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Astronomers Find 90% More Universe!

The GOODS South Field. ESO/M. Hayes

Astronomers have long known that many surveys of distant galaxies miss 90% of their targets, but they didn’t know why. Now, astronomers have determined that a large fraction of galaxies whose light took 10 billion years to reach us have gone undiscovered. This was found with an extremely deep survey using two of the four giant 8.2-meter telescopes that make up ESO’s Very Large Telescope (VLT) and a unique custom-built filter. The survey also helped uncover some of the faintest galaxies ever found at this early stage of the Universe.

Astronomers frequently use the strong, characteristic “fingerprint” of light emitted by hydrogen known as the Lyman-alpha line, to probe the amount of stars formed in the very distant Universe Yet there have long been suspicions that many distant galaxies go unnoticed in these surveys. A new VLT survey demonstrates for the first time that this is exactly what is happening. Most of the Lyman-alpha light is trapped within the galaxy that emits it, and 90% of galaxies do not show up in Lyman-alpha surveys.

“Astronomers always knew they were missing some fraction of the galaxies in Lyman-alpha surveys,” explains Matthew Hayes, the lead author of the paper, published this week in Nature, “but for the first time we now have a measurement. The number of missed galaxies is substantial.”

To figure out how much of the total luminosity was missed, Hayes and his team used the FORS camera at the VLT and a custom-built narrowband filter to measure this Lyman-alpha light, following the methodology of standard Lyman-alpha surveys. Then, using the new HAWK-I camera, attached to another VLT Unit Telescope, they surveyed the same area of space for light emitted at a different wavelength, also by glowing hydrogen, and known as the H-alpha line. They specifically looked at galaxies whose light has been traveling for 10 billion years (redshift 2.2), in a well-studied area of the sky, known as the GOODS-South field.

“This is the first time we have observed a patch of the sky so deeply in light coming from hydrogen at these two very specific wavelengths, and this proved crucial,” said team member Goran Ostlin. The survey was extremely deep, and uncovered some of the faintest galaxies known at this early epoch in the life of the Universe. The astronomers could thereby conclude that traditional surveys done using Lyman-alpha only see a tiny part of the total light that is produced, since most of the Lyman-alpha photons are destroyed by interaction with the interstellar clouds of gas and dust. This effect is dramatically more significant for Lyman-alpha than for H-alpha light. As a result, many galaxies, a proportion as high as 90%, go unseen by these surveys. “If there are ten galaxies seen, there could be a hundred there,” Hayes said.

Different observational methods, targeting the light emitted at different wavelengths, will always lead to a view of the Universe that is only partially complete. The results of this survey issue a stark warning for cosmologists, as the strong Lyman-alpha signature becomes increasingly relied upon in examining the very first galaxies to form in the history of the Universe. “Now that we know how much light we’ve been missing, we can start to create far more accurate representations of the cosmos, understanding better how quickly stars have formed at different times in the life of the Universe,” said co-author Miguel Mas-Hesse.

The breakthrough was made possible thanks to the unique camera used. HAWK-I, which saw first light in 2007, is a state-of-the-art instrument. “There are only a few other cameras with a wider field of view than HAWK-I, and they are on telescopes less than half the size of the VLT. So only VLT/HAWK-I, really, is capable of efficiently finding galaxies this faint at these distances,” said team member Daniel Schaerer.

Read the team’s paper.

Source: ESO


Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • Aqua March 25, 2010, 11:16 AM

    Signed… ahem.. an unemployed engineer looking for something to do.

  • santafedog March 25, 2010, 11:53 AM

    Now i’m having these weird visualizations of the universe. I know mathematically it is a plane, but physically i still see it as a sphere of higher mass around scattered galaxies being dragged outward by the shell and that the shell could be accelerating the stragglers rather than all that dark energy/dark mass.

  • Duncan Ivry March 25, 2010, 1:11 PM

    Uncle Fred: “How far do we have to look to find it?”

    … or how acute do we have to look? We have so much data already and will get so much more in the future. The wood and the trees, you know.

  • Greg March 25, 2010, 1:46 PM

    Wow, It looks like we may have found that missing baryonic matter. Dark matter is only peripherally related to this discovery, so no this does not in any way negate dark matter theory.
    Very timely work. This finding will have a huge impact on studies of the early universe. I wonder whether there are differences in the type of early galaxies that are Lyman emitters and those which are not. My guess is that the non Lyman emitters are larger since they must have enough material to obscure this emission line. I also think that the earliest smaller galaxies will are more likely to be Lyman emitters.

  • bugz March 26, 2010, 3:21 AM

    Very cool stuff. What if they keep searching further back and find George Burns sitting in a chair overacting? That would be pretty trippy.

  • Aodhhan March 26, 2010, 5:15 AM

    Pretty good analogy.

    We now have the technology to see more things, or to see further back in time, than ever before.

    There isn’t more dark matter, or anything else.

    The emphasis of this article is to show how the team was able to capture photons from star forming regions in the early universe, many billons of years ago.
    It never intended to state they found more matter or objects which nobody knew existed.

    The 90% comes from the fact the team is demonstrating that 90% of star forming regions emit Lyman-a. This by no means equates to 90% more universe. So the heading of this article is a bit misleading.

    The exact amount of galaxies / star forming regions they are finding isn’t exactly known, as there are error factors they must work through, and other complications such as dust…which affects luminosity. Right now, their model predictions represent 68% confidence.

  • Jean Tate March 26, 2010, 5:28 AM


    No, the mass of the Milky Way which is comprised of baryons is well-understood and well-constrained.

    There certainly are forms of baryonic mass in our galaxy which are extremely hard to see – such as ‘space rocks’, free-floating planets, etc in the halo – but there are strong upper bounds on the total mass in such forms.

  • RUF March 27, 2010, 4:04 PM

    About the photo:

    There are a few really red spiral-looking galaxies in the center (and center-left). I wonder if these were the 10 Gya galaxies targeted for a closer look.

  • n1gm4t1c March 30, 2010, 11:31 PM

    We Should Dismiss “Dark matter” and M-Theory.
    Written by P.Martone

    For decades Science has been unable to accurately explain where 90% of the mass in the Universe is. Cosmologists and Theoretical Quantum Physicists have developed one elaborate theory after another to compensate for this “missing” mass. With a simple change in how we observe the Universe it has been revealed that for decades we simply did not perceive 90% of the energy emitted by these “missing Galaxies, gas and dust clouds” with mass that “Dark Matter” and “M-Theory” (A function of String Theory) were substitutes for. With these “missing” Galaxies, gas and dust clouds now observable, we can lay down complex, abstract and incorrect theories that fail to accurately model the Mechanical Universe.
    This underscores a fundamental flaw in Physics. The flaw is a lack of understanding of how and why gravity works. Gravity as a force has been identified, measurements made and accurate predictions of its effect(s) have been developed. Because of this we keep making a fundamental mistake that has ramifications in Science and Academia. We allow side stepping of the fact that we do not have a full and complete understanding of gravity and why it works and emphasize only that it works, allowing Scientists to postulate one wrong theory after the other and incorporate them into our collective (mis)understanding of the Universe.