How many visible stars still exist?

[scratchcardiain]

Me and my buddy were drunkenly arguing last night on our walk home from town about the amount of stars that still exist. I suggested about 35-40% no longer exist, because of the amount of time the light takes to get to Earth. But he was having none of it, and thought my guess was far too high. What are peoples opinions here?<br />Iain

 

[robnissen]

The vast majority of stars are M class stars. M class stars have a life of over 100 billion years. The universe is about 13.7 billion years old. So, barring being swallowed in a black hole, or some other rare calamity, every M class star still exists as an M Class star, so most stars still exist. Plus, unless a star is very large, multiple solar masses, when it burns out, it will become a white dwarf. Thus, almost every burnt out star still exists as a white dward. Even if you ignore the white dwarfs, the majority of stars that are not M class stars, are still less massive than the sun, which has a life expectancy of around 10 billion years. Again, with a 13.7 billion year old universe, the vast majority of all stars smaller than or equal to the sun, still exists. The only thing that doesn't put the number up around 99%, is that the extremely massive stars (which are rare) only last about 100 Million years, so some massive stars could be 5th, 10th or maybe even 100th generation. But put them all together and my guess would be around 90% of all stars that ever existed still exist, and it would be closer to 99% if white dwarfs are counted as still existing as stars.

 

[dragon04]

IIRC, about 5,000 stars are visible with the naked eye.<br /><br />Of those, a vanishingly small amount could have gone nova or supernova in the last few thousand years.<br /><br />Beyond that, ALL the stars visible to telescopes exhibit a uniform behavior. Considering that over decades of observation that a supernova only occurs about once per century per galaxy, damn near everything we can see, especially in our own galaxy, is still there.<br /><br /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[scratchcardiain]

Wow that sucks, my friends an &%$#@! about being right. He's gonna gloat about this for a long time...

 

[alokmohan]

I also agree with the figure.More orless.

 

[trumptor]

I had a professor that told us at one point that there are about 200 stars close enough to us that if they went super-nova the radiation would kill off life on Earth, so there are more stars than just our sun that we should worry about. The thing is that I had this class about 15yrs ago and our understanding has surely changed during this time, but I have never heard anything about this since that one time back then. Anybody want to comment on this? Is this true or not? <div class="Discussion_UserSignature"> <p><em><font color="#0000ff">______________</font></em></p><p><em><font color="#0000ff">Caution, I may not know what I'm talking about.</font></em></p> </div>

 

[alokmohan]

We are talking of stars visible to naked eye.

 

[MeteorWayne]

Well, that's what the thread title says, but it's not what the roiginal post says. So it's a little unclear <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[trumptor]

Thanks for the explanation and link crazyeddie. I've always had it in my head that there were these 200 or so stars out there that could cause our extinction. Its nice to be wrong sometimes, lol.<br /><br />Sorry for posting here with something a little off-topic alokmohan, but since the threads were in regards to how many of the visible stars were still actually around, I figured that we were discussing how many nearby stars have gone supernova. And that's what made me remember my question about dangers of nearby supernovas. I just didn't want to start a whole new thread when this seemed pretty similar. <div class="Discussion_UserSignature"> <p><em><font color="#0000ff">______________</font></em></p><p><em><font color="#0000ff">Caution, I may not know what I'm talking about.</font></em></p> </div>

 

[robnissen]

For what its worth, I thought your question about the 200 stars was MUCH more on topic of the thread than many posts around here.