Questions of the Week

A galaxy is moving away at 0.1 light years per year and is 1.4 billion light years away.  How long did it take to get there?  14 billion years.  Age = distance/velocity = 1.4/.01 = 14

According to conservation of angular momentum, what would happen if a star orbiting in a direction opposite the neutron star’s rotation fell onto the neutron star?  The neutron star’s rotation would slow down.

Are habitable planets likely?  Billions of stars have sizeable habitable zones, but we don’t yet know how many have terrestrial planets in those zones

Are Earth-like planets rare or common?  We don’t yet know b/c we are still trying to understand all the factors that make Earth suitable for life.

Based on the value of Hubble’s constant, how old is the universe? 12 to 20 billion years

Big Bang:  made 75% H, 25% He, stars made everything else

Black hole info:  It is hard to fall into a black hole because they are small compared to the size of the universe; they can be orbited, and they don’t suck you in.  Near the event horizon, time slows

down and tidal forces are very strong.  Some x-ray binaries contain compact objects too massive to be neutron stars, so they’re probably black holes.  There are very massive black holes in the

center of most galaxies.

Could there be life on Mars?  Evidence for liquid water in the past suggests that life was once possible on Mars

Could there be life on Europa or other Jovian moons?  Jovian moons are cold, but some show evidence for subsurface and other liquids

Could there be neutron stars that appear as pulsars to other civilizations on other planets but not to us?  Yes

Does dark matter really exist?  Either it exists or our understanding of gravity is wrong and must be revised.