Main Entry: be·lieve
Inflected Form(s): be·lieved; be·liev·ing
Etymology: Middle English beleven, from Old English belEfan, from be- + lyfan, lEfan to allow, believe; akin to Old High German gilouben to believe, Old English lEof dear -- more at LOVE
1 a : to have a firm religious faith b : to accept as true, genuine, or real *ideals we believe in* *believes in ghosts*
2 : to have a firm conviction as to the goodness, efficacy, or ability of something *believe in exercise*
3 : to hold an opinion : THINK *I believe so*
1 a : to consider to be true or honest *believe the reports* *you wouldn't believe how long it took* b : to accept the word or evidence of *I believe you* *couldn't believe my ears*
2 : to hold as an opinion : SUPPOSE *I believe it will rain soon*
There is also an implication to the word "belief" that no evidence is required. Thus the CNN statement that "Astronomers believe a quasar is produced by cosmic gas as it is drawn toward the edge of a supermassive black hole" [emphasis added] is completely wrong. It implies that astronomers have no hard evidence and and are asserting it to be true for us to take on faith.
When you talk on the phone with your family, say your daughter, what evidence do you have that at the other end of your phone it's your daughter? The sound of her voice, the way she words her sentences. But you don't see her, do you? You can't touch her and know she's there. And yet you still know that it's her, right? That's how well astronomers know that quasars are produced in the system of a black hole.
We can't see the black hole directly, but we see all the evidence of one, for example, how fast the gas is moving and how far it is from the center indicates how much mass must be inside a certain radius, which tells us it must be a black hole. Computer models also show that the end of a super massive star's life is a black hole, and we'll see a disk and jets, which is what we see with quasars.
This isn't belief, it is our best knowledge.