Strange Binary Star Companions

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dougettinger
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Strange Binary Star Companions

Post by dougettinger » Fri Apr 09, 2010 7:21 pm

I understand that there are any number of combinations of star types in real binaries. How is it possible that a red older star like our Sun can be in the same binary with a younger, short-lived, more massive blue star? Or how can a massive, blue star be next to a white dwarf that already exploded? These examples of binaries certainly did not form at the same time.
Doug Ettinger
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dougettinger
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Re: Strange Binary Star Companions

Post by dougettinger » Mon Apr 12, 2010 4:39 pm

If I went beyond the boundaries of human knowledge and understanding in asking these questions, please tell me.

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Chris Peterson
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Re: Strange Binary Star Companions

Post by Chris Peterson » Mon Apr 12, 2010 4:53 pm

dougettinger wrote:I understand that there are any number of combinations of star types in real binaries. How is it possible that a red older star like our Sun can be in the same binary with a younger, short-lived, more massive blue star? Or how can a massive, blue star be next to a white dwarf that already exploded? These examples of binaries certainly did not form at the same time.
Double stars are not made up of completely arbitrary combinations. In almost all cases (rare captures excepted) the stars in multiple star systems form at the same time. It is simply that they are at different stages of stellar evolution.

I don't think you will have any double star systems containing short lived giants paired with stars that are 5 billion years old.

This reminds me of the recent discussion of globular clusters. All the stars are the same age, but they are not all the same type, or at the same stage of evolution. Globulars contain white dwarfs and other types of stars that have finished their lives, as well as stars that are only a fraction of the way through their evolution.
Chris

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dougettinger
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Re: Strange Binary Star Companions

Post by dougettinger » Wed Apr 14, 2010 3:22 pm

Chris Peterson wrote:
dougettinger wrote:I understand that there are any number of combinations of star types in real binaries. How is it possible that a red older star like our Sun can be in the same binary with a younger, short-lived, more massive blue star? Or how can a massive, blue star be next to a white dwarf that already exploded? These examples of binaries certainly did not form at the same time.
Double stars are not made up of completely arbitrary combinations. In almost all cases (rare captures excepted) the stars in multiple star systems form at the same time. It is simply that they are at different stages of stellar evolution.

Yes, most likely not all combinations have been discovered. This means that a star next to a neutron star or black hole survived the neighboring star's supernova explosion and went on to continue its life possibly affected by capturing more mass from the explosive debris. Is this a correct assumption ?

Doug Ettinger

I don't think you will have any double star systems containing short lived giants paired with stars that are 5 billion years old.

This reminds me of the recent discussion of globular clusters. All the stars are the same age, but they are not all the same type, or at the same stage of evolution. Globulars contain white dwarfs and other types of stars that have finished their lives, as well as stars that are only a fraction of the way through their evolution.
Your explanation is news to me, but also very enlightening. Astrophysicists with few exceptions assume that true binary star systems were created at the same time from a dense molecular cloud of dust and gases. The difference in the stars are their masses which leads to different life spans. Then I presume these binaries have similar content of metals. Are my statements correct ?

In reading about the binary Sirius A and B, I learned that the age of the system is determined to be between 200 and 300 million years old. How was this determination made ? by processing observed data? or by postulations made from the nucleosynthesis theory?

Doug Ettinger
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Chris Peterson
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Re: Strange Binary Star Companions

Post by Chris Peterson » Wed Apr 14, 2010 4:53 pm

dougettinger wrote:Yes, most likely not all combinations have been discovered. This means that a star next to a neutron star or black hole survived the neighboring star's supernova explosion and went on to continue its life possibly affected by capturing more mass from the explosive debris. Is this a correct assumption ?
Yes, a supernova can occur without destroying its companion. There's no reason to think the companion would capture much mass from the debris, however, since it is moving outwards at much greater than the system's escape velocity. The only material the companion will catch is that which comes right at it- a tiny amount. And that is offset by the shock wave, which may well carry away material.
Your explanation is news to me, but also very enlightening. Astrophysicists with few exceptions assume that true binary star systems were created at the same time from a dense molecular cloud of dust and gases. The difference in the stars are their masses which leads to different life spans. Then I presume these binaries have similar content of metals. Are my statements correct ?
AFAIK there are no binaries where the components have different metallicities.
In reading about the binary Sirius A and B, I learned that the age of the system is determined to be between 200 and 300 million years old. How was this determination made ? by processing observed data? or by postulations made from the nucleosynthesis theory?
I don't know for sure, but I presume it was by looking at the mass and temperature-luminosity relationship. That's the usual way that stellar ages are calculated.
Chris

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dougettinger
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Re: Strange Binary Star Companions

Post by dougettinger » Wed Apr 14, 2010 6:22 pm

Sirius B is now a white dwarf that was postulated to be about 5 solar masses before it exploded. So then the age of the system is determined by the temp-lum. relationship of Sirius A. And Sirius B's age, about 123 million years, is estimated by how long the postulated life span of a 5 solar mass is. Are these correct assumptions?

Doug Ettinger
Pittsburgh, PA
Doug Ettinger
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