Evidence for a vast prograde stellar stream in the solar vicinity

Lina Necib, Bryan Ostdiek, Mariangela Lisanti, Timothy Cohen, Marat Freytsis, Shea Garrison-Kimmel, Philip F. Hopkins, Andrew Wetzel, Robyn Sanderson

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


Massive dwarf galaxies that merge with the Milky Way on prograde orbits can be dragged into the disk plane before being completely disrupted. Such mergers can contribute to an accreted stellar disk and a dark matter disk. Here we present Nyx, a vast stellar stream in the vicinity of the Sun, which provides the first indication that such an event occurred in the Milky Way. We identify about 200 stars that have coherent radial and prograde motion in this stream using a catalogue of accreted stars built by applying deep learning methods to the Gaia data. Taken together with chemical abundance and orbital information, these results strongly favour the interpretation that Nyx is the remnant of a disrupted dwarf galaxy. Further justified by FIRE hydrodynamic simulations, we demonstrate that prograde streams like Nyx can be found in the disk plane of galaxies and identified using our methods.

Original languageEnglish (US)
Pages (from-to)1078-1083
Number of pages6
JournalNature Astronomy
Issue number11
StatePublished - Nov 2020

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics


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