How the Universe escaped its 'dark ages'

Jun 11, 2012
Image credit: Hubble/NASA

(Phys.org) -- An international team of astronomers have uncovered an important clue about how the Universe emerged from its ‘dark ages’ some 13 billion years ago. By looking at nearby galaxies, they can infer what may have happened to the first galaxies of our Universe.

For some time have known that following the big bang, a dense hydrogen ‘fog’ settled over the Universe. During this time, a lot of the light produced by the first stars could only travel short distances before it was absorbed by the fog. They call this period the ‘dark ages’ of the Universe, but little is known about what was happening at this time.

“During the dark ages, the hydrogen fog condensed in certain places, which allowed the formation of stars, black holes and the first galaxies,” said Swinburne University of Technology astrophysicist Dr Lee Spitler.

“These objects were the first significant sources of ultraviolet radiation, which eventually started to burn off the hydrogen fog much like the Sun burns off a morning fog on Earth. We call this process reionisation, because the hydrogen atoms are ionised by the ultraviolet light.

"But what was happening during the Universe’s dark ages is somewhat of a mystery because there are few light sources embedded in the hydrogen fog.

“Obtaining information about reionisation is quite challenging as it occurred so long ago. Since light takes time to reach us, astronomers can observe what was happening at that time, but it is very difficult and pushes modern telescopes to their limits.”

To address this problem, an international research team, led by Dr Spitler, tried a different approach: they looked for signs of reionisation in , which are easier to observe.

“We used nearby galaxies to understand something that happened long ago, in much the same way fossils are used to understand Earth’s history,” said Swinburne Professor Duncan Forbes.

“We can see regions around galaxies where reionisation has just finished and use that information to understand important questions about the dark ages: What were the first stars like; how were the first galaxies formed; and were there many supermassive black holes?”

When reionisation occurs in a galaxy and clears out the hydrogen fog, it also disrupts the condensation of the fog into locations of new star formation.

The research team looked for signs of this stalled star formation in ancient star clusters and were able to measure when reionisation passed through the region around a galaxy.

By measuring when reionisation took place around three galaxies, including the Milky Way, the researchers found evidence that the hydrogen fog burned off first in isolated, low-density regions of the Universe. A few hundred million years later, reionisation took place in the dense, crowded regions of the Universe.

This suggests that galaxies in crowded regions of the Universe were more likely to be shrouded in very dense pockets of hydrogen fog. Such dense regions would therefore require larger numbers of light sources and more time to burn off the fog compared to regions with relatively light fog.

“Understanding how reionisation moved through the is very, challenging. Our technique provides a novel way to tackle this problem,” Dr Spitler said.

The researchers used the Keck and Subaru telescopes in Hawaii for this work, which has been published in the Monthly Notices of the Royal Astronomical Society.

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More information: onlinelibrary.wiley.com/doi/10… 66.2012.21029.x/full

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kevinrtrs
1.5 / 5 (15) Jun 12, 2012
For some time astronomers have known that following the big bang, a dense hydrogen fog settled over the Universe.

Just to point out the obvious here: this wasn't "KNOWN", it was speculated or if you really want to have it that way, theorized. No one was there to record this supposed event/stage for anyone on earth to know. There is no eye-witness record or any documentation for this. So no one could KNOW such a history as is purported here.

Furthermore, this article now tries to fathom out a possible solution to the theoretical conundrum that the "fog" has created. Hence even more assumptions are made and from them an inference is drawn.

I just wanted to point out that there are no KNOWN facts here, only speculation about what might have happened in the past as here:
But what was happening during the Universes dark ages is somewhat of a mystery because there are few light sources embedded in the hydrogen fog

The only things known are current, actual observations.
Origin
1 / 5 (8) Jun 12, 2012
For some time astronomers have known that following the big bang, a dense hydrogen fog settled over the Universe.
If the hydrogen was formed AFTER inflation, than it couldn't be dense in any way. The average density of matter in the observable Universe (a critical density for the closure of the Universe by Friedmann equations) is 5×10--30 gram cm--3 (only 3 atoms per cubic meter).
During the dark ages, the hydrogen fog condensed in certain places, which allowed the formation of stars, black holes and the first galaxies
Such a sparse gas wouldn't condense even in its cold state, not to say about hot gas from preionization (dark ages) period.
Origin
1 / 5 (8) Jun 12, 2012
On the other hand, if the inflation would lead to the hydrogen fluctuations sufficiently inhomogeneous for spontaneous formation of stars and galaxies, then it would failed in its main target, with which it was introduced into cosmology originally - i.e. to explain the uniformity of the Universe observed.
barakn
4.3 / 5 (11) Jun 12, 2012
No one was there to record this supposed event/stage for anyone on earth to know. There is no eye-witness record or any documentation for this. So no one could KNOW such a history as is purported here.

WE are eye-witnesses, you stupid fool. The fog is visible as the CMB.
roboferret
5 / 5 (7) Jun 12, 2012
All observations are about the past. There is not such thing as "current" - there is always some latency due to the speed of light. In astronomy, this can be millions of years. We CAN observe events in the past simply by observing events increasingly far away. This is physics 101 of course. You can present your argument from ignorance however you like, it doesn't stop it being a fundamental fallacy.
Shinichi D_
5 / 5 (5) Jun 12, 2012
On the other hand, if the inflation would lead to the hydrogen fluctuations sufficiently inhomogeneous for spontaneous formation of stars and galaxies, then it would failed in its main target, with which it was introduced into cosmology originally - i.e. to explain the uniformity of the Universe observed.


Things can have patterns and be uniformly smooth at a larger scale in the same time. Think of a zebra. It's got a uniform black and white pattern, but it's not gray.
Up close, the white stripes differ greatly from black ones, but overall the zebra has a uniform colour pattern all over its body.
Terriva
1 / 5 (4) Jun 12, 2012
Think of a zebra.
Nice try, but dense aether model doesn't require the Universe inflate like the zebra - this structure follows from scattering model quite naturally.
MorituriMax
5 / 5 (3) Jun 12, 2012
kevinrtrs,
No one was there to record this supposed event/stage for anyone on earth to know. There is no eye-witness record or any documentation for this. So no one could KNOW such a history as is purported here.

Your own logic applies to the creation of the universe up to the time of adam & eve. Nobody was around to see it. So the Bible cannot document anything before they were supposedly around.

Come to think of it, unless Noah wrote everything down that happened before the flood, there were no witnesses around later to document any of those events in the bible.

The only things known are current, actual observations.

So everything in the Bible is toast. Ain't logic a bitch?
Anda
5 / 5 (3) Jun 13, 2012
Here in Europe, most religious people don't have problems with evolution or the universe being 13 billions years old. They simply say that anyway the universe and life were created by god.
I don't believe in god but I respect their point of view.
So, what is wrong with american creationists? You do have a real problem overseas.
They just think the same as integrist muslims...