In November 1572, observers were startled by the appearance of a "new star" in the sky, about as bright as the planet Venus, in a place where no star had ever been seen before. Today we know that this "star" was actually a Type Ia supernova explosion, one of the rare stellar explosions actually visible to the unaided eye. Type Ia supernovae mark the sudden death of a white dwarf star that accreted matter from a companion star, became too massive, collapsed, and blew up. Because this event was studied in detail by the great (and flamboyant) astronomer Tycho Brahe, this supernova is now called Tycho's supernova in his honor. Tycho's supernova is a particularly interesting object for astronomers, and particularly X-ray astronomers, since the material heated by the shock of the explosion still has temperatures of millions of degrees, and produces lots of X-ray emission. The image above is an new X-ray image of the Tycho supernova remnant by the Soft X-ray Telescope on India's AstroSat X-ray space observatory. The X-ray image and X-ray spectrum obtained by AstroSat will be used to study the chemical distribution of the hot material, and comparison of the new AstroSat observation to previous observations obtained by other X-ray observatories (like ROSAT, Chandra, XMM-Newton, Suzaku, and others) will help constrain the expansion and cooling of the shocked material.
<<This image from NASA's Wide-field Infrared Survey Explorer (WISE) takes in several interesting objects in the constellation Cassiopeia. The red circle visible in the upper left part of the image is SN 1572, often called “Tycho’s Supernova”. In the centre of the image is a star forming nebula of dust and gas, called S175 (in the Sharpless catalog of ionized nebula). This cloud of material is about 3,500 light years away and 35 light-years across. It is being heated by radiation from young hot stars within it, and the dust within the cloud radiates infrared light. On the left edge of the image, between the Tycho supernova remnant and the very bright star, is an open cluster of stars, King 1, first catalogued by Ivan King, an astronomer at UC Berkeley. This cluster is about 6,000 light-years away, 4 light-years across and is about 2 billion years old. Also of interest in the lower right of the image is a cluster of very red sources. Almost all of these sources have no counterparts in visible light images, and only some have been catalogued by previous infrared surveys.>>