February 22, 2011 | David F. Coppedge

Is Star Formation Understood?

Astronomers often speak with apparent confidence about regions of active star formation in nebulae or galaxies.  A look at the fine print, however, shows plenty of wiggle room when observations don’t quite match theory.

  1. Flocculent anomalies:  Astronomers expected more star forming regions in one of the “flocculent” spiral galaxies (spirals without large arms), NGC 2841.  But when the Hubble Space Telescope took its picture, Science Daily said it “currently has a relatively low star formation rate compared to other spirals.”  Several revelations in the next paragraphs indicated astronomers are not so confident about star formation:

    Star formation is one of the most important processes in shaping the Universe; it plays a pivotal role in the evolution of galaxies and it is also in the earliest stages of star formation that planetary systems first appear.

    Yet there is still much that astronomers don’t understand, such as how do the properties of stellar nurseries vary according to the composition and density of the gas present, and what triggers star formation in the first place?  The driving force behind star formation is particularly unclear for a type of galaxy called a flocculent spiral, such as NGC 2841 shown here, which features short spiral arms rather than prominent and well-defined galactic limbs.

    It would seem that if astronomers don’t understand what triggers star formation, or how it varies from place to place, they don’t understand it very much at all.

  2. Dark matter anomalies:  Dark matter sometimes appears like a kind of cosmic flubber – an unknown quantity that is useful in various amounts (sometimes none at all) when theories need fixing.  Take this article from Science Daily about recent results from the Herschel Space Telescope as an example:

    Most of the mass of any galaxy is expected to be dark matter, a hypothetical substance that has yet to be detected but which astronomers believe must exist to provide sufficient gravity to prevent galaxies ripping themselves apart as they rotate….

    Herschel is showing us that we don’t need quite so much dark matter as we thought to trigger a starburst,” says Asantha Cooray, University of California, Irvine….

    Analysis of the brightness of the patches in the … images has shown that the star-formation rate in the distant infrared galaxies is 3-5 times higher than previously inferred from visible-wavelength observations of similar, very young galaxies by the Hubble Space Telescope and other telescopes.

    And yet with these uncertainties, the article was confident that the star formation rate in this “starburst galaxy” had hit a “sweet spot” for star formation, even though the opening paragraph was puzzled that the region observed appeared too small for such luck: “The size challenges current theory that predicts a galaxy has to be more than ten times larger, 5000 billion solar masses, to be able form [sic] large numbers of stars.”

  3. Computers as alternate reality:  Meanwhile, in the computer center at Heidelberg University, astronomers concluded that “The first stars in the universe were not as solitary as previously thought.”  According to PhysOrg, whatever they programmed into their computer models was a blockbuster: it “cast an entirely new light on the formation of the first stars after the Big Bang.”  The next sentences described in graphic detail how a star is born.  Given the uncertainties in the first two entries, however, it appears their computer universe was a figment of the programmer’s imagination rather than a finding about nature.  The article contained at least six instances of may have, could have and other speculations: e.g., “It is also conceivable that some of the first stars may have been catapulted out of their birth group through collisions with their neighbours before they were able to accumulate a great deal of mass.”

We can’t even understand our own universe, but some astronomers are talking about imaginary universes.  Amanda Gefter at New Scientist, for instance, gave a positive review of Brian Greene’s new book The Hidden Reality, which purports to give “a tour of the multiverse.”  She described the book as “Arcane yet exciting physics, wrapped up in effortless prose.”  The multiverse concept has become “fashionable,” she said, even though critics “deride it as untestable metaphysics.”  Even Greene called it a “battleground for the very soul of science.

Whoever wins the battle should be able to do the Macarena to make Gefter happy.  That’s what Brian Greene did in front of an audience, she described, as he pondered a hypothetical holographic universe that made him literally dance for joy at the thought.  Gefter also was enraptured by the possibility that “reality is not what it seems.”  While speculating about hidden realities that are not what they seem, might as well go all out: “Greene doesn’t shy away from important nuances or profound philosophical questions,” she ended, winking, “I suspect that this will be a hugely popular book – in this universe and many, many others.”  See the 04/11/2009 for Gefter’s previous reaction to cosmologists’ speculations about imaginary universes.

OK, let’s take stock.  We’ve got star formation, about which we don’t understand how it gets triggered or why it varies from place to place, but somehow dark matter flubber has something to do with it – an ingredient that uses Skinner’s Constant.*  However it works, star formation, which no one has watched, bursts forth in galaxies 1/10 the size they should be for it to burst in, producing sociable stars after the Big Bang, in computers at least, contrary to expectations.  Are we still in the science lab? (cf. 04/13/2007).
    Astronomers are very smart people in terms of their ability to speak jargon and manipulate equations.  Whether they have a grasp on reality is a very different matter (01/15/2008) – a dark matter of a different sort.  It’s worth rereading Prophet Berman’s sermons every once in awhile (10/06/2004, 09/29/2007) to avoid being swept up into the cosmic euphoria that ensnared poor Amanda Gefter in Brian Greene’s fantasy bladderwort (02/17/2011).

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