Tuesday, April 26, 2011

Tycho's Supernova Remnant: NASA'S Chandra Finds New Evidence on Origin of Supernovas

Tycho's Supernova Remnant
Credit NASA/CXC/Chinese Academy of Sciences/F. Lu et al

Image Showing the "Shadow" of the Arc
This image shows iron debris in Tycho's supernova remnant. The site of the supernova explosion is shown, as inferred from the motion of the possible companion to the exploded white dwarf. The position of material stripped off the companion star by the explosion, and forming an X-ray arc, is shown by the white dotted line. This structure is most easily seen in an image showing X-rays from the arc's shock wave. Finally, the arc has blocked debris from the explosion creating a "shadow" in the debris between the red dotted lines, extending from the arc to the edge of the remnant. Credit: NASA/CXC/Chinese Academy of Sciences/F. Lu et al

This new image of Tycho's supernova remnant, dubbed Tycho for short, contains striking new evidence for what triggered the original supernova explosion, as seen from Earth in 1572. Tycho was formed by a Type Ia supernova, a category of stellar explosion used in measuring astronomical distances because of their reliable brightness.

Low and medium energy X-rays in red and green show expanding debris from the supernova explosion. High energy X-rays in blue reveal the blast wave, a shell of extremely energetic electrons. Also shown in the lower left region of Tycho is a blue arc of X-ray emission. Several lines of evidence support the conclusion that this arc is due to a shock wave created when a white dwarf exploded and blew material off the surface of a nearby companion star (see accompanying illustration below). Previously, studies with optical telescopes have revealed a star within the remnant that is moving much more quickly than its neighbors, hinting that it could be the companion to the supernova that was given a kick by the explosion.

Illustration Explaining the Arc in Tycho
This is an artist's impression showing an explanation from scientists for the origin of an X-ray arc in Tycho's supernova remnant. It is believed that material was stripped off the companion star by the explosion of the white dwarf in the Type Ia supernova explosion, forming the shock wave seen in the arc. The arc has blocked debris from the explosion, creating a "shadow" behind the arc. The force of the explosion imparted a kick to the companion star, and this combined with the orbital velocity of the companion before the explosion to give the "observed" motion of the companion. Previously, studies with optical telescopes have revealed a star within the remnant that is moving much more quickly than its neighbors, showing that it could be the companion to the supernova. The size of the companion's orbit is not shown to scale here: the separation between it and the white dwarf before the explosion is estimated to have only been about a millionth of a light year, while the full scale of the illustration is over 10 light years. Credit: NASA/CXC/M.Weiss

Other details of the arc support the idea that it was blasted away from the companion star. For example, the X-ray emission of the remnant shows an apparent "shadow" next to the arc, consistent with the blocking of debris from the explosion by the expanding cone of material stripped from the companion. This shadow is most obvious in very high energy X-rays showing iron debris.

These pieces of evidence support a popular scenario for triggering a Type Ia supernova, where a white dwarf pulls material from a "normal," or Sun-like, companion star until a thermonuclear explosion occurs. In the other main competing theory, a merger of two white dwarfs occurs, and in this case, no companion star or evidence for material blasted off a companion, should exist. Both scenarios may actually occur under different conditions, but the latest Chandra result from Tycho supports the former one.

The shape of the arc is different from any other feature seen in the remnant. Other features in the interior of the remnant include recently announced stripes, which have a different shape and are thought to be features in the outer blast wave caused by cosmic ray acceleration.

Fast Facts for Tycho's Supernova Remnant:

Scale: Image is 10 arcmin across
Category: Supernovas & Supernova Remnants
Coordinates: (J2000) RA 00h 25m 17s | Dec +64° 08' 37"
Constellation: Cassiopeia
Observation Date: 2 pointings between April 29, 2003 and May 3, 2009
Observation Time: 283
Obs. ID: 3837, 7639, 8551, 10093-10097; 10902-10904; 10906
Color Code: Energy: Red 1.6-2.0 keV, Green 2.2-2.6 keV, Blue 4-6 keV
Instrument: ACIS
Also Known As: G120.1+01.4, SN 1572
References Lu, F.J. et al, 2011, ApJ, 732:11
Distance Estimate About 13,000 light years