The Hubble Space Telescope image of the inner regions of the lensing cluster Abell 1689 that is 2.2 billion light?years away. Light from distant background galaxies is bent by the concentrated dark matter in the cluster (shown in the blue overlay) to produce the plethora of arcs and arclets that were in turn used to constrain dark energy. Image courtesy of NASA?ESA, Jullo (JPL), Natarajan (Yale), Kneib (LAM)
In many fields of science, dark energy is theorized form of energy that permeates space. It is the energy that is thought to explain the observed increase in the acceleration of the expansion of the universe. In the standard model of cosmology dark energy accounts for 74% of the total mass/energy of the universe.
Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space evenly, and scalar fields like quintessence and moduli which are dynamic quantities(energy varies) in time and space. Contributions from scalar fields can be constant and are part of the cosmological constant. The cosmological constant is physically equivalent to vacuum energy. Scalar fields which change in space can be difficult to distinguish from the cosmological constant because the change may be extremely slow.
As evidence of dark energy, scientists point to supernovae and the cosmic background radiation. Published observations of supernovae have suggested that the expansion of the universe is increasing. These observations have been corroborated by several independent sources. Supernovae are useful for cosmology because they are excellent standard candles.. They allow the expansion history of the Universe to be measured by looking at the relationship between the distance to an object and its redshift. The relationship is roughly linear. It is relatively easy to measure redshift, but finding the distance to an object is more difficult. Usually, astronomers use objects for which the absolute magnitude is known(standard candles). This allows the object’s distance to be measured from its apparent magnitude. Type Ia supernovae are the best-known standard candles across cosmological distances because of their extreme, consistent, brightness. Recent observations of supernovae are consistent with a universe made up 71.3% of dark energy and 27.4% of a combination of dark and baryonic matter.
The nature of this dark energy is speculative. It is known to be the same throughout space, not very dense, and is only known to interact with gravity. Its lack of density, thought to be 10-29g/cm3, make it hard to created realistic experiments to detect it. Dark energy can only have such a profound impact on the universe because it uniformly fills otherwise empty space. The two leading models of dark energy agree that it must have negative pressure. It would seem that this is a subject in dire need of further research.
We have written many articles about dark energy for Universe Today. Here’s an article about dark matter and dark energy, and here’s an article about building a map of dark energy.
If you’d like more information on Dark Energy, check out What is Dark Energy page, and here’s the Introduction to Dark Energy page.
We’ve done many episodes of Astronomy Cast about Dark Energy. Listen here, Episode 11: A Universe of Dark Energy.
Source: NASA
Comments on this entry are closed.