No Life Possible at Edges of the Pinwheel Galaxy

Another beautiful image from the Spitzer Space Telescope; in this case, it’s Messier 101, more commonly known as the Pinwheel Galaxy. But the pretty red highlights at the edges of the galaxy are bad news for anyone looking for evidence of life. “If you were going look for life in Messier 101, you would not want to look at its edges,” said Karl Gordon of the Space Telescope Science Institute. “The organics can’t survive in these regions, most likely because of high amounts of harsh radiation.” The red color highlights a zone where organic molecules called polycyclic aromatic hydrocarbons (PAHs), which are present throughout most of the galaxy, suddenly disappear.

PAHs are dusty, carbon-containing molecules found in star nurseries. They’re also found on Earth in barbeque pits, exhaust pipes and anywhere combustion reactions take place. Scientists believe this space dust has the potential to be converted into the stuff of life.

The Pinwheel galaxy is located about 27 million light-years away in the constellation Ursa Major. It has one of the highest known gradients of metals (elements heavier than helium) of all nearby galaxies in our universe. In other words, its concentrations of metals are highest at its center, and decline rapidly with distance from the center. This is because stars, which produce metals, are squeezed more tightly into the galaxy’s central quarters.

Gordon’s team also wanted to learn more about the gradient of the PAHs. Using Spitzer’s Infrared Array Camera and the Infrared Spectograph to carefully analyze the spectra of the PAHs, astronomers can more precisely identify the PAH features, and even deduce information about their chemistry and temperature. The astronomers found that, like the metals, the polycyclic aromatic hydrocarbons decrease in concentration toward the outer portion of the galaxy. But, unlike the metals, these organic molecules quickly drop off and are no longer detected at the very outer rim.

“There’s a threshold at the rim of this galaxy, where the organic material is getting destroyed,” said Gordon.

The findings also provide a better understanding of the conditions under which the very first stars and galaxies arose. In the early universe, there were not a lot of metals or PAHs around. The outskirt of the Pinwheel galaxy therefore serves as a close-up example of what the environment might look like in a distant galaxy.

In this image, infrared light with a wavelength of 3.6 microns is colored blue; 8-micron light is green; and 24-micron light is red. All three of Spitzer instruments were used in the study: the infrared array camera, the multiband imaging photometer and the infrared spectrograph.

Original News Source: JPL

11 Replies to “No Life Possible at Edges of the Pinwheel Galaxy”

  1. Irresponsible speculation of the day: there are no PAHs at the rim because an intelligent species has harvested all of them for use closer to the center of the galaxy!

    Seriously, what do they think is the source of the radiation breaking up all the organic molecules?

  2. Irresponsible speculation of the day, part deux: What if there is life over there but it’s inorganic? 😉

    I kid, but there’s no physical reason I can think of that precludes the possibility of non-carbon-based organisms popping up.

  3. Irresponsible speculation of the day, part III:
    T’is some alien species that live in space, and have slowly eaten it all.
    They are now spreading into the center.

    Seriously though, it is rather interesting that it suddenly stops at a certain distance.
    I can’t think of any reasons for that, i’d expect almost every star to eventually form large amounts of these.
    Maybe the ones that haven’t have less attraction and are (have already) being falling out of reach. (kinda like our little Moon)
    But even that doesn’t make much sense…

    Oh well, what is shown has already happened, now we just need to wait a good few million years.
    Damn speed of light being so slow! Hurry it up already!

  4. Irresponsible speculation of the day, part IV:
    The radiation is a fence to keep the brain-sucking aliens inside and prevent them from enslaving more peaceful civilizations… Maybe we should be looking for one of these around our own galaxy.

  5. We have no methods of searching this galaxy for life right now, but if we could…we definitely should! It must be a really old galaxy to have so much metal, so life has had plenty of time to form.
    There’s gotta be life somewhere in that thing.
    Just not at the edges, apparently.

  6. Do some homework people! There is a small habitable zone in every galaxy including our very own. Too close to the center, and the radiation will destroy life, and too far away there is not enough heavy elements!

    see wikipedia …
    “To harbor life, a solar system must be close enough to the galactic center that a sufficiently high level of heavy elements exist to favor the formation of rocky planets. Heavier elements must be present, since they form complex molecules of life, such as iron as the foundation for hemoglobin and iodine for the thyroid gland (assuming that iron is necessary for all life).

    On the other hand, the solar system must be far enough from the galaxy center to avoid hazards such as impacts from comets and asteroids, close encounters with passing stars, and outbursts of radiation from supernovae and from the black hole at the center of the galaxy. The effect of radiation from supernovae on living organisms is not clear. ”
    GHZ Galactic Habitable Zone

  7. Homework is always a nice thing to do, but you must keep in mind it is only learning what we *think* is right at a certain given time.

    Things change.

    Life as we “know it” may be one thing, but I have a hunch life as we “don’t know” it may be far more wide spread. To tell the truth, I’m not at all sure we *could* recognize life – even a truly alien intelligent life form – as easily as we might think we could.

    The GHZ might be the limits our poor, lowest rung of the evolunationary ladder species might exist, but the raw power available near the center or on the edge of the Pinwheel galaxy could, for all we know, be generating life forms we cannot even dream of.

    That’s not saying “They’re There”. But we sure can’t say they aren’t, either. We just can’t be too sure, yet.

    We don’t know enough.

  8. I would think high energy radiation (UV, X-ray) from OB associations & Wolf-Rayet stars would be energetic enough to break up PAHs in the outer arms of M 101. Notice that the pink areas in the picture seem to coincide with bright star-forming regions in the outer arms of M 101.

  9. Another wikipedia definition which gets it quite wrong; since the way it is written leads to speculation such that habitable zones would be constant. Due to different ages, types, sizes, densities of galaxies, their mergers and the fact we have yet to find another location supporting life. I don’t think anyone would credibly stand behind this entry.

  10. When I read that bit from Wikipedia, I didn’t think it implied the habitable zone would be constant at all. You have to want to read it the wrong way to get that impression.

    I know Wikipedia has its problems and that criticising it is popular here, but baggibg it on the basis of that excerpt is a bit of a stretch.

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