In a/an ____________ binary, the orbits of both stars can be ...

[Redwolflake15]

In a/an ____________ binary, the orbits of both stars can be mapped.
 
  Fill in the blank(s) with correct word

Question 2

An isolated black hole in space would be difficult to detect because
 
  a. there would be no light source nearby.
  b. it would not be rotating rapidly.
  c. it would be stationary.
  d. very little matter would be falling into it.
  e. there would be very few stars behind it whose light the black hole could block out.

[Anton]

Answer to Question 1

visual

Answer to Question 2

d