Assertion: boomerang nebula | /r/HasProperty | compelling mystery
Facets:
value: for astronomers
type: TRANSITIVE-OBJECT
value: since 1995
type: TEMPORAL
Source sentences:
text: The Boomerang Nebula, a proto-planetary nebula that was created by a dying red giant star (located about 5000 light years from Earth), has been a compelling mystery for astronomers since 1995.