Observations of distant supernovae and fluctuations in the cosmic microwave background indicate that the expansion of the universe is accelerating. Astronomers theorize that this acceleration is caused by “ Dark Energy ”. Distances to supernovae are measured using Hubble’s law
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Observations of distant supernovae and fluctuations in the cosmic microwave background indicate that the expansion of the universe is accelerating. Astronomers theorize that this acceleration is caused by “Dark Energy”.
(red shift/magnitude relation).
What is dark energy?
Matter we can observe directly
Non-luminous matter in galactic halos
Dark energy should not be confused with dark matter. Dark matter is non-luminous material detected through its gravitational effect on galaxies and galactic clusters.
The solid blue line shows a theoretical prediction for a universe with 70% dark energy. Most supernovae have brightness and red shift values that lie close to this line.
More evidence for dark energy comes from high precision maps of the cosmic microwave background (CMB) radiation measured by the WMAP satellite.
This graph shows a spectrum of CMB temperature variations with direction (anisotropies) as measured by WMAP.
The vertical axis is related to the CMB temperature fluctuation.
The horizontal axis is the angular scale on which the fluctuation occurs.
Various measurements are combined to “zero in” on the answer:
Plot the range of dark energy density (ΩΛ) versus matter density (ΩM, dark+visible) predicted by the measurement.
The sum of these adds up to about 1.02, the flat universe density measured by WMAP, so the answer lies along the dashed line and its intersection with Supernova (SN) data.
Best fit: 73% dark energy, 27% dark + ordinary matter
However, other recent findings cast doubt on dark energy interpretations.
First, XMM-Newton X-ray telescope studies of galaxy clusters show inconsistencies with WMAP data.
The X-ray Multiple-Mirror (XMM) Telescope
XMM-Newton X-ray telescope image
Second, reanalysis of WMAP data to include the Sunyaev-Zel’dovich Effect exposes another inconsistency.
Observation of galaxy clusters applying the Sunyaev-Zel'dovich Effect
The Sunyaev-Zel’dovich Effect:
Exciting young areas of science are often controversial. Stay tuned as additional data, improved analysis, and new theoretical frameworks help astronomers resolve dark energy questions in the future.