Will someone please illuminate this apparent dichotomy?

[a_quester]

Can someone please tell me which of these statements is correct? The http link is to the article making the statement.<br /><br /><br />Stunning X-ray Image Shows Pulsar at Center of Supernova<br />posted: 23 October 2001<br /><br />"Supernovae are somewhat rare, occurring only once every 50 years or so in a galaxy like our Milky Way."<br /><br />http://www.space.com/scienceastronomy/astronomy/pulsar_supernova_011023.html<br />----------------------------------------------------------------------------<br /><br /><br />Before & After: Rare Glimpse at Exploding Star<br />posted: 01 August 2005<br /><br />"A star explodes every second or so, somewhere in the universe. It's how they die, and astronomers call the events supernovas."<br /><br />http://www.space.com/scienceastronomy/050801_hubble_supernova.html<br /><br />

 

[najab]

"...only once every 50 years or so <font color="yellow">in a galaxy like</font>our Milky Way..."<br /><br />"A star explodes every second or so, <font color="yellow">somewhere in the universe</font>"<br /><br />There's a lot of galaxies in the Universe.<br /><br />

 

[rlb2]

Both answers appear to be about the same. It was once said that there are as many galaxies in the universe as they are stars in our galaxy. Well that was when they only thought there were only 100 billion stars in our galaxy, the last best guess that I heard of is that there are now about 200 billion, that may still depend on who you ask. Our galaxy is bigger than the average size galaxy. If for sake of argument, someone has finally counted all the stars in the universe and all the stars in our galaxy then we would have more of a defined answer but then we would have to throw in more unknown's which will still leave the true number of supernovas undefined. Only a certain amount of stars are large enough to go supernova. Calculate how many seconds that they are in 50 years, there is your answer.<br /><br />It is definitely not an exact science or even a close approximation since we can't count all the stars in the universe and some galaxies are older and some are younger than our own. When we look into space back 5 billion light years or more we see stars that were shining before our solar system and the sun was formed. In fact if we look back in time long enough some of the galaxies may not be there today billions of years later although we see them now. As a result the number of actual stars and galaxies shinning today may be substantially lower than we think. So the two quotes you have are just a good way to spark a person’s imagination and by no means an exact science.<br /><br />Here is another quote that was just meant to spark people’s imagination and isn't meant to be held as a exact science. I don’t know if this holds any water anymore but, it was once said that "If a supernova happened within 50 light years of earth, by the time you first see the light 2 minutes later the earth would be completely vaporized from its shock wave." That’s barely enough time to bend over and kiss your backside goodbye.<br /><br /><br /> <div class="Discussion_UserSignature"> Ron Bennett </div>

 

[CalliArcale]

Well, it would depend on how fast the shockwave was travelling. I'd expect it to take longer, though. Coronal mass ejections take several hours to reach Earth (normally), while the light from them reaches Earth a mere eight minutes after the blast. I guess it all depends on how fast the shock wave is travelling, and whether or not they slow down.<br /><br />However, the electromagnetic radiation (including microwaves and gamma radiation) will be travelling at light-speed. That will reach Earth at exactly the same time as the visible light does. Our atmosphere protects us from most gamma radiation, but I'm sure there's a limit to how much it can shield. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>