Small, but plentiful: How the faintest galaxies illuminated the early universe

How the faintest galaxies illuminated the early universe
A view of the entire simulation volume showing the large scale structure of the gas, which is distributed in filaments and clumps. The red regions are heated by UV light coming from the galaxies, highlighted in white. These galaxies are over 1000 times less massive than the Milky Way and contributed nearly one-third of the UV light during re-ionisation. The field of view of this image is 400,000 light years across, when the universe was only 700 million years old. Credit: John Wise

( —Astronomers investigating behaviour of the universe shortly after the Big Bang have made a surprising discovery: the properties of the early universe are determined by the smallest galaxies. The team report their findings in a paper published today in the journal Monthly Notices of the Royal Astronomical Society.

Shortly after the Big Bang, the was ionised: ordinary matter consisted of hydrogen with its positively charged protons stripped of their negatively charged electrons. Eventually, the universe cooled enough for electrons and protons to combine and form neutral hydrogen. This cool gas will eventually form the first stars in the universe but for millions of years, there are no stars. Astronomers therefore aren't able to see how the cosmos evolved during these 'dark ages' using conventional telescopes. The light returned when newly forming stars and galaxies re-ionised the universe during the 'epoch of re-ionisation'.

Astronomers agree that the universe became fully re-ionised roughly one billion years after the Big Bang. About 200 million years after the birth of the cosmos, ultraviolet (UV) radiation from stars began to split neutral hydrogen into electrons and protons. It took another 800 million years to complete the process everywhere. This epoch of re-ionisation marked the last major change to gas in the universe, and it remains ionised today, over 12 billion years later.

However, astronomers aren't in agreement on which type of galaxies played the most important role in this process. Most have focused on large galaxies. The new study by researchers at the Georgia Institute of Technology and the San Diego Supercomputer Center indicates scientists should also focus on the smallest ones.

A rendering of a simulation that follows the formation of the first galaxies in the universe. The field of view is adjusted to account for the expansion of the universe, where the scale bar represents 32,600 light-years (10,000 parsecs). The video shows hot and ionised gas in blue, and cold and neutral gas in red. The intensity of each pixel is set by the gas density, and the stars are not shown in this visualisation. The video runs from 200 million to 800 million years after the Big Bang. Credit: John Wise, Matthew Turk, Michael Norman, Tom Abel, Britton Smith

The researchers used computer simulations to demonstrate the faintest and smallest galaxies in the early universe were essential. These tiny galaxies – despite being 1000 times smaller in mass and 30 times smaller in size than our own Milky Way galaxy – contributed nearly 30 percent of the UV light during this process.

Other studies often ignore these small 'dwarf' galaxies as they weren't thought to form stars, because the UV light from nearby larger galaxies was too strong and suppressed these tiny neighbours.

"It turns out these did form stars, usually in one burst, around 500 million years after the Big Bang," said Prof. John Wise, of the Georgia Institute of Technology, who led the study. "The galaxies were small, but so plentiful that they contributed a significant fraction of UV light in the re-ionisation process."

The team's simulations modelled the flow of UV stellar light through the gas within galaxies as they formed. They found that the fraction of ionizing photons escaping into intergalactic space was 50 percent in small galaxies (more than 10 million solar masses). It was only 5 percent in larger galaxies (300 million solar masses). This elevated fraction, combined with their high abundance, is exactly the reason why the faintest galaxies play an integral role during re-ionisation.

"It's very hard for UV light to escape galaxies because of the dense gas that fills them," said Wise. "In small galaxies, there's less gas between stars, making it easier for UV light to escape because it isn't absorbed as quickly. Plus, supernova explosions can open up channels more easily in these tiny galaxies in which UV light can escape."

How the faintest galaxies illuminated the early universe
A zoomed-in view of the most massive dwarf galaxy in the simulation, seen when the universe was only 700 million years old. This galaxy only has 3 million solar masses of stars, compared to 60 billion solar masses in our Milky Way. The yellow points represent the older and cooler stars in the galaxy, and the blue points show the young and massive stars forming just before this snapshot of the simulation. The haze around the stars show the gas distribution in the galaxy with blue and red representing hot and cold temperatures, respectively. Credit: John Wise

The team's simulation results provide a gradual timeline that tracks the progress of re-ionisation over hundreds of millions of years. About 300 million years after the Big Bang, the universe was 20 per cent ionised. It was 50 per cent at 550 million years. The simulated universe was fully ionised at 860 million years after its creation.

"That such could contribute so much to re-ionisation is a real surprise," said Prof. Michael Norman, of the University of California San Diego and one of the co-authors of the paper. "Once again, the supercomputer is teaching us something new and unexpected; something that will need to be factored into future studies of re-ionisation."

The research team expects to learn more about these faint when the next generation of telescopes is operational. For example, NASA's James Webb Space Telescope, scheduled to launch in 2018, will be able to see them.

Explore further

Astronomers use Hubble to study bursts of star formation in the dwarf galaxies of the early Universe

More information: his research has been published in Wise J. el al., "The Birth of a Galaxy - III. Propelling reionisation with the faintest galaxies", Monthly Notices of the Royal Astronomical Society, in press, published by Oxford University Press. A preprint of the paper is available.
Citation: Small, but plentiful: How the faintest galaxies illuminated the early universe (2014, July 7) retrieved 17 September 2019 from
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Jul 07, 2014
Not surprising. Large galaxies grew by merger and cannibalism. Everything started small. Light from single candle in the dark void would go a long way.

Jul 07, 2014
The surprising (for proponents of Big Bang model) rather is, that the distant areas of universe do contain relatively larger galaxies, than these close ones. Apparently the computer simulations don't play well with observations of reality there.

Jul 07, 2014
This controversy becomes even more striking, if we realize, that in Big Bang model the Universe is supposed to expand, so that more distant galaxies should appear relatively smaller even if they wouldn't grow from scratch by accretion. Actually, most of these distant galaxies shouldn't be even visible, because their luminosity curve would cease down with metric expansion too, as the light of distant galaxies gets diluted in smaller volume of expanding space, than this one of nearby ones. Another problem arises with mutual relative distance of galaxies, which should be relatively smaller in distant tightly packed Universe, but - well - it isn't again. These problems are all ignored silently for not to threat the income and social credit of contemporary theorists - and the people who are rising them are labelled as crackpots. Did the situation with science really changed so much from medieval times?

Jul 07, 2014
I'm always amazed at how these simulations are able to lead to "greater insight into the birth of the universe".
What amazes me is that there are some really fundamental questions that are still unanswered and that are simply being ignored in all of the cosmogony so far.
The issue of how it is that the big bang delivered Hydrogen atoms but the corresponding anti-matter cannot be found is still an open question.
Furthermore, a little deeper into the theory, all and sundry glibly speak of the formation of stars and galaxies, but no one has so far delivered any plausible explanation of the actual mechanisms through which the first star (s) formed without any outside intervention.
The physics required for star formation simply defies any unassisted ignition, no matter the density of the gases reached in space.
Current star formation theories ALWAYS assume or require the pre-existence of another star!
Without star-formation, no galaxies can form. Or planets.
Just pointing out the flaws.

Jul 07, 2014
Just pointing out the flaws.

Are you that proud of them Skippy?

Jul 07, 2014
At least he stopped at just a couple. The list is long.....

Sounds like you and the John-Skippy have more than just the couple of the flaws in common. You two go to the same flawed school Cher?

Jul 07, 2014
mumble mumble skippy mumble babble mumble cher?

mumble mumble the google babble ol ira.

That makes more sense than all that magnets ruling the universes stuffs. You been studying Cher?

Jul 08, 2014
Sorry - there was No Big Bang. It is a myth.

Jul 08, 2014
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Jul 08, 2014
"...everything beyond our local group is redshifted..."

Uh, unless we look at the Virgo cluster:


In fact the two most *blue-shifted* galaxies known, VCC 846 & VCC 815, are members of the Virgo cluster:


And let's not forget the recently discovered globular cluster in the Virgo cluster(HVGC-1) with the largest measured blue shift in that cluster:


"....i apologize to God for doubting his abilities...."

You need to apologize to the authors of the papers I linked to above for making such a foolish statement as "everything beyond our local group is redshifted", for starters.

Jul 09, 2014
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Jul 09, 2014
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Jul 09, 2014
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Jul 09, 2014
So Dark matter, Dark energy and Black Holes are evidence of intelligent people making mistakes or idiots forging ahead?
@no fate
it is proof that science is exploring all the available options and trying to find the best fit for the observations...

UNLIKE the creationist attempts to mold reality to the sky-fairy tale or the attempt to manipulate data to prove a philosophy or religion.
THAT is proof of idiots forging ahead attempting to convince the uneducated of their superiority.

the problem with that is... the uneducated can eventually be educated... so their attempts are only bound to fail, unless they also plan to take over the world and force their viewpoint on others, like say... in an Inquisition or Holy War

Jul 09, 2014
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Jul 09, 2014
When an article states " because we can only see 25% of the matter in the universe" everything after that is a theory based on a hypothesis, they don't KNOW what they claim to, they have to find the 75% they claim is missing first.
@no fate
not true.
we don't have oceans creating pressure over our heads right now, but the physics that we use to describe what is going on at the ocean's bottom is just as accurate here as there... same thing about the universe.
We may not know what the other "75%" (per your post) is, BUT we know a whole LOT about that stuff we DO see, and what we know is that our modern laws of physics are pretty darn accurate


Jul 09, 2014
History is repleat with examples of the human race assuming they know how it is until physical reality demonstrates differently
[sic]and science is replete with observations that bear out as well.
History is NOT the same thing as SCIENCE. Your example is not relevant as argument because they did NOT use the scientific method either.
How many 2000 year old philosophers actually verified their findings with empirical data and put something into orbit to prove it? (this is not just exaggeration, but a cogent point)

as for your remarks about gravity...
the issue is under investigation and the theory changes with empirical data. THAT is what is so great about science. You infer that we are NOT investigating other options about gravity, but you are mistaken if that is what you are really trying to say.

Your point above about Flat earth etc? it only PROVES that the scientific method really does work well.
by the way... I find it hard to believe any sailor agreed with flat earth

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