In astronomy, there are two exact measurements of the expansion of the universe, or “Hubble constant”. One is derived from studies of supernovae in the area, while the other is based on the “cosmic microwave background,” or radiation, that began flowing freely through the Universe shortly after the Big Bang.
Although these two measurements differ by about 10%, it has sparked widespread debate among physicists and astronomers. Researchers at the University of Minnesota have successfully applied a unique technique to measure the expansion rate of the universe using data from a magnified supernova. Their findings shed light on an ongoing debate in astronomy and could help with more accurate dating of the Universe and a better understanding of the cosmos.
Patrick Kelly, lead author of both papers and an assistant professor in the College of Science and Engineering, said: “The big question is whether there is a potential problem with one or both measurements. Our research addresses that by using an independent, completely different way to measure the expansion rate of the universe.”
Researchers were able to calculate the value using data from a supernova discovered by Kelly in 2014. The telescope captured four different images of the same cosmic event. The supernova was said to resurface in a different location after its discovery in 2015 by teams around the world, and the University of Minnesota team discovered this additional image.
As the mass of the cluster of galaxies gravitationally lenses the supernova, bending and magnifying light, numerous images of the object have emerged. The researchers were able to measure the Hubble constant by applying a theory devised in 1964 by Norwegian astronomer Sjur Refsdal that was previously impractical to use, taking advantage of the time lags between the appearances of the 2014 and 2015 photos.
The study doesn’t settle the debate, but it provides crucial insight into the problem and brings physicists closer to getting the most accurate measure of how old the Universe is.
Kelly said, “Our measurement is more consistent with the value of the cosmic microwave background, although – given the uncertainties – it does not exclude the measurement of the local distance ladder. If observations of future supernovae also gravitationally lensed by clusters yield a similar result, this will identify a problem with the current supernova value or our understanding of the dark matter of galaxy clusters.”
Using the same data, the researchers found that some existing dark matter theories of galaxy clusters could explain their observations of the supernovae. This allowed them, using the most accurate models, to answer the long-standing puzzle of where dark matter is located in the cluster of galaxies.
Magazine reference:
- Patrick Kelly, Steven Rodney, et al. Constraints on the Hubble constant from the reappearance of Supernova Refsdal. Science. DOI: 10.1126/science.abh1322
