A team of scientists from the University of Minnesota He successfully used a first-of-its-kind technique to measure the Hubble constant. This was achieved thanks to observations of the Refsdal supernova, and may be useful in determining the age of the universe. The search results are described in Sciences.
The first such accurate measurement of the Hubble constant
The expansion rate of the universe is determined by the Hubble constant (H0), which we estimate either from the microwave background radiation (CMB) reflecting off the Big Bang, or from values obtained from direct observations of stars and galaxies. It is probably no secret that both values do not coincide – they differ by about 10 percent. Known as the Hubble effort, this problem baffles astrophysicists around the world.
The important question is whether there might be a problem with one or both measurements. Our research solves this problem by using an independent and completely different method for measuring the expansion rate of the universe.
Patrick Kelly, assistant professor at the University of Minnesota
The new measurement was made possible using data from the Refsdal supernova, a Type Ia supernova discovered in 2014 by Dr. Kelly, then a researcher at UCLA. From Earth, a double and quadruple image of the supernova was visible, which was caused by the bending of the light emitted from the object by the huge cluster of galaxies located between the Earth and the supernova.
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Using the time lapse between the appearance of the 2014 and 2015 images, the researchers were able to measure the Hubble constant using a theory developed in 1964 by Norwegian astronomer Sjur Refsdal, which previously could not be applied in practice.
Our measurement is in better agreement with the value due to the cosmic background radiation, although – given the uncertainties – it does not exclude the measurement from the local distance scale. If observations of future supernovae, which are also gravitational by clusters, show a similar result, this would spell a problem with the current rate of supernovae or our understanding of the dark matter of cluster galaxies.
The newly determined value of the Hubble constant (H0) is 66.6 + 4.1−3.3 (km/s)/Mpc, which means that the universe is expanding at a rate of 66.6 km/s per megaparsec. One megafarc is about 3 million light-years away. This value is consistent with theoretical models of gravitational lensing produced by dark matter, found in eg. in galactic halos.
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