<p>Stellar evolution is not a fast process. And the Galaxy is HUGE and we see a tiny fraction of it.</p>
<p>Even once the protostar is formed, the evolution from the protostar to the main sequence star takes hundret of thousand of years and until it reaches the main sequence. As the star moves during its evolution over millenia along the <a href="https://en.wikipedia.org/wiki/Hayashi_track" rel="noreferrer">Hayashi track</a>, it changes luminosity gradually. Along this path there is not one single point where you can say &quot;now it is main sequence&quot;. In terms of stellar evolution in the pre-main sequence a &quot;moment&quot; lasts thus several hundret to thousands of years - such stars are known.</p>
<p>Even if it was not such gradual and very slow process (like asking for &quot;when did the tree grow between last year and now?), it would need constant observation. The Milkyway is huge, and even with Gaia's observations we only know one percent, thus a tiny fraction of its assumed 100 billion stars. So if there is 3 per year new and even if it were a descrete moment in time... we would need to look at that time in that direction with a sufficiently powerful telescope and the right instrumentation to actually detect these changes: we'd need to measure the brightness, and for correct classification also obtain spectra, thus our set of data of <em>reasonably continuously observed objects</em> is even much much smaller than the Gaia dataset.</p>
<p>Given this very slow evolution, and the extremely limited data set in terms of the overall ensemble, and the very low star birth rate of 300 / century, it's unlikely we know a single star which we observed often and detailed enough so that we can say &quot;this was pre-main sequence back then and is main sequence now&quot;. It's similar difficult and unlikely as looking at a group of high-school students at the beginning of the year and end of the year and tell which of those became an adult in course of the year.</p>

CC BY-SA 4.0
2022-07-08T08:41:42.543Z
Thank you for the detailed answer. However, in the OP, I didn't even mention main sequence. The scenario is that during the million years or so when a star is forming, it remains undetectable by our instruments, and then suddenly someone trains the telescope on one particular spot, detects a very faint something, and goes, "Hey, that one wasn't there before. What gives?"
Ricky
CC BY-SA 4.0
2022-07-08T08:43:53.143Z
Which is to say that, so far as the scientific method goes, there is no ACTUAL, empirical, palpable EVIDENCE that star formation is still very much a thing, only conjecture.
Ricky
CC BY-SA 4.0
2022-07-08T10:16:41.357Z
@Ricky But star formation doesn't work like that! Stars don't suddenly start shining. Young protostars emit a *lot* of heat and light. It's hard to see the details of what's going on inside a big cloud of hot gas & dust, but infrared telescopes can get a bit more detail than optical scopes. As I said in the comments on your previous question, we know about numerous stellar nurseries in the Milky Way. And in those nurseries we can detect protostars at various stages of formation.
PM 2Ring
CC BY-SA 4.0
2022-07-08T11:11:18.777Z
In order to underline what @PM2Ring says: there is no switch, identically as there is no switch when you are suddenly a grown up compared to being an adolescent. It transitions slowly from one to the other.
planetmaker
CC BY-SA 4.0
2022-07-08T14:53:31.230Z
Indeed, protostars get less luminous as they develop.
ProfRob
CC BY-SA 4.0
2023-01-18T00:01:27.143Z
Funny, actually the proto-star should disappear or at least fade away to  indicate that it reached adulthood. That's somewhat counter-intuitive and a huge anti-climax :)
Maarten Bodewes
CC BY-SA 4.0
2022-07-08T07:26:45.677Z
2022-07-08T07:26:45.677Z
planetmaker
<h2>We Can See Protoplanetary Disks</h2>
<p>Numerous star forming regions have 'Proplyds' visible in them.  These are the protoplanetary disks from which the star and its planets form.  Here is an image of some Proplyds inside the Orion Nebula:</p>
<p><a href="https://i.sstatic.net/TQJWq.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/TQJWq.jpg" alt="Protoplanetary Disk in the Orion Nebula" /></a></p>
<p>Here is an image of a very young star system showing a planet in the process of being formed out of the protoplanetary disk:</p>
<p><a href="https://i.sstatic.net/jcWF2.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/jcWF2.jpg" alt="SPHERE image of PDS70 planetary formation. Image credit: ESO/A. Müller et al. " /></a></p>
<p>The young star is blacked out by a coronagraph so the planets can be imaged.</p>
<p>Also, there appears to be a very young star that has formed out of the remnants of Supernova 1987A, making it the youngest star we've yet seen.</p>

CC BY-SA 4.0
2022-07-08T23:57:36.663Z
The images are computer-enhanced (i.e. photoshopped), aren't they?
Ricky
CC BY-SA 4.0
2022-07-09T00:36:09.987Z
They are certainly processed,  but not in a way that removes or creates any new data.   If they were taken using monochrome cameras with filters,  they would be combined to make a color image.  But this is real imagery you are seeing,   It's not like the black hole 'photograph' created out of radio data - these are real images, and the only processing would be color combination and stacking to remove noise.
Dan Hanson
CC BY-SA 4.0
2022-07-09T00:37:52.263Z
If you are suggesting that these are being faked by some conspiracy,  Proplyds have been imaged by many amateur astronomers.  Here's an example:  http://www.deepsky-visuell.de/Projekte/PPN.htm  A 12" to 36" amateur scope will resolve them in Orion,  And I can tell you that the processing done in those images is primarily just noise reduction from stacking multiole images together.  No fakery.
Dan Hanson
CC BY-SA 4.0
2022-07-09T10:09:24.400Z
@DanHanson I wanted to point out that the link in your last comment doesn't contain pictures of protoplanetary __disks__, but of protoplanetary __nebulae__, which is a misnomer that doesn't have anything to do with planets or young stars. Apart from that, great answer and beautiful pictures of protoplanetary __disks__!
Prallax
CC BY-SA 4.0
2022-07-08T22:30:40.080Z
2022-07-09T00:30:44.750Z
2022-07-09T00:30:44.750Z
Dan Hanson
<ol>
<li><p>Not too long ago, Pluto was &quot;demoted&quot; because it no longer met the criteria for being a full-fledged planet. Similarly, in order to be classified as a star (and not, say, a proto-star, or ... etc.), a cosmic body must meet a number of requirements.</p>
</li>
<li><p>Imagine that your field binoculars are way out of focus and all you can see is undifferentiated blur. You start adjusting them, turning the knob ever so slowly, until suddenly there comes a <em>moment</em> when you can see shapes. They're still blurry, but they're definitely shapes: trees, houses, the sky, etc. Only a second ago you couldn't tell which was which, but now you can.</p>
</li>
</ol>
<p>In <em>that</em> sense, has the birth of a new star ever been registered?</p>
<p>It is theorized that approximately three new stars are formed in the Milky Way each year. That is the official, approved, paradigm-friendly view.</p>
<p>Three new stars. Every year. That's 300 stars in the last hundred years.</p>
<p>No matter how slow the process of star formation may be, there must <em>always</em> come a moment when a budding star enters a registerable new phase.</p>
<p>The distance between this new star and the Sun and the appropriate time lapse are irrelevant, since three stars per year has been the standard rate for billions of years. It is therefore of no consequence whatsoever whether the star entered said phase in Aristotle's time or Moses' time or even before the Earth-as-a-planet became, cosmically speaking, a thing. Formation phase changes remain formation phase changes no matter how far in the past they occurred. They don't get depreciated with time.</p>
<p>A theory (as opposed to a hypothesis) requires a healthy evidence/conjecture ratio.</p>
<p>With all of the above in mind: has the birth of a new star ever been actually <em>directly</em> observed and registered? (I.e. does direct evidence in favor of the process actually exist?)</p>
<p>And if not, is it safe to say, that <em>for all we know</em>, star formation is no longer a thing in the Milky Way, and/or, for that matter, in the rest of the Universe?</p>
<p><a href="https://i.sstatic.net/QbX08.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/QbX08.jpg" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2022-07-09T17:46:14.863Z
Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/137647/discussion-on-question-by-ricky-has-the-birth-of-a-new-star-ever-been-observed).
Connor Garcia
CC BY-SA 4.0
2024-07-24T16:42:05.157Z
Here’s a 2024 story about Hubble watching this process: https://www.space.com/hubble-telescope-new-star-fs-tau-b#
danelaverty
CC BY-SA 4.0
2024-07-24T18:31:26.063Z
@danelaverty: Well: either the story is a lot of wishful thinking; or all the answers to the OP are wrong. Which is it?
Ricky
CC BY-SA 4.0
2024-07-26T06:27:24.113Z
Please explain why this isn't a functional duplicate of https://astronomy.stackexchange.com/questions/49746/how-many-new-stars-visible-to-the-naked-eye-have-appeared-since-humanity-started
ProfRob
CC BY-SA 4.0
2024-07-27T07:18:55.127Z
This question is similar to: [How many new stars visible to the naked eye have appeared since humanity started making records?](https://astronomy.stackexchange.com/questions/49746/how-many-new-stars-visible-to-the-naked-eye-have-appeared-since-humanity-started). If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.
ProfRob
<star-formation>
Has the birth of a new star ever been observed (scientifically speaking)?
Ricky
# Has the birth of a new star ever been observed (scientifically speaking)?

(Asked by: username_0 on 2022-07-07)

1. Not too long ago, Pluto was "demoted" because it no longer met the criteria for being a full-fledged planet. Similarly, in order to be classified as a star (and not, say, a proto-star, or ... etc.), a cosmic body must meet a number of requirements.
2. Imagine that your field binoculars are way out of focus and all you can see is undifferentiated blur. You start adjusting them, turning the knob ever so slowly, until suddenly there comes a *moment* when you can see shapes. They're still blurry, but they're definitely shapes: trees, houses, the sky, etc. Only a second ago you couldn't tell which was which, but now you can.

In *that* sense, has the birth of a new star ever been registered?

It is theorized that approximately three new stars are formed in the Milky Way each year. That is the official, approved, paradigm-friendly view.

Three new stars. Every year. That's 300 stars in the last hundred years.

No matter how slow the process of star formation may be, there must *always* come a moment when a budding star enters a registerable new phase.

The distance between this new star and the Sun and the appropriate time lapse are irrelevant, since three stars per year has been the standard rate for billions of years. It is therefore of no consequence whatsoever whether the star entered said phase in Aristotle's time or Moses' time or even before the Earth-as-a-planet became, cosmically speaking, a thing. Formation phase changes remain formation phase changes no matter how far in the past they occurred. They don't get depreciated with time.

A theory (as opposed to a hypothesis) requires a healthy evidence/conjecture ratio.

With all of the above in mind: has the birth of a new star ever been actually *directly* observed and registered? (I.e. does direct evidence in favor of the process actually exist?)

And if not, is it safe to say, that *for all we know*, star formation is no longer a thing in the Milky Way, and/or, for that matter, in the rest of the Universe?

[![enter image description here](https://i.sstatic.net/QbX08.jpg)](https://i.sstatic.net/QbX08.jpg)

**Tags:** star-formation

> **Comments:**
> **username_1**: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/137647/discussion-on-question-by-username_0-has-the-birth-of-a-new-star-ever-been-observed).  
> **username_2**: Here’s a 2024 story about Hubble watching this process: https://www.space.com/hubble-telescope-new-star-fs-tau-b#  
> **username_0**: @username_2: Well: either the story is a lot of wishful thinking; or all the answers to the OP are wrong. Which is it?  
> **username_3**: Please explain why this isn't a functional duplicate of https://astronomy.stackexchange.com/questions/49746/how-many-new-stars-visible-to-the-naked-eye-have-appeared-since-humanity-started  
> **username_3**: This question is similar to: [How many new stars visible to the naked eye have appeared since humanity started making records?](https://astronomy.stackexchange.com/questions/49746/how-many-new-stars-visible-to-the-naked-eye-have-appeared-since-humanity-started). If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.  

---

## 2 answers

### Answer by username_4 on 2022-07-08. Score: 8

Stellar evolution is not a fast process. And the Galaxy is HUGE and we see a tiny fraction of it.

Even once the protostar is formed, the evolution from the protostar to the main sequence star takes hundret of thousand of years and until it reaches the main sequence. As the star moves during its evolution over millenia along the [Hayashi track](https://en.wikipedia.org/wiki/Hayashi_track), it changes luminosity gradually. Along this path there is not one single point where you can say "now it is main sequence". In terms of stellar evolution in the pre-main sequence a "moment" lasts thus several hundret to thousands of years - such stars are known.

Even if it was not such gradual and very slow process (like asking for "when did the tree grow between last year and now?), it would need constant observation. The Milkyway is huge, and even with Gaia's observations we only know one percent, thus a tiny fraction of its assumed 100 billion stars. So if there is 3 per year new and even if it were a descrete moment in time... we would need to look at that time in that direction with a sufficiently powerful telescope and the right instrumentation to actually detect these changes: we'd need to measure the brightness, and for correct classification also obtain spectra, thus our set of data of *reasonably continuously observed objects* is even much much smaller than the Gaia dataset.

Given this very slow evolution, and the extremely limited data set in terms of the overall ensemble, and the very low star birth rate of 300 / century, it's unlikely we know a single star which we observed often and detailed enough so that we can say "this was pre-main sequence back then and is main sequence now". It's similar difficult and unlikely as looking at a group of high-school students at the beginning of the year and end of the year and tell which of those became an adult in course of the year.

> **Comments:**
> **username_0**: Thank you for the detailed answer. However, in the OP, I didn't even mention main sequence. The scenario is that during the million years or so when a star is forming, it remains undetectable by our instruments, and then suddenly someone trains the telescope on one particular spot, detects a very faint something, and goes, "Hey, that one wasn't there before. What gives?"  
> **username_0**: Which is to say that, so far as the scientific method goes, there is no ACTUAL, empirical, palpable EVIDENCE that star formation is still very much a thing, only conjecture.  
> **username_5**: @username_0 But star formation doesn't work like that! Stars don't suddenly start shining. Young protostars emit a *lot* of heat and light. It's hard to see the details of what's going on inside a big cloud of hot gas & dust, but infrared telescopes can get a bit more detail than optical scopes. As I said in the comments on your previous question, we know about numerous stellar nurseries in the Milky Way. And in those nurseries we can detect protostars at various stages of formation.  
> **username_4**: In order to underline what @username_5 says: there is no switch, identically as there is no switch when you are suddenly a grown up compared to being an adolescent. It transitions slowly from one to the other.  
> **username_3**: Indeed, protostars get less luminous as they develop.  
> **username_6**: Funny, actually the proto-star should disappear or at least fade away to  indicate that it reached adulthood. That's somewhat counter-intuitive and a huge anti-climax :)  

---

### Answer by username_7 on 2022-07-08. Score: 4

## We Can See Protoplanetary Disks

Numerous star forming regions have 'Proplyds' visible in them. These are the protoplanetary disks from which the star and its planets form. Here is an image of some Proplyds inside the Orion Nebula:

[![Protoplanetary Disk in the Orion Nebula](https://i.sstatic.net/TQJWq.jpg)](https://i.sstatic.net/TQJWq.jpg)

Here is an image of a very young star system showing a planet in the process of being formed out of the protoplanetary disk:

[![SPHERE image of PDS70 planetary formation. Image credit: ESO/A. Müller et al. ](https://i.sstatic.net/jcWF2.jpg)](https://i.sstatic.net/jcWF2.jpg)

The young star is blacked out by a coronagraph so the planets can be imaged.

Also, there appears to be a very young star that has formed out of the remnants of Supernova 1987A, making it the youngest star we've yet seen.

> **Comments:**
> **username_0**: The images are computer-enhanced (i.e. photoshopped), aren't they?  
> **username_7**: They are certainly processed,  but not in a way that removes or creates any new data.   If they were taken using monochrome cameras with filters,  they would be combined to make a color image.  But this is real imagery you are seeing,   It's not like the black hole 'photograph' created out of radio data - these are real images, and the only processing would be color combination and stacking to remove noise.  
> **username_7**: If you are suggesting that these are being faked by some conspiracy,  Proplyds have been imaged by many amateur astronomers.  Here's an example:  http://www.deepsky-visuell.de/Projekte/PPN.htm  A 12" to 36" amateur scope will resolve them in Orion,  And I can tell you that the processing done in those images is primarily just noise reduction from stacking multiole images together.  No fakery.  
> **username_8**: @username_7 I wanted to point out that the link in your last comment doesn't contain pictures of protoplanetary __disks__, but of protoplanetary __nebulae__, which is a misnomer that doesn't have anything to do with planets or young stars. Apart from that, great answer and beautiful pictures of protoplanetary __disks__!  

---

