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I've heard from a lot of people that stars are "born" (usually from black holes), then grow bigger, then eventually "die" by some kind of supernova etc., but have any of these events actually been observed, from the beginning to the middle, or from the middle to the end? If not, what proof do we have that stars are born, grow, and die, and not simply they all of the stars have always existed in the same size and state they are now?

And I don't want any answers like "that's ridiculous, everything has to be born", because not necessarily.

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    $\begingroup$ lco.global/spacebook/stars $\endgroup$ – astrosnapper May 10 at 22:22
  • $\begingroup$ @astrosnapper that particular link doesnt have any information, can you just cite the relevant parts that provide the proof and data? $\endgroup$ – bluejayke May 10 at 22:28
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    $\begingroup$ The problem here is the timescale. We have seen very short glimpses of the stellar lifecycle, as cited for supernovae, but in general we don't have a chance of ever seeing the full cycle, as that takes billions of years. Millions in the rapid cases. Therefore astronomy has to content with 'snapshots' in general. So if you would rephrase your question in a way that asks 'how do we know various objects are snapshots of the same evolutionary sequence?' then probably you would get more favourable answers. I agree with the answer below, that the supernova is easily googlable. $\endgroup$ – AtmosphericPrisonEscape May 11 at 0:13
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    $\begingroup$ BTW, with some types of stars, we can easily see that they are changing, eg there are stars whose light output varies over short time scales. And we can see that Wolf-Rayet stars are ejecting large amounts of matter at high speed. We can measure the speed of that matter using Doppler techniques, the same science that police use to measure the speed of cars. $\endgroup$ – PM 2Ring May 11 at 1:16
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    $\begingroup$ +1 for asking a question that elicited three interesting answers. I think if you had worded it differently there wouldn't be so many down votes. Asking science to provide you "proof" of something makes your question sound like it might be written by a science denier, in which case this is the wrong place on the internet to ask. A better way to ask might have been "how do we know" or "evidence for" or "has X been seen.." along with a bit of research on stellar lifetimes. $\endgroup$ – uhoh May 12 at 23:36
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There are of the order of tens of millions of stars we can observe with telescopes.

We can see, in all these observations, the various stages of development of similar classes of stars (which we can classify using stellar spectra - a highly developed science). So we have observed all the stages of development in different, but similar stars.

Think of it like photographing a crowd in the park. You probably won't see a lot of events, but you'll see pregnant women, babies, young children, young adults, adults of all ages to old age. If you're lucky you'll catch a birth starting and if someone else is very unlucky you might catch a death. Astronomers observe every night and have done for centuries, so we've a lot of snap-shots to work from.

Combining these observations with extremely complex physics-based models of how stars are structured and formed, astronomers and astrophysicists have developed models which they can use with a high degree of confidence.

These models go into far, far, far more detail than simply the birth, middle and death of stars. That "stars" are born and "die" and the broad mechanisms of the stellar life cycle (which you'll find described in any level of detail you wish in online sources), is not even remotely disputable scientifically at this point.

There is no single piece of evidence for such a broad model. It is an accummulation of evidence and theory combined, refined and rechecked as well as ongoing improvements in theory and technique of measurement.

There is no way a single human could live to see the birth, life and death of a single star. If that's the only kind of evidence you will accept, as your question hints, then you will not find evidence meeting your needs.

and not simply they all of the stars have always existed in the same size and state they are now?

Again, this requires the understanding and connecting of a lot of clues and an acceptance of a key principle of science: the same physical laws apply everywhere. Based on that key principle you can treat observations sensibly.

Why accept that principle? Because it works. Results of theory based on it match observations. Science rethinks all assumptions when results don't match reality.

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  • $\begingroup$ the difference betwee photographing a large crowd and that of stars, is that we have previosly observed many people being born and aging etc., even we ourselves were once young (and born), but we have never observed the complete cycles of any one star, so while they all may appear to be at different stages, what evidecne is there that they in fact are? $\endgroup$ – bluejayke May 13 at 15:55
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    $\begingroup$ No. This is exactly wrong. You have never observed people ageing. You only observe the present you do not observe the past. There is absolutely no evidence by the ridiculous standard that you are applying, that people are born, age and die, it has never been observed, only deduced from the evidence and application of occam's razor. Damn....someone is wrong on the internet.... $\endgroup$ – James K May 15 at 20:47
  • $\begingroup$ @JamesK there is evidence people are born, because many people can actually see, with their own eyes, a literaly baby being literally born, then those parents can literally observe that child for years to literally observe taht same being, taht they themselves witnessed being born, growing up etc., how is that not evidence? None of the same statements can be said of stars (unless some data can be brought to show the contrary?) $\endgroup$ – bluejayke May 15 at 23:20
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These questions turn on an even more fundamental one. "Are stars governed by the same laws of physics that we observe in the laboratory on Earth?" If the answer is "yes" then, for example, stars can't shine forever because their energy source will run out; large clouds of warm gas cannot just remain because they will collapse under their own gravity; and the very detailed information we get from observing the spectra of stars does tell us about what elements are present, how hot they are, etc.

If the answer is "no" then we basically can't know anything except that we receive the light (and radio and X-rays and gamma rays and neutrinos and gravity waves) that we detect. They could all be an elaborate practical joke being played on us by super-powerful aliens.

Ultimately, we can never prove that the stars obey the same laws, but we become more confident of it over time, as we apply those laws to correctly predict what we will see in the future or when we look with new instruments or in new places. This is hard, because working out what the predictions of those physical laws actually is involves some really hard maths, but a lot of people have worked on it for millenia, and so far it has pretty much panned out.

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – called2voyage May 18 at 14:50
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We've certainly seen supernovae, and in at least one case we've seen the star before the supernova (and its not there afterwards)

Stars are not born from black holes [I wonder where you got that idea from. A little better prior research would help you ask better questions] Black holes are formed at the end of the life of some stars (those much larger than the sun)

Stars are born from clouds of gas (which we see) which collapse under gravity, forming a warm knot of gas with a disc of dust etc orbiting it (which we see), then we see stars that are still surrounded by the gas from which they were born. In a few cases we have seen these young object maturing from one state to the next.

So either a god is deliberately and maliciously attempting to deceive us by creating objects that appear to be young stars and stars in the process of being born. Or these really are different stages in the early life of stars, and stars are born and die.

I've never seen a human being born, nor have I seen a human die. I've never actually seen a person getting older (sure my kids used to be babies and now they are teens, but how do I know that they are the same people? Perhaps new people are swapped with the old ones every night). Yet I have no problem believing that birth and death occur, based on my observations (of people of different ages). It is possible that the same malicious god could be deceiving me. But I prefer not to believe in god like that.

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  • $\begingroup$ very interesting theory, can you provide some data for the cases where we have seen the a star, then a supernova, then no star in the same place, and the same for the star forming? $\endgroup$ – bluejayke May 10 at 22:31
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    $\begingroup$ No, you go do the investigation. $\endgroup$ – James K May 10 at 22:53
  • $\begingroup$ But what investigation is there to do? So far I have found nothing, so would that disprove it ? (unless some proof can be shown) $\endgroup$ – bluejayke May 10 at 22:56
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    $\begingroup$ @bluejayke How the site works was explained to you in a previous Q&A and you must respect that if you wish to use the site. You are expected to "run with the ball" yourself, we simply have facility to provide in-depth discussion or debate of fine detail to the extent you seem determined to follow. $\endgroup$ – StephenG May 10 at 23:40
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    $\begingroup$ @bluejayke Yes they do, literally: "There can be little doubt that the Sanduleak star has disappeared" $\endgroup$ – mmeent May 14 at 10:24
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There is of course a vast, vast literature that tests stellar evolutionary theory against observations of stars (and protostars).

Starting with the basics. Stars shine; they emit energy. Energy is conserved and must come from somewhere in the star. In the case of the Sun we nothing going in, but $3.83\times 10^{26}$ Watts coming out. Now you could just (unscientifically) argue that that's just the way it is and that conservation of energy doesn't apply everywhere (I doubt a power company would accept that as an argument for not paying your bill), but most, curious people would want to know where the energy comes from.

So it could be that stars are contracting - getting smaller and turning gravitational potential energy. Turns out to be correct for protostars but wrong for stars like the Sun. Either way, such a mechanism would imply that stars change on timescales of millions of years.

So maybe it's chemical reactions, some sort of combustion? OK, we know now that is wrong, but even if it were right, would imply that the Sun will be burned up in another million years or so.

It turns out that it is nuclear fusion reactions at the core that power stars. How do we know that is true? Because we observe neutrinos coming from the Sun at exactly the rate predicted if the nuclear reactions produce the luminous energy the Sun outputs. But nuclear reactions are not self-sustaining; they cannot go on forever. They started when the core got hot enough to initiate nuclear fusion, and will stop when all the hydrogen in the core has been turned into heavier elements. i.e. There must be a beginning and an end to the process.

All this takes billions of years, so how do you think that it can be possible to see things changing on timescales observable in human lifetimes or on the timescales even of recorded history?

Fortunately stars are not all born at once and have a wide range of lifetimes. We can therefore test models of how stars work, not just by looking at the Sun, but by looking at billions of other stars in our own Galaxy (and others) and comparing their physical properties (luminosities, temperature, rotation, chemical abundances) with the predictions of our models.

But what about direct evidence that things are changing?

Well, there are variable stars of many, many sorts. Some of that variability you might argue is "sustainable" (e.g. pulsations, although we all know that perpetual motion machines do not exist); other variability is associated with the birth of stars (e.g. the flare-ups of FU Ori stars associated with accretion of mass from their birth environment). There is plenty of evidence of destructive variability - we see mass loss occurring from red giants at rates such that they would totally evaporate within 100,000 years; we see examples of stars exploding at the ends of their lives, sometimes leaving behind a remnant (e.g. the Crab supernova in 1054 AD), and in some cases, the progenitor of the supernova has been identified and then disappeared afterwards with no remnant observed (e.g. SN1993J, SN2003gd, Maund & Smartt 2009). In other cases, stars have been observed to disappear entirely (so called "failed supernovae" like N6946-BH1), interpreted as direct collapse to a black hole.

Apart from these violent events, some phases of a star's life do take place rapidly enough that they can be observed on human timescales. Examples include the luminous blue variable P-Cygni, nearing the end of its life, first observed and recorded in 1600 and which has been growing brighter since 1700 (Israelian & de Groot 1999; or Sakurai's object, which is undergoing rapid changes in the brief evolutionary phase between the tip of the asymptotic red giant branch and becoming a cooling white dwarf.

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An analogy

You can not sit in a forest, and watch as the trees grow, mature and die. You have no time for that, because the trees live typically longer than you.

However, if you are a forester, then you have seen enough trees enough long, and you know enought about them. You have enough knowledge from the trees to know, how do they live. Even if you did not see the birth, maturation and death of a single tree with your own eyes.

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  • $\begingroup$ Yes that makes sense by trees, because people have actually seen other trees advance, be planted, and fall down, but if no one has ever witnessed a star atually being formed, or actualy witnessed it advancing, how can we assume that it does? $\endgroup$ – bluejayke May 15 at 22:48
  • $\begingroup$ @bluejayke Yes, all of them were seen, with good telescopes. Their forming (google keywords: protoplanetary discs), their life (google keywords: sky surveys), and their death (keywords: nova supernova white dwarf stellar remnants). $\endgroup$ – peterh - Reinstate Monica May 15 at 23:18
  • $\begingroup$ also, analogies re not sources $\endgroup$ – bluejayke May 15 at 23:21
  • $\begingroup$ What evidence is ther ethat " protoplanetary discs" is the beginnings of a star? By trees people can observe a seed being planted, and at least see the first few years of a tree forming. Can the same be said by " protoplanetary discs", has anyone seen them "develop" into an actual star? $\endgroup$ – bluejayke May 15 at 23:22
  • $\begingroup$ What are you even talking about at all? I'm trying to have a scientific discussion, and you're bellowing off into personal insults and assumptions without even attempting to answer the question?? What's going on here? $\endgroup$ – bluejayke May 15 at 23:29
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Stars are not biological organisms, so they aren't born and don't die. Saying that stars are born and die is a metaphor and so is not correct.

vast clouds of gas and dust in interstellar space can slowly become denser and eventually collapse into stars, vast spheres of plasma that become so hot and dense at their cores that atoms fuse and emit radiation. That is how stars are "born" metaphorically.

The metaphorical "death" of stars may be swifter. When light from a nova or supernova reaches Earth and astronomers note the sudden increase in brightness, they begin recording the luminosity and spectrum of the star. They record how the luminosity increases or decreases over time until it fades to the luminosity of a white dwarf.

There is a branch of astronomy called astrophysics, meaning the physics of stars. Thousands of astrophysicists spend most of their working hours studying the physics of stars and related astronomical subjects. Since stars shine by thermonuclear fusion, astrophysicists have to know nuclear physics.

Over a century ago, scientists didn't know how stars got the energy to shine. The best theory they had was that gravitational contraction from the formation of stars provided the energy. According to calculations, the Sun could only shine for a few tens of millions of years through this process. Geologists insisted that the Earth had existed for hundreds of millions of years or even billions of years, and that the Sun must have shined steadily for all that time, and astronomers and physicists said they must be wrong, that there was no possible way for a star to shine that long. At one scientific meeting an astronomer and a geologist argued so hard about this that the astronomer punched the geologist.

Then in the early 20th century, the atomic theory of matter was developed. Atomic physicists eventually calculated that it was possible for atoms of lighter elements to fuse together to produced heavier elements, and astrophysicists began to calculate how fusion could occur in the unimaginable heat and density calculated to exist in stellar cores.

By 1941, theoretical knowledge of fusion had progressed so much that during the US Manhattan Project, Enrico Fermi suggested the concept of thermonuclear device to Edward Teller. The Manhattan Project eventually began a sub project to develop such a thermonuclear bomb, lead by Teller. The first thermonuclear bomb was detonated in the Ivory Mike test on November 1, 1952.

Today there are thousands of thermonuclear bombs in the arsenals of the USA, Russia, the UK, France, China, India, and possibly also Pakistan, Israel, and North Korea.

For decades there have been projects to develop thermonuclear power generation. Thus the scientific data from the many tests in such projects is available to help astrophysicists refine their theoretically understanding of thermonuclear physics.

So calculations of what is happening in a star at the moment and how it will change in the future become more and more detailed and precise with time. And as computers become more and more advanced more and more detailed computer simulations of the "life cycle" of stars are made, and the metaphorical "birth" and "death" of stars becomes more and more certain.

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  • $\begingroup$ So it wouuld seem that all of the knowledge scientists have about stars' energy, and how long they last, are all theories (which may be partially backed by bombs etc.), but is there any evidence that it works that way, or is it ambiguous? Also at the beginning paragraph, is there any evidence that stars actually resulted from the gas etc., or only theory that its possible it might have? $\endgroup$ – bluejayke May 13 at 20:14
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    $\begingroup$ @bluejayke. What kinds of evidence would you accept? There are lots of cases of predictions based on those theories which have come true. Are those evidence? $\endgroup$ – Steve Linton May 14 at 15:07
  • $\begingroup$ @SteveLinton A set of data published from an official government website, showing in its entirety what steps were taken to measure the size, and an explanation of how all of the assumptions made in that data sheet are correct $\endgroup$ – bluejayke May 15 at 23:01
  • $\begingroup$ @bluejayke I don't know about an official government website, but otherwise all of that data exists. However there is a lot of it -- many milions of pages. Just read the scientific literature starting at the beginning. Of course it may take you a while.... $\endgroup$ – Steve Linton May 16 at 3:43

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