A newsletter published today by the W.M. Keck Observatory reports on
a novel way of making observations of gravitationally lensed
quasar systems to provide another data set for determining the
expansion rate of the universe.
This latest finding supports others that the universe is not only expanding
but that the rate of expansion is increasing with time.
The Problem
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Originally Posted by W.M. Keck Observatory
This model of the expansion history of the universe is assembled using traditional Hubble Constant measurements, which are taken from “distant” observations of the cosmic microwave background (CMB) – leftover radiation from the Big Bang when the universe began 13.8 billion years ago.
Recently, many groups began using varying techniques and studying different parts of the universe to obtain the Hubble Constant and found that the value obtained from “local” versus “distant” observations disagree.
“Therein lies the crisis in cosmology,” says Fassnacht. “While the Hubble Constant is constant everywhere in space at a given time, it is not constant in time. So, when we are comparing the Hubble Constants that come out of various techniques, we are comparing the early universe (using distant observations) vs. the late, more modern part of the universe (using local, nearby observations).”
This suggests that either there is a problem with the CMB measurements, which the team says is unlikely, or the standard model of cosmology needs to be changed in some way using new physics to correct the discrepancy.
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The Technique
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Originally Posted by W.M. Keck Observatory
Quasars are extremely bright, active galaxies, often with massive jets powered by a supermassive black hole ravenously eating material surrounding it.
Though quasars are often extremely far way, astronomers are able to detect them through gravitational lensing, a phenomenon that acts as nature’s magnifying glass. When a sufficiently massive galaxy closer to Earth gets in the way of light from a very distant quasar, the galaxy can act as a lens; its gravitational field warps space itself, bending the background quasar’s light into multiple images and making it look extra bright.
At times, the brightness of the quasar flickers, and since each image corresponds to a slightly different path length from quasar to telescope, the flickers appear at slightly different times for each image – they don’t all arrive on Earth at the same time.
With HE0435-1223, PG1115+ 080, and RXJ1131-1231, the team carefully measured those time delays, which are inversely proportional to the value of the Hubble Constant. This allows astronomers to decode the light from these distant quasars and gather information about how much the universe has expanded during the time the light has been on its way to Earth.
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The Finding
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Originally Posted by W.M. Keck Observatory
The unblinding revealed a value that is consistent with Hubble Constant measurements taken from observations of “local” objects close to Earth, such as nearby Type Ia supernovae or gravitationally-lensed systems; Chen’s team used the latter objects in their blind analysis.
The team’s results add to growing evidence that there is a problem with the standard model of cosmology, which shows the universe was expanding very fast early in its history, then the expansion slowed down due to the gravitational pull of dark matter, and now the expansion is speeding up again due to dark energy, a mysterious force.
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Newsletter here :-
http://www.keckobservatory.org/hubble-constant/