A group of researchers at the Harvard-Smithsonian Center for Astrophysics (CfA) found a reverse shock wave in Tycho’s supernova remnants. It’s moving inwards at a speed of about Mach 1.000, which is 1.000 times the speed of sound. This phenomenon is heating the nucleus, causing an emission of X-rays.
Tycho’s supernova is known by that name though officially it’s called SN 1572 because its observation was recorded for the first time on November 11, 1572 by astronomer Tycho Brahe. For some months it was visible to the naked eye and at its peak was even brighter than Venus. Other astronomers spotted it even earlier but Brahe published the essay “De nova et nullius aevi memory prius visa stella” (“Concerning the Star, new and never before seen in the life or memory of anyone”) about it.
Observations made during the 20th century with instruments much more sophisticated than those available to Tycho Brahe and his contemporaries have allowed to establish that it was a Type Ia supernova. In essence, a white dwarf accreted materials from a companion until the mass was close to the Chandrasekhar limit and exploded.
In October 2004 the discovery of a Sun-like star was announced that probably was Tycho’s supernova’s companion. According to subsequent studies, it was originally more massive but most of its outer layers were stripped away by the supernova. Its speed is much higher than that of all the other stars in the vicinity, a fact that may also have been caused by the supernova. Other analyzes are more skeptical so the research continues.
An observation of the Tycho supernova remnant made with the Suzaku X-ray Space Telescope of JAXA, the Japanese space agency, allowed to discover the peculiar reverse shock wave. The supernova caused an outwards shockwave when the ejecta collided with the interstellar gas at very high speeds. This shock wave still goes on today but that interaction has also caused a reverse shock wave.
The speed of the reverse shock wave is about 1,000 times higher than that of sound. It may seem strange to use references to sound in space but in this case we’re dealing with a lot of material that can conduct sound waves so it makes sense to speak of Mach 1.000.
The observation of the X-rays produced by this reverse wave shock allowed to discover that electrons that pass through it and are heated very quickly, causing that emission. The cause of that warming hasn’t been found yet so its study will continue and the team that made this study will look for similar phenomena in other supernovas remnants spotted in the last few centuries.
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