When a star much heavier than the Sun exhausts its nuclear fuel, its core collapses and the outer layers rebound in a supernova. For decades, astronomers assumed that such explosions distribute newly forged heavy elements evenly through the surrounding gas, like dye stirred into water. Recent radio surveys of expanding supernova remnants complicate that picture. The surveys reveal that elements such as iron and nickel are not spread smoothly but are concentrated in dense clumps and narrow filaments, with large pockets of gas left nearly untouched.
The leading explanation attributes this unevenness to instabilities that arise during the collapse itself. As the rebounding shock wave pushes outward, slight irregularities in pressure grow rapidly, fracturing the once-smooth shell into fingers of enriched material. Because these fingers travel at different speeds, the heavy elements they carry are deposited at varying distances from the original star.
The finding matters for understanding how later generations of stars and planets form. If enrichment is patchy rather than uniform, then two young stars condensing only a few light-years apart from the same remnant could inherit markedly different chemical compositions. Some researchers now suspect that this variability, long treated as measurement noise, may instead carry a genuine record of the explosions that preceded each star's birth.
Which of the following best states the main idea of the passage?
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