APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Comments and questions about the APOD on the main view screen.
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Re: APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Postby Chris Peterson » Sun Apr 09, 2017 1:29 am

jpicciri wrote:I've read many explanations for runaway stars that involve a supernova that then "releases" its companion star.
Doesn't the companion still revolve around the center of mass? Does the runaway happen after the supernova
remnants pass the orbit of the companion star? I'm not understanding the kinematics.

The mass that ends up outside the orbit of the star is effectively a shell, and it therefore exerts no net gravitational force on any objects inside it. So there is an effective loss of mass, with the consequence that the runaway star ends up converting its elliptical orbit to a hyperbolic one (meaning it's traveling very nearly in a straight line once it's far from its sibling binary).
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Re: APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Postby Ann » Sun Apr 09, 2017 4:13 am

jpicciri wrote:I've read many explanations for runaway stars that involve a supernova that then "releases" its companion star.
Doesn't the companion still revolve around the center of mass? Does the runaway happen after the supernova
remnants pass the orbit of the companion star? I'm not understanding the kinematics.

Thanks,
John-


Well, I'm sticking my neck out and offering an answer, even though I'm not sure of it.

When a star goes supernova, it is blowing away much of its mass. If it has a companion, the two stars were orbiting the common center of mass at a speed that would keep both of them in orbit. But now that one star suddenly loses a lot of mass, the speed of its companion may be too high for it to stay in orbit. It may then escape in the tangential direction.

Can't the neutron star or the black hole, the compact remnant of the star that went supernova, get a kick that sends it flying away, too? I would think that this might happen.

Bear in mind that a supernova typ Ia will not leave a compact remnant behind, except in, possibly, a few extremely rare cases. I read about something like that some weeks ago, but I don't think I can find that information now.

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Postby neufer » Sun Apr 09, 2017 11:42 am

Mokurai wrote:
It is incorrect to say that Zeta Oph was "flung out" of its binary system when its companion exploded. It simply continued at the same speed it had in orbit, in the direction it was going when the supernova blew past it. This is just Newton's First Law:
An object in motion tends to remain in motion in a straight line.

Is it incorrect to say that David flung a stone at Goliath :?:

fling (v.) c. 1300, "to dash, run, rush," probably from or related to Old Norse flengja "to flog," which is of uncertain origin, perhaps from Proto-Germanic *flang- (source also of Old Swedish flenga "strike," Danish flænge "slash, gash"). Meaning "to throw, cast, hurl" is from mid-14c. Related: Flung; flinging, but in Middle English with past tense flang, past participle flungen.
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Re: APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Postby Case » Mon Apr 10, 2017 3:07 am

Image
APOD Robot wrote:The image spans about 1.5 degrees or 12 light-years at the estimated distance of Zeta Ophiuchi.

Superimposed over a DSS2 image (from Wikisky: blue/red/near infrared) of the same area, it is made obvious how different the Spitzer Space Telescope sees things than a ground based survey does. Not just the brightness of Zeta, but also the invisibility of that nebulosity in the DSS2 plates, which is so prominent in the APOD.

Ann wrote:The velocity of Zeta Ophiuchi is probably measured either relative to the Sun, or, perhaps more likely, relative to other stars at more or less the same distance from us in more or less the same part of the sky. Zeta (ζ) Ophiuchi is moderately close to Beta1 (β) Scorpii, Graffias, in the sky. The two stars belong to very similar spectral classes and are at relatively similar distances from us. It's just possible that these two stars are related.

They have very different proper motions, which makes sense if one of them is a runaway star.

Wikipedia has an interesting article about Beta Scorpii, in that it is a system with no less than six stars. β¹ would then be a subgroup of three stars. The article also mentions the common origin of the Scorpius-Centaurus Association of stars.

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Re: APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Postby Ann » Mon Apr 10, 2017 4:37 am

Case wrote:
Image
APOD Robot wrote:The image spans about 1.5 degrees or 12 light-years at the estimated distance of Zeta Ophiuchi.

Superimposed over a DSS2 image (from Wikisky: blue/red/near infrared) of the same area, it is made obvious how different the Spitzer Space Telescope sees things than a ground based survey does. Not just the brightness of Zeta, but also the invisibility of that nebulosity in the DSS2 plates, which is so prominent in the APOD.


Thanks, Case, that is a brilliant "image comparison"!

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Re: APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Postby BDanielMayfield » Mon Apr 10, 2017 12:52 pm

Ann wrote:Thanks, Case, that is a brilliant "image comparison"!


I agree Ann. Very well done Case :!: :clap:
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Re: APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Postby starsurfer » Mon Apr 10, 2017 1:14 pm

Case wrote:
Image
APOD Robot wrote:The image spans about 1.5 degrees or 12 light-years at the estimated distance of Zeta Ophiuchi.

Superimposed over a DSS2 image (from Wikisky: blue/red/near infrared) of the same area, it is made obvious how different the Spitzer Space Telescope sees things than a ground based survey does. Not just the brightness of Zeta, but also the invisibility of that nebulosity in the DSS2 plates, which is so prominent in the APOD.

Ann wrote:The velocity of Zeta Ophiuchi is probably measured either relative to the Sun, or, perhaps more likely, relative to other stars at more or less the same distance from us in more or less the same part of the sky. Zeta (ζ) Ophiuchi is moderately close to Beta1 (β) Scorpii, Graffias, in the sky. The two stars belong to very similar spectral classes and are at relatively similar distances from us. It's just possible that these two stars are related.

They have very different proper motions, which makes sense if one of them is a runaway star.

Wikipedia has an interesting article about Beta Scorpii, in that it is a system with no less than six stars. β¹ would then be a subgroup of three stars. The article also mentions the common origin of the Scorpius-Centaurus Association of stars.

The nebulosity in the Spitzer image is also visible in the optical if someone took a deep narrowband image with Ha and OIII. It is true most bowshocks are infrared only.

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Re: APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Postby BDanielMayfield » Mon Apr 10, 2017 1:52 pm

As bowshocks go, this one doesn't appear particularly violent. At least, that's the impression it gives me. This fits with its [the star's] velocity being not that extraordinarily fast.

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Re: APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Postby Chris Peterson » Mon Apr 10, 2017 2:32 pm

BDanielMayfield wrote:As bowshocks go, this one doesn't appear particularly violent. At least, that's the impression it gives me. This fits with its [the star's] velocity being not that extraordinarily fast.

I'm not sure any bowshocks are really what I'd call "violent". They are slow, evolving over thousands to millions of years. Their densities are lower than the hardest vacuums we make in a lab. Really, it's just particles colliding with particles resulting in enough heat to produce rather high energy photons. But the total energy is small.
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Re: APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Postby BDanielMayfield » Mon Apr 10, 2017 6:15 pm

Chris Peterson wrote:
BDanielMayfield wrote:As bowshocks go, this one doesn't appear particularly violent. At least, that's the impression it gives me. This fits with its [the star's] velocity being not that extraordinarily fast.

I'm not sure any bowshocks are really what I'd call "violent". They are slow, evolving over thousands to millions of years. Their densities are lower than the hardest vacuums we make in a lab. Really, it's just particles colliding with particles resulting in enough heat to produce rather high energy photons. But the total energy is small.

Thanks. Art's list of APOD bow shocks shows that most aren't all that "violent" looking either.
Since "violent" really doesn't fit I'm a bit perplexed as to what word to use make my point. The bend in Zeta Oph's bow shock appears rather gently flowing instead of the sharp bends of some bow shocks that rap around the stars that cause them.

Art's list did have one example of a rather violent looking bow shock:

But BZ Cam is a scene of some violence, since it is a cataclysmic variable. Its bow has a violent bend to it too. Another comparable use of the word violent would be the golf expression "violent lip-out", sometimes followed by violence being inflicted upon one's putter.

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Last edited by BDanielMayfield on Mon Apr 10, 2017 6:34 pm, edited 1 time in total.
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Re: APOD: Zeta Oph: Runaway Star (2017 Apr 08)

Postby Ann » Mon Apr 10, 2017 6:27 pm

Ultraviolet bow shock and tail of cool star Mira.
Photo: GALEX.
An interesting case of a bow shock is the ultraviolet one made by cool red giant Mira.

Mira's got a splendid tail, too.

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