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CaptainToonces
2014-Jul-16, 11:10 PM
Is Sirius B accreting matter from Sirius A?

antoniseb
2014-Jul-16, 11:20 PM
No. It is thousands of times too far away.

CaptainToonces
2014-Jul-17, 01:38 AM
No. It is thousands of times too far away.

I thought it was only about 30 AU away.

Hornblower
2014-Jul-17, 12:30 PM
I thought it was only about 30 AU away.
Yes, it is. That still is vastly greater than the separation in binaries in which a significant amount of mass transfer and accretion is occurring, which typically is well under 1/10 AU, if I am not mistaken.

ngc3314
2014-Jul-17, 01:18 PM
We can get some numbers. Wikipedia summarizes some fitting formulae (http://en.wikipedia.org/wiki/Roche_lobe) for the (spherical-equivalent) radius of a Roche lobe. Taking masses 2.0 Msun for Sirius A and 1 Msun B, and 20 AU for the separation, the Roche lobe around Sirius A has radius of about 8.8 AU, much larger than even its estimated radius when it becomes a red giant.

CaptainToonces
2014-Jul-18, 07:14 AM
We can get some numbers. Wikipedia summarizes some fitting formulae (http://en.wikipedia.org/wiki/Roche_lobe) for the (spherical-equivalent) radius of a Roche lobe. Taking masses 2.0 Msun for Sirius A and 1 Msun B, and 20 AU for the separation, the Roche lobe around Sirius A has radius of about 8.8 AU, much larger than even its estimated radius when it becomes a red giant.

So if the distance to the companion star is more than the radius of the Roche lobe, the accretion is pretty much negligible?

antoniseb
2014-Jul-18, 11:03 AM
So if the distance to the companion star is more than the radius of the Roche lobe, the accretion is pretty much negligible?
Not just negligible, but negative. Stars slowly lose mass as they age, and the wind and radiation prevent incidental infall of dust or free atoms. Comets and asteroids are still possible, but are less total mass per time interval than the outbound wind.

CaptainToonces
2014-Jul-20, 09:01 AM
Not just negligible, but negative. Stars slowly lose mass as they age, and the wind and radiation prevent incidental infall of dust or free atoms. Comets and asteroids are still possible, but are less total mass per time interval than the outbound wind.

Well, but don't you think the rate of mass loss for a white dwarf is a lot less than other spectral types, owing to gravity's grip on it and the lack of thermonuclear counter-pressure emanating from its core?

antoniseb
2014-Jul-20, 11:21 AM
Well, but don't you think the rate of mass loss for a white dwarf is a lot less than other spectral types, owing to gravity's grip on it and the lack of thermonuclear counter-pressure emanating from its core?
Are you thinking that pressure in the core is somehow reflected in the behavior on the surface? White dwarfs have hot surfaces compared to the Sun. It is possible that they have a lower rate of mass loss because they need to blow off Helium or Carbon as their stellar wind, but the trend is still loss not gain.

Hornblower
2014-Jul-20, 04:42 PM
At Sirius B's vast distance from the primary it subtends only about a trillionth of the celestial sphere around the primary, so it will intercept only a vanishingly small fraction of the outgoing stellar wind. With the close binaries in which major mass transfer does occur, what would have been a red giant envelope with a radius many times the separation spills through the spot where the Roche lobes of the two stars meet, and a sizeable percentage of it accretes onto the companion. It is not a simple interception such as would occur with Sirius, and it involves far more material.

Googling "roche lobe mass transfer" will find some good explanations.

galacsi
2014-Jul-20, 07:22 PM
Are you thinking that pressure in the core is somehow reflected in the behavior on the surface? White dwarfs have hot surfaces compared to the Sun. It is possible that they have a lower rate of mass loss because they need to blow off Helium or Carbon as their stellar wind, but the trend is still loss not gain.

You may be right . . .But gravity surface is very strong and may prevent any signifiant stellar wind. And also, I suppose , (Don' know for sure) accretion is done with the magnetosphere of the white dwarf and so the cross section of accretion maybe much larger than its diameter. Just my two cents . . . What do you think of this ?

antoniseb
2014-Jul-20, 08:45 PM
... What do you think of this ?
I think the main reason the OP asked about accretion of Sirius B was to determine whether it might someday be a type 1a supernova, and the answer is that it won't.

Hornblower
2014-Jul-20, 11:05 PM
Even if Sirius B had an accretion cross section as large as something like Betelgeuse, it would intercept only on the order of 1% of the outgoing stuff for the duration of the primary's evolution, which is not nearly enough to push it over the load limit. We need the dynamics that happen in a really close binary, where we get transfer of material that ordinarily would remain gravitationally bound to the source star.

CaptainToonces
2014-Jul-21, 06:25 AM
I think the main reason the OP asked about accretion of Sirius B was to determine whether it might someday be a type 1a supernova, and the answer is that it won't.

That is incorrect, I asked only to further all of our collective understandings of the universe.

CaptainToonces
2014-Jul-21, 06:27 AM
Even if Sirius B had an accretion cross section as large as something like Betelgeuse, it would intercept only on the order of 1% of the outgoing stuff for the duration of the primary's evolution, which is not nearly enough to push it over the load limit. We need the dynamics that happen in a really close binary, where we get transfer of material that ordinarily would remain gravitationally bound to the source star.

Yes but can a gravitational "chain" develop between the two stars where the matter in the chain itself aids the flow of material to the secondary?

galacsi
2014-Jul-21, 08:06 AM
That is incorrect, I asked only to further all of our collective understandings of the universe.

Yes , your question was very open , andI think there is an other reason to it than the fear of a supernova !

galacsi
2014-Jul-21, 08:35 AM
I think the main reason the OP asked about accretion of Sirius B was to determine whether it might someday be a type 1a supernova, and the answer is that it won't.


But , Antoniseb, Supernovae are not the only game in this galaxy ! You can play in a minor league and have just a nova.

From wikipedia :
A nova (plural novae (http://en.wiktionary.org/wiki/nova) or novas) is a cataclysmic (http://en.wikipedia.org/wiki/Cataclysmic_variable_star) nuclear explosion (http://en.wikipedia.org/wiki/Nuclear_explosion) on a white dwarf (http://en.wikipedia.org/wiki/White_dwarf), which causes a sudden brightening of the star. Novae are not to be confused with other brightening phenomena such as supernovae (http://en.wikipedia.org/wiki/Supernova) or luminous red novae (http://en.wikipedia.org/wiki/Luminous_red_nova). A nova is caused by the accretion (http://en.wikipedia.org/wiki/Accretion_%28astrophysics%29) of hydrogen onto the surface of the star, which ignites and starts nuclear fusion (http://en.wikipedia.org/wiki/Nuclear_fusion) in a runaway manner. Novae are thought to occur on the surface of a white dwarf in a binary system (http://en.wikipedia.org/wiki/Binary_system). If the two stars are close enough, material can be pulled from the companion star's surface onto the white dwarf.

So if , and it is a big IF , I agree, Sirius B is able to accrete enough gas from its environment ,it could go nova and even be a recurring nova.

And there is a reason for this speculation : It is the Sirius mystery ! :doh:

Not , not the Dogon story, something historically confirmed !

One again Wikipedia is my friend :
Red controversy

Around 150 AD, the Greek astronomer of the Roman period Claudius Ptolemy (http://en.wikipedia.org/wiki/Claudius_Ptolemy) described Sirius as reddish, along with five other stars, Betelgeuse (http://en.wikipedia.org/wiki/Betelgeuse), Antares (http://en.wikipedia.org/wiki/Antares), Aldebaran (http://en.wikipedia.org/wiki/Aldebaran), Arcturus (http://en.wikipedia.org/wiki/Arcturus) and Pollux (http://en.wikipedia.org/wiki/Pollux_%28star%29), all of which are clearly of orange or red hue.[69] (http://en.wikipedia.org/wiki/Sirius#cite_note-Holberg2007-157-74) The discrepancy was first noted by amateur astronomer Thomas Barker (http://en.wikipedia.org/wiki/Thomas_Barker_%28meteorologist%29), squire of Lyndon Hall (http://en.wikipedia.org/wiki/Lyndon,_Rutland) in Rutland (http://en.wikipedia.org/wiki/Rutland), who prepared a paper and spoke at a meeting of the Royal Society (http://en.wikipedia.org/wiki/Royal_Society) in London in 1760.. . . . .[ (http://en.wikipedia.org/wiki/Sirius#cite_note-Ceragioli1995-75)

There are several "explanations" : One was that Sirius B was a red giant at this time , it is clearly wrong , others was like
either that the description as red is a poetic metaphor for ill fortune, or that the dramatic scintillations (http://en.wikipedia.org/wiki/Scintillation_%28astronomy%29) of the star when it was observed rising left the viewer with the impression that it was red. Wikipedia again.

Well the mystery has not been resolved , could I dare say that Sirius B going nova, just a little, could be a solution ?

Hornblower
2014-Jul-21, 09:05 AM
Yes but can a gravitational "chain" develop between the two stars where the matter in the chain itself aids the flow of material to the secondary?I see no reason to believe that such a process could occur. The tiny amount of matter originating in the primary and going to the orbital radius of the secondary and beyond consists of atoms and ions moving at a velocity much greater than the escape velocities of the respective stars.

Hornblower
2014-Jul-21, 10:06 AM
But , Antoniseb, Supernovae are not the only game in this galaxy ! You can play in a minor league and have just a nova.

From wikipedia :

So if , and it is a big IF , I agree, Sirius B is able to accrete enough gas from its environment ,it could go nova and even be a recurring nova.

And there is a reason for this speculation : It is the Sirius mystery ! :doh:

Not , not the Dogon story, something historically confirmed !

One again Wikipedia is my friend :

There are several "explanations" : One was that Sirius B was a red giant at this time , it is clearly wrong , others was like Wikipedia again.

Well the mystery has not been resolved , could I dare say that Sirius B going nova, just a little, could be a solution ?I see no reason to continue trying to invoke astrophysical ideas which are strongly ruled out by the current body of theory when the non-astrophysical possibilities cannot be ruled out.

galacsi
2014-Jul-21, 08:49 PM
I see no reason to continue trying to invoke astrophysical ideas which are strongly ruled out by the current body of theory when the non-astrophysical possibilities cannot be ruled out.

Strongly ruled out by the current body of theory ? What are your evidences , your references to be so affirmative ?

And don't you have any curiosity ?

antoniseb
2014-Jul-21, 08:58 PM
The lack of a cloud from such a recent nearby nova is also a reason to doubt it. My understanding about that reference is that it was about observing Sirius setting in the desert, and that the star was red from atmospheric reddening.

Hornblower
2014-Jul-21, 11:01 PM
Strongly ruled out by the current body of theory ? What are your evidences , your references to be so affirmative ?

And don't you have any curiosity ?
I am curious as to why anyone doubts the findings of the experts in astrophysics, who have concluded that Sirius B has been a white dwarf for over 100 million years, gradually cooling to its present 25,000K from a much hotter state after it transitioned from a dying-gasp red giant to a planetary nebula center. They have based their inferences on what has been learned about nuclear energy from experiments in atom smashers, along with the thermal properties of the material that makes up a star. Theoretical inferences about stellar evolution have come a long way in the past several decades, and decisively rule out any serious possibility that the final red giant stage could have been as recent as the writings in ancient languages that often are difficult to translate into English or any modern Indo-European language.

galacsi
2014-Jul-22, 07:59 PM
The lack of a cloud from such a recent nearby nova is also a reason to doubt it.

Maybe or not ,I found only one reference about that, and it is rather negative : http://www.guide-to-astronomy.narod.ru/stars/questions_22_34.html

23. What happens to the material expelled from a nova?

The material is thrown into space. Sometimes no trace of it can later be seen near the exploded star.
Sometimes, as in the case of the Nova Persei, 1901, it remains as a cloud around the star, and forms much dust and gas in space.

My understanding about that reference is that it was about observing Sirius setting in the desert, and that the star was red from atmospheric reddening.

Like the sun setting down. But that is not what the ancients said ,Sirius was red like Betelgeuse, Antares, Aldebaran, Arcturus and Pollux which are still red today.

So IMO there still is an unsolved problem.

galacsi
2014-Jul-22, 08:12 PM
I am curious as to why anyone doubts the findings of the experts in astrophysics, who have concluded that Sirius B has been a white dwarf for over 100 million years, gradually cooling to its present 25,000K from a much hotter state after it transitioned from a dying-gasp red giant to a planetary nebula center. They have based their inferences on what has been learned about nuclear energy from experiments in atom smashers, along with the thermal properties of the material that makes up a star. Theoretical inferences about stellar evolution have come a long way in the past several decades, and decisively rule out any serious possibility that the final red giant stage could have been as recent as the writings in ancient languages that often are difficult to translate into English or any modern Indo-European language.

I don't doubt any of this , I know that the red giant phase is about 120 million years old. And I wrote this in post #17 :
There are several "explanations" : One was that Sirius B was a red giant at this time , it is clearly wrong. I didn't feel it was necessary to waste time to refute such a naive and ill informed view.
You did not read really my posts but somehow I started up your debunking mode :doh:

Hornblower
2014-Jul-23, 03:34 PM
I don't doubt any of this , I know that the red giant phase is about 120 million years old. And I wrote this in post #17 : . I didn't feel it was necessary to waste time to refute such a naive and ill informed view.
You did not read really my posts but somehow I started up your debunking mode :doh:
My apology, when I saw the nova idea immediately afterward, I missed you acknowledgement that the recent red giant idea was wrong.

Considering the vast separation and the resulting minuscule accretion of the tenuous stellar wind out there, I would likewise consider the possibility of a nova, even a dwarf type, to be far less than that of a garbled rendering of the ancient writings about the appearance of Sirius.

chornedsnorkack
2014-Jul-23, 04:54 PM
Sun is a main sequence star that has deep convective zone (about a third of radius!), spots, protuberances, flares. Sun also somehow manages, while having surface temperature of under 6000 K, and even colder above that, to somehow heat its corona to 1 to 3 million K. So despite escape speed of over 600 km/s, corona keeps escaping Sun at about 400 km/s solar wind.

Sirius A is also a main sequence star, but much hotter, at 10 000 K. Now Sirius A is alleged to have tranquil atmosphere whence heat escaped by radiation, with little or no convection. Is that true?

Does Sirius A manage to heat a corona so that it escapes as wind, the way Sun does? What is the temperature profile above the surface of Sirius A?

And Sirius B is a white dwarf with no internal heat source and surface temperature of 25 000 K. Does Sirius B feature flares and a hot corona? Even if it were hot, the escape speed of Sirius B is over 6000 km/s. So does Sirius B possess any solar wind at all?

CaptainToonces
2014-Jul-27, 07:12 AM
Sun is a main sequence star that has deep convective zone (about a third of radius!), spots, protuberances, flares. Sun also somehow manages, while having surface temperature of under 6000 K, and even colder above that, to somehow heat its corona to 1 to 3 million K. So despite escape speed of over 600 km/s, corona keeps escaping Sun at about 400 km/s solar wind.

Sirius A is also a main sequence star, but much hotter, at 10 000 K. Now Sirius A is alleged to have tranquil atmosphere whence heat escaped by radiation, with little or no convection. Is that true?

Does Sirius A manage to heat a corona so that it escapes as wind, the way Sun does? What is the temperature profile above the surface of Sirius A?

And Sirius B is a white dwarf with no internal heat source and surface temperature of 25 000 K. Does Sirius B feature flares and a hot corona? Even if it were hot, the escape speed of Sirius B is over 6000 km/s. So does Sirius B possess any solar wind at all?

I think we can safely say that there is sufficient reason to doubt AntoniseB's explanation that all stars lose matter over time. First of all, Sirius B is a white dwarf, and no one has given a definitive answer on mass-loss-rates for white dwarfs. They figure to be small, but how small? Furthermore, Sirius B has a giant companion that is 30 AU away. That is a significant distance to overcome for mass-transfer, but the question remains could there be enough mass transfer to overcome Sirius B's slowed-down rate of mass loss, therefore giving it a positive net gain of mass?

Githyanki
2014-Aug-01, 02:12 AM
A Sirius question requires Sirius answers.

Sol Station says that,

"Its mass and diameter are consistent with the theoretical size for a carbon-core white dwarf, one that may have evolved from a 5.05 +0.374/-0.276 Solar-mass, B-type main-sequence star about 124 +/- 5 million years ago, after 101 to 126 million years as a giant star."

This means that recently, it was a red-giant, spending half of its life as a main-sequence, and the other half has a red giant.

Now, since the orbit is eccentric, 8.1 and 31.5 AUs, and despite the system being about 250MY, there is a good chance planets could have formed, but the HZ is 2.7AUs for Sirus, and, with the nebula accretion from Sirius B, it is unlikely there are habitable worlds near Sirius.

My guess, since the iron-rich stars and 250MY of bright lights, most of the water vapor has been pushed into interstellar space, but any water Sirius B puffed out, might have replaced it.

And since all that matter coming from Sirius B, would have played havoc on planets orbiting both stars. At best, Sirius has maybe one primordial world in an eccentric orbit; it is most likely a super-Earth or gas-giant.

CaptainToonces
2014-Aug-01, 04:52 AM
Thanks for the response, Githyanki! That's some interesting information.

The last 3 paragraphs of your post seem to be dealing with the question of habitable worlds in the Sirius system, but that is not the question of this thread. I referred to Sirius A and B as the two STARS in the system.