Is the 15% shrinkage refering to the diameter or the volume? I believe that would effect any calculation of the shrinkage rate. The shrinkage (accompanied by dimming) may be a repeating pulsation, which Betelgeuse does, but I have not seen wether this one is consistant with historical measurements.
Also, I'm not sure that Betelgeuse is that far apart from the final size before supernova compared to Eta Carinae. Massive stars shed a large proportion of thier mass when thay are in thier red giant stage. If Betelgeuse is in it's last few years, it was probably ~ 2-3 times as massive when it was young. Also, it is thought that the mass of Eta Carinae is devided between two orbiting massive stars.
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Dan Tibbets
Betelgeuse to Nova
Dan: Quoting (freely) one of the Betelgeuse study team members, the Diameter has shrunk from 56 to 47 milliarcseconds in 15 years.
Quoting another physicist, the density of Betelgeuse is very low, in fact so low that a jar full of Betelgeuse here on Earth would make a good vacuum.
And by the way, there has not been any appreciable dimming associated with the shrinkage observed so far. This has been commented on, but not discussed in the papers I've seen.
Quoting another physicist, the density of Betelgeuse is very low, in fact so low that a jar full of Betelgeuse here on Earth would make a good vacuum.
And by the way, there has not been any appreciable dimming associated with the shrinkage observed so far. This has been commented on, but not discussed in the papers I've seen.
Aero
Why would it dim as it shrunk? I would expect it to brighten...Aero wrote:Dan: Quoting (freely) one of the Betelgeuse study team members, the Diameter has shrunk from 56 to 47 milliarcseconds in 15 years.
Quoting another physicist, the density of Betelgeuse is very low, in fact so low that a jar full of Betelgeuse here on Earth would make a good vacuum.
And by the way, there has not been any appreciable dimming associated with the shrinkage observed so far. This has been commented on, but not discussed in the papers I've seen.
What is the difference between ignorance and apathy? I don't know and I don't care.
I don't know but I would guess that instruments cannot resolve the surface of the star to any area less than the whole star. Looking at the complete star, as it shrunk from 56 to 47 milliarcseconds in diameter, one would expect to see a smaller area of brightness in the otherwise dark sky, hence less total light. But that is not what is being observed.
Aero
Yeah, but the same amount of light would be emitted by the star if everything was equal. And the contraction should heat up the outer shell somewhat.Aero wrote:I don't know but I would guess that instruments cannot resolve the surface of the star to any area less than the whole star. Looking at the complete star, as it shrunk from 56 to 47 milliarcseconds in diameter, one would expect to see a smaller area of brightness in the otherwise dark sky, hence less total light. But that is not what is being observed.
What is the difference between ignorance and apathy? I don't know and I don't care.
Betelgeuse has some surprising characteristics. One of them is that its density is about 1/10,000 of air. I haven't found a more specific value, but at that rarefied density, with a temperature of around 3100 degrees (C?), I wonder if a compression of 40% would make a detectable difference in luminosity. (40% is the approximate volume difference between 56 and 47 milliarcseconds diameter.)
I'm also wondering what the speed of sound would be in Betelgeuse, if such a phenomenon even exists within that strange star. I'm thinking along the lines of a spherically converging shock wave driven by the contraction of the star. The experts seem to think that the hydrogen in the core is exhausted and Betelgeuse is fusing helium to carbon in the core with some remaining hydrogen in the mantel and atmosphere which is also fusing. I'm speculating that a compressive shock wave could have a spectacular effect on the fusion rate of the remaining hydrogen, which could augment the shock wave all the way down, as long as there were some hydrogen remaining. Think of it as a huge helium/carbon bomb. Please note that this idea has no basis in the literature that I can find, its just my harebrained idea. Don't blame it onto anyone else.
I'm also wondering what the speed of sound would be in Betelgeuse, if such a phenomenon even exists within that strange star. I'm thinking along the lines of a spherically converging shock wave driven by the contraction of the star. The experts seem to think that the hydrogen in the core is exhausted and Betelgeuse is fusing helium to carbon in the core with some remaining hydrogen in the mantel and atmosphere which is also fusing. I'm speculating that a compressive shock wave could have a spectacular effect on the fusion rate of the remaining hydrogen, which could augment the shock wave all the way down, as long as there were some hydrogen remaining. Think of it as a huge helium/carbon bomb. Please note that this idea has no basis in the literature that I can find, its just my harebrained idea. Don't blame it onto anyone else.
Aero
Red gients in general are bright because of thier size, not thier mass. My understanding is that as the star leaves the main sequence (starts burning helium), the core contracts and heats up. This increased temperature causes the envelope of the star to expand and become less dense. The photosphere of this bloated star is dimmer and redder than the original star. But the glowing surface is much larger. The luminosity is less per square meter of surface but the surface is much larger.
A made up example- The Sun has a luminosity of say 100 units per square meter of surface. When it becomes a red giant, the diameter will increase from ~ 1 million to ~ 100 million miles. Suppose the luminosity of the red giant Sun is 1 unit per square meter and the surface area is increased by a factor of 10,000. The total brightness is increased by 10,000/ 100= 100 times as bright to a distant observer that sees it as a point source. I'm not certain how much energy is being produced by the helium core compared to the hydrogen core, but the longer wavelengths of light escaping (red) have less energy per photon, so ther is room in the energy balance to put out more (lower energy) photons.
I may have errored when I said shrinkage goes with dimming. Based on surface area it would, but the gravitational energy would also heat the gas at the same time so it is more complex, so I'm not sure where the balance would be. It would be interesting to know if there has been any color shift along with the shrinkage. Certiainly there are pulsating stars that can vary widely in brightness. Looks like I might need to dig out some books.
Dan Tibbets
A made up example- The Sun has a luminosity of say 100 units per square meter of surface. When it becomes a red giant, the diameter will increase from ~ 1 million to ~ 100 million miles. Suppose the luminosity of the red giant Sun is 1 unit per square meter and the surface area is increased by a factor of 10,000. The total brightness is increased by 10,000/ 100= 100 times as bright to a distant observer that sees it as a point source. I'm not certain how much energy is being produced by the helium core compared to the hydrogen core, but the longer wavelengths of light escaping (red) have less energy per photon, so ther is room in the energy balance to put out more (lower energy) photons.
I may have errored when I said shrinkage goes with dimming. Based on surface area it would, but the gravitational energy would also heat the gas at the same time so it is more complex, so I'm not sure where the balance would be. It would be interesting to know if there has been any color shift along with the shrinkage. Certiainly there are pulsating stars that can vary widely in brightness. Looks like I might need to dig out some books.
Dan Tibbets
To error is human... and I'm very human.
Rember that Eta Carinae's mass is distributed between two stars. Also, Eta Carnea may shed a substantial percentage of thier masses before they reach the end of thier super red gient atage, so they (each) may end up only one to two times as massive as Betelgeuse (if it is indead at the end of it's super red gient stage.kurt9 wrote:Betelgeuse is 20 solar masses. Eta Carinae is estimated to be 100-150 solar masses. Can anyone tell me how the energy of the supernova scales with the mass of the star?
I'm uncertain about what happens with the actual super nova event in these stars. Generally it is thought that the core collapses untill all the core matter is compressed untill it forms a clump of neutrons, the collapsing matter outside this limit then rebounds off of this surface and the supernova is born. What happens if the mass in the core is great enough that the neutrons are crushed into a tighter volume and a black hole is formed? Is there now a surface for the shock wave to bounce off of?. Is the super nova now a super wimp?. Is the matter accelerating to light speed as it approaches the event horizon now emiting so much radiation that the total outward energy/mass flow is equal or greater than the neutron star rebound mechanism? Is a greater percentage of this energy directed into polar beams?
http://www.space.com/scienceastronomy/0 ... rnova.html
Dan Tibbets
To error is human... and I'm very human.
This argument reminds me of a well-known prayer, posted at 12steps.org:
GOD, grant me the serenity to accept the things I cannot change,
Courage to change the things I can,
And the wisdom to know the difference.
We can learn to make energy by sustainable means.
We can learn to protect ourselves from asteroids and comets.
We can even learn to leave this solar system before our sun dies.
Supernovae, well, God grant us the serenity ....
GOD, grant me the serenity to accept the things I cannot change,
Courage to change the things I can,
And the wisdom to know the difference.
We can learn to make energy by sustainable means.
We can learn to protect ourselves from asteroids and comets.
We can even learn to leave this solar system before our sun dies.
Supernovae, well, God grant us the serenity ....
I would like to see one or both of these stars pop. A supernova bright to outshine the full moon would be an impressive sight. One sufficiently bright to read while sitting outside at night would be like living on a planet with two suns. It would be a wild experience. I read that these things last a couple of months. Eta Carinae is in the southern sky. So, I would have to go to Australia or Argentina to see it. Betelgeuse is in the northern sky. So, we should all get to see it when it pops.
I went through St. Helens when the mid-day sky got as dark as midnight. I got stoned and listened to some Blue Oyster Cult Music (On Your Feet or On Your Knees) while watching the sky grow darker and darker. It was quite the surrealistic experience.
I went through St. Helens when the mid-day sky got as dark as midnight. I got stoned and listened to some Blue Oyster Cult Music (On Your Feet or On Your Knees) while watching the sky grow darker and darker. It was quite the surrealistic experience.
Don't Fear The Reaper.kurt9 wrote:I would like to see one or both of these stars pop. A supernova bright to outshine the full moon would be an impressive sight. One sufficiently bright to read while sitting outside at night would be like living on a planet with two suns. It would be a wild experience. I read that these things last a couple of months. Eta Carinae is in the southern sky. So, I would have to go to Australia or Argentina to see it. Betelgeuse is in the northern sky. So, we should all get to see it when it pops.
I went through St. Helens when the mid-day sky got as dark as midnight. I got stoned and listened to some Blue Oyster Cult Music (On Your Feet or On Your Knees) while watching the sky grow darker and darker. It was quite the surrealistic experience.
Engineering is the art of making what you want from what you can get at a profit.
I have seen one similiar on another forumTom Ligon wrote:This argument reminds me of a well-known prayer, posted at 12steps.org:
GOD, grant me the serenity to accept the things I cannot change,
Courage to change the things I can,
And the wisdom to know the difference.
....
GOD, grant me the serenity to accept the things I cannot change,
Courage to change the things I can,
And the wisdom to hide the bodies.....