Re: [Utah-astronomy] White dwarfs and YOU
Chuck, I imagine a black dwarf would be very difficult to observe, he must think the Universe is very young. I think there was mention that some planetary nebula gases are excited enough by a "very cool white dwarf" (they have a wide range of temperatures) that can't be observed, hence its a "black" dwarf. In essence some nebulas outlive (or at least cease to exist at the same time of) the white dwarf. Her explanation was that it is the heat from the white dwarf that illuminates the nebula. As Dan has pointed out amateurs commonly have the need equipment to see white dwarfs in nebula, but to see difficult companion stars not so much. You also mention that he is talking about white dwarfs from cataclysmic double stars. Perhaps in the case of planetary nebula (I believe most of these are not from cataclysmic doubles), that there is nothing to see until the "life" of White Dwarf is turned on, to illuminate the gases expelled from the red giant. Simply the intermediate period is before the nebula is visible. Again, I imagine most white dwarfs are not the product of double star systems gone wrong. Erik --- chuck.hards@gmail.com wrote: From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Subject: Re: [Utah-astronomy] White dwarfs and YOU Date: Sun, 25 Jan 2009 19:17:50 -0700 Yes, the pressure remains constant, independant of temperature, as does gravity, which is dependent on mass; the dwarf stays the same size as it cools. As to why the star continues to shine post-fission, here is Bishop's explanation: "Because of their immense thermal energy and small surface area, white dwarfs cool extremely slowly. The universe is not yet old enough for any white dwarf to have cooled sufficiently to become a "black dwarf"." He continues, "Also, white dwarfs are intrinsically very faint; thus only those close to the solar system can be seen. *Only one white dwarf is easily observable with a small telescope*." This supports the idea that for distant white dwarfs that are part of cataclysmic binary systems, it's the infalling matter that is seen and not the dwarf itself. But, like Kim I'm curious as to the details of the intermediate stage between the formation of the planetary nebula (the asymptotic giant star throwing-off its outer atmosphere), and true "white dwarf" status, after the nebula has faded. It could be that fusion doesn't turn off quickly, but slowly peters-out, in fits and starts, during the same time-frame as the lifespan of the nebula itself. I wonder... All the argument about the definition of "easily observable" and "small telescope" is superfluous and unnecessary, especially when we begin bringing things like averted vision into the argument. On Sun, Jan 25, 2009 at 6:14 PM, <zaurak@digis.net> wrote:
Kim, I am quoting from the article I posted earlier.
"Under the extreme conditions which prevail within a white dwarf, the laws of quantum mechanics become important. Quantum mechanics is the study of how subatomic particles (such as electrons, protons, and neutrons) behave. Subatomic particles do not always obey the same laws as large objects. Hence, the laws of quantum mechanics sometimes seem contrary to common sense.
One rule of quantum mechanics (known as the Pauli exclusion principle) is this: Two identical electrons, located in the same region of space, cannot have the same velocity. In a dense white dwarf, where the electrons are packed close to each other, some of the electrons are forced to have high velocities, and hence provide a high pressure. In a degenerate object such as a white dwarf, the fast-moving high-energy electrons provide a pressure which is independent of temperature. Even as the temperature of a white dwarf falls toward absolute zero, the Pauli exclusion principle demands that the high-velocity electrons keep moving at the same speed. Hence, the pressure exerted by the electrons remains constant as the temperature falls."
_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com
No, I didn't mention that. Jerry was the one who posted about the visibility of white dwarfs in a cataclysmic variable system, not Bishop. I was attempting to distance that from Bishop and try to underline the differences. In my post, Bishop's comments were in quotes, mine were not. Sorry for the apparent confusion. Also, I need to research this, but I'm not sure that planetary nebula are illuminated by the central star, but by the expelled material colliding with material ejected previously. These are glowing, ionized nebula, not merely reflection nebula. On Sun, Jan 25, 2009 at 8:05 PM, <zaurak@digis.net> wrote:
You also mention that he is talking about white dwarfs from cataclysmic double stars. Perhaps in the case of planetary nebula (I believe most of these are not from cataclysmic doubles), that there is nothing to see until the "life" of White Dwarf is turned on, to illuminate the gases expelled from the red giant. Simply the intermediate period is before the nebula is visible. Again, I imagine most white dwarfs are not the product of double star systems gone wrong.
I need to add that I don't think residual heat emmanating from a white dwarf is going to ionize nebular material. It's got to be energy from a pre-white-dwarf stage star that's doing it, while there is still some dying shreds of fusion taking place and some fairly energetic particles from a remnant solar-wind are still in play. On Sun, Jan 25, 2009 at 8:18 PM, Chuck Hards <chuck.hards@gmail.com> wrote:
Also, I need to research this, but I'm not sure that planetary nebula are illuminated by the central star, but by the expelled material colliding with material ejected previously. These are glowing, ionized nebula, not merely reflection nebula.
Like you, Chuck, I haven't had the time to do any immediate research, but I seem to recall that the radiation energy (what radiation I can't say - I'm no physicist, either) that causes the pn to be visible is ionizing radiation causing the pn to emit light from O3 emissions - therefore, not merely a reflection phenomena, but I’m certain that could also be a component. Kim -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Sunday, January 25, 2009 8:18 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] White dwarfs and YOU No, I didn't mention that. Jerry was the one who posted about the visibility of white dwarfs in a cataclysmic variable system, not Bishop. I was attempting to distance that from Bishop and try to underline the differences. In my post, Bishop's comments were in quotes, mine were not. Sorry for the apparent confusion. Also, I need to research this, but I'm not sure that planetary nebula are illuminated by the central star, but by the expelled material colliding with material ejected previously. These are glowing, ionized nebula, not merely reflection nebula. On Sun, Jan 25, 2009 at 8:05 PM, <zaurak@digis.net> wrote:
You also mention that he is talking about white dwarfs from cataclysmic double stars. Perhaps in the case of planetary nebula (I believe most of these are not from cataclysmic doubles), that there is nothing to see until the "life" of White Dwarf is turned on, to illuminate the gases expelled from the red giant. Simply the intermediate period is before the nebula is visible. Again, I imagine most white dwarfs are not the product of double star systems gone wrong.
_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com No virus found in this incoming message. Checked by AVG. Version: 7.5.552 / Virus Database: 270.10.13/1914 - Release Date: 1/24/2009 8:40 PM No virus found in this outgoing message. Checked by AVG. Version: 7.5.552 / Virus Database: 270.10.13/1914 - Release Date: 1/24/2009 8:40 PM
I don't know, I think the lion's share of the emission is from the ionization, not reflection. The dwarf is intrinsically very dim. But what could energize the OIII from a merely thermally radiating body? See, this is what makes me think that during the brief lifetime of the nebula itself, the central star has not become a true white dwarf. I think it's still sputtering the last dregs of fusion- from matierial on it's surface, not core- before settling down to true "white dwarf" status. And much of the ionization is due to the nebula material colliding with older material previously expelled. It doesn't always happen just once. I think lecturers don't make the distinction because it's a brief, transitory phase, and their lecturing to a general audience, not graduate students. And of course, I could be completely wrong! Invoking Ocham's razor, I'm probably wrong, lol. 2009/1/25 Kim <kimharch@cut.net>
Like you, Chuck, I haven't had the time to do any immediate research, but I seem to recall that the radiation energy (what radiation I can't say - I'm no physicist, either) that causes the pn to be visible is ionizing radiation causing the pn to emit light from O3 emissions - therefore, not merely a reflection phenomena, but I'm certain that could also be a component.
Kim
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Sunday, January 25, 2009 8:18 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] White dwarfs and YOU
No, I didn't mention that. Jerry was the one who posted about the visibility of white dwarfs in a cataclysmic variable system, not Bishop. I was attempting to distance that from Bishop and try to underline the differences. In my post, Bishop's comments were in quotes, mine were not. Sorry for the apparent confusion.
Also, I need to research this, but I'm not sure that planetary nebula are illuminated by the central star, but by the expelled material colliding with material ejected previously. These are glowing, ionized nebula, not merely reflection nebula.
On Sun, Jan 25, 2009 at 8:05 PM, <zaurak@digis.net> wrote:
You also mention that he is talking about white dwarfs from cataclysmic double stars. Perhaps in the case of planetary nebula (I believe most of these are not from cataclysmic doubles), that there is nothing to see until the "life" of White Dwarf is turned on, to illuminate the gases expelled from the red giant. Simply the intermediate period is before the nebula is visible. Again, I imagine most white dwarfs are not the product of double star systems gone wrong.
_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com
No virus found in this incoming message. Checked by AVG. Version: 7.5.552 / Virus Database: 270.10.13/1914 - Release Date: 1/24/2009 8:40 PM
No virus found in this outgoing message. Checked by AVG. Version: 7.5.552 / Virus Database: 270.10.13/1914 - Release Date: 1/24/2009 8:40 PM
_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com
I'm sure I've mis-used the terms Pop. I and Pop. II stars. What I intended to convey was the concept of the first generation of stars vs. stars that coalesced more recently. IIRC, the first stars to form in the universe had no metalicity. Could they even blow-off an envelope of sulfur, oxygen, iron, and other heavier elements to form a planetary nebula? Assuming they were small enough in mass to fall below the Chandresekhar limit of 1.4(?) solar masses; I had thought that first generation of stars were predominantly massive giants- their end product would be neutron stars or black holes. This is what was making me think that white dwarfs form from a later generation of stars with a higher percentage of heavy elements, such as the sun- which has only been around for something like 1/3 of the lifetime of the solar system.
The "black dwarf" that Bishop refers to is what's left when the white dwarf has lost all residual heat; a cold cinder. The "cool white dwarf" definition of black dwarf you are quoting is unknown to me; I suggest that the lecturer you are referring to may have made some generalizations or used a term loosely. Certainly by the time a white dwarf has cooled that much, it no longer has a planetary nebula. White dwarfs are the product of stars up to about 1.4 solar masses and generally Population I stars- "metal rich", second-generation stars. Again, I'm no expert but if it's possible that a white dwarf can evolve from a Pop. II star then there very well may have elapsed enough time since the formation of the first generation of stars for a black dwarf to exist today. And yes, there probably is no way to detect them at astronomical distances except by the effect of their gravity on a companion, if any. On Sun, Jan 25, 2009 at 8:05 PM, <zaurak@digis.net> wrote:
Chuck,
I imagine a black dwarf would be very difficult to observe, he must think the Universe is very young. I think there was mention that some planetary nebula gases are excited enough by a "very cool white dwarf" (they have a wide range of temperatures) that can't be observed, hence its a "black" dwarf. In essence some nebulas outlive (or at least cease to exist at the same time of) the white dwarf. Her explanation was that it is the heat from the white dwarf that illuminates the nebula. As Dan has pointed out amateurs commonly have the need equipment to see white dwarfs in nebula, but to see difficult companion stars not so much.
participants (3)
-
Chuck Hards -
Kim -
zaurak＠digis.net