Astronomers Now Closer to Understanding Dark Energy

Understanding something we can’t see has been a problem that astronomers have overcome in the past. Now, a group of scientists believe a new technique will meet the challenge of helping to solve one of the biggest mysteries in cosmology today: understanding the nature of dark energy. Using the strong gravitational lensing method — where a massive galaxy cluster acts as a cosmic magnifying lens — an international team of astronomers have been able to study elusive dark energy for the first time. The team reports that when combined with existing techniques, their results significantly improve current measurements of the mass and energy content of the universe.

Using data taken by the Hubble Space Telescope as well as ground-based telescopes, the team analyzed images of 34 extremely distant galaxies situated behind Abell 1689, one of the biggest and most massive known galaxy clusters in the universe.

Through the gravitational lens of Abell 1689, the astronomers, led by Eric Jullo from JPL and Priyamvada Natarajan from Yale University, were able to detect the faint, distant background galaxies—whose light was bent and projected by the cluster’s massive gravitational pull—in a similar way that the lens of a magnifying lens distorts an object’s image.

Using this method, they were able to reduce the overall error in its equation-of-state parameter by 30 percent, when combined with other methods.

The way in which the images were distorted gave the astronomers clues as to the geometry of the space that lies between the Earth, the cluster and the distant galaxies. “The content, geometry and fate of the universe are linked, so if you can constrain two of those things, you learn something about the third,” Natarajan said.

The team was able to narrow the range of current estimates about dark energy’s effect on the universe, denoted by the value w, by 30 percent. The team combined their new technique with other methods, including using supernovae, X-ray galaxy clusters and data from the Wilkinson Microwave Anisotropy Probe (WMAP) spacecraft, to constrain the value for w.

“Dark energy is characterized by the relationship between its pressure and its density: this is known as its equation of state,” said Jullo. “Our goal was to try to quantify this relationship. It teaches us about the properties of dark energy and how it has affected the development of the Universe.”

Dark energy makes up about 72 percent of all the mass and energy in the universe and will ultimately determine its fate. The new results confirm previous findings that the nature of dark energy likely corresponds to a flat universe. In this scenario, the expansion of the universe will continue to accelerate and the universe will expand forever.

The astronomers say the real strength of this new result is that it devises a totally new way to extract information about the elusive dark energy, and it offers great promise for future applications.

According to the scientists, their method required multiple, meticulous steps to develop. They spent several years developing specialized mathematical models and precise maps of the matter — both dark and “normal” — that together constitute the Abell 1689 cluster.

The findings appear in the August 20 issue of the journal Science.

Sources: Yale University, Science Express. ESA Hubble.

10 Replies to “Astronomers Now Closer to Understanding Dark Energy”

  1. This measure the curvature due to dark energy evaluated on the area enclosed by the two paths of an image. The space is flat, for a k = 0 cosmology, and the spacetime has a curavture the describes how the space is stretched apart, or how points of space are accelerated away. The total curvature in the area enclosed by the two paths is analogous to evaluating and electric or magnetic field flux in a region enclosed by a conducting loop.

    Dark energy is not as mysterious as some think. It is due to the quantum vacuum that fills spacetime. Of course having said that the real questions begin: In particular why is is so small and how it fits into something called the gauge Hierarchy problem.

  2. The previous comment is very seriously in breach of the rules for posting comments…. and then there is that crazy “theory”…. ah, well…

  3. Could the higgs field be causing the planck course grainy border, where quantum repulsive cassimir effects surrounding the vacuum pervading the universe, are actually dark energy repulsion? mass increases the shorter is the particle distance from the higgs field, which could be the event horizon of a supermassive feeding black hole that everything is on top of theory. A supercluster or galaxy could actually be closer to the higgs field then our sun or planet, giving it much more energy mass radii to warp space with gravity and have more cassimir dark energy repulsion??

  4. that guys website says the sun is the only star and the universe is the solar system, because a space mirror causing sunspots reflects back our own eye sight perceptions only out to 150 million kilometers similar to mirage using a telescope will distort further. HAH How would it explain new alien planets discovered photographed? My theory is better I hope, it is that Dark Energy has a Density as LC said. I figure DE begins at the higgs field, which surrounds the vacuum of nothing atheism nature little understood because it is not really a nothing universe. outside of nothing vacuum there is the higgs field, where the repulsive force of Dark energy increases as does gravity mass the nearer an accelerating particle approaches it, which is near light speed. As it gains mass approaching near c, its repulsive cassimir force will instantly give it large dark energy and redshift it to farther distances from every point that light must take to travel to that observers frame of referenece with regard to the vacuum of the universe, which incidently, always seems to be a black hole nothing original of course even poplawski stole the idea! Gravity is instantaneous because it is a quantum effect, like a black hole universe gathering dust and light from distances, so the vacuum is a shortcut in space-time that light cannot cross forming particles because of the event horizon and the higgs field!

  5. Interesting. The traditional idea of gravitational lensing was that a dense cluster of mass curved space-time into something approximating a concave lens. Am I right in thinking that dark energy (a replusive and essentially anti-gravity force) should instead create a convex lens – so we get a macro-lens wide field view, rather than magnification?

  6. The physics here is entirely classical. There is nothing involving quantum field theory or the quantization of gravity directly involved. There are also two elements to this. The first is that the gravitational lens is due to a cluster of elliptical galaxies, which is approximated by a spherical distribution of matter. As Steve Nerlich indicates, this is similar to a concave lens in optics. The gravity field is a curvature of spacetime in such as way that diverging rays of light are focused back after passing near this source of gravitation. This is no different from the apparent change in the position of a star measured by Eddington in the 1919 confirmation of general relativity. There is then a secondary effect, which is how the expansion of the universe plays a role here. There is a curvature of spacetime for the entire universe, and this curvature is measured as a field measured on the area enclosed by the two paths of light from the source. This secondary part with the expansion of the universe requires a bit of explanation.

    Think of the curvature of the universe as being similar to a vector field of some type, which we will call V. The optical paths from the distant source start from the same point and diverge with some small angle. These light rays are then refocused by the intervening galaxy cluster. There are then two paths that share the same point of origin and reconnect at our telescope. These two paths enclose some area of spacetime. This is spacetime because the distant galaxy source is far back in time. So this vector V pierces the area enclosed by the two light rays, and there is a curvature flux Q = V*A. This paper discusses a measurement of this flux. How this is calculated in detail requires some detailed knowledge of general relativity, but this curvature “vector field” V and the area A can be computed from data. So this flux is something which contributes to the Einstein lensing of the elliptical galaxy cluster.

    Now the next thing to discuss is some qualitative physics of this cosmological contribution. The question is whether this is anti-gravity. Strictly speaking it is not anti-gravity as such, though it is similar. Anti-gravity involves the defocusing of geodesic paths due to a negative energy of some gravity field or spacetime curvature. The eternal inflation of the universe is this accelerated motion of galaxies apart from each other. This is a type of defocusing, but it is not due to a negative energy. It is due to a negative pressure. The Einstein field equation is written for illustrative purposes G_{aa} = T_{aa}, “curvature = gravity source,” where I have assumed a diagonal form where the indices a run from 0 for time and a = 1, 2, 3 (denoted by i) for space. The time-time part of this is G_{00} = T_{00}, and the T_{00} is the energy density contribution we call rho. This is positive, and so there is no negative energy usually associated with so called anti-gravity. However, the spatial part G_{ii} = T_{ii} has the T_{ii} = p_i. for p_i a pressure. The equation of state is

    p_i =w*rho

    and for the de Sitter vacuum or cosmology w = -1. So there is a curious negative pressure. Now this curvature part G_{00} and G_{ii} define that vector above V. The G_{00} is larger, and in fact larger by a multiplicative factor of the speed of light. So the cosmological curvature has a focusing effect on the light rays. This in spite of the fact the negative pressure term forces points in space, and matter particles on these points, to accelerate away from each other.

    The suggestion is raised this somehow involves a Casimir effect. In a broad sense this is correct, for the energy density rho above is due to a quantum vacuum in the universe. This aspect of the physics does not contribute in detail to the calculation above, for the rho is input from measurements of the cosmological constant to compute expected outcomes which are compared with data. So this is a measurement of classical spacetime curvature on a cosmological scale. The source of that cosmological curvature is due to some deeper physics with the quantum vacuum and how conformal quantum field theories are associated with cosmological quantum gravity.


  7. As An Aside:

    The website looks great. The text is big, the hyperlinks are distinctive, the captions are blue and italics, and the boxes in the comment section are right on.

    Well done.

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