Q&A: Galaxies, Galaxy Clusters, AGN, and Quasars

Q:
Could galaxies represent embryo stages? To me some stages seem like human life cycles at birth. What happens to a planet if it were to be sucked into a black hole? Does it disapeer? What starts a black hole - supernova, planet burst, star burst?

A:
Yes, some galaxies are in their early stages, but others have evolved and have far fewer star forming regions, and are in general colder and older. But we don't know what the end state of a galaxy is, so we could indeed still be in the somewhat early stages of life in the universe.

Chandra has recently made an observation of a star that came too close to a black hole and was torn apart. Please see our Chronicles article to explain how this happens:
http://chandra.harvard.edu/chronicle/0104/tidal/index.html
and our photo album explains in greater detail:
http://chandra.harvard.edu/photo/2004/rxj1242/

A black hole may be formed from a massive star which accretes matter from a companion star, it may be formed by the collapse and explosion of a massive star (a supernova), although we do not yet have evidence for a black hole in the remains of such an explosion. A black hole is formed by any process which could squeeze enough matter into a small enough space such that the density reaches the black hole limit. Please check out our Q&A page on black holes
http://chandra.harvard.edu/resources/faq/black_hole/bhole-main.html
and note that there are links at the top of the page to the black hole field guide, which may also be useful for you.