A group of astronomers led by the University of California, Davis has received new data suggesting that the universe is expanding faster than predicted.
The study comes on the heels of a hot debate about how quickly the universe balloons; Measurements so far disagree.
The team's new measurement of Hubble Constant, or the degree of expansion of the universe, involved another method. They used NASA's Hubble Space Telescope (HST) in combination with W. M. Keck Observatory's Adaptive Optics (AO) system to observe three gravitational lens systems. This is the first time ground-based AO technology has been used to get Hubble Constant.
"When I first started working on this problem more than 20 years ago, the available instrumentation limited the amount of useful data you could get from the observations," says co-author Chris Fassnacht, professor of physics at UC Davis. "In this project, we use Keck Observatory AO for the first time in the full analysis. I have known for many years that AO observations can greatly contribute to this effort. "
The team's results are published in the latest online edition of Monthly Notices from the Royal Astronomical Society .
To exclude any bias the team performed a blind analysis; during the treatment, they kept the final answer even hidden until they were convinced that they had taken up as many possible sources of error as they could think of, which prevented them from making any adjustments to to arrive at the "correct" value and avoid confirmation
"When we thought we had taken care of all possible problems with the analysis, we uncheck the answer with the rule that we must publish the value we find, even if it is crazy. It is always a tense and exciting moment, "says lead author Geoff Chen, a research student at the UC Davis Physics Department. Chen's team used the latter objects in their blind analysis.
The team's results provide increasing evidence that there is a problem with the standard model of cosmology, which shows that the universe expanded very early in its history, then decreased its expansion due to of the gravitational pull of dark matter, and now expansion is accelerated again by dark energy, a mysterious force.
This model of the universe's expansion history is combined with traditional Hubble Constant measurements taken from "distant" observations of the cosmic microwave background. (CMB) – residual radiation from Big Afraid when the universe began 13.8 billion years ago.
Recently, many groups began using different techniques and studying different parts of the universe to get Hubble Constant and found that the value obtained from "local" versus "distant" observations did not agree.
"That's where the crisis lies 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 compare Hubble constants coming out of different technologies, we compare the early universe (with 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 that the cosmetologist model must be changed in some way by to use new physics to correct the deviation.
Using Keck Observatory's AO system with Near-Infrared Camera, second-generation (NIRC2) instruments on the Keck II telescope, Chen and his team obtained local measurements of three well-known lens quasar systems: PG1115 + 080, HE0435-1223 and RXJ1131-1231.
Quasars are extremely bright, active galaxies, often with massive jet planes driven by a super-massive ravine with black holes of silly-eating material surrounding it.
Although quasars are often extremely long, astronomers can detect them through gravitational lensing, a phenomenon that acts as the magnifying glass of nature. When a sufficiently massive galaxy nearer the earth gets in the way of light from a very distant quasar, the galaxy can act as a lens; its gravitational field rotates in space and bends the background quasars into multiple images, making it look extra bright.
Sometimes the brightness of quasars flickers, and since each image corresponds to a slightly different path length from tassels to telescope, the flickers appear at slightly different times for each image – they do not all arrive on Earth at the same time.
With HE0435-1223, PG1115 + 080 and RXJ1131-1231, the team carefully measured the time delays that are inversely proportional to the value of 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 that light has been traveling to Earth.
"One of the most important ingredients for using gravitational lenses to measure Hubble Constant is sensitive and high-resolution imaging," Chen said. "So far, the best lens-based Hubble Constant measurements have all been involved using HST data. When we blinded we found two things. First, we had consistent values with previous measurements based on HST data, which proved that AO data can provides a powerful alternative to HST data in the future. Secondly, we found that combining AO and HST data gave a more accurate result. "
Chen and his teams, as well as many other groups across the planet do more research and observations to investigate further. Now that Chen's team has proven that the Keck Observatory's AO system is as powerful as HST, astronomers can add this methodology to its bucket of techniques when measuring Hubble Constant.
"We can now try this method with more lensed quasar systems to improve the precision of our measurement of the Hubble constant. Perhaps this will lead us to a more complete cosmological model of the universe," says Fassnacht.
Astronomers measure universe expansion, get hints of "new physics" (Update)
Geoff C-F Chen et al. A SHARP image of H0LiCOW: H0 from three gravitational lens systems with time delay with adaptive optics imaging, Monthly Notices of the Royal Astronomical Society (2019). DOI: 10.1093 / mnras / stz2547
A crisis in cosmology: New data suggests that the universe is expanding faster than expected (2019, October 23)
Retrieved October 23, 2019
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