I was looking at the night-sky a few days ago when I came to think about this. All the known star-signs are still there (that covers at-least a few thousand years of human history), all the stars used for navigation throughout relatively modern times are still there (that's at-least 500 years of human history), and that just made me wonder if there are any examples at all of known stars that were once observed but can't be today (and in extension of that I came to think of black-holes)
My own personal quick first-hand evaluation of this was to simply count how many stars I have seen myself through time that I can't locate anymore, which is zero. All stars I can recognize are still there, thus zero is missing. Rough and basic, certainly, but the most direct observation of the night-sky none-the-less
Star signs won't degrate because the stars will eventually die. They will degrade because the stars are moving. Every star has it's own velocity around the galactic center, so relatively to the Sun those velocities are in the range of a few 10 km/s.
There were a few stars visible from Earth that went nova, got brighter for a few weeks, then disappeared completelly. The two most prominent that I can think of are these two:
SN 1054 - Wikipedia, the free encyclopedia
SN 1604 - Wikipedia, the free encyclopedia
These two became very bright.
How many observed/confirmed stars has disappeared from sight for no known natural reason, if any?
Stars which, based on the current mainstream understanding of how they should evolve, should still be there, but aren't.
Stars that behave in explainable ways, such as those 2 you describe, does not fall into the category I'm after in this thread. But thanks for the links anyway though
The reason I mentioned star-signs is because they are probably the safest way to reference earlier astronomic observations, which would increase the time-span of useful observation.
A very faint star _could_ have been spotted a long time ago (several thousand years perhaps) and be missing today, but if the star is only referenced as, for example, the Bethlehem star, then we can't deduce any real useful info from that. We don't know with any high probability what star the Bethlehem star actually is/was, only that there is talk about it having been seen around year zero.
However, if the North star could not be seen today we would be pretty certain it was once there simply because many references of it are very clear and hard to mistake for other stars.
And if it did not show any signs of having gone nova before disappearing, then that would be the kind of star I'm asking about in this thread
So far I'm still at zero such stars.
Stars don't just go poof and disappear.
If a star has 1 solar mass of material, there will still be roughly that amount in the area. Some mass is usually consumed by the fusion, but material is always left over...
If a star were to collapse into a black hole a few thousand years ago, it wouldn't suck in all gas. The remenatns would still be visible today. The crab nebula, as a result of SN 1054 has a neutron star in the middle...
You need to take into account that stars move around and that earlier civilisations might have seen different shapes in same star patterns, or they could have seen same shapes in different patterns.
Whatever the early civilisations saw, we can see now with ease. We have telescopes that allow us access to the universe that would leave the early skywatching civilizations in awe.
Link: [ame="http://en.wikipedia.org/wiki/Polaris"]Polaris - Wikipedia, the free encyclopedia[/ame]Recent research reported in Science suggests that Polaris is 2.5 times brighter today than when Ptolemy observed it, changing from third to its current second magnitude. Astronomer Edward Guinan considers this to be a remarkable rate of change and is on record as saying that "If they are real, these changes are 100 times larger than [those] predicted by current theories of stellar evolution."
Another explanation for the Bethlehem star is that it might be Jupiter and Saturn very close together - within less then a degree. That happens every 20 or so years. One such occurance is in October of "year -6" and another in December of year 14. Might also be Venus and Jupiter, but not sure if they'd appear in the "correct" part of the sky.
There are many references of dragons in various civilisations that never had any contact. Does that mean that dragons were real, even though we can't find them today?
Stars don't just go poof and vanish into pitch black. There's always stuff left behind, at least in a timeframe as short as we're talking about...
Material glows after the star dies because it's ionized, so you can clearly see it with a telescope...
In a Milky Way sized galaxy, a star goes supernova once every roughly 50 years. Only a few of those will be visible with the naked eye from Earth.
Stars live for a minimum of a few millions to a maximum of a few billion years before they die, so I hope you're not actually watching to see one evolve in front of your eyes.
Uh, no they can't. That would be against the laws of physics! The estimated age of the universe itself is about 14.6 billion years and given than billion is less than trillion, you're reply is very much off the mark, no where near close to be considered correct.Some red dwarfs can burn for trillions of years.
Uh, no they can't. That would be against the laws of physics! The estimated age of the universe itself is about 14.6 billion years and given than billion is less than trillion, you're reply is very much off the mark, no where near close to be considered correct.
The lower the mass of a red dwarf, the longer the lifespan. It is believed that the lifespan of these stars exceeds the expected 10 billion year lifespan of the sun by the third or fourth power of the ratio of their masses to the solar mass; thus a red dwarf with 0.1 solar mass may continue burning for 10 trillion years.
Are you suggesting that if a star collide with a black-hole that a supernova would then always be the result of such collision?
That does not appear to be what current mainstream theories believe according to the wiki-page: Supernova - Wikipedia, the free encyclopedia
SN 1054 is called a core-collapse supernova, on the wiki-page, and there are no suggestions of any collisions being the cause for the core-collapse.
So apparently this star followed the current established mainstream rules for star-behavior, so to speak, and thus didn't do anything un-natural.
But for exactly the reason you point out, earlier limitations in observing capabilities relative to present-days, we are limited to using only the stars we can be relatively sure are identified the same by them and us. We can't use our own recent discoveries in a historic context, since they are exactly that; recent discoveries. But Polaris is a long-known star, 2000 years of history, and well-known, and thus is the type of star we can be pretty sure is identified the same by both them and us (It was easy enough to observe distinctively even back then)
Incidentally, I just read this about Polaris:
Link: Polaris - Wikipedia, the free encyclopedia
Not exactly what I was looking for, since it's not missing, but since it may be an anomaly it's in the same ball-park. Another possible opportunity to learn something further, maybe
I've got to thank you for that actually, RisingFury, since talking with you is what made me find this piece of fascinating info
Here you pinpoint the problem yourself, by saying 'might'. It doesn't matter how good our present-day technology is if we don't know what to look for. We don't have a clear enough account of exactly what the Bethlehem star was, no one at that time gave any, and therefore we don't know exactly what to point our super-technology at. I've even read suggestions that it might have been a comet.
Warped said:Some red dwarfs can burn for trillions of years.
The lower the mass of a red dwarf, the longer the lifespan. It is believed that the lifespan of these stars exceeds the expected 10 billion year lifespan of the sun by the third or fourth power of the ratio of their masses to the solar mass; thus a red dwarf with 0.1 solar mass may continue burning for 10 trillion years.
From Wikipedia- Red Dwarf: Description and characteristics:
Not sure if that's old or incorrect data though.
Alternately (and more likely), that's how you can manage to lead a scientific career without anyone ever knowing your name.IThere *are* people activelly looking for annomalies with the goal of toppling currently established laws of Physics, but their research is on the cutting edge. That's how you get rich and famous in science...
Hey, it's on Wikipedia, so you know it must be right!I asked my professor about that and he said he was sceptical. He said optimistically he'd put them at 100 billion years.
Yea, but what else should we do in this case? We're looking for possible events. A bright object that appears in the sky for a while and then disappears? What options do we have? A combination of two planets close together, a comet, a sudden brightening of a star, possibly a failed nova, or a nova itself. For one, we can't really be sure that it happened, we can't really be sure that the description is correct (given the source text has been translated and modified so many times over time) and even if it was true, there might be a more reasonable explanation, then our stellar models not being correct...
As for the dragon analogy...
What I meant is that you're looking through historical sources to try to find events, but just because they're referenced, that doesn't mean that they occured... just like dragon that don't exist
I very much doubt you'll find any annomalies by looking through historical texts... the reason is that even if you find something weird that turns out to be correct, you don't have enough data to actually figure out what might have been different about the star. You might know that before it disappeared it glowed red and twinkled a lot and then disappeared suddenly without brightening... but given that that's as much as you can get, the description is still subject to interpretation.
A much better chance of finding something wrong with our stellar models would be to actually survey the sky - you have hundreds of billions of star in just this galaxy, at various stages of their development. If you're gonna find an annomally, you're gonna find it there.
Uh, no they can't. That would be against the laws of physics! The estimated age of the universe itself is about 14.6 billion years and given than billion is less than trillion, you're reply is very much off the mark, no where near close to be considered correct.
However, if the North star could not be seen today we would be pretty certain it was once there simply because many references of it are very clear and hard to mistake for other stars.
Polaris has not been the north star for all of recorded history.
All the known star-signs are still there (that covers at-least a few thousand years of human history), all the stars used for navigation throughout relatively modern times are still there (that's at-least 500 years of human history)