Type 1a supernovae (SN1a) are extremely handy dead stars. No matter where they occur in the universe, all observed SN1a's have extremely similar peak luminosities, making them useful as a means of measuring cosmic distances independent of the expansion of the universe. Previous work on SN1a's revealed that the universe's expansion is actually accelerating.
A mysterious discovery in 2010 seemed to throw an intriguing wrench into our knowledge of SN1a's. Supernova PS1-10afx was discovered by the Panoramic Survey Telescope & Rapid Response System 1 (PanSTARRS1) in Hawaii, which observes the entire visible sky each month. PS1-10afx matched other SN1a's in color and light curve, the fluctuations in that star's brightness over time. However, its greatest brightness was 30 times more than what was expected. Some scientists suggested that PS1-10afx represented an entirely new class of superluminous supernova.
This explanation was not universally considered satisfactory. Supernova that are more luminous that an SN1a have bluer colors, indicating higher temperatures, and slower light curves, indicating a larger size. PS1-10afx does not fit these criteria. Therefore, a team of scientists led by Robert Quimby of the University of Tokyo Kavli Institute for the Physics and Mathematics of the Universe proposed that the unusual brightness of PS1-10afx was an artifact of its light being bent by a gravitational lens. A gravitational lens is an object situated between an observer and a more distant object; the gravity of the lensing object can bend light emitted by the more distant object, producing a magnified image of the more distant object.
According to a Kavli Foundation press release, Quimby and colleagues spent seven hours in September 2013 using the Low-Resolution Imaging Spectrograph on the Keck-1 telescope in Hawaii to observe the location of the PS1-10afx. They found that the comparative brightness of PS1-10afx's host galaxy had obscured the light of a fainter galaxy in the foreground. This newly-found galaxy was the right size to be the lensing object for the light emitted by PS1-10afx. Not only is Quimby and team's discovery the first gravitationally-lensed supernova ever confirmed, it also verifies their hypothesis of why PS1-10afx appeared anomalously bright.
Quimby and team's methodology will be used to recognize other lensed Type 1a supernovae in the future. When an object's light is magnified by a gravitational lens, multiple images are created, which travel to the observer along different paths. Measuring the time delay between the arrival of each image can serve as a test of cosmic expansion; the faster the expansion, the shorter the time delays. Comparing the measured time delays to the expected delays given the structure of the lens can shed light on the history of the universe's expansion.
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Source : http://thespacereporter.com/2014/04/puzzling-supernova-magnified-by-gravitational-lens/
