavy star populations which literally funnel the dust and gases into the zones we now see as dark lanes in spiral galaxies. These areas, in turn, will start their own star formation as we can see in the Orion clouds.
1 / 5 (4) May 08, 2017
However, the simulations were unable to reproduce the hydrogen around the most massive galaxies, which contain quasars – the most energetic objects in the Universe.

Of coarse not. How can a merger maniac simulation give accurate results? They cannot allow for the formation of the gas from within the core, and ejected therefrom, thereby accounting for the hydrogen around the more massive, more core active galaxies. Such consideration would be a career killer, and is therefore not permitted.
Da Schneib
not rated yet May 08, 2017
@RNP, I've been seeing these results for quite a while. Why is this finding significant?
4.2 / 5 (5) May 09, 2017
I would suggest that the paper is chiefly of interest to those involved in the modeling of galaxy formation. It addresses the complex topic of feedback processes in the IGM (stellar and supernova winds and AGN feedback). The strengths of these processes are poorly constrained, making their impacts on gas densities difficult to predict. To-date simple models for these mechanisms have not accurately reproduced the observed densities, underestimating them by a factor ~2.

The authors use models that more realistically describes stellar and supernova winds and, for the first time, achieve good agreement with observations in star-forming galaxies.
For QSOs, the model still fails, demonstrating the importance of AGN feedback in these objects. The important implication is that current models CAN reproduce observations of star-forming galaxies without the need for new physics. The same is probably true for QSOs once AGN feedback is accurately included in the models.
Da Schneib
not rated yet May 09, 2017
@RNP, awesome, exactly what I wanted to know. I'll be watching for the more realistic AGN feedback to appear in models of quasar star formation, then. Thanks!

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