Powerful Galaxies Found in Infrared

demachina writes "NASA's Spitzer Infrared space telescope has discovered 'a mysterious population of distant and enormously powerful galaxies radiating in the infrared spectrum with many hundreds of times more power than our Milky Way galaxy.' They are 80% of the way back to the big bang. They found them by comparing a visible and infrared scan of the sky and looking at the places where there was a big infrared signature and no visible one. They are shrouded in dust."

Comments

Other life forms are out there...

[hhlost]

and if they're smart, they're hiding from us. fp?

They're watching

[Anonymous Coward]

in the constellation Bootes the Herdsman, the IRS team selected and observed 31 that are quite bright in the infrared but invisible in the NOAO survey.

So you really can't hide from the IRS :(

Is it only me...

[born_to_live_forever]

... or is it hilarious to see the pop-up ads that are linked to words like "radio", "satellite" and "software"? Their content is so commercial, and so divorced from relation to the scientific news of the article, that instead of being ads, they become parodies of themselves.

Is Dark Matter just hidden matter?

[Kraemahz]

This begs one to ask, if we keep finding these galaxies that are emitting energy but no light, is this dark matter or is it just normal matter that we just haven't been able to find yet? There might be a hell of a lot more dust out there than we thought there was originally.

Re:Is Dark Matter just hidden matter?

[adeydas]

http://astron.berkeley.edu/~mwhite/darkmatter/dm.h tml

Re:Is Dark Matter just hidden matter?

[luna69]

Infrared "energy" IS light.

Electromagnetic radiation takes many forms: radio, microwave, infrared, visual (what we see as "light"), UV, Xrays, gamma rays. They are all "light".

Sorry to be a pedant.

Re:Is Dark Matter just hidden matter?

[DjCameron]

You can do spectral analysis to determine the original emission spectra. The stars have emission and absorption lines at certain wavelengths, and these all get shifted by a certain amount. If it was due to redshift alone, we would know it, i'm pretty sure.

Re:Is Dark Matter just hidden matter?

[mbrother]

That's because you're not an astronomy professor. Radio waves are light, and no one should give me a funny look about it, especially during lecture. Hammering in a basic point like this helps students remember that radio waves travel at the speed of light (NOT SOUND! Oh I see that a lot), suffer diffraction like other wavelengths of light, etc. Of course, I then make a big point of saying how visible light is just EM radiation.

Re:Is Dark Matter just hidden matter?

[deglr6328]

No. The amount of ALL baryonic light emitting (or reflecting) or not is tightly constrained with high confidence by the WMAP result at ~4%. This number may change in the future with more precise CMBE measurements but certainly not by more than mere fractions of a percent.

Re:Is Dark Matter just hidden matter?

[Bootsy Collins]

This begs one to ask, if we keep finding these galaxies that are emitting energy but no light, is this dark matter or is it just normal matter that we just haven't been able to find yet? There might be a hell of a lot more dust out there than we thought there was originally.

Certainly some of the dark matter is in baryonic (i.e. normal) matter. In fact, it's interesting to note that the the first "missing matter" found was baryonic. While the rotation curves of spiral galaxies provide the most clear-cut evidence for missing matter at present, the history of the dark matter problem started much earlier, with Fritz Zwicky's observation that clusters of galaxies had to have a lot of mass not shining in the visible spectrum in order to be bound objects; their galaxies were moving too fast for clusters to be gravitationally bound objects otherwise. Then, starting in the 1960s, a significant fraction of that dark matter was found when it was discovered that the space between galaxies in clusters is filled with a 10-100 million degree gas (well, plasma) known as the intracluster medium or ICM. In very large clusters, the ICM can have several times as much mass as the mass of all the cluster galaxies. That was a good sized chunk of the missing matter on cluster scales, right there.

However, despite that, it still left most of the apparent mass of galaxy clusters unaccounted-for, a situation that remains today. And that's been the same story with pretty much all the dim or dark baryonic matter we've found since then: it's crucial to know about, since it has important things to tell us about the evolution of the Universe, the history of galaxy formation, etc., but it doesn't make a big impact on the dark matter problem. Our measurements of the compnents of the density of the Universe are at low redshift, and we don't know what the low-redshift counterparts of these high-redshift ultraluminous IR galaxies are. But if they turn out to be something we haven't yet detected, and thus it turns out we've underestimated the number of low-redshift galaxies by a factor of three (very doubtful), that still won't put an appreciable dent in the dark matter problem. There's just so much dark matter out there to find, compared to the amount of known baryonic matter.

Finally, it's worth noting that if baryonic matter were able to explain away all the dark matter, that would actually pose a serious problem for the standard relativistic hot big bang model. One of the observational lynchpins of the model is its set of predictions for light element abundances. We think we know all the relevant physics at the energies of nuclear processes; that, combined with the evolution of the background Universe as dictated by the Big Bang model, allows one to calculate the abundances of light elements. It turns out that the theory of Big Bang Nucleosynthesis is able to make pretty good predictions for the abundances of hydrogen, helium, lithium, etc., provided the density of the Universe in baryons is within a small range. The predicted values are significantly larger than the contribution to the mass density of the Universe from the luminous matter in galaxies, so we already expected that that there would be some baryonic dark matter. But the predicted values are also much much much smaller than the apparent density of the Universe in dark matter. In other worse, if Big Bang Nucleosynthesis is correct, you expect there to be baryonic dark matter, but you also expect much much more non-baryonic dark matter. Of course, that doesn't mean that all the dark matter isn't baryonic -- nature is under no obligation to follow our theories! -- but the theory's done reasonably well up to know, so it's worth remembering and is a reminder to be careful.

Re:Is Dark Matter just hidden matter?

[mbrother]

I'll just reply to a few of the questions raised.

The hot intercluster medium IS hot, but temperture is a funny thing in some astronomical settings. In this case, the density of particles is so low, a better vacuum than you'd get in Earth laboratories, that the heat content would be pretty low. You wouldn't get incinerated, for instance. But a conventional thermometer wouldn't work either since it probably wouldn't get into thermodynamic equilibrium. It would radiate away its heat faster than the ambient gas could warm it.

Astronomers have excellent limits on the amount of normal matter, as the parent poster says. We've got an excellent idea what is out there based on emission in the far infrared, interstellar scintillation, absorption line studies, reddening studies, etc. We have very good limits on the Oort cloud density, too, from comet statistics. There are even a number of direct observations based on microlensing surveys, and there's a shadow survey, too, looking at large star fields. In short, we've got pretty good numbers and we're not going to discover that there's more normal dark baryonic matter out there than we already know about.

Something i have always wondered

[X0563511]

If all the stars and celestial bodies (galaxies, ect.) are all different distances from us, and are all moving in relation to each other...

How do we know where they really are? If any EM radiation takes time to get here... Our night sky view is a view of something that has never happened, is not happening now, and will not happen (at least the particular configuration we see). The same thing goes for our radio telescopes, thermal, x-ray, ect.

That galaxy they found could not even exist now, or it may actually be 180 degrees relative to where we see it now.

Am i just crazy? Or do we have NO hope of actually figuring out where things are unless we figure out how to use quantum mechanics somehow to do it?

We must rename the milky way

[Timesprout]

If these are really powerful galaxies then they will think the milky way is a girly sounding name and beat it up. I propose 'the hard as coffin nails' galaxy be adopted.

Re:Large Blobs of Heat?

[AndroidCat]

I thought a galaxy had to be a collection of stars; which omit visible light?

So? These ones are omitting visible light. :)

Their paper?

[Anonymous Coward]

Couldn't find a link to the published ApJL paper, but this might be the preprint or related to it.

Re:Large Blobs of Heat?

[luna69]

IAAA (I am an astronomer).

All galaxies (with the exception of the recently discovered and dubiously titled "dark matter galaxy" mentioned here a few days ago) emit light at a wide variety of wavelengths, from radio all the way to gamma rays. The wavelengths at which a star emits is related to its temperature (google "blackbody radiation" or "planck spectrum"); other astrophysical processes can produce or modify passing emissions as well (molecular & plasma clouds, various types of "dead" stars like neutron stars, white dwarfs, etc. can create emissions due to non-blackbody radiation - google "bremstrahllung", "cerenkov", "synchrotron", etc.).

The reason that these particular galaxies are only visible in the infrared is that a) intervening dust reddens emissions across intergalactic (and, for that matter, INTRAgalactic) distances, and b) they are so far away that as the universe has expanded, the light traveling from them has been redshifted - stretched along with the spacetime through which they have been traveling. Thus, what we see as infrared now was originally of much shorter wavelength when it was emitted.

Hope that's useful, let me know if I can clarify.

galaxies full of dyson spheres?

[Anonymous Coward]

a dyson sphere is said to only radiate infrared. wiki

Re:How come?

[mbrother]

Because these galaxies are surrounded by dust (likely from massive starbursts, which produce dust). Dust, because of it's scattering properties, preferentially lets long wavelength light pass through it (ie. infrared) but scatters shorter wavelength light (ie. visible light) into other directions. This is the same effect you see when looking at a sunset. The setting sun looks redder because there is dust (small, scattering particles of various sorts) letting more red light through to you than blue light. In these galaxies, it is more extreme.

The effect is called "dust reddening." I have some slides about it for the lastest entry (March 2) for my Astronomy 1050 class at my astronomy webpage if you want to see examples.

Re:Large Blobs of Heat?

[luna69]

> why do we care?

That's a good question, and worth a better answer than I have time do do here (mbrother?). The short answer is that they're so far away that we're actually seeing galaxies as they were very early in the universe. When we look at nearby galaxies, we only see galaxies as they exist after billions (current estimates are, if I'm up to date, that galaxy evolution has been going on for around 13Gy) of years of evolution. By looking FAR AWAY, we're also looking BACK IN TIME, and are thus able to see things we'd otherwise have no ability to observe.

A surprising amount can be gleaned from spectroscopic analysis of faint, red (& ancient) galaxies. What ionization levels are observable? Do we see lots of heavy elements, or none at all? Such observations can also be very powerful probes of the stuff IN BETWEEN here and there. If we can make certain assumptions about the original emissions, then by looking at the OBSERVED emissions, we can infer, to some degree, the conditions in the intervening space (and time) between emitter and collector. There is lots of good work being done in this area currently.

Hope that helps, let me know if I can clarify!

Re:Huh?

[Aardpig]

The big bang is a theory, NOT fact.

You seem to equate 'theory' with 'guess'. Actually, the word 'theory' in a scientific context indicates an extremely well-tested, valid model of the natural world --- essentially, as close as one can possibly get to the truth behind what is going on. Newton's gravitation is a theory. Einstein's relativity is a theory. Maxwell's electromagnetism is a theory. Darwin's evolution is a theory.

In the specific case of the big bang, there is very strong evidence pointing towards its occurrence --- things like the uniform recession of the galaxies, and the cosmic microwave background (basically, an afterglow from the event itself). This is hard, cold evidence --- nothing unsound about it.

we don't know how big the universe is, so there would be no way to calculate a point of 'bang.'

In fact, we do know how big the Universe is. And furthermore, since spacetime itself was created in the big bang, the event didn't happen at a single point, but everywhere.