Light Blows Away Giant Molecular Clouds

Article written: 7 Jun , 2011
Updated: 24 Dec , 2015
by

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Although they only make up about one percent of the interstellar medium, giant molecular clouds are a rather formidable thing. These dense masses of gas can reach tens of parsecs in diameter and we know them as star forming regions. But, what we didn’t know is that light from massive stars can tear them apart.

New findings presented by Dr. Elizabeth Harper-Clark and Prof. Norman Murray of the Canadian Institute for Theoretical Astrophysics (CITA) show that radiation pressure is not a thing which should be discounted. It has widely been theorized that supernovae accounted for GMC disruption, but “Even before a single star explodes as a supernova, massive stars carve out huge bubbles and limit the star formation rates in galaxies.”

Galaxies harbor stellar nurseries and, as stars are born, the galaxy evolves. It is our understanding that stellar birth occurs within giant molecular clouds where low temperatures, high density and gravity work together to ignite the stellar process. It happens at a smooth and steady rate – a pace which we surmise occurs from the outflow of energy from other stars and possibly black holes. But just what exactly is the life expectancy of a GMC?

To understand a giant molecular cloud is to understand the mass of the stars contained within it. This is key to star formation rates. “In particular, the stars within a GMC can disrupt their host and consequently quench further star formation.” says Harper-Clark. “Indeed, observations show that our own galaxy, the Milky Way, contains GMCs with extensive expanding bubbles but without supernova remnants, indicating that the GMCs are being disrupted before any supernovae occur.”

What’s happening here? Ionization and radiation pressure are blending together within the gases. Electrons are being forced out of atoms during ionization… an action which happens incredibly fast, heating up the gases and increasing pressure. The often over-looked radiation is far more subtle. “The momentum from the light is transferred to the gas atoms when light is absorbed.” says the team. “These momentum transfers add up, always pushing away from the light source, and produce the most significant effect, according to these simulations.”

The simulations performed by Harper-Clark are just the beginning of new studies. The work shows calculations of the effects of radiation pressure on GMCs and reveal they are capable of not only disrupting star-forming regions, but completely blowing them apart, cutting off further formation when about 5 to 20% of the clouds mass had been converted to stars. “The results suggest that the slow rate of star formation seen in galaxies across the Universe may be the result of radiative feedback from massive stars,” says Professor Murray, Director of CITA.

So what of supernovae? Incredibly enough, it would seem they are simply unimportant to the equation. By calculating the results both with and without star light radiation, supernova events didn’t change star formation nor did they alter the GMC. “With no radiation feedback, supernovae exploded in a dense region leading to rapid cooling. This robbed the supernovae of their most effective form of feedback, hot gas pressure.” says Dr. Harper-Clark. “When radiative feedback is included, the supernovae explode into an already evacuated (and leaky) bubble, allowing the hot gas to expand rapidly and leak away without affecting the remaining dense GMC gas. These simulations suggest that it is the light from stars that carves out nebulae, rather than the explosions at the end of their lives.”

Original Story Source: Canadian Astronomical Society More information on Dr. Harper-Clark’s work can be found here.


32 Responses

  1. Anonymous says

    wondering how they named this cloud :)))))

  2. Anonymous says

    wondering how they named this cloud :)))))

  3. J. Major says

    I feel like I’m being flipped off by the Universe!

    • Jamie Kitchen says

      I agree. Tammy, how could you write this article and not make at least one poke at this? You must have some heavy duty will power. I expect this image to show up on a supermarket tabloid with some stupid caption declaring that God has had enough with us and is sending us a message or something along those lines.

      • Member
        Tammy Plotner says

        giggle! ok… i see it, too. but you know that every article i write contains a bit of “tounge-in-cheek” humor – even if some folks don’t “get it”. 😉

  4. ? ? says

    It looks like a hand.

  5. Anonymous says

    The FU nebula?

  6. Looks like the “Flying Fickle Finger of Fate”

    I know that comment dates me 🙂

  7. Anonymous says

    The Finger of God.

  8. Anonymous says

    I first saw this image a couple of years ago. It was transmitted to “send a message,” and I thought it was photoshopped.

    It is my understanding that supernovae generate such clouds by sending a sort of shock wave that “snowplows” clouds into formation. This article appears to be in line with my understanding. The photon pressure of emergent stars then appears to exert a pressure which destroys these clouds.

    LC

  9. Anonymous says

    How can light have momentum and push around gases if it has no mass? Wouldn’t the pressure come from the solar wind, which does have mass?

    • Anonymous says

      Did you ever see these clear vacuum glasses with something that can rotate in? And it starts to rotate when you shine a light on it?

    • WaxyMary says

      @Kawarthajon

      You read the following, since this all relates to the absorption of those massless photons BY the gases — the following needs to be read from beginning to end and then you need to finish by re-reading.

      From the article above, 5th paragraph, toward the tail…

      “The momentum from the light is transferred to the gas atoms when light is absorbed.” says the team. “These momentum transfers add up, always pushing away from the light source, and produce the most significant effect, according to these simulations.”

      Common sense carries us to the brink and logic tips us over…

      Mary

      • Anonymous says

        I still don’t understand because your reply does not contain an explanation, just a repeat of the original article.

        BTW I don’t appreciate the condescending comments.

      • Member
        Tammy Plotner says

        it’s one of those cases when i probably could have written better.

        the movement of the light itself – spreading away from the star in all directions – gets transfereed to the gas atoms in the molecular cloud. (one of those cool, newton laws of physics!) remember, light acts like a particle in space until it meets a medium, then it becomes a wave. when it becomes absorbed by the gases, the gases also absorb the movement. these little movements all add up, like a rolling snowball effect.

        a snowball cruising around at 299,792.458 kilometers per second!

      • WaxyMary says

        @Tammy

        Photons act like a wave in a vacuum and when absorbed by some particle as a part of some transformational chemistry or ionization the photon imparts the force (momentum) with which it traveled, the polarity with which it was imbued –the frequency of the light is intrinsic to almost all these collusions (yes, as in conspiratorial theory) is more than just an agent of the combination of the chemistry, it is very much the purgation of the event which created that photon source.

        If the photon is not combined as a result of the chance encounter then it too shows what interaction took place to some extent, if enough photons show these effects we can use that data as a part of our observations. Adjusting any theory or premise for how much interaction is required for our observations so as to enable some test or other to reveal some result is all in the fine tuning and is inspected in many cases by the ‘peerage’ (really just a joke folks, save the rotten cabbages) first before the analytics sections of the papers so see what biases might be present on the part of the reporter.

        It is all in the EM where we find the rhyme for our affects and their effects –all sublime.

        Mary

      • Anonymous says

        Is there a blog of physics poetry we can read?

      • WaxyMary says

        Alas no blog nor
        haiku lines for
        any, eyes do see.

      • Anonymous says

        Is there a blog of physics poetry we can read?

      • Member
        Tammy Plotner says

        it’s one of those cases when i probably could have written better.

        the movement of the light itself – spreading away from the star in all directions – gets transfereed to the gas atoms in the molecular cloud. (one of those cool, newton laws of physics!) remember, light acts like a particle in space until it meets a medium, then it becomes a wave. when it becomes absorbed by the gases, the gases also absorb the movement. these little movements all add up, like a rolling snowball effect.

        a snowball cruising around at 299,792.458 kilometers per second!

      • WaxyMary says

        If you dislike repetition and feel as if I am descending with you to some depth, please remember, someone needs to be above to pull up. Bootstrapping in real life does not happen. Self education is always suspect and others always test us, try us, and torment us. Welcome to the club.

        Mary

      • Torbjörn Larsson says

        That is condescending too.

        It is true that successful learning like science is a community effort. It is true that science is elitist.

        But it is not true that one can place oneself as “somebody … to pull up”. Circumstances does that.

        Pledging that it is but part of the membership of a “club”, implying that all including the writer participates, doesn’t change that. Also, one always have the choice to be member or not in real clubs.

        It is better to offer than to pull and push.* See Potatoswatter response, for a good example!

        ———–
        * Exception being incompetents/crackpots, because they don’t have the capacity to understand context whatsoever. It is best to handle them as the sheep they behave like.

      • WaxyMary says

        @TL

        Thank you for your insightful comments, both now and in the past. I acknowledge we choose our memberships in any clubs, real, imagined and virtual, and that our classification may at times require some amount of clarification by ourselves. Additionally you are correct in saying push/pull is to be avoided and this is an area I need to improve myself.

        The circumstance of answering a quest for knowledge with an answer which assumes more knowledge on the part of the reader than the question indicates causes some to offer in their answer fuller details than is needed by an average layman, as is the case by many here including the authors and astute readers responses.

        Answering with a request to actually read what is written, plainly and concisely, is what was called for in the first place. The continued question was again answered and that, too, was called condescension. The author says the same things, with some scientific error, as a reply to the question and that answer is acknowledged as definitive — I corrected Tammy, she does not say I was guilty of condescension. Do you see a pattern here?

        Mary

      • Anonymous says

        I knew it, he’s in drag!

    • Anonymous says

      Photons have momentum p = E / c. They have no *rest* mass, but like other relativistic particles, exhibit potentially large mass-energy.

      http://en.wikipedia.org/wiki/Photon#Physical_properties

      According to Wikipedia, radiation pressure was discovered before photons, though. The question of photon mass is apparently irrelevant, although I haven’t really read this article:

      http://en.wikipedia.org/wiki/Radiation_pressure

      And, it’s a little bizarre that so much discussion and bickering is here with no references or discussion as simple as this.

  10. Tony Scharf says

    This is the best nebula ever.

Comments are closed.