Image around SN 2012dn obtained by the Kanata Telescope at Higashi-Hiroshima Observatory. SN 2012dn is seen near the center of this figure. The host galaxy ESO 462-G016 is seen on the left side of SN 2012dn. The distance to this galaxy is known to be 130 mega-light-years. Because the supernova is a point source, the expansion cannot be measured, but the evolutions of the brightness and color are obtained. Credit: Higashi-Hiroshima Observatory
Using Optical and Infrared Synergetic Telescopes for Education and Research (OISTER), researchers discovered an anomalously strong infrared emission from ‘the extraordinary supernova’ SN 2012dn, which has never been observed in other Type Ia supernovae to date. Through detailed analysis, the researchers concluded that the infrared emission comes from the material ejected from the progenitor system.The new information will help improve measurements of the Universe’s expansion, and of the Dark Energy which controls the final fate of the cosmos.
Type Ia supernovae are a type of exploding star which are used as references when studying the Universe. What makes these supernovae useful is that the physics governing their evolution ensures that they all change from a stable state to an explosion at almost exactly the same point in their evolution. This means that the brightness of a Type Ia supernova explosion is consistent from one star to the next. By using the known brightness of these supernovae, astronomers can use them to calibrate observations. eg in late 1990’s, the accelerating expansion of the Universe was discovered by using the properties of Type Ia supernovae. Drs. Perlmutter, Riess, and Schmidt were awarded the Novel Prize in Physics in 2011 for this work.
But there’s a problem. In addition to normal Type Ia supernovae, astronomers have discovered ‘extraordinary supernovae’ which are much brighter than they should be. These ‘extraordinary supernovae’ may be contaminating the samples used for cosmological research, thereby skewing the calibration. To correctly measure the expansion of the Universe and understand the Dark Energy driving the expansion, it is important to determine the origins of both typical supernovae and ‘extraordinary supernovae’ so that the latter can be more accurately excluded from the sample.
Despite 3 decades of debate, astronomers still haven’t agreed on the origin of these supernovae. There are 2 popular scenarios, ‘accretion’ or ‘merger’, as the path to the supernova explosion. Both scenarios consider a ‘binary system,’ i.e., 2 stars orbiting around each other. The ‘accretion’ scenario uses binary systems composed of a white dwarf and a normal star, and ‘merger’ scenario uses binary systems formed by 2 white dwarfs.
The mass of the ejected material strongly supports the ‘accretion scenario.’ In the accretion scenario, gas is transferred onto the surface of the white dwarf from the companion star in the binary system. During the transfer, a part of the material escapes from the gravitational potential of the system, forming a dense gas surrounding the pre-supernovae-explosion star system. The observation results indicate that SN 2012dn exploded while surrounded by this dense gas. From here, the team will pursue new observations to determine if typical Type Ia supernovae are also the results of accretion. http://www.nao.ac.jp/en/news/science/2016/20160607-oister.html
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