Writing the history of the 'Cosmic Dark Ages'

Sep 02, 2013 by Pete Zrioka
Writing the history of the 'Cosmic Dark Ages'
An arrangement of Murchison Widefield Array (MWA) elements in the Australian outback. Credit: Natasha Hurley-Walker

For millions of years after the Big Bang, there were no stars, or even galaxies to contain stars. During these "Cosmic Dark Ages," neutral hydrogen gas dominated the universe. When clouds of primordial hydrogen gas started to collapse from gravity, they became stars. The infant stars' nuclear reactions emitted ultraviolet radiation, stripping the surrounding hydrogen atoms of their lone electrons, making them ionized.

This launched the Epoch of Reionization, when burned away the neutral hydrogen, creating pockets of ionized hydrogen around the first . However, this chapter of the universe's life story is largely blank. We don't know how long it took the first stars to form, or even when they began to do so.

Using radio telescopes, scientists from ASU's School of Earth and Space Exploration are working with a multinational team to probe deep into our universe's mysterious formative , searching for answers to fundamental questions about this time period.

"We know a lot about the Big Bang, we know a lot about how the universe started and a lot about how the universe looks today, but for most of the first billion years we have almost no observations," says Judd Bowman, an assistant professor in the school.

Bowman is the project scientist for the Murchison Widefield Array (MWA), one of two low-frequency radio telescopes attuned to the unique redshift wavelength that neutral hydrogen emits. The other is the Precision Array to Probe the Epoch of Reionization (PAPER), which SESE postdoctoral fellow Danny Jacobs works on, along with the MWA.

Unlike most , both PAPER and the MWA are not dishes, like the National Radio Astronomy Observatory's Very Large Array (VLA).

"Normally, when you're building a radio telescope, you're building a dish," says Jacobs. "Waves come in and bounce to a central point, which focuses your field of view very tightly on the sky."

PAPER and the MWA are comprised of many separate, small antennae arranged in groups, providing a broad view of the sky. Jacobs compares the function of MWA and PAPER to wide-angle camera lenses. Dish telescopes like the VLA are more like standard or zoom lenses that can focus on one area very accurately.

Both arrays function similarly to cameras, as well. Just like light hits a digital camera's sensor to create an image, radio waves hit the arrays in different places with different intensities, giving researchers a "picture" of where those signals come from and, consequently, an idea of how the first bubbles of ionized hydrogen formed.

To pick up the faint signals from the Epoch of Reionization, both arrays have been constructed in very remote locations. PAPER's 128 antennas are spread across the Karoo desert in South Africa. The MWA consists of more than 2,000 elements located in Western Australia's outback.

Writing the history of the 'Cosmic Dark Ages'
As the first luminous cosmic objects began to blast radiation into the universe, pockets of ionized hydrogen began to form around them, eventually meeting one another and structuring the universe. ASU researchers are determined to uncover what the first were, when they formed and how they affected the following formations. Credit: Illustration by Charles Shockley

"The reason we go there is to minimize radio frequency interference. Anything from phones, computers and lights generate radio interference that swamps our signal," says Jacobs. "It's so bad we have to go to the most remote parts of the world and our telescopes still detect satellites and planes, and reflections from meteors."

Hydrogen's rest wavelength (the distance it takes for the wave's shape to repeat itself) is 21 centimeters. However, both arrays are tuned to much longer wavelengths. Due to the expansion of the universe, radio waves from hydrogen during Cosmic Dawn are stretched out to multiple meters by the time they reach Earth.

Both MWA and PAPER are stepping-stones to a larger project called the Hydrogen Epoch of Reionization Array (HERA), a massive radio telescope that will be capable of observing the cosmic processes that led to the universe as we see it today.

But even the basic components of those processes remain in question. Did stars form first, or galaxies, or black holes? HERA will help determine which was the inaugural celestial body.

"It's a chicken or egg problem," says Bowman. "All of those things today show up in the same place. Our Milky Way is one of billions of known galaxies and it contains billions of stars, and at its center is a supermassive black hole. So today, we see all of these objects interacting together. But which came first?"

Determining the incipient object will also shed light on everything that followed it. The first stars and galaxies would have had a tremendous influence on the neutral gas around them, altering the formation process of the next generation of objects. Understanding these effects is just as important as finding the objects themselves.

"Did the first objects make it easier or harder for more stars to form?" asks Bowman. "Did they make it so only big galaxies were able to survive through time, or did they allow little galaxies to thrive and grow?"

Such far-reaching, fundamental questions require a huge effort from people all over the world. ASU's contribution alone comes from researchers and students of all levels from SESE, Physics and the joint Cosmology Initiative.

"When a project gets to the scale we're talking about, with hundreds of antennas, the science is very hard, the analysis is very hard, you have to draw on the resources of the entire community to make it happen," says Bowman.

Actually, MWA and PAPER are competing projects. The most effective methods and processes from each telescope will be carried over to HERA when construction begins next year.

"But we're one team when it comes to the next generation," says Bowman. "It's an interesting form you see in science a lot, where competitors can be collaborators at the same time."

The difficulty and complexity of this long-term project is actually what most interests Bowman, who began work on the MWA when he was a grad student at MIT in 2005.

"What's exciting to me is working on a project that is hard, a project that takes time and real effort," says Bowman. "I want to see something that's never been seen before, I want to learn something that's important to the history of our universe."

Jacobs is also motivated by curiosity.

"I want to live in a world where we can, as a society, ask lots of questions about our world. Whether or not they're useful shouldn't matter because we are curious people ... and the more we know about the universe, the better off we are," says Jacobs.

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User comments : 23

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cantdrive85
1.5 / 5 (17) Sep 02, 2013
The "cosmic dark ages" certainly describes the current state of space science.

"After all, to get the whole universe totally wrong in the face of clear evidence for over 75 years merits monumental embarrassment and should induce a modicum of humility." Halton Arp

This creation theory of the BB is laughable.
IMP-9
5 / 5 (7) Sep 02, 2013
After all, to get the whole universe totally wrong in the face of clear evidence for over 75 years merits monumental embarrassment and should induce a modicum of humility.


Arp speaking on his career and failed alternative cosmology.

This creation theory of the BB is laughable.


Forgive me for thinking that an unsupported claim won't change anyone's mind.
Torbjorn_Larsson_OM
5 / 5 (6) Sep 02, 2013
EDIT: Oh, I forgot the rules of troll: don't feed them.
vacuum-mechanics
1.1 / 5 (16) Sep 02, 2013
For millions of years after the Big Bang, there were no stars, or even galaxies to contain stars. During these "Cosmic Dark Ages," neutral hydrogen gas dominated the universe. When clouds of primordial hydrogen gas started to collapse from gravity, they became stars. The infant stars' nuclear reactions emitted ultraviolet radiation, stripping the surrounding hydrogen atoms of their lone electrons, making them ionized.


By the way, it is interesting to note that even a simple hydrogen atom in which we thought that we knew it detail via quantum mechanics, actually there is still problem about it…
http://www.vacuum...19〈=en

Gmr
3.4 / 5 (5) Sep 03, 2013
EDIT: Oh, I forgot the rules of troll: don't feed them.

Talking about them in third person without addressing them directly is pretty effective however.
yep
1.4 / 5 (10) Sep 05, 2013
Big Bang is as real as any other creation story, thats why my vote is in for Pastafarianism!
May his noodly appendages touch us all.

"some scientists would rather be wrong than uncertain"

Halton Arp, like many other great men in history, is maligned for showing the emperor wears no clothes.
Fleetfoot
5 / 5 (5) Sep 06, 2013
"some scientists would rather be wrong than uncertain"

Halton Arp, like many other great men in history, is maligned for showing the emperor wears no clothes.


Arp is maligned for continuing to promote false ideas when observations from new telescopes proved he was wrong.
Gmr
3 / 5 (2) Sep 07, 2013
"some scientists would rather be wrong than uncertain"

Halton Arp, like many other great men in history, is maligned for showing the emperor wears no clothes.


Arp is maligned for continuing to promote false ideas when observations from new telescopes proved he was wrong.


Yes, oddly enough - a behavior apparently laudatory in the crank community. I'm wondering if other behavior is similarly lauded: beating your head against a wall because you don't believe it hurts, continuing not to eat because you haven't been eating constantly so food must not be necessary, deciding that opening your mouth is sufficient for respiration rather than actually moving your chest and breathing...
cantdrive85
1 / 5 (8) Sep 07, 2013
"some scientists would rather be wrong than uncertain"

Halton Arp, like many other great men in history, is maligned for showing the emperor wears no clothes.


Arp is maligned for continuing to promote false ideas when observations from new telescopes proved he was wrong.

Lie much? His most recent papers (2008) show the same results using modern surveys. Odd how NASA must release doctored images to show "proof" Arp was wrong.
Fleetfoot
5 / 5 (3) Sep 07, 2013
"some scientists would rather be wrong than uncertain"

Halton Arp, like many other great men in history, is maligned for showing the emperor wears no clothes.


Arp is maligned for continuing to promote false ideas when observations from new telescopes proved he was wrong.

Lie much?


Yes, he did that too but I prefer to leave personal attacks to you. See Wright on Narlikar for examples.

His most recent papers (2008) show the same results using modern surveys. Odd how NASA must release doctored images to show "proof" Arp was wrong.


Claiming images have been "doctored" is just another aspect of his denial.
cantdrive85
1 / 5 (7) Sep 08, 2013
Claiming images have been "doctored" is just another aspect of his denial.

Actually, it was Dr. Jack Sulentic, a professor of astronomy at The University of Alabama, that made the claim, not Arp.
According to Sulentic;
"He says that a quick glance at the HST composite image reveals that the image of the galaxy-quasar pair is presented in a way that emphasizes the brightest parts of the galaxy and the quasar so that the impression is given that there is no light between the two objects."

http://graduate.u...0802.htm

What it shows is that the astronomical community has very little integrity. NASA is the Vatican of modern religion of the "standard model".
Fleetfoot
5 / 5 (3) Sep 11, 2013
Claiming images have been "doctored" is just another aspect of his denial.


According to Sulentic;
"He says that a quick glance at the HST composite image reveals that the image of the galaxy-quasar pair is presented in a way that emphasizes the brightest parts of the galaxy and the quasar so that the impression is given that there is no light between the two objects."

http://graduate.u...0802.htm

What it shows is that the astronomical community has very little integrity. NASA is the Vatican of modern religion of the "standard model".


In the same article: ""Our work showed that the connection was of low surface brightness," he says. "In order to see it one would have to "burn out" the bright parts of the image and emphasize the fainter light levels.""

In other words, he is complaining because NASA did NOT "doctor" the image.

The only way to prove Arp's claim would be to show a progression of redshift along the so-called bridge.
Q-Star
5 / 5 (1) Sep 11, 2013
The whole concept of Cosmic Dark Age is ad-hoced and redundant in Big Bang cosmology, because there is no apparent reason, why the distant areas of Universe should be invisible because of some hydrogen ionization.


It's not invisible because of re-ionization, Zeph, it's the "Dark Ages" because the hydrogen had not yet collapsed to form stars.

The speed of space-time expansion raises with distance, and when it exceeds the speed of light at certain distance, it becomes infinitely red-shifted and as such unobservable.


We seem to be able to see the other side of the "Dark Ages" just fine Zeph,,,, it's called the Cosmic Microwave Background. .

This distance denoted so-called particle horizon of observable Universe and it's analogous to event horizon of black holes - just observed from opposite intrinsic perspective.


I have no idea what ya are trying to say there, so ya can have that one. Some kind of intrinsic gobbledygook, it seems.
cantdrive85
1 / 5 (7) Sep 11, 2013
To be sure, every NASA image intended for the public is "doctored" so to speak. The difference here is the claim that was made (obviously false) with the image presented in a particular way to support the claim. And since then there has been no retraction of the obviously spurious claim.
yyz
5 / 5 (3) Sep 12, 2013
I think it's funny to see cantdrive parrot the critique of a *press release* (instead of, you know, actual science) by Dr. Sulentic. Cantdrive's ignorance is understandable here, given his unfamiliarity with the published work, but Sulentic's criticism is totally irrelevant.

As long ago as 1985, a paper by Cecil and Stockton already revealed the existence of a luminous feature between NGC 4319 and Mrk 205: http://adsabs.har...88..201C

Why is this not even mentioned by Sulentic, especially when he comments on the C&S 85 work in a 1987 paper with Arp: http://articles.a...19..687S

Who is being deceitful here? And further, why is there no mention of absorption lines from NGC 4319 being detected in the spectrum of Mrk 205: http://articles.a...03L..55B

This is just more evidence that Mrk 205 lies behind NGC 4319. And yet not a word from Sulentic on the finding. Again, who is neglecting evidence?
Q-Star
not rated yet Sep 12, 2013
We seem to be able to see the other side of the "Dark Ages" just fine Zeph,,,, it's called the Cosmic Microwave Background
Well, you just got it - if the CMBR is the remnant of Big Bang, it should be shielded with hydrogen plasma. It shouldn't be here.


Zephyr, the cosmic microwave background IS the 3000 kelvin hydrogen plasma, redshifted to microwave frequencies.

I have no idea what ya are trying to say there, so ya can have that one
Maybe http://www.aether...e_dm.gif will help you to understand it. But be warned, the dumb dog will not understand even the trivial Pythagorean theorem: with picture or without it.


No AWT gobbledygook for me Zeph, I've seen it all, it's not compelling. But I will congratulate ya on your first convert, it took 8 years, but now ya have a following (of one.)
Q-Star
not rated yet Sep 12, 2013
The redshifted 3000 K hydrogen plasma wouldn't follow the black body radiation spectrum, which we can observed in CMBR today.


Zeph, at z=1000, the ENTIRE universe was one big ball of 3000 kelvin plasmas,,, the most perfect black body object that has ever existed since then. The temperature variation throughout the entire universe was on the order of ONE PART per ONE HUNDRED THOUSAND! Name one object that has ever existed since then that would be a better black-body radiator then the universe as a whole at z=1000? Just one. (And if it has aether or dense vacuum in the answer, it's gobbledygook.)
Fleetfoot
3.7 / 5 (3) Sep 14, 2013
The whole concept of Cosmic Dark Age is ad-hoced and redundant in Big Bang cosmology,


Garbage, look up the "Gunn Peterson Trough" (and for background the "Lyman Alpha Forest"). It is an observed phenomenon which needs to be modelled. Steady state cosmology cannot explain it but standard cosmology can and in fact predicted it.

because there is no apparent reason, why the distant areas of Universe should be invisible because of some hydrogen ionization.


Wrong way round, distant areas of Universe are visible because of re-ionization. The Lyman Alpha line is due to neutral hydrogen atoms.

Even if we admit, that the notion of expanding universe is correct, then the most distant areas of Universe should be invisible for us, because they're expanding too fast.


Correct, they are! That is why the "observable universe" is only a tiny fraction of the whole. In practice, using EM, we can't see beyond the dense plasma that produced the CMBR at a redshift of 1090.
Fleetfoot
not rated yet Sep 14, 2013
deleted spurious duplicate
Fleetfoot
3.8 / 5 (4) Sep 14, 2013
the cosmic microwave background IS the 3000 kelvin hydrogen plasma, redshifted to microwave frequencies
Not according to mainstream cosmology theory - the CMBR photons are supposed to be a Big bang gamma rays, redshifted to microwave frequencies.


The CMBR has a temperature today of 2.725K and the redshift is 1089. Multiply 2.725 by (z+1) and you get 2970K. Put that value into this applet and it will show you the colour:

http://webphysics..._mjl.htm

It's a pale yellow shade compared to the white of the Sun at 5880K.

The Lyman Alpha line is at 121.6nm, so far to the left on the graph that is has no effect on what we see.

The Sun's spectrum departs from a pure black body because we see a mix of photons from slightly different depths and deeper material is hotter. In the CMB, photons released were from hotter material too but they are more redshifted which makes the observed temperature the same, hence the very accurate match.
Fleetfoot
5 / 5 (2) Sep 14, 2013
Correct, they are! That is why the "observable universe" is only a tiny fraction of the whole. In practice, using EM, we can't see beyond the dense plasma that produced the CMBR at a redshift of 1090
This is exactly what I'm saying here. You should decide, whether the "observable universe" is only a tiny fraction of the whole because the remote areas are expanding too fast, or because they're beyond some dense plasma.


Both statements are true but they refer to different limits.

The definition of "observable universe" means that which can be observed in principle without consideration of the limits of technology.

In my previous reply I said "in practice" to emphasise that the EM barrier of hot, opaque gas which produced the CMB is not the theoretical limit, just the farthest back in time we can see using EM. What we can infer from nucleogenesis goes back a lot farther and if we could observe relic neutrinos, they we let us see a little beyond that.
Fleetfoot
5 / 5 (2) Sep 14, 2013
If we would see the red-shifted hydrogen plasma glowing in Dark Ages (it has usually nearly monochromatic reddish color), then we would see red shifted spectral lines of hydrogen in it - not the smoothly distributed black body radiation.


Look at the surface of the Sun, it has nearly the same composition and similar temperature but it is not monochromatic red! The spectrum must be a black body because it is the plasma is opaque in both cases.

We don't see hydrogen in emission from the dark ages because the gas had cooled and already recombined. As I said before, we do see it in absorption lines, specifically the Lyman Alpha forest and Gunn-Peterson Trough, just as we see absorption features produced by cooler gas between us and the photosphere of the Sun. Here are example spectra showing the forest:

http://www.astro....est.html