quasars

This topic has expert replies
User avatar
Master | Next Rank: 500 Posts
Posts: 208
Joined: Sun Sep 28, 2008 12:30 pm
Thanked: 22 times

quasars

by neoreaves » Sun Apr 25, 2010 6:08 am
Quasars--celestial objects so far away that their light takes at least 500 million years to reach Earth--have been seen since 1963. For anything that far away to appear from Earth the way quasars do, it would have to burn steadily at a rate that produces more light than 90 billion suns would produce. But nothing that burns at a rate that produces that much light could exist for more than about 100 million years.

  If the statements above are true, which one of the following must also be true on the basis of them?

  (A) Instruments in use before 1963 were not sensitive enough to permit quasars to be seen.

  (B) Light from quasars first began reaching Earth in 1963.

  (C) Anything that from Earth appears as bright as a quasar does must produce more light than would be produced by 90 billion suns.

  (D) Nothing that is as far from Earth as quasars are can continue to exist for more than about 100 million years.


  (E) No quasar that has ever been seen from Earth exists any longer.

source:
LSAT preptests

Master | Next Rank: 500 Posts
Posts: 232
Joined: Sun Feb 28, 2010 10:47 pm
Thanked: 10 times

by Phirozz » Sun Apr 25, 2010 12:21 pm
IMO E
Quasars' light takes 500 million years to reach earth.
But nothing that burns at a rate that produces that much light could exist for more than about 100 million years.

So by the times their light reaches earth quasars must be extinct.

Senior | Next Rank: 100 Posts
Posts: 53
Joined: Tue Feb 17, 2009 11:14 pm
Location: India
Thanked: 2 times

Junior | Next Rank: 30 Posts
Posts: 26
Joined: Tue Apr 13, 2010 10:17 pm

by bleedthegmat » Tue Apr 27, 2010 1:19 am
neoreaves wrote:Quasars--celestial objects so far away that their light takes at least 500 million years to reach Earth--have been seen since 1963. For anything that far away to appear from Earth the way quasars do, it would have to burn steadily at a rate that produces more light than 90 billion suns would produce. But nothing that burns at a rate that produces that much light could exist for more than about 100 million years.

  If the statements above are true, which one of the following must also be true on the basis of them?

  (A) Instruments in use before 1963 were not sensitive enough to permit quasars to be seen.

  (B) Light from quasars first began reaching Earth in 1963.

  (C) Anything that from Earth appears as bright as a quasar does must produce more light than would be produced by 90 billion suns.

  (D) Nothing that is as far from Earth as quasars are can continue to exist for more than about 100 million years.


  (E) No quasar that has ever been seen from Earth exists any longer.

source:
LSAT preptests
E is the only plausible choice.

Probably what we are seeing right now does not exist.. but since it took almost 500 years to reach that is the reason why it is visible now... In short we are seeing the PAST :D