(a) WISE IR false color image of Pa 30; (b)false-color IR image with XMM-Newton X-ray contoursthe emission from the central star is highlighted in blue from the GALEX near-UV data, while the XMM-Newton contours; (c) deep KPNO optical image showing the diffuse SN shell
Credit: Ritter et al. (2021, the Astrophysical Journal)

Mysterious Guest Star Identified?

There have been nine supernovae in the Milky Way bright enough to be seen by the unaided eye. The last such supernova was seen in AD 1604 (and is commonly named for Johannes Kepler, one of its more reknowned eyewitnesses). Supernovae typically occur every 50-100 years, so we're a bit overdue for one of these titanic stellar explosions (keep an eye on Eta Carinae, a good candidate for the next blast). Five of these nine have been identified with hot, expanding blast waves (and sometimes the compact objects left behind by the blast have also been identified). A well-known example is the Crab Nebula (and the Crab pulsar, a rapidly-spinning neutron star at the heart of the nebula), which was observed in AD 1054. The remnants of some of these other supernovae are a bit more difficult to identify, given the imprecisions of estimating positions of these blasts seen centuries ago. One Milky Way supernova was recorded in AD 1181 by sky watchers in China and Japan, and evidently remained visible for about 3 months before fading away. Now, after nine centuries, astronomers believe they have finally found the remnant of this supernova, and have even identified the compact object left behind by the explosion. In 2013, an astronomer working with the "Deep Sky Hunters" group of amateur astronomers, discovered a rather inocuous extended nebula in some infrared images obtained by NASA's WISE space telescope (shown above left). This object is within a few degrees of the reported position of SN 1181. Deep optical observations (above right) revealed a blast wave speeding through space at more than 2 million miles per hour, suggesting an origin in an explosion that happened about 1000 years ago. X-ray observations by the XMM-Newton X-ray telescope (middle, shown as contours superimposed on an infrared image) revealed a strong point-like source of X-rays from near the center of the nebula. This X-ray source is an unusual object, a rare, extremely hot, mass-losing star. Astronomers believe that this weird star is the result of the collision and merger of two white dwarf stars, which would have produced an unusual type of supernova. If so, then this would be the first recorded double-white-dwarf merger known in the Milky Way, and the only one whose remnants can be studied in detail.
Published: September 20, 2021

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Page Author: Dr. Michael F. Corcoran
Last modified Tuesday, 28-Sep-2021 08:29:26 EDT