|
From ground-based telescopes, the so-called "ant nebula"
(Menzel 3, or Mz3) resembles the head and thorax of a
garden-variety ant. This dramatic NASA/ESA Hubble Space
Telescope image, showing 10 times more detail, reveals the
"ant's" body as a pair of fiery lobes protruding from a
dying, Sun-like star.
The Hubble images directly challenge old ideas about the last
stages in the lives of stars. By observing Sun-like stars
as they approach their deaths, the Hubble Heritage image of Mz3
-- along with pictures of other planetary nebulae -- shows
that our Sun's fate probably will be more interesting, complex,
and striking than astronomers imagined just a few years ago.
Though approaching the violence of an explosion, the ejection
of gas from the dying star at the center of Mz3 has intriguing
symmetrical patterns unlike the chaotic patterns expected from
an ordinary explosion. Scientists using Hubble would like to
understand how a spherical star can produce such prominent,
non-spherical symmetries in the gas that it ejects.
One possibility is that the central star of Mz3 has a closely
orbiting companion that exerts strong gravitational tidal
forces, which shape the outflowing gas. For this to work,
the orbiting companion star would have to be close to the
dying star, about the distance of the Earth from the Sun.
At that distance the orbiting companion star wouldn't be far
outside the hugely bloated hulk of the dying star. It's
even possible that the dying star has consumed its
companion, which now orbits inside of it, much like the
duck in the wolf's belly in the story "Peter and the Wolf."
(See http://oposite.stsci.edu/pubinfo/qt/ssudec.mov for an
animation that shows how this might work.)
A second possibility is that, as the dying star spins, its
strong magnetic fields are wound up into complex
shapes like spaghetti in an eggbeater. Charged winds moving at speeds
up to 1000 kilometers per second from the star, much like those in
our sun's solar wind but millions of times denser, are able to follow
the twisted field lines on their way out into space. These dense winds
can be rendered visible by ultraviolet light from the hot central star
or from highly supersonic collisions with the ambient gas that excites
the material into florescence.
No other planetary nebula observed by Hubble resembles Mz3
very closely. M2-9 comes close, but the outflow speeds in
Mz3 are up to 10 times larger than those of M2-9. (See
http://oposite.stsci.edu/pubinfo/PR/97/38/content/9738aw.jpg).
Interestingly, the very massive, young star, Eta Carinae,
shows a very similar outflow pattern (see
http://oposite.stsci.edu/pubinfo/PR/96/23.html).
Astronomers Bruce Balick (University of Washington) and Vincent
Icke (Leiden University) used Hubble to observe this planetary
nebula, Mz3, in July 1997 with the Wide Field Planetary 2 camera.
One year later, astronomers Raghvendra Sahai and John Trauger
of the Jet Propulsion Lab in California snapped pictures of
Mz3 using slightly different filters. This intriguing image,
which is a composite of several filters from each of the two
datasets, was created by the Hubble Heritage Team.
|
