Astronomers discover a Large Cavity around the Tycho’s Supernova

Chinese astronomers have detected a large cavity existing around Tycho’s supernova, SN 1572, exhibiting stream-like structures. The findings show that the environments of the supernovae may be much more complicated than previously thought. SN 1572 lies between 8,000 to 10,000 light years from the Earth in the constellation Cassiopeia. It is a well-established type Ia supernova, 1 of about 8 supernovae visible to the naked eye in historical records. As one of the most popular supernova remnants in our galaxy, it has been widely observed in the entire electromagnetic spectrum, and astronomers have discovered a shell-like structure produced by the shocks from the explosion as well as circumstellar material and dust.

Recently they used 13.7-meter mm-wavelength telescope of the Qinghai station of PMO at Delingha in China to perform large-field and high-sensitivity CO molecular line observations of SN 1572. The scientists observed the supernova from November 2011 to February 2016 as part of the Milky Way Imaging Scroll Painting (MWISP) survey, which investigates the nature of the molecular gas along the northern Galactic Plane. “We present large-field CO (1-0) molecular line observations toward the Tycho’s supernova remnant, using the PMO 13.7-meter telescope. Based on the CO observations, we find a large cavity with radii of 0.3 degrees by 0.6 degrees around the remnant, which is further confirmed by the complementary infrared images from the space telescopes,” the researchers wrote in the paper.

The team estimated that the cavity is located about 8,000 light years away and has radii of 42 and 88 light years. Their calculations allowed them to estimate that this cavity is expanding at ~4 km s-1. Moreover, they distinguished stream-like structures in the cavity that could be part of a larger cavity seen along the line of sight. They noted that these structures may also record the accretion winds from the progenitor system. Due to these uncertainties, the team calls for further observations that could illuminate the real nature of these structures.

“In the wind-regulated accretion models, the accretion wind could last for few million years, and the white dwarf may explode as a type Ia supernova while the accretion wind is still active. Therefore, another possible explanation is that these stream-like structures actually record the accretion winds from the progenitor system. This scenario is somehow supported by the infrared observations, in which knot-like structures are also found in the southwest and west of the cavity,”. The scientists also investigated the origin of the cavity. They excluded the possibility that it could be produced by bright star in the region or the option that it was randomly distributed. The most plausible hypothesis is that it could be explained by the accretion wind from the progenitor system of the Tycho’s supernova.

“The discovery of the Tycho’s cavity also gives us an alert that the environments of the supernovae Ia may be much more complicated than we thought before,” the researchers concluded.
http://phys.org/news/2016-08-astronomers-large-cavity-tycho-supernova.htmljCp https://arxiv.org/abs/1608.05329