Can Gravitational Lensing Cause a Star to Appear Twice Simultaneously?

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Discussion Overview

The discussion centers around the phenomenon of gravitational lensing and whether it can cause a star to appear twice simultaneously on either side of a gravitational source. Participants explore the implications of gravitational lensing, including the possibility of seeing halos or arcs of light due to intervening mass.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that gravitational lensing can displace the apparent direction of a star, potentially allowing it to be seen twice simultaneously around a gravitational source.
  • Others mention that such haloes have been observed when a nearby galaxy is in front of a more distant one, suggesting that the light must come from a specific line of sight.
  • A participant refers to the phenomenon as an "Einstein Ring," indicating a specific case of gravitational lensing where multiple images of a source are formed.
  • One participant shares a personal observation of a TV program that demonstrated the same star appearing at two points in the sky simultaneously.

Areas of Agreement / Disagreement

Participants express varying degrees of agreement on the possibility of seeing a star twice due to gravitational lensing, with some supporting the idea and others providing examples of observed phenomena. The discussion remains unresolved regarding the specifics of how this occurs and the conditions required.

Contextual Notes

Some claims depend on specific definitions of gravitational lensing and the conditions under which it occurs. The discussion includes references to observational evidence but does not resolve the underlying complexities of the phenomenon.

Nickelodeon
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Gravitational lensing displaces the apparent direction of a star outwards away from a gravitational source. Do you think it would be possible to see the same star at least twice simultaneously, one either side of this gravitational source?
Even more likely, if the gravitational source was great enough, I would have thought that you would see a halo.

Nick
 
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Nickelodeon said:
Gravitational lensing displaces the apparent direction of a star outwards away from a gravitational source. Do you think it would be possible to see the same star at least twice simultaneously, one either side of this gravitational source?
Even more likely, if the gravitational source was great enough, I would have thought that you would see a halo.

Nick

You would and such haloes have been seen when there's a nearby galaxy in front of a more distant one. The light has to come from almost immediately on the line of sight between the the intervening mass and the observer. A light source a bit to the side just appears as an arc of light.
 
qraal said:
You would and such haloes have been seen when there's a nearby galaxy in front of a more distant one. The light has to come from almost immediately on the line of sight between the the intervening mass and the observer. A light source a bit to the side just appears as an arc of light.

amazing - thanks for that.
 
Nickelodeon said:
Gravitational lensing displaces the apparent direction of a star outwards away from a gravitational source. Do you think it would be possible to see the same star at least twice simultaneously, one either side of this gravitational source?
Even more likely, if the gravitational source was great enough, I would have thought that you would see a halo.

Nick

Yyyyyyep. Called an Einstein Ring. Google away...
 
I've seen a TV programme demonstrating the same star seen at two (near) points in the sky at the same time.
 
HSTgravlens.jpg
 
seb7 said:
I've seen a TV programme demonstrating the same star seen at two (near) points in the sky at the same time.

Do you remember what the TV programme was called and when it was shown?
 

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