A Star-Making Blob from the Cosmic Dawn

Article written: 21 Dec , 2011
Updated: 24 Dec , 2015


Looking back in time with some of our best telescopes, astronomers have found one of the most distant and oldest galaxies. The big surprise about this blob-shaped galaxy, named GN-108036, is how exceptionally bright it is, even though its light has taken 12.9 billion years to reach us. This means that back in its heyday – which astronomers estimate at about 750 million years after the Big Bang — it was generating an exceptionally large amount of stars in the “cosmic dawn,” the early days of the Universe.

“The high rate of star formation found for GN-108036 implies that it was rapidly building up its mass some 750 million years after the Big Bang, when the Universe was only about five percent of its present age,” said Bahram Mobasher, from the University of California, Riverside. “This was therefore a likely ancestor of massive and evolved galaxies seen today.”

An international team of astronomers, led by Masami Ouchi of the University of Tokyo, Japan, first identified the remote galaxy after scanning a large patch of sky with the Subaru Telescope atop Mauna Kea in Hawaii. Its great distance was then confirmed with the W.M. Keck Observatory, also on Mauna Kea. Then, infrared observations from the Spitzer and Hubble space telescopes were crucial for measuring the galaxy’s star-formation activity.

“We checked our results on three different occasions over two years, and each time confirmed the previous measurement,” said Yoshiaki Ono, also from the of the University of Tokyo.

Astronomers were surprised to see such a large burst of star formation because the galaxy is so small and from such an early cosmic era. Back when galaxies were first forming, in the first few hundreds of millions of years after the Big Bang, they were much smaller than they are today, having yet to bulk up in mass.

The team says the galaxy’s star production rate is equivalent to about 100 suns per year. For reference, our Milky Way galaxy is about five times larger and 100 times more massive than GN-108036, but makes roughly 30 times fewer stars per year.

Astronomers refer to the object’s distance by a number called its “redshift,” which relates to how much its light has stretched to longer, redder wavelengths due to the expansion of the universe. Objects with larger redshifts are farther away and are seen further back in time. GN-108036 has a redshift of 7.2. Only a handful of galaxies have confirmed redshifts greater than 7, and only two of these have been reported to be more distant than GN-108036.

About 380,000 years after the Big Bang, a decrease in the temperature of the Universe caused hydrogen atoms to permeate the cosmos and form a thick fog that was opaque to ultraviolet light, creating what astronomers call the cosmic dark ages.

“It ended when gas clouds of neutral hydrogen collapsed to generate stars, forming the first galaxies, which probably radiated high-energy photons and reionized the Universe,” Mobasher said. “Vigorous galaxies like GN-108036 may well have contributed to the reionization process, which is responsible for the transparency of the Universe today.”

“The discovery is surprising because previous surveys had not found galaxies this bright so early in the history of the universe,” said Mark Dickinson of the National Optical Astronomy Observatory in Tucson, Ariz. “Perhaps those surveys were just too small to find galaxies like GN-108036. It may be a special, rare object that we just happened to catch during an extreme burst of star formation.”

Sources: Science Paper by: Y. Ono et al., Subaru , Spitzer Hubble

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4 Responses

  1. Anonymous says

    I am curious to know how easily we can test whether this is brighter than its contemporaries because somehow light from it has passed through less pre-reionizd universe. I’d *like* this thing to be bright of its own accord, but I don’t know that it is.

    • Torbjörn Larsson says

      I was thinking much the same thing, maybe a random outcome.

      But maybe the idea is something like this: reionization was pretty much uniform since matter was, pretty much (see the CMB data). So if there were clear patches, something else must have reionized more efficiently. So the easiest consistent choice would be that we see what we see.

    • magnus.nyborg says

      The spectra should tell to some degree how much of the original light has been absorbed by intervening neutral gas compared to other similarily located galaxies. Not sure if this comparison have been done, but if the spectra does not show differences in absorbtion then this galaxy probably is extra luminous.

  2. Anonymous says

    The Lyman-alpha line is a transition from the n = 2 to n = 1 orbital in the Rydberg levels of the hydrogen atom. The photons emitted are ? = 121. nm wavelength which puts them in the UV domain of the EM spectrum. The galaxy observed here is at z ~ 7, where the redshifting is (z – 1)? ~ 726nm, which is in the red color domain of the optical spectrum. The image appears to corectly show the “true colors.” Also consider that this galaxy is moving out at 7 times the speed of light. This motion is due to the dynamics of space itself, which permits this sort of thing to happen. Also this motion does not involve bodies moving past each other or interacting directly (collisions etc) at these speeds.

    This paper does not appear to mention PopIII stars, but I suspect that is what populates this early galaxy. There is probably some distribution of matter clumping, or caustic focusing of relatistics particles in the earlier universe, where this represents a highly concentrated gravitational accretion of hydrogen.


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