How nature shapes the birth of stars

May 11, 2012
A Hubble Space Telescope image of the massive star cluster R 136 in the Large Magellanic Cloud. R136 is a potential birth site of much more massive stars, although unconfirmed, than observed in "normal" sites of present-day star formation. Credit: NASA, J. Trauger (JPL), J. Westphal (Caltech)

(Phys.org) -- 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.

Stars are thought to form in from dark clouds of gas and dust. Their properties are expected to depend on the conditions of their dusty birth environment, in the same way that the temperature and constitution of clouds on Earth determines whether we experience drizzly weather, rain with large or small , or a hail shower. In contrast, until now stars have appeared to unexpectedly form in the same manner everywhere. "Sites of are the regions in a galaxy and the forming stars are, in a very rough analogy, like the condensing out of this material", comments team member Prof. Dr. Pavel Kroupa.

The group of scientists now have evidence that the mass distribution of stars does indeed depend on the environment in which they form. "Surprisingly, this evidence does not come to us from young regions of ongoing star formation, but from a very old class of objects, so called globular star clusters", says Dr. Michael Marks, lead author of the new paper. "The number of observed stars less massive than our Sun in is at odds with their structure."

Globular clusters are massive congregations of thousands stars surrounding our Galaxy, the Milky Way. Star formation in these clusters ceased billions of years ago. "Nevertheless, using our simulations we found that the connection between star formation and birth environment can be understood when invoking a process that occurs very early in the life of any cluster, called residual-gas expulsion", continues Marks.

Once a star completes its formation it starts to shine and eventually the radiation coming from the cluster of freshly-hatched stars quickly drives out the gas from which they formed. The region of star birth is then destroyed, leaving behind stars of different masses. "This process leads to expansion of the whole aggregate of stars with the accompanying stripping of some of the stars from the cluster by the gravitational attraction of the young Milky Way. The faster the gas is blown out the stronger is the expansion and the more stars are removed", Kroupa explains. He adds, "The imprint of this process is still visible in the present-day ". This means that careful observations of present-day stellar populations in globular clusters allow their initial star content to be reconstructed.

The astronomers find globular clusters must have formed with many more massive stars than are counted in individual star forming regions today. "Otherwise the star birth region a globular cluster formed from is not destroyed quickly enough and the subsequent expansion is too weak to remove enough stars from the cluster", says Marks. "If this had happened the distribution of masses of stars we see today would be quite different". The deduced differences in the number of massive stars having formed in globular clusters depending on the cloud conditions is indeed in agreement with theoretical expectation.

According to their results, differences in the initial star content appear only when conditions in the star birth regions are very extreme compared to those we see today. "We do not observe these extreme environments in the present day, but these may have well been frequent when globular clusters were born around 12 billion years ago", Marks states. Their work predicts that stars form in the same way, with the same range of masses, in different sites in the present day .

Kroupa summarises their results. "With this work, we might have uncovered the long expected systematic differences in the star formation process". The Bonn astronomers now plan to use further simulations to study the effect of these differences on the long-term evolution of globular .

Explore further: Image: Hubble looks at light and dark in the universe

More information: The new work appears in "Evidence for top-heavy stellar initial mass functions with increasing density and decreasing metallicity", M. Marks, et al., Monthly Notices of the Royal Astronomical Society. A preprint of the paper can be seen at arxiv.org/abs/1202.4755

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Tuxford
1 / 5 (4) May 11, 2012
Once again, these mainstream black-hole-believers miss a key point in their 'residual-gas expulsion' conclusion:

'globular clusters must have formed with many more massive stars than are counted in individual star forming regions today'

Most globular clusters likely are simply baby new galaxies, having a intermediate-class GREY black hole in the center, which grows from within over time and periodically ejects new matter into the surrounding region. This massive star over time becomes so active that the periodic massive wind blows clean the surrounding medium, and likely shuts down the star-forming process for a time, leaving the stable globular cluster observed. Eventually, the core grows large enough and becomes so active that the periodic ejections seed the region through explosive activity, and the cluster grows rapidly into a galaxy.

Think different. You might like it.

HannesAlfven
1.7 / 5 (6) May 11, 2012
Re: "Nevertheless, using our simulations ..."

It's important for people to realize that parallax only works to 1% the diameter of the Milky Way. We have a very similar problem at the bottom end of the scale of existence too -- orders and orders of magnitude of distance, for which assumptions and speculations become increasingly important, in order to propose an explanation for what's going on.

The zone of uncertainty extends from 10^-19 meters down to the Plank distance, and from 10^19 meters up to somewhere around 10^24 (the farthest distance we can see).

The point here is that investigations into cosmology, astrophysics and quantum-scale phenomena lack the certainty necessary to justify a unilateral approach to conjecture. There is insufficient certainty to justify the exclusive investigation of one single idea.

This is the glaring problem with these simulations. They all beg the question: "Compared with what ...?!"
Tuxford
1.5 / 5 (8) May 11, 2012
I think the minds of cosmologists have fallen into a black-hole. They can't escape their rigid conclusions. Rather than risk the mocking of the physics community, they fall in line. Afterall, research funding and careers are at stake. Where are the brave? Judging from the comments on this board, there are not many clear-thinking brave minds left. Only defenders of the status quo. This condition is a consequence of widespread egomania. Just look at the over-reaction to most of my comments. Egomania abounds.
foofighter
5 / 5 (8) May 11, 2012
its probably just a byproduct of having to deal with creationist trolls constantly
MorituriMax
5 / 5 (5) May 11, 2012
Tuxford,
I think the minds of cosmologists have fallen into a black-hole.
Or maybe yours has. Hmmm? How does the body of your work compare to the body of work of the people you are referring to here?
Russkiycremepuff
1 / 5 (1) May 17, 2012
I think the minds of cosmologists have fallen into a black-hole. They can't escape their rigid conclusions. Rather than risk the mocking of the physics community, they fall in line. Afterall, research funding and careers are at stake. Where are the brave? Judging from the comments on this board, there are not many clear-thinking brave minds left. Only defenders of the status quo. This condition is a consequence of widespread egomania. Just look at the over-reaction to most of my comments. Egomania abounds.
- Tuxford -

I have given you a five for your insight into the malaise that quite often envelops the scientific community in western countries. Too many new discoveries and the threats of having to learn and apply new laws if applicable seem to render them wide-eyed and resistant to change. The clinging to the status quo happens with every generation. It is learned process that affects the newest scientists who have just arrived and it stays with them for life.