What the study found
The study found a measurable reflex motion in the Milky Way’s outer halo stars that is associated with the Large Magellanic Cloud’s infall. Using this motion, the authors estimated the speed of the Milky Way’s lurch toward the Large Magellanic Cloud and the Large Magellanic Cloud mass enclosed within 50 kiloparsecs.
Why the authors say this matters
The authors conclude that their inference framework can provide rapid constraints for future surveys that measure the velocities of outer halo stars. They also suggest that their mass estimate implies the Large Magellanic Cloud’s total mass is at least about 10–15% of the Milky Way’s.
What the researchers tested
The researchers used a simulation-based inference framework, which uses simulations and neural networks to estimate parameter distributions. They analyzed mean radial and tangential velocities of outer Milky Way halo stars in distance and on-sky bins, and trained neural networks on 128,000 rigid Milky Way–Large Magellanic Cloud simulations conditioned on velocity data from DESI and from the combined H3+SEGUE+MagE outer halo surveys.
What worked and what didn't
Using the H3+SEGUE+MagE data set with on-sky quadrants, they reported a distance-averaged reflex motion velocity of 26.4^{+5.5}_{-4.4} km s^{-1} and an enclosed Large Magellanic Cloud mass within 50 kiloparsecs of 9.2^{+1.9}_{-2.3} × 10^{10} solar masses. The abstract says they constrained the reflex motion velocity and enclosed Large Magellanic Cloud mass using either the DESI or H3+SEGUE+MagE data set while varying survey sky coverage and depth, but it does not specify which configurations performed better beyond these reported estimates.
What to keep in mind
The quoted uncertainties are statistical. The abstract does not describe additional limitations beyond the scope of the surveys and simulations used, and it notes that the results come from a rigid Milky Way–Large Magellanic Cloud simulation framework.
Key points
- The study links the Large Magellanic Cloud’s infall to a reflex motion in outer Milky Way halo stars.
- The authors estimate a Milky Way travel speed toward the Large Magellanic Cloud of 26.4^{+5.5}_{-4.4} km s^{-1}.
- They estimate the Large Magellanic Cloud mass within 50 kiloparsecs as 9.2^{+1.9}_{-2.3} × 10^{10} solar masses.
- The authors suggest the Large Magellanic Cloud’s total mass is at least about 10–15% of the Milky Way’s.
- Their framework was trained on 128,000 rigid Milky Way–Large Magellanic Cloud simulations and applied to DESI and H3+SEGUE+MagE data.
Disclosure
- Research title:
- LMC infall is linked to Milky Way halo reflex motion
- Authors:
- Richard A. N. Brooks, Jason L. Sanders, Vedant Chandra, Nicolás Garavito-Camargo, Adam M. Dillamore, Adrian M. Price-Whelan, Yuan-Sen Ting
- Institutions:
- Center for Astrophysics Harvard & Smithsonian, Simons Foundation, Simons Foundation, The Ohio State University, University College London, University College London, University College London, University of Maryland, College Park
- Publication date:
- 2026-07-01
- OpenAlex record:
- View
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