A ghostly “hand” reaching through the cosmos has just revealed new information about massive stars’ violent deaths.
The spectacular structure is the ejecta from a core-collapse supernova, which astronomers have been able to observe as it blasts into space at around 4,000 kilometers (2,485 miles) per second by taking images of it over a 14-year period.
At the very tips of the “fingers”, the supernova remnant and blast wave – named MSH 15-52 – is punching into a cloud of gas called RCW 89, generating shocks and knots in the material, and causing the expanding supernova to decelerate.
MSH 15-52 is 17,000 light-years away from Earth, and it appears to be one of the Milky Way’s newest supernova remnants. Light from the stellar explosion reached Earth approximately 1,700 years ago, as the progenitor star ran out of fuel to support fusion, exploding its outer material into space, and collapsing its core.
That collapsed core became a pulsar, a type of “dead” star with neutrons packed so densely that they take on some of the properties of an atomic nucleus, pulsing light from its poles as it rotated at high speeds.
The X-ray nebula of ejected stellar material expanding into space is also shaped by this rotation.
A new study analyzes changes in RCW 89 as the supernova remnant plunges into it, using images from 2004, 2008, and 2017-2018.
We can better understand the velocity of the shock wave and knots of ejected stellar material in MSH 15-52 by calculating the distance traveled by these features over time. This is illustrated in the image below.
The blast wave, which is located near one of the hand’s fingertips, is a feature formed when MSH 15-52 collides with RCW 89, which is moving at a speed of 4,000 kilometers per second, but some knots of material are moving even faster, at speeds of up to 5,000 kilometers per second.
These knots are believed to be clumps of magnesium and neon that formed in the star before the supernova explosion and are moving at different speeds. Even the slowest seem insanely fast, around 1,000 km/s.
Supernova ejecta at the higher velocity range has also been observed in the supernova remnant Cassiopeia A, located 11,000 light-years away. This is also thought to have been a core-collapse supernova, but we observed it much more recently – light from the explosion reached Earth a mere 350 years ago.
We don’t know what caused the fast-moving clumps in either supernova yet, but gathering more data and studying such explosions at different timespans, will help astronomers painstakingly piece the puzzle together.
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