The Race to Stellar Formation


Racing is rarely the term that comes to mind when one considers astronomy. However, many events are a race to reach stability before a system flies apart or implodes. The formation of stars from gigantic interstellar clouds is just such a race in which stars struggle to form before the cloud is dispersed. Although a rough estimation of the requirements for collapse are discussed in introductory astrophysics classes (See: Jeans Mass Criterion) this formulation leaves out several elements that come into play in the real universe. Unfortunately for astronomers, these effects can be subtle but significant but untangling them is the subject of a recent paper uploaded to the arXiv preprint server.

The Jeans Mass Criterion only takes into consideration a gas cloud in isolation. Whether or not it will collapse will depend on whether or not the density is sufficiently high. But as we know, stars don’t form in isolation; They form in stellar nurseries which form hundreds to thousands of stars. These forming stars contract under self gravity, and in doing so, heat up. This increases the local pressure and slows contraction as well as giving off additional radiation that also affects the cloud at large. Similarly, solar winds (particles streaming from the surface of formed stars) and supernovae can also disrupt further formation. These feedback mechanisms are the target of a new study by a group of astronomers led by Laura Lopez from the University of California Santa Cruz.

To investigate how each feedback mechanism operated, the group selected the Tarantula Nebula (aka, 30 Doradus or NGC 2070), one of the largest star forming regions easily accessible to astronomers since it resides in the Large Magellanic Cloud. This region was selected due to its large angular size which allowed the team to have good spatial resolutions (down to scales smaller than a parsec) as well as being well above the plane of our own galaxy to minimize interference from gas sources in our own galaxy.

To conduct their study, Lopez’s team broke 30 Dor into 441 individual regions to assess how each feedback mechanism worked in different portions of the nebula. Each “box” consisted of a column slicing through the nebula that was a mere 8 parsecs to a side to ensure sufficient quality of the data across the entire spectrum since observations were used from radio telescopes to X-ray and used data from Spitzer and Hubble.

Perhaps unsurprisingly, the team found that different feedback mechanisms played varying roles in different places. Close the the central star cluster (<50 parsecs), radiation pressure dominated the effects on the gas. Further out, pressure from the gas itself played the stronger role. Another potential feedback mechanism was that of “hot” gas being excited by X-ray emission. What the team uncovered is that, although there is a significant amount of this material, the nebula’s density is insufficient to entrap it and allow it to have a large effect on the overall pressure. Rather, they described this portion as “leaking out of the pores”.

This research is some of the first to observationally explore, on a large scale, many of the mechanisms that have been proposed by theorists in the past. Although such research may seem inconsequential, these feedback mechanisms will have large effects on the distribution of stellar masses (known as the Initial Mass Function). This distribution determines which the relative amounts of massive stars which help to create heavy elements and drive the chemical evolution of galaxies as a whole.

8 Replies to “The Race to Stellar Formation”

  1. This appears to be work on the role of shock waves or the expansion of an SN pressure front of material as it intrudes or impinges on a gas gloud. Observationally this seems quite obvious. The Triffid nebular “towers of creation” seem to be a case of this.


  2. Just a couple of nitpicks…

    At the second paragraph, in the sixth line, it should be affects — which (as a verb) means “acts on” or “moves” — and not “effects”, which, as a verb, means “brings about” or “accomplishes”; as a noun, it means “results” or “consequences”.

    Also, at the third paragraph, in the fourth line, that “it’s” should be an its — the possessive form of the pronoun it. 🙂

    Um… I’ll now get my coat and see myself out…


    The Triffid nebular “towers of creation” seem to be a case of this.

    Actually, it is called the “Pillars of Creation”, and it is in the Eagle Nebula, not in the Trifid (one “f”) Nebula. 🙂

  4. IVAN3MAN_AT_LARGE : Well at least you knew what I was talking about. I am not quite an expert on the local geography of space. I can find my way around the main constellations in the sky, track the planets and get my 6″ scope to look at a few things. But I am reminded of Woody Allen who said something to the effect, “How can I find my way around the universe when I don’t know where Chinatown is?”


  5. Lawrence: Yes – This does relate to shockwaves as such things can be one of the dispersal/feedback mechanisms from stars that affects the cloud at large. However, as noted, such shockwaves aren’t the only method and that’s what this group was studying: The relative effects of different mechanisms at different distances.

    IVAN: Thanks for those corrections. I can never remember the difference between affects and effects. I originally put affects and then second guessed myself. I don’t have an excuse for the its/it’s except that my pinky just gets trigger happy with that apostrophe.

  6. The one thing I will say is that this Tarantula nebula is one of the more beautiful ones, and this picture has made it into my collection.


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