Columbia subject headings:
Active galaxies--Congresses.
Astrophysics--Congresses.
Black holes (Astronomy)--Congresses.
Quasars--Congresses.
Harvard subject headings:
Active galaxies--Congresses.
Astrophysics--Congresses
Black holes (Astronomy)--Congresses
Quasars--Congresses
Princeton subject headings:
Active galaxies--Congresses.
Astrophysics--Congresses.
Black holes (Astronomy)--Congresses.
Quasars--Congresses.