Sunday, June 8, 2008

A Rather Boring Title (with VERY Interesting Implications)

I saw this a couple of weeks ago, actually the day after it hit the major news services, but I haven't gotten around to commenting on it.

There has been a paper published recently in Astrophysical Journal Letters under the unassuming title of THE ENERGY OUTPUT OF THE UNIVERSE FROM 0.1 μM TO 1000 μM (preprint here). This may seem like an unamazing title to a paper but it has the potential to make a rather large splash in the astrophysics community. Here's why: it gives a correction to the mass to light ratio (MLR) of galaxies (in the paper they call it the galaxy luminosity function). The MLR is a measure of how much mass you expect there to be in a galaxy based on how bright it is.

So the interesting part is that this changes all of the standard (textbook and literature) estimates of the mass of galaxies. What this does is it affects the estimates of dark matter inside (and around) of a galaxy. But the ramifications do not stop there. By changing the accepted MLR of galaxies this also affects the estimates of how much mass is in a galaxy cluster. This goes all the way back to Fritz Zwicky and his "discovery" of dark matter in the coma cluster of galaxies. So this effectively changes all our estimates of how much "normal" matter there is in the universe.

So here is the basic argument (here are also some simple news articles about it that give a general overview:, NYTimes): Galaxies emit light, all types. We see it. Interstellar dust emits infrared radiation. The power output of the interstellar dust is more than the power absorbed by the light coming from the nearby galaxy. So the galaxy must be emitting more light than we think it is. If we correct for dust and increase our estimate of the MLR then there are more stars producing more light. The galaxy is brighter than we think and suddenly the amount power absorbed from the light of the galaxy equals the unaccounted for infrared radiation!

The articles that I gave links to above give a good overview of what lead them to this conclusion, and it is quite interesting. They did a statistical analysis of the galaxies in the sky and saw that there were more face on galaxies than edge on galaxies. This raised some questions because if you have a random distribution of galaxies then you shouldn't see this.

I will not go into depth about their argument, but I will emphasize that this changes all of our estimates of mass in galaxies and the amount of dark matter in the universe, and by extension the amount of dark energy. There will be a lot of things that will have to be recalculated. I can't wait to see how this will affect things, and I want to be part of it. Their work seems very good and will not be easy to refute. I just wanted you guys to be aware of this because you will most likely hear something about this in the future.


  1. This is interesting Ryan. It will be a good day when we finally figure out what is going on with Dark Matter/Dark Energy.

    It would really be interesting if MLR data is off. However, it seems like there are still other reasons to think dark matter estimates are still valid. For example, WMAP says there should be a lot of dark matter.

    But perhaps, this paper you are referring to would offset those results too. I'll have to look more into it. Great post.

  2. This obviously doesn't account for all dark matter but the important point is it just shot a hole through the number 1 measuring stick used to measure dark matter. Even if all this does is give a correction to our estimates, it casts doubt on all our other estimates.

    It's kind of like, "Well we were off on this one...but wait! That means we have to change this other thing as well because it was based on our first estimate...but that changes this other thing also because...." etc. It's like finding that in a chain of devices used in an experiment the first one wasn't calibrated right.


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