Gravitational Lensing Brings Dark Energy Into Focus

By Andrew Moseman | August 20, 2010 11:43 am

Galaxy Cluster Abell 1689One of the top three priorities for the next decade of astrophysics and astronomy, we noted this week, is unraveling dark energy, the weird force that pushes the universe apart. Given that scientists know next-to-nothing about dark energy—besides the fact that it makes up most of the universe—any step could be an important one. Thanks to a study out this week in Science, astrophysicists at least can have more confidence in this phenomenon that can’t be directly seen or measured: Their estimates for dark matter’s extent appear to be on target.

The technique scientists used in this study is called gravitational lensing, and the lens in this case is a huge galactic cluster called Abell 1689.

Because of its huge mass, the cluster acts as a cosmic magnifying glass, causing light to bend around it. The way in which light is distorted by this cosmic lens depends on three factors: how far away the distant object is; the mass of Abell 1689; and the distribution of dark energy [BBC News].

Gravitational lensing is a trick predicted by Einstein’s general relativity, and scientists have used it before to study dark matter (which tends to be a little easier to study than its dark counterpart). But study author Priyamvada Natarajan and her colleagues got such great images from the Hubble Space Telescope that they were able to map out the dark energy distribution.

Natarajan and her colleagues carefully measured the way each image was distorted to determine how far the background galaxies were from the lens. They then combined that information with data on how far the galaxies are from Earth to come up with a parameter that describes the density of dark energy in the universe, and how the density changes with time. “Knowing exactly where the object is, and knowing about the big lump that is causing the bumps in space-time, allows us to accurately calculate the light path,” Natarajan said. “The light path depends on geometry of space-time, and dark energy manifests itself there. That’s how we get at it” [].

The importance of Natarajan’s paper is that it backed up the earlier estimates for the matter vs. energy density of the universe by providing a robust independent measure. Specifically, the study found that the matter density of the universe is about 0.3, reinforcing the idea that dark energy constitutes nearly three-quarters of everything that is.

It’s not clear yet whether having a more refined measure of its presence will bring us any closer to identifying the properties of dark energy, but the fact that it shows up as a consistent value in a number of independent measures suggests that it may not be as mysterious as its name implies [Ars Technica].

So we can breathe a little easier that all that dark energy is really out there—just as long as we can deal with the sting of more cosmic insignificance. Dark energy is thought to comprise 72 percent of the universe and dark matter makes up another 24 percent; that means that the matter making up you and me accounts for only 4 percent of the universe.

Related Content:
80beats: Astronomers Announce Priorities: Dark Energy, Exoplanets, Cosmic Origins
80beats: Galaxy Clusters Stunted by Gravity’s Bizarro Twin: Dark Energy
Cosmic Variance: Dark Energy: No Longer a Surprise
Cosmic Variance: The Next 10 Years of Astronomy

Image: NASA‐ESA, Jullo, Natarajan, Kneib

  • Dr. Edward Henry Dowdye, Jr.

    Subject: Significant Findings: No direct interaction between light and
    gravity in empty vacuum space

    Dear Fellow Researchers:

    There’s not a shred of evidence for a direct interaction between light and gravity in the empty vacuum space just above the plasma rim of the sun; a direct counter to the light bending theory of General Relativity

    Recent findings in observational Astrophysics convincingly show that the important fundamentals of Mathematical Physics and astrophysical observations have been incorrectly applied to the so-called gravitational lenses. Since the discovery of solar light bending, researchers have always assumed that gravitational lenses are due to a direct interaction between light and gravity. Historically, astronomers have noted that light rays from stars that pass near the plasma rim of the sun appear to deviate from their linear trajectories. The astronomical observations reveal that the effects of the gravitational field of the sun on the rays of light from the stars have been due to an indirect interaction between light and gravity and not due to direct interaction. An application of Gauss’ law that encloses the gravitating mass of the sun inside of an analytical Gaussian sphere shows that a direct interaction between the gravitational field of the sun and the rays of light from the stars in empty vacuum space just slightly above the solar plasma rim does not take place. A recent press release:


    A paper on this subject has been published in the renown refereed journal Astronomische Nachrichten, “Time resolved images from the center of the Galaxy appear to counter General Relativity”, Dowdye, Jr., E.H., Astronomische Nachrichten, 328, Issue 2, 2007, pp 186 -191

    Comments and Feedback are welcome.

  • Richard

    It would seem that dark energy and dark matter would be the aftermath of the big bang when matter and anti-matter collided. As they canceled each other they left a footprint and the 4% of matter that was more matter than anti-matter is confirmed. Maybe we should look at the universe as a bubble structure along the string where a matter anti-matter string touch.

    Richard L Erickson, PhD

  • Anders Feder

    “Gravitational lensing is a trick predicted by Einstein’s general relativity, and scientists have used it before to study dark matter (which tends to be a little easier to study than its dark counterpart). ”

    Do you mean “energy counterpart”?

  • ChH

    “… the fact that [dark energy] makes up most of the universe …”

    The point of the article is that we now have a little more evidence in the existance of dark energy, yet it referred to as a fact? How about “other than that it theoretically makes up most of the universe…”

    It looks to me that dark matter & energy are merely fudge factors to account for observation and theory not matching.

  • Brian Too

    @4. ChH,

    I tend to agree. It takes chutzpa to claim that these things are experimentally proven. They are merely asserted.

    We’re not the only one to be sceptical. Lee Smolin has issues with the way that certain edgy hypotheses are regularly referred to as though they have entered the territory of widely accepted theories:

    Among these hypotheses that have precious little evidence to back them up: Dark Matter, Dark Energy, String Theory. What is worse is that, when pressed, nearly everyone agrees that not only are these not proven, they may not be provable at all, ever!

    All you need to know about DM & DE is contained in the phrase “…this phenomenon that can’t be directly seen or measured”.

    I’ve said it before. If you believe in unobservable phenomena, then I have some unobservable Yetis, leprechauns, and snerts that you’re gonna just love!

  • ChH

    Brian Too, I saw a snert once. At least it looked like a snert. I’ve also had gold coins disappear.

    But I’ve never seen dark matter or dark energy – apparently because it is unobservable by its nature.

  • Brian Too

    OK, now I’ve been thinking about this. Is it possible to draw any parallels with certain quantum phenomena? I’m thinking about quarks in particular, which I’m given to understand have been inferred to exist via some pretty esoteric particle collider results. In other words, they may not have been directly observed either.

    So here’s my question. What is the standard of evidence, before a hypothesis becomes a theory? I mean, quarks are widely accepted to exist, right? And yet, I am still skeptical of DM & DE which is asserted to comprise the majority of everything, and yet is unobservable.

    I assert that Occam’s razor points to simpler answers than inventing an unobservable “something” that we call “dark” because, quite honestly, science does not have a clue on the issue. Science has experienced unexplained phenomena before, many times. It’s more honest to say “we don’t know” than it is to say “Dark Matter. Take it to the bank. Dark Energy. Count on it.”

    Hey, I’m willing to give the scientists some time. They deserve that much. However if there’s no direct experimental evidence in 50 years (maybe that should be 20), then DM & DE is going to be properly viewed as a house of cards.

  • Pachomius

    And some skeptics who claim science as their heirloom speak so confidently of the empirical evidence supporting the existence of dark matter and dark energy.

    They ironically forget their skepticism.



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