Updated

Updated · Universe Today · Jun 3

Small Magellanic Cloud Expands at 17 km/s as Study Challenges Rotating-Disk Model

Updated

Updated · Universe Today · Jun 3

Small Magellanic Cloud Expands at 17 km/s as Study Challenges Rotating-Disk Model

Q: How does gravity from one galaxy cause another to expand, seemingly pushing stars away from each other?

Gravity is not pushing the Small Magellanic Cloud outward in a repulsive sense. The Large Magellanic Cloud’s gravity is stretching it through tidal forces. That happens because gravity is stronger on the side of the SMC that is closer to the LMC than on the far side. This difference in pull acts like a cosmic tug-of-war: instead of moving every star in the same way, it distorts the whole dwarf galaxy. Some stars are pulled more strongly than others, their orbits are altered, and the system becomes elongated and stirred up. To an observer, that can look like the galaxy is “expanding,” because stars are moving away from the center and from one another along preferred directions. The new proper-motion maps show exactly that pattern. After removing the SMC’s overall motion, astronomers found stars moving outward along a southeast-northwest axis, roughly pointing toward the LMC, at about 17 kilometers per second. That is the signature expected from tidal stripping and tidal heating, not from a stable rotating disk. In effect, the LMC is injecting orbital energy into the SMC’s stars during repeated close encounters, and possibly a direct collision in the past few hundred million years. That leaves the SMC out of equilibrium: its stars no longer follow neat circular paths, and some are being drawn into extended structures or pushed onto wider orbits. So the galaxy is not inflating like a balloon; it is being gravitationally stretched, disrupted and slowly pulled apart.

2 articles · Updated · Universe Today · Jun 3

New VISTA survey measurements show the Small Magellanic Cloud is undergoing large-scale tidal expansion, with stars moving outward along southeast and northwest directions even in its central regions.
An 11-year observing baseline and threefold better proper-motion precision let researchers subtract the galaxy’s bulk motion and isolate the residual pattern, which they say matches stretching caused by the Large Magellanic Cloud.
The findings indicate the SMC is out of equilibrium and its internal stellar motions are dominated by repeated gravitational encounters rather than orderly rotation.
At about 17 km per second, the outward motion is well below an estimated 60 km-per-second escape speed, but over billions of years it could still deform the dwarf galaxy and eventually help unbind some stars.
Older red giant stars also drift northward, suggesting the SMC’s present structure preserves signatures of multiple past interactions, not a simple rotating disk.

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Universe Today4d ago

Small Magellanic Cloud Undergoing Tidal Expansion Due to LMC Interactions, New Research Finds

MSN4d ago

Trouble near the Milky Way: The Large Magellanic Cloud is ripping its smaller neighbor galaxy apart

As the Small Magellanic Cloud unravels, how will its dramatic death reshape our own Milky Way galaxy?

If our galactic neighbor isn't a simple spinning disk, what other cosmic assumptions are we getting wrong?

How does gravity from one galaxy cause another to expand, seemingly pushing stars away from each other?

Sources

2 total

Universe Today4d ago

Small Magellanic Cloud Undergoing Tidal Expansion Due to LMC Interactions, New Research Finds

MSN4d ago

Trouble near the Milky Way: The Large Magellanic Cloud is ripping its smaller neighbor galaxy apart

Small Magellanic Cloud Expands at 17 km/s as Study Challenges Rotating-Disk Model

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