In the merger process that produces these galaxies, a lot of the stars get flung out to fairly large distances, and they end up in highly elongated orbits that take them far away and then back in close to the center.

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Massive dark matter halos are clearly detected in disk galaxies, so where did they disappear to during the mergers?

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We predict that other velocity tracers in the same elliptical galaxies will show higher velocities if they are less concentrated toward the galaxy center or if they move on more circular orbits. This is likely to be the case for compact star clusters, which are also observable in the outskirts of elliptical galaxies.

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It seems that we have identified the main solution to the problem.

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