The novelty of this latest Hubble constant measurement means it is possible that there are sources of uncertainty that have not yet been identified. “This is an independent measurement of the Hubble constant,” says Kelly. Finally, after using redshift to determine the supernova’s velocity relative to Earth, the team was able to derive a value for H 0. The researchers modeled the mass distribution of the galaxy cluster, which is composed mostly of dark matter, to help figure out the path taken by the lensed light and thus the distance to the supernova. Patrick Kelly, an astronomer at the University of Minnesota who was on the team that discovered the supernova while he was a postdoctoral researcher, and his colleagues used the time delay to calculate the angular distance between the supernova and the foreground galaxy cluster that acted as the gravitational lens. Postman (STScI) and the CLASH team and Z. Lotz (STScI) and the Frontier Fields team M. Kelly (UC Berkeley), and the GLASS team J. As a result, Hubble observations captured the supernova in several locations at different times. The light from Supernova Refsdal (right in the diagram) took multiple paths as it traversed the massive galaxy cluster MACS J1149.6+2223. Just over a year later, another image appeared of the supernova, which is located about 14 billion light-years from Earth. That collaboration’s latest result is a value of about 73 km/s/Mpc, which is consistent with standard candle measurements.Ī team of astronomers at the University of California, Berkeley, first spotted multiple images of Supernova Refsdal in 2014 during a survey for gravitationally lensed supernovae. Previously, the H0LiCOW (H 0 Lenses in COSMOGRAIL’s Wellspring) collaboration used gravitationally lensed quasars to measure H 0.
#Gravitational redshift galaxy plus#
That distance, plus a measure of velocity via redshift, would enable the calculation of H 0 with great precision. Refsdal realized that by measuring the differences in arrival time of the photons from the respective images, astronomers could find the absolute distance between the galaxy and the object it is lensing. As a result, the light takes different paths around the galaxy, and the object appears to observers as multiple images. When in line with a distant object, such as a supernova, a massive foreground galaxy or galaxy cluster bends the object’s light via strong gravitational lensing. Time-delay cosmography was pioneered in the 1960s by the namesake for the newly analyzed supernova, Norwegian astrophysicist Sjur Refsdal. “Measuring the Hubble constant using many different techniques is the way we’re going to ultimately convince ourselves that an accurate measurement has been made,” says Wendy Freedman, an observational cosmologist at the University of Chicago who was not involved in the research. Measurements of H 0 made using the cosmic microwave background (CMB) radiation from the early universe, on the other hand, yield a rate of about 67 km/s/Mpc.Īlthough the new time-delay measurement is closer to the CMB value, there is still enough wiggle room for an agreement with standard candle measurements.
That compares with values of 70–74 km/s/Mpc attained through measurements of standard candles-objects such as type Ia supernovae and pulsing red giant stars called Cepheids that have known luminosities, which allow astronomers to determine their distance from Earth by measuring how bright the objects appear. Using a method called time-delay cosmography with a burst named Supernova Refsdal, a team of astronomers has reported in Science an H 0 value of 66.6 + 4.1 – 3.3 km/s/Mpc. Over the decades, different methods of measuring the universe’s expansion rate, also known as the Hubble constant or H 0, have produced different values.Ī novel analysis of a supernova provides an important new result for H 0. What continues to be up for debate is how fast the expansion is happening. Another image of the burst appeared the following year, enabling a novel measurement of the Hubble constant. In this 2014 Hubble Space Telescope portrait, four images of Supernova Refsdal appear surrounding the yellow galaxy above the bright blue star.
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