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Friday
Mar252011

Zzzzzzzzs and Galaxies

A note about this article:

1. I was going through the Astrophysical Journal recent archives, or so I thought, looking for an article to write about, and I was all, "This one is cool. I'll write about this one," and only just now, as I am posting, do I realize that it's from way back in 2010, so I apologize for the non-timely nature of this post, but I've already written it, so I hope it's interesting anyway.

When did galaxies form? When did the stars that make up the galaxies form? What is the trajectory of star formation rates throughout the evolution of a galaxy? How does a galaxy's luminosity relate to the number of stars it has and to the rate at which it is forming new stars? How are old (aka far-away, since one has to look distantly to see into the distant past) galaxies different from newer galaxies? Who are you? Who is John Galt? Why are you here? Why isn't your savings account balance over $10,000, and why don't you have life insurance, and how many stars do you form per year in units of solar masses per megaparsec cubed per year?

</barrage of questions>

A recent study by Bouwen, et al., used a new camera on the Hubble Space Telescope to look at galaxies farther away, and thus much older because of the way light can only travel to us at the speed of light, than any galaxies we've seen before.

These galaxies are moving away from us. Well, all galaxies are moving away from us, as the universe is expanding, and as it is expanding faster as time goes on, meaning that if we observe how fast a galaxy is moving away from us today, and then we measure it 10 years from now, it will be running from us more quickly in 2021.

The observed expansion of the universe is proportional to the separation between the observer and the observed. So if you're looking at something far away, it's going to be moving away from you faster than, say, your mom.

Astronomers, always prepared, have a variable--z, or cosmological redshift--that represents how fast something is moving away from us due to the expansion of the universe.

Regular redshift, and its evil twin, blueshift, are measurements of the Doppler Effect, which I won't go into in detail because you've all heard how an ambulance siren--made of sound waves--changes pitch (higher when it's coming toward you, lower when it is moving away from you toward that guy who accidentally shot a nail gun into his stomach). The same is true of light waves.
z, however, is a little more complicated, because expansion velocities are so high that relativity must be taken into effect. In addition, it's not actually due to the Doppler Effect, since it has nothing to do with the object's motion through space, but the expansion of spacetime itself and the attendant carrying-along of everything within it.
Anyway, z=(wavelength_observed - wavelength_emitted)/wavelength_emitted, and it tells you how far away what you're looking at is, and thus how long after the Big Bang its light was emitted.

Bouwen, et al., used Hubble's WFC3, a near-infrared camera, to find at galaxies of z~8 (meaning about 600 million years after the first neutral hydrogen atoms were formed) and found five of them, including one with z~10. The group wanted to investigate their luminosity, star formation rate, and dust content, to see how those parameters compared to those of galaxies with lower z. The light from these galaxies has been cosmologically stretched from the standard visible-light wavelengths to near-infrared light, and this is the first near-infrared camera powerful enough to see their faint emission.

A new telescope, the James Webb Space Telescope, will soon be, as the name implies, in space, after it has gobbled up all of the federal astronomy budget. It will observe infrared and near-infrared wavelengths: it will thus be powerful enough and sensitive to the right (longer) wavelengths to see galaxies even farther away, with even higher z. Astronomers estimate that z=15 galaxies can be detected. It is believed that the first stars formed between z=15 and z=30.

Here is a picture of their main result:

This graph shows UV intensity (translated to star formation rate density in solar masses per year per unit volume of space) plotted against cosmological redshift. What this plot demonstrates is how star formation changes across the life of a galaxy, since z=0 galaxies are younthful compared to z=8 fogeezers. The blue line represents star formation rate inferences based just on the UV light received here in Earth, while the tan-orange-weird-color line represents star formation rate if we correct for the amount of light that would be absorbed by dust present in the galaxy. What's interesting is where the two meet up and take a journey together, telling us that from about z=6 onward, there is little->no dust.

To me, though, what's exciting about this paper is not what was found, but the fact that it could be found. This seems like more of a 'we have proven that new technology means new discoveries' paper than a 'new discoveries' paper.

As our technological capabilities continue to expand, and as the government decides to give science more and more money because it's so awesome and why would they give money to dumb things like the public school system and fighter jets, we'll be able to venture farther and farther into the observable universe.

ResearchBlogging.orgBouwens, R., Illingworth, G., Oesch, P., Stiavelli, M., van Dokkum, P., Trenti, M., Magee, D., Labbé, I., Franx, M., Carollo, C., & Gonzalez, V. (2010). DISCOVERY OF

∼ 8 GALAXIES IN THE HUBBLE ULTRA DEEP FIELD FROM ULTRA-DEEP WFC3/IR OBSERVATIONS
The Astrophysical Journal, 709 (2) DOI: 10.1088/2041-8205/709/2/L133

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Reader Comments (2)

A little off topic: Remember when you told me that they (who are they? I don't know) were close to watching the Big Bang b/c they (not the general they) could see back into the past with telescopes? I remember you saying that they (umm) wouldn't be able to actually see it because it would be black. Can you tell me A) Who "they" is? B) Is this true or was this thought up when we were drinking tequila? C) If this is true, has there been any updates?

March 28, 2011 | Unregistered CommenterBrooke N.

'They' are the people who are out to get you.

No, 'they' are just 'the astronomers,' collective.

And it's true! Even if we were drinking tequila. Right after the Big Bang, the photons that existed were absorbed almost immediately, so they can never reach our telescopes. While there was light, we won't be able to see it! The first light that we can observe, ever, is the cosmic microwave background (it has a radio wave frequency; go, radio astronomy!), which is thermal radiation with temperature 2.725 Kelvin. Little, tiny differences in this temperature, mapped over all space, give astronomers information about the first structures formed in the universe.

March 28, 2011 | Unregistered CommenterSarah Scoles

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