Scientists may have discovered how a supernova relatively close to Earth became adorned with a remarkable "string of pearls" formation.
Supernova 1987A (SN 1987A) represents the remnants of a massive cosmic explosion that ripped apart a massive star and left behind a neutron star surrounded by stellar material. It is located in a satellite galaxy of the Milky Way called the Large Magellanic Cloud, or LMC. This region is about 160,000 light years away from us.
What's especially remarkable about SN 1987A is the fact that it is surrounded by clumps of glowing hydrogen plasma - a structure that has long been a mystery in astrophysics. A phenomenon called Rayleigh-Taylor instability is often used to explain the formation of liquid structures in plasma, like what we see around SN 1987A, but this concept alone cannot fully explain the cosmic jewelry of the supernova remnant.
Now, however, researchers at the University of Michigan will finally understand how this "string of pearls" was forged. They believe the structure may be related to the way contrails are made. These are the fluffy white streaks that airplanes leave in the sky as they fly over the Earth's surface.
Related: James Webb Space Telescope spots neutron star hidden in supernova wreckage
"The same mechanism that disrupts aircraft wake-up could be at play here," Michael Wadas, a team member and researcher at the California Institute of Technology, said in a statement.
With this plane in parallel, the team suggests that the formation of SN1987A's hydrogen clumps could be the result of a mechanism called 'Crow instability'. Closer to home, this phenomenon occurs when the air currents from each wing of a jet aircraft, known as wingtip vortices, merge into each other. This creates gaps in what would otherwise be smooth cloud lines, visible due to water vapor in the aircraft's exhaust.
Crow instability can also do something Rayleigh-Taylor can't: help researchers predict the number of clumps that should be seen around the supernova remnant.
"The Rayleigh-Taylor instability might tell you that there might be clumps, but it would be very difficult to pick some of them out," Wadas said.
Dress up as a superstar supernova
SN 1987A's proximity to Earth is only part of what makes it one of the most famous and well-studied supernovae.
Moreover, this cosmic explosion occurred at a time when its light could reach Earth, at a time when humanity was equipped with the instruments necessary to monitor its evolution. In fact, SN 1987A became the first supernova visible to the naked eye since Kepler's supernova was observed in 1604. All this makes SN 1987A an incredibly rare astrophysical event that has had a huge impact on our understanding of the evolution and eventual death of stars.
Supernovae like SN 1987A form when massive stars deplete their fuel supplies needed for nuclear fusion in their cores. This causes a stellar core to rapidly contract, creating a shock wave that generates a powerful explosion, or supernova, that expels the outer layers of the dying star. This stellar core is transformed into a neutron star or a black hole, depending on its mass.
Scientists are still somewhat in the dark about the star that died, leaving behind the wreckage that scientists call SN 1987A. Only this year, thanks to observations with the James Webb Space Telescope (JWST), we were able to determine that there is actually a neutron star at the heart of SN 1987A.
However, scientists theorize that a ring of gas around the star that exploded to create SN 1987A was formed by the merger of two stars. This collision would have ripped hydrogen from the two stars, with the element escaping into space as the merger created a blue supergiant star.
This would have happened tens of thousands of years before the supernova itself. In the intervening time before that explosion, strong stellar winds, composed of high-speed charged particles coming from the star, would have bombarded this gas. That could have formed the clumps of hydrogen around the star before it became a supernova, meaning the string of pearls adorning SN 1987A may have been there before the supernova happened.
To confirm this origin story, the University of Michigan team created an advanced simulation of the cloud being pushed outward by the stellar wind, as the stream of particles exerts a kind of drag force on the cloud.
This resulted in the top and bottom of the gas cloud being pushed out further and faster than the middle region. The cloud curled in on itself and this behavior caused the so-called Crow instability. This, in turn, caused the cloud to break up into even clumps: the pearls that SN 1987A now bears.
The team's simulation specifically predicted that SN 1987A would be decorated with 32 beads, which is pleasingly close to the 30 clumps of hydrogen seen around this supernova wreckage by actual observations.
"That's a big part of why we think this is the Crow instability," lead researcher and University of Michigan scientist Eric Johnsen said in the statement.
The team's simulation also predicted that Crow's instability around SN 1987A could have actually created more strands of hydrogen beads that are weaker than the first cosmic chain.
This is something that seems to manifest itself in a JWST image of the supernova wreckage captured in August 2023. This suggests that the famous supernova could be even more beautifully decorated with cosmic finery than astronomers can currently see.
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Studying these hydrogen beads could also help scientists determine whether Crow instability plays a role when planets form in the collapsing clouds of gas and dust found around young stars.
The team's research was published March 13 in the journal Physical Review Letters.
