The Universe so bright, it’s gotta wear shades

Contributed by
May 15, 2008

Every now and again I see a news release that makes me sit back and say, "Really? Wow!" This latest one falls squarely in that category: European and Australian astronomers are reporting that the Universe is almost twice as bright as we had thought.

Really? Wow.*

The dust in galaxy NGC 4545 blocks our view right along its mid-plane. From the side, our Milky Way would look just like this. Picture courtesy Bruce Hugo, Leslie Gaul, Adam Block/NOAO/AURA/NSF.

Basically, it has to do with dust. What astronomers call dust is actually a relatively complex molecule, based on carbon and created in red giants, exploding stars, and winds from black holes (as matter falls in dust is generated and gets blown outward before the Final Plunge). The Universe is lousy with the stuff. On a clear summer night in the northern hemisphere it's easy to see: look toward the constellation Cygnus, and you can see the fuzzy glow of the Milky Way split right down the middle by dark stuff. That's dust.

Dust absorbs starlight and re-emits it in the infrared. So it's possible, in theory, to be able to determine the amount of dust in the Universe by mapping the infrared light. And since energy in = energy out, you can determine how much energy stars emit as well.

Turns out, according to this new report, our old models were wrong. We knew that already; there were some problems with them. But this new model -- where the math appears to check out correctly -- indicates that there is twice as much starlight being generated in the Universe than we previously thought.


If you want numbers, then on average, stars in the nearby Universe produce about 4,600,000,000,000,000 Watts per cubic light year, but we see only 2,600,000,000,000,000 Watts of it. The rest is absorbed by dust. That's enough energy to run a typical American house for... let's see... carry the two... a gazillion years. More or less.

Seriously, that's a vast amount of power. Put it this way: a typical rate for electricity is about $0.10 per kiloWatt-hour. So in an hour (if the new model is correct), a typical cubic light year of your local Universe creates $460 billion worth of power.

Awesome. Of course, finding an outlet in a cubic light year (which is 1039 cubic kilometers) might be an issue.

I'm curious to see if this model holds up, but if it does it'll mean some retooling of models across the board. I don't know how much this will affect other fields. In some cases, there won't be much change. For example, the whole idea of dark energy was found due to unexpected brightnesses of distant supernovae; they were fainter than expected. However, all manners of dusty modeling were used in those calculations, and the results held up. So I don't expect this to change much when it comes to the new model.

But the light from distant clusters of galaxies is measured and used to determine some properties of them. If the intrinsic amount of light is actually higher than previously thought, then astronomers may have to adjust to the new parameters. This will also affect how we model individual galaxies; the amount of light we see from them depends on their angle to us. If we see a spiral galaxy edge-on (like NGC 4565, one of my faves, shown above) then we'll have to account for the missing light. Seen face-on the change won't be as great.

Anyway, this should provide some fun fireworks in galactic astronomy over the next few months. It'll be very interesting to see how this plays out.


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