tidal debris vs spiral arms

• by zysyx

  When are spiral arms NOT tidal debris? This clearly has two arms, but what about the "margin?" Is that considered tidal debris?

  Posted December 16, 2016 5:48 PM

• by Budgieye moderator

  To me, they look quite undisturbed, so they are spiral arms. You are correct that sometimes it can be difficult to decide if a stream of stars is an arm or tidal debris.

  Posted December 16, 2016 9:06 PM