What specific function does the inferred Dark Matter halo serve regarding outlying stars in spiral galaxies?
Answer
It provides the necessary gravitational tether to keep the outermost stars moving at high speed.
The existence of Dark Matter halos is inferred precisely because they provide the missing gravitational force required to explain the flat rotation curves. In the outer regions where visible mass density is negligible, the orbital velocity must be maintained at a high, constant level. The Dark Matter halo, described as massive and extended, supplies this necessary gravitational influence. This continuous, pervasive gravitational pull acts as a tether, ensuring that stars and gas clouds located far beyond the luminous disk maintain the high speeds dictated by the observation rather than slowing down as predicted by visible matter alone.
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