by Scientists may have discovered how a supernova located close enough to Earth came to be decorated with a remarkable “string of pearls” formation.
Supernova 1987A (SN 1987A) shows the remnants of a massive cosmic explosion that tore apart a massive star and left behind a neutron star ringed with stellar material. It is located in a satellite galaxy of the Milky Way known as the Large Magellanic Cloud, or LMC. This region is located approximately 160,000 light years away.
The most remarkable thing about SN 1987A is the fact that it is ringed by clumps of glowing hydrogen plasma — a structure that has long been a mystery in astrophysics. A phenomenon known as the Rayleigh-Taylor instability is often used to explain the formation of fluid structures in the plasma like we see around SN 1987A, but this concept alone cannot fully explain the cosmic jewels of the supernova.
Now, however, researchers from the University of Michigan may finally understand how this “string of pearls” was created. They believe the structure may be linked to the way contractors are created. Those are the fluffy white streaks that airplanes leave behind in the sky as they fly over the Earth’s surface.
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“The same mechanism that breaks up airplane wakes could be at work here,” Michael Wadas, a staff member and researcher at the California Institute of Technology, said in a statement.
With this parallel plane, the team suggests that the formation of SN1987A’s hydrogen clumps could be the result of a mechanism known as the “Crow instability.” Closer to home, this phenomenon occurs when the air from each jet wing, known as wingtip vortices, flows into another. This creates gaps in the otherwise fine cloud lines, visible due to water vapor in the jet’s wake.
Crow instability can also do something that Rayleigh-Taylor cannot: Help researchers predict the number of clumps that should be seen around the supernova remnant.
“The Rayleigh-Taylor instability could tell you that there might be clumps, but it would be very difficult to put a number on it,” Wadas said.
Dressed like a supernova super star
The proximity of SN 1987A to Earth is only part of what makes it one of the most famous and most studied supernovae.
Furthermore, this cosmic explosion occurred at a time when its light was able to reach the Earth, during a period when humanity was equipped with the necessary instruments to observe its evolution. In fact, SN 1987A was the first supernova visible to the unaided eye since Kepler’s supernova was observed in 1604. All of this makes SN 1987A an extremely rare astrophysical event that has had an enormous impact on our understanding of evolution and the eventual death of the star.
Supernovas like SN 1987A occur when massive stars exhaust their supplies of fuel necessary for nuclear fusion within their cores. This rapidly creates a stellar core, which creates a shock wave that generates a powerful explosion, or supernova, that ejects 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 a little in the dark about the star that died leaving behind the wreckage scientists call SN 1987A. In fact, it was only this year, thanks to observations with the James Webb Space Telescope (JWST), that we were able to determine that SN 1987A actually has a neutron star at its core.
However, scientists theorize that a ring of gas around the star that exploded to form SN 1987A was created by the merger of two stars. This collision would rip the hydrogen from both stars, with the element escaping into space as the merger sparked a brilliant blue star.
This would have happened thousands of years before the supernova itself. Meanwhile before that stellar explosion, there would have been strong stellar winds made up of high-speed charged particles coming from the star after hitting this gas. That could have formed the clusters of hydrogen around the star before it went supernova, meaning that the string of pearls adorning SN 1987A could have existed before the supernova even happened.
To confirm this origin story, the University of Michigan team created a sophisticated simulation of the cloud being pushed out by the stellar wind and the stream of particles exerting some kind of pressure on the cloud.
As a result the top and bottom of the gas cloud is pushed out further and faster than its central region. The cloud folded in on itself, and this behavior triggered the so-called Crow instability. This, in turn, caused the cloud to break up into even clusters – the pearls now wear SN 1987A.
The team’s simulation specifically predicted that SN 1987A should be decorated with 32 pearls, which is pleasingly close to the 30 hydrogen clumps seen around this supernova wreckage according to actual observations.
“That’s a big part of why we think this is the Crow instability,” said the lead author of the research and University of Michigan scientist Eric Johnsen in the statement.
The team’s simulation also predicted that the Crow instability could have created more strings of hydrogen pearls around SN 1987A that are smaller than the first cosmic necklace.
This appears to be visible in a JWST image of the supernova wreckage captured in August 2023. This suggests that the famous supernova may be even more decorated with cosmic fine art than astronomers can currently see.
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Studying these hydrogen grains could help scientists determine whether the Cluster instability is at play when planets form in the clouds of gas and dust found around infant stars.
The team’s research was published on March 13 in the journal Physical Review Letters.
