- 4486
- SUPERNOVAE 1987A
- what are the string of
pearls? - Astronomers finally have an explanation
for the “String of Pearls” in Supernova 1987a.
Not long after the explosion of Supernova 1987a, astronomers were making
predictions about how it might look in a few years.
--------------- 4486 - SUPERNOVAE 1987A - what are the string of pearls?
- Astronomers suggested a pulsar would show
up soon and many said that the expanding gas cloud would encounter earlier
material ejected from the star. The collision would light up the region around
the event and sparkle like diamonds.
-
- Today, astronomers look at the site of the
stellar catastrophe and see an expanding, glowing ring of light. Over the
years, its shape has changed to a clumpy-looking string of pearls.
-
- What’s happening to affect its appearance?
The answer lies in something called the “Crow Instability.” We see this aerodynamical process when
vortexes off the wingtips of airplanes interact with the contrails from their
engines. The instability breaks up the contrail into a set of vortex “rings”.
-
- This type of instability could explain why
Supernova 1987a formed a string of pearls.
The fascinating part about this is that the same mechanism that breaks
up airplane wakes could be in play here.
-
- Light and neutrinos from Supernova 1987a
reached Earth on February 23, 1987. The original star, “Sanduleak -69 202”, lay
about 168,000 light-years away in the Large Magellanic Cloud. It exploded as
Type II, the first one in modern times to show astronomers the details of a
core-collapse supernova.
-
- Since then, astronomers watched as a ring
of ejected material and a shockwave from the explosion itself spread to space.
It slammed into the material shed earlier in the star’s life. It does have a
neutron star in the center. Astronomers detected it in 2019 and observed it
using X-ray and gamma-ray
observatories.
-
- Several months after the explosion,
astronomers used the Hubble Space Telescope to image bright rings surrounding
the explosion site. That material came from the stellar wind of the progenitor
star. Ultraviolet light from the explosion ionized the gases in the cloud. The
inner ring lay about 2/3 of a light-year from the original star.
-
- The expanding ejecta from the supernova
eventually collided with it in 2001. That heated it further. The shockwave has
now expanded beyond the rings, leaving behind pockets of warm dust and glowing
clouds of gas. The turbulence of that shockwave and the damage it did to
regions of the inner ring is created the “pearls”.
-
- Astronomers have tried to explain the
string using something called a Rayleigh-Taylor instability. That occurs when
two fluids (or plasmas) of different densities interact with each other. Think
of oil and water trying to mix, or a heavy pyroclastic flow streaming out of a
volcano. The interaction forms interesting and predictable shapes in the
fluids.
-
- For 1978a, the denser “fluid” is the
material ejected during the supernova explosion. It is colliding with a less
dense cloud of material ejected earlier that has spread out to space. A simulation shows the shape of the gas
cloud on the left and the vortices, or regions of rapidly rotating flow. Each
ring represents a later time in the evolution of the cloud. The gas cloud
starts as an even ring with no rotation. It becomes a lumpy ring as the
vortices develop. Eventually, the gas breaks up into distinct clumps.
-
- The “Rayleigh-Taylor instability” could
tell you that there might be clumps, but it would be very difficult to pull a
number out of it. The “Crow Instability”
shows jet contrails are a better comparison because the wingtip vortices break
up the long smooth line of a jet contrail. The vortices flow into each other,
leaving gaps that can be predicted.
-
- The top and bottom of the cloud got pushed
out faster than the middle. That caused it to curl in on itself, triggering a
Crow Instability that broke the cloud apart into 32 even clumps similar to the
string of pearls at 1987a (which has 30-40 clumps). That predictable number of
clumps is why the team suggested the Crow Instability as a formation agent for
the string.
-
- Astronomers also think it could help
predict the formation of more beaded rings around the explosion site or when
dust around a star coalesces to form planets. Recent JWST infrared images seem
to show even more clumps that have appeared in the ring, and it will be
interesting to see if more of them appear in the future.
-
-
May 22, 2024 SUPERNOVAE
1987A - what are the string of pearls? 4472
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--------------------- --- Wednesday, May 29, 2024
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