The Mystery of Fragile Satellites: Dark Matter Under Tidal Assault

Original: "The tidal features of the classical Milky Way satellites: Expected in MOND but inconsistent with cold dark matter models"

· Elena Asencio, Indranil Banik, Pavel Kroupa

arXiv:2607.05502v1 · 2026-07-06 · CC BY 4.0 · ⏱ 1 min · Galaxies

Tidal disruption of the Milky Way’s dwarf satellite galaxies casts doubt on dark matter and points toward modified gravity.

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Astronomers have noticed that the Milky Way’s satellites are stretching and crumbling, as if torn apart by an invisible tide. In standard cosmology this is impossible—dark matter halos act as a shield. But the numbers show otherwise: the tidal susceptibility of many dwarfs exceeds the disruption threshold. It’s like seeing cracks in a spaceship’s armor. More and more scientists are turning to MOND—a theory where gravity becomes stronger in weak fields. Abandoning dark matter promises a revolution in physics, comparable to the discovery of the Universe’s accelerated expansion.

🎯 The 'roundest' of the classical galaxies—Leo II—has an ellipticity of only 0.07, meaning it’s almost a perfect sphere, while the 'flattest'—Ursa Minor—reaches 0.55, likely a result of powerful tidal impacts from the Milky Way.

🎬 The idea that galaxies can be torn apart by tides evokes the concept of the 'Gravity Well' from Peter F. Hamilton's novel 'Pandemonium', where entire star streams emerged after galactic collisions. In MOND, such processes are more dramatic and ubiquitous.

\eta \equiv \frac{r_{h,3D}}{r_{tid}}

The ratio of the half-mass radius to the tidal radius—a key measure of a galaxy’s vulnerability to a neighbor’s gravity.

\nu(g_N) = \frac{1}{2} + \sqrt{\frac{1}{4} + \frac{a_0}{g_N}}

A factor that strengthens gravity at ultra-low accelerations. When the Newtonian acceleration g_N is much less than a0, the gravitational force increases severalfold.

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The Mystery of Fragile Satellites: Dark Matter Under Tidal Assault