If we observe one edge of a star to be redshifted and the opposite edge to be blueshifted, what can we conclude about the star?

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BlackTom AI · Accepted Answer

The prompt asks us to interpret a scenario where one edge of a star is redshifted while the opposite edge is blueshifted. 
The first thing to note is that the list of answer choices is missing in the provided data, so we cannot reason about each option individually. Nevertheless, we can reason about the physics that such an observation would imply.
A primary interpretation of opposite edges exhibiting opposite Doppler shifts is that the star surface is rotating. If the star spins, one limb is moving toward us (blueshift) while the opposite limb is moving away from us (redshift), causing a measurable shift difference across the stellar disk. This is a classic signature of rotation when observed via spectral lines.
Consider other potential explanations and why they are less compatible with the observation:
- A purely translational motion of the entire star relative to the observer would produce a uniform Doppler shift across the entire star (all parts redshifted or all blueshifted), not a gradient from one edge to the opposite edge. Therefore, a simple bulk motion cannot account for opposite-edge shifts.
- Pulsations or localized surface phenomena could, in principle, create complex line profiles, but to produce a systematic redshift on one edge and a symmetric blueshift on the opposite edge across the star’s disk, rotation provides a straightforward, coherent model that matches the geometry of a rotating sphere.
- If there were strong differential motion or multiple unresolved sources, the signal could become tangled, but the clean dichotomy of red on one edge and blue on the other strongly points to a rotating surface with a velocity field that is antisymmetric about the rotation axis.
- Instrumental effects or observational biases could mimic small shifts, but to consistently observe opposite edges at opposite extremes would require a robust physical mechanism like rotation rather than random instrumental error.
In summary, given the described edge-to-edge Doppler shifts, rotation is the most natural and widely accepted interpretation among standard stellar physics explanations. If there were actual multiple-choice options, the correct option would typically be the one stating that the star is rotating, or that the observed pattern indicates rotational motion of the stellar surface.

COS SPR 25 class 2 Jan 30 Test1 (USE GOOGLE CHROME)

If we observe one edge of a star to be redshifted and the opposite edge to be blueshifted, what can we conclude about the star?

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COS SPR 25 class 2 Jan 30 Test1 (USE GOOGLE CHROME)

If we observe one edge of a star to be redshifted and the opposite edge to be blueshifted, what can we conclude about the star?

View Explanation

Log in for full answers

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