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 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?

[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]

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?

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.

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.