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.
Whoa.
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.
*See?
May 15th, 2008 at 10:57 am
So, the universe needs a maid to clean the bric-a-brac?
May 15th, 2008 at 11:05 am
Does this have implications for the total baryonic matter in the universe?
May 15th, 2008 at 11:28 am
Mr. Magoos of the universe we are, but getting better all the time.
May 15th, 2008 at 11:36 am
So, if this checks out I assume the estimates for the amount of dark matter in the universe can be reduced as well?
Imagine: just when the LHC is turned on to look for dark matter, the astronomers go: “Oh, uhm… guys? Never mind…”
May 15th, 2008 at 11:45 am
Well, this probably reduces the mass-to-light ratio a bit, but not enough to eliminate the need for WIMPy dark matter cause there’s apparently a lot of it out there. Elliptical galaxies, for example, don’t have too much dust in them but still require a *ton* of dark matter to account for stellar motions. Galaxy clusters, as well, require lots of dark matter to bind them together with the observed velocities of the individual galaxies.
So even though this may imply that we have twice the amount of normal (baryonic) matter in the universe, it’s still not enough to account for many observational facts which imply the existence of dark matter.
May 15th, 2008 at 11:46 am
C’mon, Phil… you of all people should know better than to use power where you mean energy!
May 15th, 2008 at 11:47 am
No, ShavenYak, he means power.
May 15th, 2008 at 11:49 am
Sorry, was thinking you were referring to the power thing above that … you’re right in this context. My bad!
May 15th, 2008 at 12:35 pm
Pretty picture.
I … um … like pretty pictures.
May 15th, 2008 at 1:00 pm
And I thought my workplace was short of outlets. I am SO not hoovering the universe. Not without some serious extension cords at least!
May 15th, 2008 at 1:15 pm
Not that that ain’t bright, Phil, but isn’t that still only about .00000000001 solar mass stars per cubic light year? Still pretty lonely out there.
May 15th, 2008 at 1:24 pm
When I look up NGC 4545 in the World Wide Telescope I see a totally different galaxy …….????
May 15th, 2008 at 1:44 pm
@Bryan: Proabably in diffuse gas. Rules of thumb that I know: 1) there’s about 1 particle per cm^3 in gas in the “typical” interstellar medium, and 2) the mean distance between stars in the disk is about 1 parsec (~3 light years).
Using these numbers I get about 0.001 solar masses per cubic light year in gas and about 0.03 solar masses per cubic light year in stars.
The sun’s luminosity is 3.8×10^26 Watts and using this as a “typical” star, that gives us about 10^25 Watts/LY^3 (so I don’t know where Phil gets fewx10^15 Watts/LY^3 above…my estimate can’t be that far off.)
May 15th, 2008 at 1:48 pm
Pieter Kok & bswift:
My thoughts exactly! This doubles (more-R-less) the baryonic slice of the universe’s pie! Go baryons! W00t! W00t!
Take that, dark matter! (Well give us a little ground anyway…)
Richard Drumm the Astronomy Bum
(If I can think of a better nickname, I’ll start using it ASAP)
… in Charlottesville till the cows come home…
May 15th, 2008 at 1:53 pm
Interesing. And the picture of the galaxy is simply beatiuful. It reminds me of the Sombrero Galaxy, only with less dust.
May 15th, 2008 at 2:08 pm
Wow.*
I don’t get it.
*See?
May 15th, 2008 at 2:19 pm
Ok, I reread the intro and I get it now.
May 15th, 2008 at 2:25 pm
Niice. Do you know what parameters, in particular, were tweaked to give this new result?
Also: you (a) may want to clairfy the power output as 460 billion dollars *per second* [I'm assuming], and (b) Pleeease use scientific notation for the numbers of huge!
Though there is a bit of a nifty-factor in seeing a massive number of zeroes following a digit.
May 15th, 2008 at 2:50 pm
If the universe is “producing” (i.e. converting) 4.6e15 joules/second (power), at the rate of $0.10 per kWh ($/energy), according to google, that’s 1.27e8 $/second or about 4000 trillion dollars a year.
May 15th, 2008 at 4:30 pm
[...] According to Badastronomy the universe generates (or is that consumes?) half a trillion dollars of power per cubic light year per hour, not a quarter of a trillion as was thought until yesterday. [...]
May 15th, 2008 at 5:09 pm
Didn’t you just say the other day that we’re actually missing about half the baryonic matter we need according to the distribution of light elements and the WMAP? This seems to fit nicely with that number.
As brought up by Pieter Kok, bswift and Richard B. Drummon.
May 15th, 2008 at 5:32 pm
Given what I read about carbon stars pumping out all their dust, I figured they had to be clouding up the universe.
I find it a bit ironic too; here on Earth, we worry about the carbon we dump into the air, and thus try to reduce it.
Out in space, these stars that produce power by a rather clean method for our means on Earth also are pumping out carbon.
Funny, isn’t it?
Not that’s it’s a reason to ignore our issues with carbon….
May 15th, 2008 at 7:47 pm
“What astronomers call dust is actually a relatively complex molecule, based on carbon and created in red giants,”
“We are Stardust, We are Golden,
And we’ve got to get ourselves,
Back to the Garden”
“Of course, finding an outlet in a cubic light year (which is 1039 cubic kilometers) might be an issue.”
I have enough touble finding the outlet behind the couch – finally found it while watching “Blink”…
May 15th, 2008 at 8:07 pm
Oddly enough, I just finished the proof corrections on my paper about correcting galaxy luminosities and colours for dust when seen at different inclinations.
May 15th, 2008 at 8:53 pm
Um, can we assume that stars are a major component of the baryonic mass?
This pie chart, which must be dated, claims that it is 10 % of the gas component. bswift gets the reverse ratio, so I’m uncertain to within two orders of magnitude here.
May 15th, 2008 at 10:11 pm
@Torbjörn: There is indeed much more baryonic gas (that is not in stars), and I believe a lot of it is in intergalactic space, which has a relatively much larger volume. The number I quoted was, as I said, a rule-of-thumb for the average gas density in the galactic disk. I don’t have a good feel for the average intergalactic medium gas density, so I can’t quote that for you, but it’s got to be quite a bit less (down by ~2 orders of mag or so? more?)…what saves you is the enormous volume of the IGM that this low-density gas occupies.
So, yes, there’s a lot more mass in gas than in the stars in the universe, but in galaxies, usually there’s more mass in stars.*
*I personally don’t study galaxies, and this is just based on what I’m recalling offhand. However, I’m pretty certain this is right.
May 15th, 2008 at 10:36 pm
At the moment I’m a little too tired to start digging through the paper, so I’m probably just missing something obvious here. But as I look at the abstract there is one thing that bothers me. It describes the attenuation at specific wavelengths, but as I recall from our discussion of Obler’s Paradox back in cosmology class, on any meaningful timescale dust can only redistribute the light to different wavelengths, it can’t really eliminate it. So if this dust is absorbing 87% of the light at 2.1 microns, that just means that there is a lot more light coming out at some other wavelength, probably out at 10, 20 or 30 microns instead.
So, haven’t people already been observing the amount of light coming out of galaxies in the far infrared (and maybe even microwave bands)? And if so, hasn’t that been included in the typical mass-to-light ratios for those galaxies?
May 15th, 2008 at 11:59 pm
Sorry about the mess : (madge dons her rubber gloves and whips out her feather duster to clean up : ) Prolly caused by my son! I seem to spend my life clearing up after him. Age 13, a science geek par excellence and yet can’t work a vacuum cleaner! Sheesh
May 16th, 2008 at 7:45 am
Ever since I saw that ’someone is wrong on the internet’ post by xkcd, I can’t leave these things alone.
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.
Scientists usually aren’t unclear on Units of Measure as such, but they sometimes speak fast and use words in their ‘civilian’ context (I used to wax raging when hippies would talk about energy), not stopping to think someone who thinks less clearly will be confused. Power and energy look pretty much the same to a layperson.
Energy is the inherent ability to do work, and has the same units as work. Power is work done or energy transmitted (or wasted, or created) per time unit. If the Universe produces 4.6E15 Watts, this means Joules per second, or roughly how many kilograms you could lift one meter high each second in Earth gravity. In an hour, the energy thus accrued would be 4.6E12 kWh.
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.
I’d have to agree with ShavenYak and disagree with bswift. Strictly speaking, you put a price tag on energy, not power.
May 16th, 2008 at 8:29 am
‘That’s enough energy to run a typical American house for… let’s see… carry the two… a gazillion years. More or less.’
… or Al Gore’s house for maybe a day and a half.
GC
May 16th, 2008 at 9:51 am
Thank you Varn Nine, for saving me the trouble of typing all that.
May 17th, 2008 at 3:14 pm
Varn Nine, I corrected myself in my hasty response to ShavenYak about 9 seconds after I posted it. Thanks.
May 18th, 2008 at 12:21 am
Phil, thanks again for yet another fascinating post. I loved the picture and I learned a bit from your lucid explanation.
Keep them coming!