Leibniz Institute for Astrophysics Potsdam

A team used a first-of-its-kind technique to measure the expansion rate of the Universe, providing insight that could help more accurately determine the Universe's age and help physicists and astronomers better understand the cosmos. Thanks to data from a magnified, multiply imaged supernova, a team led by University of Minnesota Twin Cities researchers has successfully used a first-of-its-kind technique to measure the expansion rate of the Universe. Their data provide insight into a longstanding debate in the field and could help scientists more accurately determine the Universe's age and better understand the cosmos. The work is divided into two papers, respectively published in Science, one of the world's top peer-reviewed academic journals, and The Astrophysical Journal, a peer-reviewed scientific journal of astrophysics and astronomy. In astronomy, there are two precise measurements of the expansion of the Universe, also called the "Hubble constant." One is calculated from nearby observations of supernovae, and the second uses the "cosmic microwave background," or radiation that began to stream freely through the Universe shortly after the Big Bang. However, these two measurements differ by about 10 percent, which has caused widespread debate among physicists and astronomers. If both measurements are accurate, that means scientists' current theory about the make-up of the universe is incomplete. "If new, independent measurements confirm this disagreement between the two measurements of the Hubble constant, it would become a chink in the armor of our understanding of the cosmos," said Patrick Kelly, lead author of both papers and an assistant professor in the University of Minnesota School of Physics and Astronomy. "The big question is if there is a possible issue with one or both of the measurements. Our research addresses that by using an independent, completely different way to measure the expansion rate of the Universe." The University of Minnesota-led team was able to calculate this value using data from a supernova discovered by Kelly in 2014 -- the first ever example of a multiply imaged supernova, meaning that the telescope captured four different images of the same cosmic event. After the discovery, teams around the world predicted that the supernova would reappear at a new position in 2015, and the University of Minnesota team detected this additional image. These multiple images appeared because the supernova was gravitationally lensed by a galaxy cluster, a phenomenon in which mass from the cluster bends and magnifies light. By using the time delays between the appearances 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 that had previously been impossible to put into practice. The researchers' findings don't absolutely settle the debate, Kelly said, but they do provide more insight into the problem and bring physicists closer to obtaining the most accurate measurement of the Universe's age. "Our measurement favors the value from the cosmic microwave background, although it is not in strong disagreement with the supernova value," Kelly said. "If observations of future supernovae that are also gravitationally lensed by clusters yield a similar result, then it would identify an issue with the current supernova value, or with our understanding of galaxy-cluster dark matter." Using the same data, the researchers found that some current models of galaxy-cluster dark matter were able to explain their observations of the supernovae. This allowed them to determine the most accurate models for the locations of dark matter in the galaxy cluster, a question that has long plagued astronomers. This research was funded primarily by NASA through the Space Telescope Science Institute and the National Science Foundation. In addition to Kelly, the team included researchers from the University of Minnesota's Minnesota Institute for Astrophysics; the University of South Carolina; the University of California, Los Angeles; Stanford University; the Swiss Federal Institute of Technology Lausanne; Sorbonne University; the University of California, Berkeley; the University of Toronto; Rutgers University; the University of Copenhagen; the University of Cambridge; the Kavli Institute for Cosmology; Ben-Gurion University of the Negev; University of the Basque Country; the University of Cantabria; Consejo Superior de Investigaciones Cientificas (the Spanish National Research Council); the Observatories of the Carnegie Institution for Science; the University of Portsmouth; Durham University; the University of California, Santa Barbara; the University of Tokyo; the Space Telescope Science Institute; the Leibniz Institute for Astrophysics Potsdam; the University of Michigan; Australian National University; Stony Brook University; Heidelberg University; and Chiba University.

Researchers have digitized historical photographic plates showing negatives of the night sky and published the images online. After a total of 10 years, the project has now been completed successfully. Lots of little dots with no apparent pattern: where laypeople may just see milky gray photos sprinkled with what looks like random crumbs, it is enough to make astronomers' hearts miss a beat. We are talking about historical photographic plates showing negatives of the night sky. Together with the Leibniz Institute for Astrophysics Potsdam and the universities of Hamburg and Tartu (Estonia), researchers at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have digitized the images and published them online. After a total of 10 years, the project has now been completed successfully, thanks to the financial support of the German Research Foundation (DFG). Even though the oldest image is "only" 129 years old, just a blink of an eye compared to the timescales usually associated with astronomy, they are of great historical value and are a treasure trove for academic purposes. Images such as these are the only way astronomers today can trace how stars move or change in intensity over several decades. They can be used to answer new research questions and take a closer and more objective look at millions of stars. Since 2012, the research team has been working on digitizing images from the archives of their partner institutes dating from 1893 to 1998 in the database APPLAUSE -- which stands for Archives of Photographic Plates for Astronomical USE -- and recording them in a catalog with details on the images such as date, section of sky and where the images were taken. In addition, the research consortium has developed software that uses artificial intelligence to remove errors on the plates caused by scratches or dust and to calibrate the images, thereby allowing them to be compared with each other for scientific purposes for the first time. Researchers across the globe now have access to 4.5 billion measurements of celestial light sources for their research. Over 94,000 photographic plates digitized A major share of the total of 94,090 plates is accounted for by the 40,000 photographic plates from the Dr. Karl Remeis Observatory Bamberg, Astronomical Institute of FAU. These include photographs taken by Franconian researchers between 1963 and 1976 at observatories in the southern hemisphere. These unique images show the southern sky, and are the only ones of their kind available anywhere in the world, as no other astronomical projects documented this part of the sky during this period. Since the last images were published four years ago, the photographic plates taken in Bamberg between 1912 and 1968 showing the northern sky have now been added to the project. These 17,600 images are the most important addition to what is now the final data update. But that is not all: the project came to the attention of other observatories during an academic conference in Bamberg. The Thüringer Landessternwarte Tautenburg, for example. It gave the research team access to the archive of the Karl Schwarzschild Observatory, the former observatory of the Academy of Sciences of the GDR for the years from 1960 to 1998. Researchers at the astronomical observatory of the Vatican State in Castel Gandolfo also expressed an interest in having their archive incorporated into the database and made available to the global scientific community. New knowledge from old images But what knowledge can be gained from the historical photographic plates, and does it have any relevance for today? The surveys of the northern and southern skies conducted during the last century by the Bamberg observatory aimed to investigate stars that varied in intensity. The physical properties of some of the objects, in other words which gases they are composed of, are still unclear. Star "HD49798" is a particularly interesting example. Its erratic fluctuations in intensity were registered on the photographic plates from Bamberg in the 1960's and early 1970's, but scientists were only able to analyze them last year. They show that the star constantly increased in intensity between 1964 and 1965, but then started to shine less brightly until 1974. There were also rapid changes in the light it gave off within a space of just a few days. In 1999, satellite readings revealed that the star was emitting x-rays. Today, scientists suspect that these rays are being emitted by an invisible, more compact accompanying object, possibly a neutron star. Until now, scientists had been unable to track long-term variations in intensity, as measurements stretching over such a long period of time, namely ten years, were not available. The historical data from the photographic plates are therefore a valuable source of astronomical information that researchers will now analyze over coming years. This particular duo of stars is still the only constellation of its kind to have been discovered anywhere in the universe. Access to the published data from APPLAUSE: