by neufer » Tue Apr 17, 2018 2:28 pm
Chris Peterson wrote: ↑Tue Apr 17, 2018 1:37 pm
mjsakers wrote: ↑Tue Apr 17, 2018 1:31 pm
How do we know that the central star (white dwarf) seen in the image is in fact the central star of the nebula and not just a background star that happens to line up with the center. There's no way to be certain of this it seems. I hope it is not just an assumption.
Well, it's a pretty safe assumption. A planetary nebula has to have a central star, and that's the only candidate in the right place.
- It should shine brightly in both the ultraviolet & infrared...like the Helix Nebula (NGC 7293):
https://apod.nasa.gov/apod/ap091231.html wrote:
APOD Explanation: <<Dust makes this cosmic eye look red. The eerie Spitzer Space Telescope image shows infrared radiation from the well-studied Helix Nebula (NGC 7293) a mere 700 light-years away in the constellation Aquarius. The two light-year diameter shroud of dust and gas around a central white dwarf has long been considered an excellent example of a planetary nebula, representing the final stages in the evolution of a sun-like star. But the Spitzer data show the nebula's central star itself is immersed in a surprisingly bright infrared glow. Models suggest the glow is produced by a dust debris disk. Even though the nebular material was ejected from the star many thousands of years ago, the close-in dust could be generated by collisions in a reservoir of objects analogous to our own solar system's Kuiper Belt or cometary Oort cloud. Formed in the distant planetary system, the comet-like bodies would have otherwise survived even the dramatic late stages of the star's evolution.>>
https://www.nasa.gov/mission_pages/spitzer/multimedia/pia15817.html wrote:
Helix Nebula - Unraveling at the Seams
<<A dying star is throwing a cosmic tantrum in this combined image from NASA's Spitzer Space Telescope and the Galaxy Evolution Explorer (GALEX), which NASA has lent to the California Institute of Technology in Pasadena. In death, the star's dusty outer layers are unraveling into space, glowing from the intense ultraviolet radiation being pumped out by the hot stellar core.
Planetary nebulae are actually the remains of stars that once looked a lot like our sun. When the hydrogen fuel for the fusion reaction runs out, the star turns to helium for a fuel source, burning it into an even heavier mix of carbon, nitrogen and oxygen. Eventually, the helium will also be exhausted, and the star dies, puffing off its outer gaseous layers and leaving behind the tiny, hot, dense core, called a white dwarf. The white dwarf is about the size of Earth, but has a mass very close to that of the original star; in fact, a teaspoon of a white dwarf would weigh as much as a few elephants!
The glow from planetary nebulae is particularly intriguing as it appears surprisingly similar across a broad swath of the spectrum, from ultraviolet to infrared. The Helix remains recognizable at any of these wavelengths, but the combination shown here highlights some subtle differences.
The intense ultraviolet radiation from the white dwarf heats up the expelled layers of gas, which shine brightly in the infrared. GALEX has picked out the ultraviolet light pouring out of this system, shown throughout the nebula in blue, while Spitzer has snagged the detailed infrared signature of the dust and gas in yellow A portion of the extended field beyond the nebula, which was not observed by Spitzer, is from NASA's all-sky Wide-field Infrared Survey Explorer (WISE). The white dwarf star itself is a tiny white pinprick right at the center of the nebula.
The brighter purple circle in the very center is the combined ultraviolet and infrared glow of a dusty disk circling the white dwarf (the disk itself is too small to be resolved). This dust was most likely kicked up by comets that survived the death of their star. Before the star died, its comets, and possibly planets, would have orbited the star in an orderly fashion. When the star ran out of hydrogen to burn, and blew off its outer layers, the icy bodies and outer planets would have been tossed about and into each other, kicking up an ongoing cosmic dust storm. Any inner planets in the system would have burned up or been swallowed as their dying star expanded.>>
[quote="Chris Peterson" post_id=281574 time=1523972271 user_id=117706]
[quote=mjsakers post_id=281573 time=1523971910]
How do we know that the central star (white dwarf) seen in the image is in fact the central star of the nebula and not just a background star that happens to line up with the center. There's no way to be certain of this it seems. I hope it is not just an assumption.
[/quote]
Well, it's a pretty safe assumption. A planetary nebula has to have a central star, and that's the only candidate in the right place.[/quote]
[list]It should shine brightly in [b][u]both[/u] the [color=#0000FF]ultraviolet[/color] & [color=#FF0000]infrared[/color][/b]...like the [b][u]Helix Nebula[/u][/b] (NGC 7293):[/list]
[quote=" https://apod.nasa.gov/apod/ap091231.html"]
[float=left][img3="Spitzer Space Telescope infrared image of the Helix Nebula (NGC 7293) "]https://apod.nasa.gov/apod/image/0912/helix_spitzer_720.jpg[/img3][/float]APOD Explanation: <<Dust makes this cosmic eye look red. The eerie Spitzer Space Telescope image shows infrared radiation from the well-studied Helix Nebula (NGC 7293) a mere 700 light-years away in the constellation Aquarius. The two light-year diameter shroud of dust and gas around a central white dwarf has long been considered an excellent example of a planetary nebula, representing the final stages in the evolution of a sun-like star. But the Spitzer data show the nebula's central star itself is immersed in a surprisingly bright infrared glow. Models suggest the glow is produced by a dust debris disk. Even though the nebular material was ejected from the star many thousands of years ago, the close-in dust could be generated by collisions in a reservoir of objects analogous to our own solar system's Kuiper Belt or cometary Oort cloud. Formed in the distant planetary system, the comet-like bodies would have otherwise survived even the dramatic late stages of the star's evolution.>>[/quote][quote=" https://www.nasa.gov/mission_pages/spitzer/multimedia/pia15817.html"]
[float=left][img3="Infrared data from Spitzer for the central nebula is rendered in green (wavelengths of 3.6 to 4.5 microns) and red (8 to 24 microns), with WISE data covering the outer areas in green (3.4 to 4.5 microns) and red (12 to 22 microns). Ultraviolet data from GALEX appears as blue (0.15 to 2.3 microns)."]https://www.nasa.gov/images/content/693949main_pia15817-43_946-710.jpg[/img3][img3="A cloud of dirt & dust follows Pig-Pen in the comic strip Peanuts wherever he goes"]https://upload.wikimedia.org/wikipedia/en/thumb/e/e1/PigPen_%28Peanuts%29.png/220px-PigPen_%28Peanuts%29.png[/img3][/float]Helix Nebula - Unraveling at the Seams
<<A dying star is throwing a cosmic tantrum in this combined image from NASA's Spitzer Space Telescope and the Galaxy Evolution Explorer (GALEX), which NASA has lent to the California Institute of Technology in Pasadena. In death, the star's dusty outer layers are unraveling into space, glowing from the intense ultraviolet radiation being pumped out by the hot stellar core.
Planetary nebulae are actually the remains of stars that once looked a lot like our sun. When the hydrogen fuel for the fusion reaction runs out, the star turns to helium for a fuel source, burning it into an even heavier mix of carbon, nitrogen and oxygen. Eventually, the helium will also be exhausted, and the star dies, puffing off its outer gaseous layers and leaving behind the tiny, hot, dense core, called a white dwarf. The white dwarf is about the size of Earth, but has a mass very close to that of the original star; in fact, a teaspoon of a white dwarf would weigh as much as a few elephants!
The glow from planetary nebulae is particularly intriguing as it appears surprisingly similar across a broad swath of the spectrum, from ultraviolet to infrared. The Helix remains recognizable at any of these wavelengths, but the combination shown here highlights some subtle differences.
The intense ultraviolet radiation from the white dwarf heats up the expelled layers of gas, which shine brightly in the infrared. GALEX has picked out the ultraviolet light pouring out of this system, shown throughout the nebula in blue, while Spitzer has snagged the detailed infrared signature of the dust and gas in yellow A portion of the extended field beyond the nebula, which was not observed by Spitzer, is from NASA's all-sky Wide-field Infrared Survey Explorer (WISE). The white dwarf star itself is a tiny white pinprick right at the center of the nebula.
The brighter purple circle in the very center is the combined ultraviolet and infrared glow of a dusty disk circling the white dwarf (the disk itself is too small to be resolved). This dust was most likely kicked up by comets that survived the death of their star. Before the star died, its comets, and possibly planets, would have orbited the star in an orderly fashion. When the star ran out of hydrogen to burn, and blew off its outer layers, the icy bodies and outer planets would have been tossed about and into each other, kicking up an ongoing cosmic dust storm. Any inner planets in the system would have burned up or been swallowed as their dying star expanded.>>[/quote]