page_title: Type Ia supernova
section_title: Observation
hierarchical_section_title: Type Ia supernova / Observation
caption_attribution_description: English: This image, taken with the NASA/ESA Hubble Space Telescope, shows the supernova remnant SNR 0509-68.7, also known as N103B (top of the image). N103B was a Type Ia supernova, located in the Large Magellanic Cloud — a neighbouring galaxy of the Milky Way. Owing to its relative proximity to Earth, astronomers observe the remnant to search for a potential stellar survivor of the explosion. The orange-red filaments visible in the image show the shock fronts of the supernova explosion. These filaments allow astronomers to calculate the original centre of the explosion. The filaments also show that the explosion is no longer expanding as a sphere, but is elliptical in shape. Astronomers assume that part of material ejected by the explosion hit a denser cloud of interstellar material, which slowed its speed. The shell of expanding material being open to one side supports this idea. The gas in the lower half of the image and the dense concentration of stars in the lower left are the outskirts of the star cluster NGC 1850, which has been observed by Hubble in the past heic0108.
context_page_description: A type Ia supernova is a type of supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.
  Physically, carbon–oxygen white dwarfs with a low rate of rotation are limited to below 1.44 solar masses. Beyond this "critical mass", they reignite and in some cases trigger a supernova explosion. Somewhat confusingly, this critical mass is often referred to as the Chandrasekhar mass, despite being marginally different from the absolute Chandrasekhar limit where electron degeneracy pressure is unable to prevent catastrophic collapse. If a white dwarf gradually accretes mass from a binary companion, or merges with a second white dwarf, the general hypothesis is that its core will reach the ignition temperature for carbon fusion as it approaches the Chandrasekhar mass. Within a few seconds of initiation of nuclear fusion, a substantial fraction of the matter in the white dwarf undergoes a runaway reaction, releasing enough energy to unbind the star in a supernova explosion.
context_section_description: Unlike the other types of supernovae, Type Ia supernovae generally occur in all types of galaxies, including ellipticals. They show no preference for regions of current stellar formation. As white dwarf stars form at the end of a star's main sequence evolutionary period, such a long-lived star system may have wandered far from the region where it originally formed. Thereafter a close binary system may spend another million years in the mass transfer stage (possibly forming persistent nova outbursts) before the conditions are ripe for a Type Ia supernova to occur.
  A long-standing problem in astronomy has been the identification of supernova progenitors. Direct observation of a progenitor would provide useful constraints on supernova models. As of 2006, the search for such a progenitor had been ongoing for longer than a century. Observation of the supernova SN 2011fe has provided useful constraints. Previous observations with the Hubble Space Telescope did not show a star at the position of the event, thereby excluding a red giant as the source. The expanding plasma from the explosion was found to contain carbon and oxygen, making it likely the progenitor was a white dwarf primarily composed of these elements.
  Similarly, observations of the nearby SN PTF 11kx, discovered January 16, 2011 (UT) by the Palomar Transient Factory (PTF), lead to the conclusion that this explosion arises from single-degenerate progenitor, with a red giant companion, thus suggesting there is no single progenitor path to SN Ia. Direct observations of the progenitor of PTF 11kx were reported in the August 24 edition of Science and support this conclusion, and also show that the progenitor star experienced periodic nova eruptions before the supernova – another surprising discovery.
  
  However, later analysis revealed that the circumstellar material is too massive for the single-degenerate scenario, and fits better the core-degenerate scenario.
caption: Supernova remnant N103B taken by the Hubble Space Telescope.[37]
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