hi- i was wondering how many of the stars that we see at night are actually extinct and how is this knowledge confirmed?
-starsister
-starsister
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Hmm, interesting question. I'm not entirely sure what you mean though. I assume you are asking how many stars we see now are actually "dead" in the sense that they have reached the end of their life.
There are several different ways that a star dies depending on its mass, so a "dead" star can take on several different forms. If a large enough star dies, it becomes a black hole and won't emit any more light. Smaller stars form neutron stars and white dwarfs, which although no longer burn nuclear fuel, they still emit light and some of them we can see with telescopes.
Determining whether a star is currently dead can be much more difficult if it has not collapsed yet. We can determine that a star appears very near the end of its life, and if it is far enough away (several million light years at least), we may be able to assume that it has probably collapsed by now. Although, the physics behind stellar collapse aren't fully understood and it is very difficult to predict when a star will collapse within several million years error.
I don't know the number of stars currently known to be near the end of their life, though. Maybe someone has an estimate for how many stars visible to the naked eye are close to the end of their life cycles?
Welcome to SDC, by the way.
There are several different ways that a star dies depending on its mass, so a "dead" star can take on several different forms. If a large enough star dies, it becomes a black hole and won't emit any more light. Smaller stars form neutron stars and white dwarfs, which although no longer burn nuclear fuel, they still emit light and some of them we can see with telescopes.
Determining whether a star is currently dead can be much more difficult if it has not collapsed yet. We can determine that a star appears very near the end of its life, and if it is far enough away (several million light years at least), we may be able to assume that it has probably collapsed by now. Although, the physics behind stellar collapse aren't fully understood and it is very difficult to predict when a star will collapse within several million years error.
I don't know the number of stars currently known to be near the end of their life, though. Maybe someone has an estimate for how many stars visible to the naked eye are close to the end of their life cycles?
Welcome to SDC, by the way.
I'd imagine relatively few. So most of the stars we can see within the night sky are within a few hundred light years or so, and most stars die on the order of billions of years. Even the shortest-lived stars take millions of years. So of the couple of thousand stars we can see with the eye, very few are likely to go supernova in the few hundred years since we're seeing them.
Think about it this way: how often do we see a supernova visible to the naked eye? A few times a millenium? And how many of those (like SN 1987A) are far, far away (in places like the LMC) so we'd never have seen the progenitor star with the naked eye beforehand?
The answer is probably 0 - maybe 1 or 2, tops.
That said, the farthest stars we see have to be very bright - and it's the guys who are far away and live the shortest lives that are likely to have gone supernova since they emitted the light we see
Think about it this way: how often do we see a supernova visible to the naked eye? A few times a millenium? And how many of those (like SN 1987A) are far, far away (in places like the LMC) so we'd never have seen the progenitor star with the naked eye beforehand?
The answer is probably 0 - maybe 1 or 2, tops.
That said, the farthest stars we see have to be very bright - and it's the guys who are far away and live the shortest lives that are likely to have gone supernova since they emitted the light we see
Yeah, I'm looking at the Wiki pages for some of the supernovae observed in the early parts of the last millenium - all of them were really far away. And good thing, too - we'd be in pretty bad shape if a supernova occured that close!
I agree, of the naked eye stars we see at present, likely zero or one are black holes, neutron stars or white dwarfs. Of the stars we can resolve to individuals with the most powerful telescopes, I'll guess one in 1000 have become black holes, neutron stars or white dwarfs, while the light was en route to our telescope. That may be one percent with the next generation of Hubble telescope equivelent. Neil
hi, wow, thanks for the great responses. this is a neat site and i'm glad that i joined it as i have so many questions about space. i had always thought that many ( even most) were already extinct as it takes the light so long to reach us here on earth. it's somehow comforting to know that they're all up there still madly burning away thanks for replying.
thanks for replying.There may be a billion times as many stars that we can't resolve as individuals, compared to those we can resolve with our best telescopes. Perhaps 3% of the ones we can't resolve have become black holes, neutron stars or white dwarfs.
Likely all of the class m stars are still shining dimly and we think 90 plus percent of all the stars are class m, even though all the class m stars are too dim to be seen with the naked eye. Neil
Likely all of the class m stars are still shining dimly and we think 90 plus percent of all the stars are class m, even though all the class m stars are too dim to be seen with the naked eye. Neil
Starsister - many stars out there are already dead by the time their light reaches us, but most of those stars are too far away for us to see individually! The stars we see with the naked eye are all VERY close.
hi- thanks again for these responses, it's given me a lot to think about and learn. i think that my confusion lies mostly in having such a hard time contemplating distance in space - light years- and understanding how far in space that we can see with the naked eye. this clarifies a lot. so, this leads me to another question and please forgive me here with my questions as i am aware that they are quite basic and simple in terms of all of the knowledge about space that you all but i am extremely interested and eager in learning more. anyway, so the stars that are 'close' to us, or near enough to us that their extinction or collapse would obviously affect us here on earth- how are they studied and/or examined to know or try and understand where they are in their 'life spans'? are the ones that we can see all about the same general age? also, how old ( or young) is our sun?
thanks, starsister
thanks, starsister
Hi starsister - aging a star is tricky business, but can be done. The important thing in terms of knowing which stars die is that we know what stages of life stars go through, so a star like our Sun isn't going to die anytime soon since we know big yellow stars like our Sun have to expand into a red giant phase first.
Ironically enough, it seems with that post you were upgraded to nucleus It's a matter of how many posts you have.
starsister":37iwx0oo said:p.s. am i a 'proton' because i just joined or is there another meaning
Ironically enough, it seems with that post you were upgraded to nucleus
It's a matter of how many posts you have.oh okay, yes it does look like now i'm at nucleus level so i have a new question. i have a new ( yet very tiny) telescope and was looking at jupiter the other night. i could see 2 of the moons ( pinhead size mind you this telescope is nothing great) and also saw what looked like a 3rd moon but it was much further away yet seemed to be a moon like the others. is that what i was looking at or are they all closer due to jupiters gravity? also, is there an approximate age known of our sun? how many millions of years will it be until it reaches the red giant phase? oh and one more thing. i recently bought a beginners astronomy/physics book but is there one that anyone would recommend as a 'not to miss' beginners book? i got 'from here to infinity' by gribbin. thanks, starsister
so i have a new question. i have a new ( yet very tiny) telescope and was looking at jupiter the other night. i could see 2 of the moons ( pinhead size mind you this telescope is nothing great) and also saw what looked like a 3rd moon but it was much further away yet seemed to be a moon like the others. is that what i was looking at or are they all closer due to jupiters gravity? also, is there an approximate age known of our sun? how many millions of years will it be until it reaches the red giant phase? oh and one more thing. i recently bought a beginners astronomy/physics book but is there one that anyone would recommend as a 'not to miss' beginners book? i got 'from here to infinity' by gribbin. thanks, starsisterstarsister":12t42dsw said:
Here is a breif guide from Sky and Telescope to viewing Jupiter and its' moons.
http://www.skyandtelescope.com/observin ... 35094.html
Here is Sky and Telescopes' chart showing the positions of four of Jupiters brightest moons for the month of August (the link to these monthly charts are on the page I linked to).
http://media.skyandtelescope.com/docume ... 908Jup.pdf
S&T is an excelent resource for this type of thing. I hope it helps you sort out what you were viewing! Also take into consideration when consulting the chart that your telescope may have flipped the image upsidedown or even upsidedown and backwards.
starsister,
Subscribing to Sky and Telescope or Astronomy is also not a bad idea since they generally keep up with the latest news. And of course hanging around SDC is pretty good.
The sun is about 4.5 billion years old (4,500 million) and is about halfway through it's lifetime as a normal star.
Wayne
Subscribing to Sky and Telescope or Astronomy is also not a bad idea since they generally keep up with the latest news. And of course hanging around SDC is pretty good.
The sun is about 4.5 billion years old (4,500 million) and is about halfway through it's lifetime as a normal star.
Wayne
hi- thanks for those links- really interesting and now i just wish i had a stronger/better telescope :-( however, after reading those articles and looking again, i think that i can see 3 of the moons, which is still quite exciting to me. so, i have a new question - where in the u.s. - mainly in the southwestern part of the u.s. - are there any large observatories/major telescopes that are open to the public for viewing? i'm looking for the nearest one to colorado. also, is it hazardous to the eyes to view the moon when it is full or near full with a telescope? can the intense brightness do damage to our eyes? thanks so much, starsister
Unfortunately, large observatories - while abundant in the Southwest (the national observatory is in Arizona, and there are some heavy duty telescopes around those states) - aren't usually open to the public for observation. Every night on those telescopes is very much in demand and goes to astronomers for doing research But you don't need a major observatory, just check out any decent university. Most of them have astronomy departments with public observing nights. U Colorado Boulder has one of the better astro departments in the country, I'm sure they have something!
But you don't need a major observatory, just check out any decent university. Most of them have astronomy departments with public observing nights. U Colorado Boulder has one of the better astro departments in the country, I'm sure they have something!okay, thanks, i'll check things out around here. unfort. it's about a 7 hour drive to get to boulder. does the national observatory in arizona ever allow for public visits? oh and did you see my previous question about moon viewing? i am concerned about damaging my eyes. thanks so much, starsister
Here's information on the national observatory at Kitt Peak:
http://www.noao.edu/outreach/kpvc/
Looks like they have nightly public observing at one of the smaller telescopes
Not sure about the moon thing.
http://www.noao.edu/outreach/kpvc/
Looks like they have nightly public observing at one of the smaller telescopes
Not sure about the moon thing.
A telescope with with a large lens (or mirror) could possibly cause eye damage viewing the Moon, but it is very unlikely for small inexpensive telescopes. The Sun is very dangerous, so be careful not to point the telescope anywhere close to the Sun, even when the sun is barely visable though the clouds.
Viewing the moon is best done after viewing stars and planets, as the moon is bright enough to cause your pupils to contact which reduces your ability to see very dim stuff for perhaps a half hour. Neil
Viewing the moon is best done after viewing stars and planets, as the moon is bright enough to cause your pupils to contact which reduces your ability to see very dim stuff for perhaps a half hour. Neil
starsister":3vjfwaxu said:
You should try looking for an amature astronomy club near you and find out when they meet. This page from the skyandtelescope.com might help you find one. http://www.skyandtelescope.com/community/organizations
This is a great way to get started because you will get to view all kinds of objects through many different tellescopes.
Extinct Stars:
Since light takes time to reach us a star we see them as they were. The look-back time is the same as the distance when measured in light years. So a star we see now could in principle be "gone" now ie become a white dwarf, neutron star or even black hole. To have this the star must have died withing the look-back time.
Most of the stars we see are in middle age (on the main sequence) and will last from 1 million (high mass O stars like Zeta Puppis) to billions of years (sun like and lower mass stars). With you eye the most distant stars are several hundred ligh years away. So there is little chance even for the shortest lived stars to have died with such a short look-back time.
Of the visible stars it is often said that the stars most likely stars to "die" soon are the red super-giants like Betelgeuse. However this is still very unlikely. The red super-giant stage can last 15 million years so with look back times (distances) of a few hundred years to Betelgeuse, Antares or Aldebaran ... it is very unlikely.
Given my luck one will go supernova just to prove me wrong. That would be spectacular !
Using a moderate to large telescope you can see stars in the process of changing from a red giant to a white dwarf; look at the central star of a planetary nebula. M57 "ring nebula" is the most famous example, but to see the central star you need a large-ish telescope.
Small telescope: you can see an lot with even a small telescope and even do valuable science; takes some knowledge and effort. An astronomy club can point you right direction. Enjoy !
Since light takes time to reach us a star we see them as they were. The look-back time is the same as the distance when measured in light years. So a star we see now could in principle be "gone" now ie become a white dwarf, neutron star or even black hole. To have this the star must have died withing the look-back time.
Most of the stars we see are in middle age (on the main sequence) and will last from 1 million (high mass O stars like Zeta Puppis) to billions of years (sun like and lower mass stars). With you eye the most distant stars are several hundred ligh years away. So there is little chance even for the shortest lived stars to have died with such a short look-back time.
Of the visible stars it is often said that the stars most likely stars to "die" soon are the red super-giants like Betelgeuse. However this is still very unlikely. The red super-giant stage can last 15 million years so with look back times (distances) of a few hundred years to Betelgeuse, Antares or Aldebaran ... it is very unlikely.
Given my luck one will go supernova just to prove me wrong. That would be spectacular !
Using a moderate to large telescope you can see stars in the process of changing from a red giant to a white dwarf; look at the central star of a planetary nebula. M57 "ring nebula" is the most famous example, but to see the central star you need a large-ish telescope.
Small telescope: you can see an lot with even a small telescope and even do valuable science; takes some knowledge and effort. An astronomy club can point you right direction. Enjoy !
I still dont know how many stars exist on the galaxy,and for a ordinary people its hard to count the stars...hehe
resell rights
resell rights
As for the ages of nearby stars, they vary quite a bit. Bigger stars tend to have shorter lifetimes. The star nearest to the Sun is Proxima Centauri, a small red dwarf star. It is about 5 billion years old, nearly the same age as our Sun. Another red dwarf is Barnard's star, the closest star besides the three int the Centuari system. Barnard's star is more like 11 to 12 billion years old, so it was formed much earlier. The Universe is only about 13.7 billion years old. Barnard's star is so old and tired that its spin has slowed, it has almost stopped its flare activity, common among young red dwarfs. And it is traveling at 142 km/sec, relative to the Sun, giving it the largest angular speed, as seen from the Earth, of any star. So it's moving on a much different orbit through the galaxy than our Sun.
Red dwarfs burn their nulcear fuel so slowly that they last a very long time - the smaller, the longer. Their lifetimes are measured in trillions of years. Provided the Universe last that long! When they finally run out of fuel, they will turn into black dwarfs.
Our Sun will go through a red giant stage, then a white dwarf stage, and in 40 billion years or so, it will also end its life as a black dwarf.
There are no black dwarfs yet, though. According to theory, at least. The Universe is not old enough yet to have produced any. Just wait.
PL
Red dwarfs burn their nulcear fuel so slowly that they last a very long time - the smaller, the longer. Their lifetimes are measured in trillions of years. Provided the Universe last that long! When they finally run out of fuel, they will turn into black dwarfs.
Our Sun will go through a red giant stage, then a white dwarf stage, and in 40 billion years or so, it will also end its life as a black dwarf.
There are no black dwarfs yet, though. According to theory, at least. The Universe is not old enough yet to have produced any. Just wait.
PL
aaprilruth":2r6vorg2 said:I still dont know how many stars exist on the galaxy,and for a ordinary people its hard to count the stars...hehe
There's somewhere between 200,000,000,000 & 500,000,000,000 stars in our galaxy (that's between 200 & 500 billion).
There's 'estimated' to be about 1,000,000,000,000,000,000,000 stars in the visible universe - a figure roughly equivalent to all the grains of sand on this planet (including all the deserts, beaches etc)
I had not heard the black dwarf theory before. Does it also apply to low mass K stars? Perhaps K stars become compact yellow dwarf stars for a few billion years before cooling to compact orange dwarf stars, then compact red dwarf stars, following more billions of years of cooling? I understand compact white dwarf stars (and neutron stars) have a distinct blue tint, because they are very hot at their surface. Nearly all K stars are still main sequence even if they are 13 billion years old.
I suppose sub M class stars, cool in millions of years (without achieving main sequence) instead of billions of years to Jupiter like back bodies, but larger in diameter. Neil
I suppose sub M class stars, cool in millions of years (without achieving main sequence) instead of billions of years to Jupiter like back bodies, but larger in diameter. Neil
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