We recently gained fresh knowledge about the dramatic demise of huge stars thanks to a phantom "hand" reaching through space.
Astronomers have been able to watch as the magnificent structure, which is the ejecta from a core-collapse supernova, shoots into space at about 4,000 kilometres (2,485 miles per second) by collecting pictures of it over a 14-year period.
The supernova remnant and blast wave, designated MSH 15-52, is smashing into a cloud of gas designated RCW 89 near the tips of the "fingers," triggering shocks and knots in the material and slowing the expanding explosion.
MSH 15-52, which is 17,000 light-years from Earth, appears to be one of the Milky Way's newest supernova remnants. About 1,700 years ago, the progenitor star ran out of fuel to conduct fusion, bursting its outer material into space and collapsing its core. Light from the stellar explosion eventually reached Earth.
That compressed core evolved into a particular kind of "dead" star known as a pulsar, an incredibly dense object with neutrons packed so closely that they resemble atomic nuclei that pulses light from its poles as it rotates quickly.
The X-ray nebula formed by star debris flung into space is similarly shaped by this spin.
A recent study that uses photos from 2004, 2008, and 2017–2018 to track changes in RCW 89 as the supernova remnant plunges into it has provided details on how quickly it is expanding.
We can better comprehend the shock wave velocity and knots of ejected star material in MSH 15-52 by measuring the distance travelled by these characteristics over time. This is depicted in the picture below.
The blast wave, where MSH 15-52 meets RCW 89, is a feature that is travelling at a speed of 4,000 kilometres per second. However, some knots of material are moving even faster, at up to 5,000 kilometres per second.
These knots, which are travelling at various speeds, are likely to represent clumps of magnesium and neon that formed in the star before the supernova explosion. Even the slowest, at about 1,000 km/s, seem incredibly fast.
However, as they interact with the information in RCW 89, these features are becoming slower. About 75 light-years separate the pulsar from RCW 89; to cross this gap, MSH 15-52's outer edge must expand at a mean velocity of 13,000 km/s.
This indicates that the substance would have encountered RCW 89 after passing through a relatively low-density hole or bubble in the gas surrounding the exploding star. The core-collapse supernova model can explain this.
A strong stellar wind would have blown into the area around the precursor star as it approached the end of its main-sequence existence, depleting the star of its hydrogen and leaving a vast cavity. The leftover stellar material was then thrown into this largely vacant region of space when the star's core eventually imploded in a supernova.
RCW 89 is the cavity's exterior wall. This higher-density zone was encountered by MSH 15-52, and the accident resulted in a sharp deceleration.
Cassiopeia A, a supernova remnant 11,000 light-years away, has also been found to have supernova ejecta in the higher velocity range. Although we only discovered it much more recently—light from the explosion only reached Earth 350 years ago—this is likewise believed to have been a core-collapse supernova.
Although we still don't fully understand the cause of the fast-moving clumps in either supernova, astronomers will eventually put the mystery together with the help of additional data and studies of these explosions over time.
Reference: The Astrophysical Journal Letters.
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