Saturday, April 25, 2015
Happy 25th Birthday to the Hubble Space Telescope! Type Ia supernovae were once thought to all have the same brightness. Using these exploding stars as standard candles to measure distance, physicists in 1998 concluded that the universe is accelerating due to a repulsive "dark" energy. Speculation about an accelerating universe has occupied physics for years. Now a new study says that Type Ia don't all have the same luminosity after all. A new study published in the Astrophysical Journal finds that Type Ia supernovae form at least two groups, distinguished by colour and luminosity. The authors used results from the Hubble Space Telescope and the SWIFT satellite. This shows that they are not standard candles, and estimates of the universe's expansion could be way off. The paper is at: The Changing Fractions of Type Ia Supernova NUV The researchers conclude that differences between Type Ia supernovae could account for at least some of the apparent "acceleration". The so-called "dark" energy might not be as prevalent as thought. In the scientists' words: "Not accounting for this effect should thus produce a distance bias that increases with redshift and could significantly bias measurements of cosmological parameters". In English, what was thought about an accelerating universe could be wrong. GM=tc^3 predicts that the speed of light has been changing. Since redshifts are roughly proportional to v/c, instead of v increasing c has been slowing down. The answer could be in light rather than imaginary "dark" energies.