Hubble finds universe may be expanding faster than expected
Astronomers using NASA's Hubble Space Telescope have discovered that the universe is expanding 5 percent to 9 percent faster than expected.
"This surprising finding may be an important clue to understanding those mysterious parts of the universe that make up 95 percent of everything and don't emit light, such as dark energy, dark matter, and dark radiation," said study leader and Nobel Laureate Adam Riess of the Space Telescope Science Institute and The Johns Hopkins University, both in Baltimore, Maryland.
The results will appear in an upcoming issue of The Astrophysical Journal.
According to the paper they used 300 SNe Ia along with Cepheid variables, as a basis for determining cosmological distances. With the exception of 19 SNe Ia, which were calibrated using nearby Cepheids, the remaining 281 SNe Ia were based purely on their light curve to determine their type. There is a fundamental problem with this methodology, when it is the only basis used to determine the type of a SNe. It is not always accurate. SNe Iax have the exact same light curve, including the lack of hydrogen in its spectrum as SNe Ia, except that they are several orders of magnitude dimmer than SNe Ia.
All SNe Ia have an absolute magnitude of -19.3, which is why they are used as a "standard candle." However, unless one also looks at other factors, such as the velocity of the ejecta, you cannot rule out the possibility of a SNe Iax, which could have an absolute magnitude anywhere from -14.2 to -18.9. All SNe Ia have ejecta with velocities that equal or exceed 10,000 km/s, whereas all SNe Iax ejecta velocities are less than 8,000 km/s. But if you only look at the light curve of the SNe, then there is no way to be certain if it is actually a SNe Ia. It is estimated that anywhere from 18% to 48% of all the SNe Ia have been misclassified and should actually be the much dimmer SNe Iax. That is a significant margin for error, and would have a profound effect determining the rate of expansion.
A 2.4% Determination of the Local Value of the Hubble Constant - arXiv 1604.01424
Type Iax Supernovae: A New Class of Stellar Explosion - The Astrophysical Journal, Volume 767, Number 1, March 25, 2013 (free issue)