- 4598 - SUPERNOVAE - new and unusual? - In 1181, Japanese and Chinese astronomers saw a bright light appear in the constellation Cassiopeia. It shone for six months, and those ancient observers couldn’t have known it was an exploding star. To them, it looked like some type of temporary star that shone for 185 days
---------------------------------- 4598 - SUPERNOVAE - new and unusual?
- In the modern astronomical age, we’ve
learned a lot more about this object. It was a supernova called “SN 1181 AD”,
and we know that it left behind a remnant “zombie” star. New research examines
the supernova’s aftermath and the strange filaments of gas it left behind.
-
- Though it was seen almost 850 years ago,
only modern astronomers have been able to explain SN 1181. For a long time, it
was an orphan. While astronomers were able to identify the modern remnants of
many other historical supernovae, SN 1181 was stubborn.
-
- Finally, in 2013, amateur astronomer Dana
Patchick discovered a nebula with a central star and named it “Pa 30”. Research
in 2021 showed that Pa 30 is the remnant of SN 1181. The SN exploded when two
white dwarfs merged and created a Type 1ax supernova.
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- SN 1181 is unusual. When supernovae
explode, there’s usually only a black hole or a neutron star left as a remnant.
But SN 1181 left part of a white dwarf behind, an intriguing object astronomers
like to call a zombie star. Strange filaments resembling dandelion petals
extend from this strange star, adding to the object’s mystery.
-
- Researchers have gotten a new, close-up look
at Pa 30. Their research is titled
“Expansion Properties of the Young Supernova Type Iax Remnant Pa 30 Revealed. This recently discovered Pa 30 nebula, the
putative type Iax supernova remnant associated with the historical supernova of
1181 AD, shows puzzling characteristics that make it unique among known
supernova remnants, including a “unique radial and filamentary structure.
-
- The hot stellar remnant at Pa 30’s center
is also unique. Its presence, as well as the lack of hydrogen and helium in its
filaments, indicates that it’s the result of a rare Type1ax supernova. Since
hydrogen and helium make up 90% of the chemicals in the Universe, objects
without either of them are immediately interesting.
-
- The astronomers used the Keck Cosmic Imager
Spectrograph (KCIS) to examine the 3D structure and the velocities of the
filaments. The KCIS was built to observe the cosmic web, the intricate
arrangement of gas, dust, and dark matter that makes up the large-scale
structure of the Universe. The gas and dust are extremely dim, and the KCIS was
made to perform spectroscopy on these types of low surface brightness
phenomena.
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- KCIS is a powerful spectrograph that can capture
spectral information for each pixel in an image. It can also measure the
redshift and blueshift of objects it observes, meaning it can determine their
velocity and direction of movement. The researchers were able to show that
material in the filaments travelled ballistically at approximately 1,000
kilometres per second.
-
- This means that the ejected material has not
been slowed down, or sped up, since the explosion. Thus, from the measured velocities, looking
back in time allowed us to pinpoint the explosion to almost exactly the year
1181.
-
- “Pa 30” has some unusual features. It’s
unusually asymmetrical, while most SN remnants are more spherical. Its
filamentary structure displays significant variation in ejecta distribution
along the line of sight. Some filaments are more prominent than others and
extend further, creating an irregular and lopsided appearance.
-
- Some parts of the nebula are travelling at
different speeds and in different directions. Elements in the nebula are also
distributed unevenly. Iron is far more concentrated in some regions than
others. All of these features suggest that the initial explosion mechanism was
asymmetric and that the ejecta in the filaments stem from the initial explosion
observed in 1181. “Pa 30” also has a
very sharp inner edge with an inner gap that surrounds the zombie star.
-
- Many of Pa 30’s features suggest an
asymmetric explosion as the cause. The
ejecta show a strong asymmetry in flux along the line of sight, which may hint
at an asymmetric explosion. The researchers found that the total flux from
redshifted filaments is 40% higher than from blueshifted filaments.
-
- An asymmetric supernova explosion suggests
that the underlying physics are complex. Rotation, complex magnetic fields, and
the presence of a stellar companion can all contribute to asymmetry. Coupled
with the unusually hot white dwarf left behind and its high-velocity stellar
wind, the evidence suggests that it was a “Type 1ax supernova”.
-
- That means the “zombie star” is likely the
remnant of a failed thermonuclear explosion in a white dwarf. The white dwarf
could have been just below the Chandrasekhar mass and not exploded completely.
-
- Or, it could’ve been one of the
theoretically possible but elusive super-Chandrasekhar mass white dwarfs. These
objects are of great interest because they could be the cause of unusually
bright supernovae. If Pa 30’s progenitor was a super-Chandrasekhar mass white
dwarf, it could explain some of the remnant’s unusual characteristics.
-
- 3D characterization of the velocity and
spatial structure of a supernova remnant tells us a lot about a unique cosmic
event that our ancestors observed centuries ago. But it also raises new
questions and sets new challenges for astronomers to tackle next.
-
- Further IFU spectroscopic observations with
wider coverage of the nebula will confirm if there exists a global asymmetry in
the nebula ejecta.
-
-
November 4, 2024 SUPERNOVAE - new
and unusual? 4598
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--------------------- --- Tuesday, November 5,
2024
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