- 4456 - RING NEBULA - interaction of three stars? - Southern Ring Nebula has an unexpected structure. Submillimeter wavelength radio observations of the Southern Ring Nebula have identified that it's actually a double ring, shaped by the interactions of three stars.
----------------------------- 4456 - RING NEBULA - interaction of three stars?
- The billowing Southern Ring Nebula is the
cocoon of a dying star and it has a secret. Scientists have found this nebula
to exhibit a double-ring structure that evidences not one, but possibly three
stars at its heart.
-
- The Southern Ring Nebula, “NGC 3132”, is a
planetary nebula located about 2,000 light-years away in the constellation of
Vela, “the Sails”. The name "planetary nebula" is a misnomer. Such
nebulas have nothing to do with planets.
-
- Instead, they are the final exhalations of
dying, sun-like stars, which transform inside the nebulous chrysalis until
finally blossoming into a white dwarf. A nebula is formed from the dying star's
outer envelope, which is puffed off into space following the star's red giant
phase.
-
- The Southern Ring Nebula was imaged in
December 2022 by the James Webb Space Telescope (JWST), which revealed
molecular hydrogen gas forming the nebula's "exoskeleton." This
refers to warm gas radiating with a temperature equal to 1,340 degrees
Fahrenheit, as it gets illuminated and heated by ultraviolet light coming from
the white dwarf itself. That exoskeleton, however, only represents a small
fraction of the molecular gas in the nebula.
-
- Astronomers went hunting for more of the
nebula's molecular gas, specifically searching for carbon monoxide gas using
the Submillimeter Array (SMA), which is a group of eight radio telescopes on an
inactive volcano named Mauna Kea in Hawaii.
-
- Carbon monoxide is mixed in with hydrogen
and other molecular gases inside the nebula, so observing the carbon monoxide
content is actually a proxy for observing all those other molecules that are
not as easy to detect. The SMA was able
to measure both the distribution and velocities of the carbon monoxide
molecules, showing which parts are moving towards us and which are moving away
from us.
-
- As the Southern Ring's name suggests, it is
primarily shaped from our point of view as a ring. The SMA observations showed
that this ring is expanding, which is to be expected as the nebula slowly grows
before eventually dispersing. The data
allowed them to create a three-dimensional map of the nebula's molecular
exoskeleton. This offered up a surprise. Not only were the researchers able to
show that what we see as a ring is merely a lobe in a bi-polar nebula seen
end-on, but they also found a second ring perpendicular to the first.
-
- When we started to turn the whole nebula
around in 3D, we immediately saw it was really a ring, and then we were amazed
to see there was another ring. The
whole bizarre arrangement paints a fascinating tail of not one, not even two,
but quite possibly three stars at the heart of the nebula. Only one of these
stars, the most massive of the three, will have reached the end of its life but
the stellar trio, if all three really exist, are likely either too close to one
another or too faint to be separately resolved, even by the JWST.
-
- There's growing evidence that some
planetary nebulas, at least those that sport complex structures, are formed
from the interference of a companion star to the central dying star. For the
Southern Ring, a triple system formed of
a close binary is orbited by a more distant, third star within an orbital
radius of 60 astronomical units of the binary.
-
- One astronomical unit, AU, is the distance
between Earth and the sun, and in our solar system 60 AU would be out at the
far edge of the Kuiper Belt.
-
- The two lobes of the Southern Ring have a
narrow, or "pinched," waistline, like an hourglass, which is a common
feature of planetary nebulas emanating from a binary star system in which one
of the stars is reaching the end of its life. The binary companion is able to
corral the material shed by the dying star so that it escapes along a polar,
rather than equatorial, direction, forming the two lobes.
-
- The JWST's mid-infrared observations
support this hypothesis, having found an excess of infrared light coming from
the central star system, which is a classic signature of a dusty disk formed
from interactions between the red giant and a close binary companion.
-
- Though the Southern Ring appears bi-lobed,
some material must have been emitted as a roughly spherical or ellipsoidal
envelope of material cast off by the red giant, a rapid mass-loss event that
perhaps represented its final exhalation of material to leave behind the white
dwarf.
-
- The binary star system produces a series of
fast, narrow jets, but if a third star is present, then the extra star's
gravity would act on the inner binary, causing the direction of the jets to
"wobble," like a spinning top. Those precessing jets would have
carved out a circular hollow in the ellipsoidal component of the nebula,
thereby creating the second ring.
-
- This explanation is still speculative, but
the nebula's central ionized cavity does bear the evidence of such jets in its
structure.
-
- Other ring-shaped planetary nebulas, such as
the Helix Nebula (NGC 7293 in Aquarius), have also been shown to have bi-lobed
structures by which we are looking "down" the end of one lobe. The
discovery of the second ring in the Southern Ring Nebula is prompting
astronomers to revisit some of those other well-known ring nebulas to see if
they have missed second rings in them, too.
-
- Where does the carbon and the oxygen and
the nitrogen in the universe come from?
We're seeing it generated in the sun-like stars that are dying, like the
star that's just died and created the Southern Ring.
-
- As an expanding planetary nebula disperses
into interstellar space, it spreads those molecules across the cosmos, where
they wind up in giant molecular clouds that form the next generation of stars
and planets. A lot of that molecular gas
would wind up in planetary atmospheres and atmospheres can enable life. All the elements on Earth heavier than
hydrogen and helium originated inside stars and were then ejected into space
when those stars died.
-
- We are literally star-stuff. When we marvel at the beauty of stellar
death in nebulas such as the Southern Ring, we can also imagine it as a stellar
phoenix to one day rise from the ashes and begin the cycle of star-birth and
death all over again. All this has
happened before, and all of this will happen again.
-
-
May 4, 2024 RING
NEBULA - interaction of three stars? 4456
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