Astronomers Discover Ancient ‘Ultra-Red’ Galaxies

Article written: 2 Dec , 2011
Updated: 26 Apr , 2016

[/caption]A team of astronomers, led by Jiasheng Huang (Harvard-Smithsonian Center for Astrophysics) using the Spitzer Space Telescope, have discovered four ‘Ultra-Red’ galaxies that formed when our Universe was about a billion years old. Huang and his team used several computer models in an attempt to understand why these galaxies appear so red, stating, “We’ve had to go to extremes to get the models to match our observations.”

The results of Huang’s research were recently published in The Astrophysical Journal

Using the Spitzer Space Telescope helped make the discovery possible, as it is more sensitive to infrared light than other space telescopes such as the Hubble. The newly discovered galaxies are sixty times brighter in the infrared than they are at the longest/reddest wavelengths HST can detect.

What processes are at work to create these extremely red objects, and why are they of interest to astronomers?

There are several reasons a galaxy could be reddened. For starters, extremely distant galaxies can have their light “redshifted” due to the expansion of the universe. If a galaxy contains large amounts of dust, it will also appear redder than a galaxy with less dust. Lastly, older galaxies will tend to be redder, due to a higher concentration of old, red stars and less younger bluer stars.

According to the paper, Huang and his team created three models to determine why these galaxies appear so red. Of their models, the one which suggests an old stellar population is currently the best fit to the observations. Supporting this conclusion, co-author Giovanni Fazio stated, “Hubble has shown us some of the first protogalaxies that formed, but nothing that looks like this. In a sense, these galaxies might be a ‘missing link’ in galactic evolution”.

Studying these extremely distant galaxies helps provide astronomers with a better understanding of the early universe, specifically how early galaxies formed and what conditions were present when some of the first stars were created. The next step in understanding these “ERO” galaxies is to obtain an accurate redshift for the galaxies, by using more powerful telescopes such as the Large Millimeter Telescope or Atacama Large Millimeter Array.

Huang and his team have plans to search for more galaxies similar to the four recently discovered by his team. Huang’s co-author Giovanni Fazio adds, “There’s evidence for others in other regions of the sky. We’ll analyze more Spitzer and Hubble observations to track them down.”

If you’d like to learn more, you can access the full paper (via at:

Source: Harvard-Smithsonian Center for Astrophysics press release ,


6 Responses

  1. Richard Summers says

    If these galaxies appear as they would a “mere” 1 billion years after the Big Bang, would that be sufficient time to have “older stellar populations” accrue? Perhaps the implication here, if this model seems appropriate, supports the notion that early universe stellar life cycles were vastly more compact than now, 13 billion odd years later.

  2. Anonymous says

    Well asked, Richard! Nothing like finding a gigantic hole in the information as printed. Very young, new galaxy all red with ancient stars? Of course the scientists involved had to think of that simple argument. Maybe it is a mistake in the translation. Seems like a theory made to fit the view.

    • Torbjörn Larsson says

      Um, what prompted that inference of “holes”? People have been looking for the first generation stars for a long time:

      “Soon after the Big Bang, without metals, it is believed that only stars with masses hundreds of times that of the Sun could be formed; near the end of their lives these stars would have created the first 26 elements up to iron in the periodic table via nucleosynthesis.[3]

      Because of their high mass, current stellar models show that Population III stars would have soon exhausted their fuel and exploded in extremely energetic pair-instability supernovae. Those explosions would have thoroughly dispersed their material, ejecting metals throughout the universe to be incorporated into the later generations of stars that are observed today. The high mass of the first stars is used to explain why, as of 2010, no Population III stars have been observed. Because they were all destroyed in supernovae in the early universe, Population III stars should only be seen in faraway galaxies whose light originated much earlier in the history of the universe, and searching for these stars or establishing their nonexistence (thereby invalidating the current model) is an active area of research in astronomy.”

      So this is no new theory nor an idle speculation that stars, like the first stars, could grow old quickly. The “hole in the information” seems to be on your part =D, or possibly the article that keeps a low profile on exactly what the result means.

      Also, you touch on one of my pet peeves. Even if this would have been an ad hoc hypothesis, there is nothing inherently wrong with that. It is a start of a process that eventually results in hypotheses that connect with earlier theory as it always have done.

  3. Torbjörn Larsson says

    So is this informative on, or observations of, the often mentioned first population of stars?

    • magnus.nyborg says

      I wouldnt jump to any conclusion, but one of the possibilities includes Dark-Matter stars, wich would be large stars fueled by dark-matter annihilation, with no or very little hydrogen fusion in the core . These stars would be much larger and cooler than ‘normal’ stars of the same mass, and as the dark-matter is consumed they gradually would turn into ‘normal’ pop III stars. Speculative, but it has at times been considered as a possibility.

      Many huge ultraluminous red stars in a young galaxy would make it appear redder. I would await more evidence though.

  4. Adam Kendall says

    Slightly unrelated comment, but does anyone know of a cheap, or free, way to access the Astrophysical Journal without being a university student?

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