Mgławica dwubiegunowa
Mgławica dwubiegunowa – mgławica charakteryzująca się parą symetrycznych płatów. Takie cechy posiada wiele mgławic planetarnych, choć nie wszystkie.
Mgławice dwubiegunowe mogą mieć kształty przypominające klepsydrę lub skrzydła motyla (w rzucie na sferę niebieską, jako że cała struktura jest trójwymiarowa). Najprawdopodobniej powstają wskutek działalności dżetów wyrzucających materię z układu podwójnego prostopadle do orbit składników. Na ukształtowanie mgławicy potencjalnie może mieć także wpływ układ planetarny umierającej gwiazdy. Jako że kierunki obrotu gwiazd i układów gwiezdnych w Galaktyce są zasadniczo losowe, orientacja mgławic planetarnych obserwowanych w otoczeniu Słońca także jest losowa. Jednak obserwacje mgławic dwubiegunowych w centralnym zgrubieniu galaktycznym wskazują, że długie osie tych struktur układają się w płaszczyźnie dysku galaktycznego. Jeżeli wynik ten potwierdzą badania większej próby mgławic dwubiegunowych, będzie z niego wynikało, że na ich kształtowanie ma wpływ także czynnik zewnętrzny – w tym przypadku silne pole magnetyczne, które mogło istnieć w czasie formowania się zgrubienia centralnego[1].
Przypisy
- ↑ Dziwaczne ustawienie mgławic planetarnych. Europejskie Obserwatorium Południowe, 2014-09-04. [dostęp 2017-04-10].
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This celestial object looks like a delicate butterfly. But it is far from serene.
What resemble dainty butterfly wings are actually roiling cauldrons of gas heated to more than 36,000 degrees Fahrenheit. The gas is tearing across space at more than 600,000 miles an hour -- fast enough to travel from Earth to the moon in 24 minutes!
A dying star that was once about five times the mass of the Sun is at the center of this fury. It has ejected its envelope of gases and is now unleashing a stream of ultraviolet radiation that is making the cast-off material glow. This object is an example of a planetary nebula, so-named because many of them have a round appearance resembling that of a planet when viewed through a small telescope.
The Wide Field Camera 3 (WFC3), a new camera aboard NASA’s Hubble Space Telescope, snapped this image of the planetary nebula, catalogued as NGC 6302, but more popularly called the Bug Nebula or the Butterfly Nebula. WFC3 was installed by NASA astronauts in May 2009, during the servicing mission to upgrade and repair the 19-year-old Hubble telescope.
NGC 6302 lies within our Milky Way galaxy, roughly 3,800 light-years away in the constellation Scorpius. The glowing gas is the star’s outer layers, expelled over about 2,200 years. The "butterfly" stretches for more than two light-years, which is about half the distance from the Sun to the nearest star, Alpha Centauri.
The central star itself cannot be seen, because it is hidden within a doughnut-shaped ring of dust, which appears as a dark band pinching the nebula in the center. The thick dust belt constricts the star’s outflow, creating the classic "bipolar" or hourglass shape displayed by some planetary nebulae.
The star’s surface temperature is estimated to be about 400,000 degrees Fahrenheit, making it one of the hottest known stars in our galaxy. Spectroscopic observations made with ground-based telescopes show that the gas is roughly 36,000 degrees Fahrenheit, which is unusually hot compared to a typical planetary nebulae.
The WFC3 image reveals a complex history of ejections from the star. The star first evolved into a huge red-giant star, with a diameter of about 1,000 times that of our Sun. It then lost its extended outer layers. Some of this gas was cast off from its equator at a relatively slow speed, perhaps as low as 20,000 miles an hour, creating the doughnut-shaped ring. Other gas was ejected perpendicular to the ring at higher speeds, producing the elongated "wings" of the butterfly-shaped structure. Later, as the central star heated up, a much faster stellar wind, a stream of charged particles travelling at more than 2 million miles an hour, plowed through the existing wing-shaped structure, further modifying its shape.
The image also shows numerous finger-like projections pointing back to the star, which may mark denser blobs in the outflow that have resisted the pressure from the stellar wind.
The nebula's outer edges are largely due to light emitted by nitrogen, which marks the coolest gas visible in the picture. WFC3 is equipped with a wide variety of filters that isolate light emitted by various chemical elements, allowing astronomers to infer properties of the nebular gas, such as its temperature, density, and composition.
The white-colored regions are areas where light is emitted by sulfur. These are regions where fast-moving gas overtakes and collides with slow-moving gas that left the star at an earlier time, producing shock waves in the gas (the bright white edges on the sides facing the central star). The white blob with the crisp edge at upper right is an example of one of those shock waves.
NGC 6302 was imaged on July 27, 2009 with Hubble’s Wide Field Camera 3 in ultraviolet and visible light. Filters that isolate emissions from oxygen, helium, hydrogen, nitrogen, and sulfur from the planetary nebula were used to create this composite image.
These Hubble observations of the planetary nebula NGC 6302 are part of the Hubble Servicing Mission 4 Early Release Observations.
The Ant planetary nebula (Menzel 3 or Mz 3). STScI-PRC2001-05
This NASA/ESA Hubble Space Telescope image reveals the ant's body as a pair of fiery lobes protruding from a dying, Sun-like star. 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 the Hubble space telescope 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."
A second possibility is that, as the dying star spins, its strong magnetic fields are wound up into complex shapes. Charged winds moving at speeds up to 1000 kilometers per second from the star, 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.
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.