The universe, 99.9 (and at least 58Ceother 9s) per cent of which is already outside Earth's atmosphere, is expanding (into we know not what) at 74km per second per megaparsec
. (One megaparsec
is approximately 3.26 million light-years.) Astronomers are studying light that has taken perhaps 12 billion years to reach their instruments.
The new estimate of the Hubble constant is 74 kilometres (46 miles) per second per megaparsec
. This means that for every 3.3 million light-years farther away a galaxy is from us, it appears to be moving 74 kilometres (46 miles) per second faster, as a result of the expansion of the universe.
* The Hubble constant is defined currently within H = 55 / 75 km/ (s Megaparsec
The new value, which lies between 66.2 and 68.4 kilometers per second per megaparsec
, is consistent with the value derived from the Planck mission's measurements of the cosmic background radiation, but it's still lower than that obtained from observations of Cepheid variable stars and Type la supernovae.
At the present time the expansion rate of the universe, named the Hubble constant, is estimated to be approximately 73 km/s per megaparsec
. The inverse value of this quantity gives for the corresponding age of the universe 13.7 gigayears.
Measurements based on observations of supernovas, massive stellar explosions, indicate that distantly separated galaxies are spreading apart at 73 kilometers per second for each megaparsec
(about 3.3 million light-years) of distance between them.
Based on the data acquired with Hubble, the team has released a highly accurate value for the expansion of the universe, which is known as the Hubble Constant - 45.5 miles (73.2 km) per second per megaparsec
. A megaparsec
, by the way, is 3.26 million light years.
The newly refined value for the Hubble constant is 74.3 2.1 kilometres per second per megaparsec
. A megaparsec
is roughly 3 million light-years.
In 2001, as part of the Hubble Space Telescope Key Project, a team of astronomers led by Carnegie's Wendy Freedman determined precision distances to individual far-off galaxies and used them to determine that the universe is expanding at the rate of 72 kilometers per second per megaparsec
. While the debate had previously raged over a factor-of-two uncertainty in the Hubble constant, Freedman and her team cut that uncertainty down to just 10%.
(1 Mpc equals 1 Megaparsec
, or 3.26 million light years.) For decades before (our project) the uncertainty had remained a factor of two (50 to 100).
But bigger still by a factor of about 16 is the megaparsec
, defined succinctly as follows: one million parsecs.
A kiloparsec is 1,000 parsecs, and a megaparsec
is a million parsecs.