How MASSIVE can a STAR get?
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- čas přidán 20. 05. 2024
- Go to brilliant.org/drbecky to get a 30-day free trial and the first 200 people will get 20% off their annual subscription! We know there's a limit to how small a star can be, but is there a limit to how BIG stars can get? Is there some aspect of Physics that limits how big they can grow, or do big stars just get rarer and rarer so we're less likely to see them? The biggest star we've ever found is R136a1 at around 200 times heavier than the Sun, and that is very challenging for our models of star formation to explain...
My previous video on the lower limit to the mass of stars - • Planemos | When is a s...
Salpeter (1955; first analysis of the IMF) - articles.adsabs.harvard.edu/p...
Hopkins (2018; review on the IMF) - arxiv.org/abs/1807.09949
Larson & Starrfield (1971; the limit from models of star formation) - articles.adsabs.harvard.edu/p...
Nakano (1989; increasing the limit with models of star formation) - articles.adsabs.harvard.edu/p...
Jijina & Adams (1996; increasing the limit with models of star formation) - articles.adsabs.harvard.edu/p...
Feast, Thackery & Wesselink (1960; catalogue of stars in the Magellanic Clouds) - academic.oup.com/mnras/articl...
Ebbets & Conti (1982; R136a1 is 2000 times the mass of the Sun?) -
Bestenlehner et al. (2020; mass estimate of R136a1) - arxiv.org/pdf/2009.05136.pdf
Kalari et al. (2002; new estimate of mass of R136a1) - arxiv.org/pdf/2207.13078.pdf
Weidner & Kroupa (2003; limit from star clusters) - arxiv.org/pdf/astro-ph/031086...
JWST proposal 1802 - www.stsci.edu/jwst/phase2-pub...
00:00 - Introduction
00:50 - The Initial Mass Function of stars with a lower and upper limit?
03:00 - Simulating stars forming - is there a physical process limiting the mass?
05:19 - Finding the most massive star known R136a1
07:35 - If we don't find more massive stars, does that mean there's really a limit?
07:57 - How can JWST help solve this problem?
09:06 - Brilliant
10:15 - Bloopers
Video filmed on a Sony ⍺7 IV
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👩🏽💻 I'm Dr. Becky Smethurst, an astrophysicist at the University of Oxford (Christ Church). I love making videos about science with an unnatural level of enthusiasm. I like to focus on how we know things, not just what we know. And especially, the things we still don't know. If you've ever wondered about something in space and couldn't find an answer online - you can ask me! My day job is to do research into how supermassive black holes can affect the galaxies that they live in. In particular, I look at whether the energy output from the disk of material orbiting around a growing supermassive black hole can stop a galaxy from forming stars.
drbecky.uk.com
rebeccasmethurst.co.uk - Věda a technologie
I like that you put faces to all the names in these papers; it helps to make it all seem more real and not just a weird footnote or random news story.
I was thinking the same
Totally! It helps make it clear that science comes from people, and these names are not just more data points.
Agree
I was actually thinking it was a new trend in academic papers until the insert about 7:30 where there is a big curvy arrow pointing from the picture to the name. :-)
I like this details as well. My PhD advisor always told me that science is done by people, which is why I made sure that I put a face next to every person I named who helped me getting my PhD.
Dr. Becky is truly one of the shining "brightnessessess" in the world of astrophysics. 😉
Would the word "luminosities" come in handy? Many thanks for your terrific videos Dr. Becky!
or add a word to it: "brightness levels"
It's been determined that scientists who communicate their fields to laypersons not only tend to be excellent communicators, but also more knowledgeable of their fields than those scientists who follow the tradition of strictly writing technical papers and attending conferences.
She's so smart, so funny and more importantly, didactic. And her eyes and accent are so cute!
For someone who specializes in black holes. She is definitely a beacon of light in education. Cheers
Minor correction around 7m40s, when you annotated the dN/dlog(M) graph curving off to the right. Instead, that should have just continued the straight line, then had it curve straight downwards, since that graph already uses log-scaling on both axes. A horizontal curve off to the right would mean *more* supermassive stars, not fewer, since this is a probability density graph, not cumulative distribution graph.
Yeah that bothered me as well.
@@the_mad_bunnyx9537 Like a scene from The Big Bang Theory.
"Let's start back in 1955"
Great Scott!! This star is heavy.
I decided to try to emulate the old PC game Master of Orion in C#. I had to generate a field of stars that made the base of the game. Off I fell into a rabbit hole of adding random sized stars of different masses and ages, I added a list of random elements with percentages, hydrogen, helium, carbon, etc simulating a stars age. Eventually I failed at finishing writing the game but I did get the random star field working.
So did Bethesda
I just asked my husband this the other week! Dr. Becky, thank you for being such an awesome human who shares the love of astronomy with the world. I could almost pass for smart these days thanks to you! 😂
Yep, this channel is definitely one of my favourites. I first watched it because of Dr. Becky's looks (I'm only human) but stuck around and came back again and again because of the way the subject was presented and how I was able to understand it and to understand more and more each episode. That's a great teacher.
It seems to me that once you see the rings of Saturn through a telescope you can't go back. You're hooked. So be careful.😂
@@user-cl4lg8hs4s She inspired me to purchase a 10" Dobsonian 250P Skywatcher this year. Watching Saturn dance across my viewfinder was the best drug experience of my life. I am now permanently hooked to a very expensive hobby! lol
I hope you become a brighter person than you already are.
@@FortescueGimlet Your comment says far more about your character than anything you could say against me. Your account has been muted, bless your little heart.
I asked for "A Brief History of Black Holes" for Christmas! Can't wait to read it! Love your work Dr. Becky!
You will love it
Best read of 2023!
Ooo that sounds great!
Get the JWST hoodie too
Really cosy
@@JaSon-wc4pn Hey now that's a great idea! Thanks!
My question...and more importantly....is there a limit to how awesome Dr Beck can be? I think not
Physics breaks when trying to find her limit. She is infinite.
Someone should plot a graph from ALL of her videos containing data from: 1. Her enthusiasm. 2. If the data has been repeated in an earlier video. 3. The number of bloopers done. Night sky information vs. technical data*.
*The technical data would somehow be a ration of how complicated the data is to how simplified the doctor was able to make it. This would have to be based on a sample audience.
OK, this couldn't be that hard for one or two of the audience to accomplish. 😊
I love your teaching ability. But you killed me in your bloopers when you said “ space is hard, words are harder” lmao. Cheers
I sometimes forget to click like on these videos but when Dr. Becky sings at the end, I ALWAYS remember.
Google says "Betelgeuse is about 7,500 to 14,000 times brighter than the Sun. It's about 700 times the size of the Sun and around 15 times more massive." It's interesting that at such a brightness and size, its mass is relatively low.
Betelgeuse is near end of life, having consumed most of the available fusion fuel especially the lighter elements like hydrogen and Helium that fuse at lower temperatures. Its core, fusing heavier elements, is extremely hot and energetic, which causes all the outer layers to greatly expand, as they convect that heat flux out. Also the gravitational pull is less, that far from the core... so it is so a very thin gas compared to air pressure on Earth... we'd say most of the envelope of a red supergiant is a hot hard vaccuum.
Luminosity (brightness or power output) increases in relation to mass by about a power of 3.5 in large mass stars. So 15^3.5 is about 13000 times the power output of the Sun, so about right. Stars of this mass have a core so hot and dense (crushed by gravity) that the fusion reaction rates are way higher than in our Sun, especially in stars close to the end of their lives like the supergiant Betelgeuse. This heat also puffs up the size of the star and makes the surface of the star cooler and therefore redder. The increased fusion reaction rate also decreases their lifetime by a factor of at least their mass squared (they also lose mass through winds over their lifetime so their initial mass is slightly higher) so that a star like Betelgeuse will have a lifetime of tens of millions of years or less.
@@JamesPerkinsInteresting. Didn't Dr. Becky recently review a projection that Betelgeuse will supernova in the next 100 years or less? When it does will it likely kick a lot of heavier elements out into the void from it's core and convection currents?
@fedfraud.protection.servic2557 I don't recall exactly what she said, though on the scale of the lifetime of stars, I am sure most astrophysicists would say Betelgeuse has very little time left in it's current state.
Dr. Becky, I truly appreciate that you explain and sometimes highlight portions of the charts and graphs. Thank you!
In 1966 Edwin SalPeter taught me stellar structure. He wrote the differential equations used to determine the temperature at the center of the sun. And then he replaced the differentials with deltas. And then he simply solved the equations with algebra. The result that he got, he said, was only a factor of two off from the actual number. By the way, the computer he used to solve his differential equations was a DEC PDP 11 minicomputer. He was a good guy.
I was watching a documentary on the JWST launch on Netflix, and who should show up in the compilation of people reacting to the first images but Dr. Becky! Your enthusiasm then and now is one of the reasons I love learning from you. 😊
Me too! I was so excited when I saw her in that episode of unknown!!!
This has to be the most adorable bloopers from Dr. Becky to date. LOVE how she fights with the plural for of brightnessesesesesesesesesesese ... s see? Not hard at all! 🙂
Thank you for another great video Dr. Becky. I find all the videos really interesting.
Thanks for the release!
A very interesting topic.
👍🏼
your willingnessesesses to present your bloopers impressesesses me the mostest.
Thank you for your videos, Dr. Becky! The world is more science-literate and engaged thanks to you! 🌟
She should do Star Talk
Well, that really brightnesses-ed my day. Thanks, Doc.
'...different brightnesseses...' 🤪It happens to the best of us! Thanks fir the presentation, Becky.
Thank you Dr. Becky.
I really appreciate and look forward to your more advanced topics.
Dr. Becky, great video as ever, thanks for sharing, educating and entertaining! ❤
Very much a display of ... brightnessessessessessessessessess... 🙂 Love you, Dr. Becky! You're awesome!
Sometimes, all the explanations go right over my head.
But i still let the video run til the end because it's really interesting and Dr Becky is so passionate about it ♪
I love your inclusion of the bloopers. So relatable! I also loved the cover of Under Pressure with the lyrics about star formation.... 😆
Thank you for your content Dr. Becky!
Just intuitively, without knowing anything about astrophysics, I would think that a star that got too massive would collapse on itself into a black hole.
This.
Always enjoy listening to you. Particularly enjoyed the under-pressure song at the end!😂😂Seriously though, your videos are always informative and easy to follow. Thanks
How amazing! Just when I’ve heard every Mike Rowe narration about stars and space here comes beautiful Dr. Becky.
The nobel prize short is soooo fun ... can't wait for next thursday!!
It's predicted that there were quasi-stars with thousands of solar masses in the early universe. They are thought to have had black hole cores, and they are thought to be what formed supermassive black holes.
This is halfway to what I expected this video to lead. That at some point the physics breaks down and you get a black hole. Analogy in guess is the standard candle supernovae (type 1A?) which are a similar idea?
That wasn't a 'proper' star though, and it was in circumstances vastly different to 'present' universe...
Really enjoyed your latest book. More briefed now.
great video as always. New camera by any chance?, the footage looks very pro
Thank you for your efforts in educating us about the universe. As an undergraduate, I helped a professor simulate the collision of rotating black holes on a computer. Of course, this was extremely difficult. I finished and did other things but I wonder if this has been solved
Thank you for the video.
Brilliant non-scientist explanation for answering a complex question. Interesting nail polish colour. Thank you.
Love your videos. Don’t fret your bloopers, leave them in, press on and ease your editing time.
Thanks Dr. Becky! Fascinating video! 🌟 🌟🌟
Great video Dr Becky.. Many years ago I had a long talk with someone about metalicity and stellar interiors and whether Population III stars could become more massive. The we talked about how metalicity effects convective heat transfer, radiative transfer and the nuclear processes. Back then there just wasn't as much data or knowledge about Pop III star formation. I always liked this topic. Sadly I'm not in the astrophysics circles these days.
I appreciate the collaboration between theory and observation. In other endeavors, observation and reality are ignored.
Another great video!
For enthusiasm and excellent energy. It's a Gold Star for Dr B. Every time. A shining pulsar of star knowledge ❤🎉
without burning so tightly our brains melt down.
I appreciate your love of word play... Dr Starrfield had to be an astrophysicist made me laugh loudly.
Sometimes I miss the earlier days when you had fewer followers and more interaction because of the fewer comments. On the other hand that this many people are interested in learning more about astronomy and astrophysics is wonderful.
Thank you for continuing, I/we are much more informed through your efforts!
Am major scientist on a number of missions to comets and asteroids was Jessica Sunshine! I even corresponded with her. Smart lady.
Wonderful to see Prof Micheal Feast there! He was the director of SAAO (South African Astronomical Observatory) when I started as the resident electronics technician in our Sutherland outstation 36 years ago. He lived to around 90 and was still publishing to the end.
I just saw your book on amazon. i'll definitely be buying it asap.
Always a joy with your vids. :-)
Great channel.. Heard about it from Joe Scott's channel 👍👍👍
It feels like there should be two different questions: how big a star can form? and how big a star can be (before it collapses, or explodes, or whatever)?
This video and these research papers try to answer the first question.
The two graphs between 1:20 and 1:40 having flipped X axis was trippy
I've been wondering if stars start fusion with the DP reaction to make He3 then go onto making He4 in final stage. This skips the initial deuterium formation shown in the usual PP reaction since the pressures won't be great enough till enough mass has arrived. This early fusion is the same as that in brown stars, slow and weak, so wouldn't likely effect the further gas acquisition. Once the mass reaches the near sun level mass then the deuterium can be replenished with the PP reaction and things pick up.
The other issue with large stars is the CNO cycle which runs 10,000 faster than the PP reaction. But what happens in the early universe before carbon is present. I'd guess that the PP path would have to be used but as soon as some carbon is produced, it takes over completely shortening the life of large stars.
I always look forward to the bloopers Becky ! 😂
Wonderful, you make learning fun.
I can listen to you for the rest of my life. ❤
I haven’t had time to watch recently but still a fan 👍
Okay, this is the BEST thumbnail EVER!
If there may be no upper limit to size of stars could this be applied to black holes? I have heard you mention super/hyper massive black holes but could there be an upper limit for the mass of black holes?
Dr Becky, thanks again. Always great content. I have some questions:
(1) why are brightness and mass considered joined indicators (I’m not sure the best word for this)? I’m wondering if there’s ways in which brightness could increase but mass remain smaller.
(2) thinking about the gravity metaphor with stretched fabric and a ball in the center, wouldn’t these large clumped stars create more gravity warping near each other and perhaps force more mass toward the stars, creating a process for extra large star formation?
Dr. Becky forgot to mention that she talking about *main sequence stars* and not bright giants which have evolved off the main sequence.
An interesting hypothesis, that i appreciate is one that tries to figure out the issue of no, or very few, middle size black holes, but super massive and stellar black holes. Or that supers black holes existed to early to quickly.
So the theory is that there where atars so massive that they had black holes as cores and only lived very beiefly in the early universe to allow for the rapid growth of these super massive black holes.
The core of the Tarantula nebula is going to be an insane place once those stars all reach the ends of their short lives! It would be amazing to be able to witness the ends of so many massive stars in such a small place!
Yeah there are so many stars packed so closely that the cluster R136 is basically a baby Globular cluster, Based on what I've read it seems proto globular clusters known as Super Star Clusters aren't as rare as we once expected its just that if they remain in the disk of the galaxy tidal forces will eventually rip them apart so they only survive long term if they get ejected from the galaxy plain during the starburst event induced by the merger which seeded their formation.
@@Dragrath1 makes sense. But I think most globular clusters date back to almost the birth of the universe, most of them have some of the oldest stars in existence at this point, red dwarfs etc.
@@Locut0s Yes and no while it is true that many of them are ancient its not as overwhelming as they once thought some of the globulars are significantly younger and they are still forming in a sense at a much lower rate.
The key in this model of globular formation is that the bias towards old ages is a product of major galaxy mergers of relatively comparable weight gas rich galaxies being much more common in the Early universe. This is particularly relevant in the case of the LMC and its smaller satellite the SMC as newer research is revealing the LMC is quite a bit more interesting than had been apricated as a galactic fossil which has stayed relatively unevolved due to having been largely isolated due to their presence within our local cosmic void meaning they are low metallicity star poor gas rich galaxies.
Recent astrometry and more comprehensive survey data indicates that the LMC is surprisingly far more massive than the visible stellar mass would have indicated carrying a significant retinue of its own satellites despite its proximity to the Milky Way and a much larger relative velocity than would have been possible for an object bound in a stable orbit to the Milky Way, appearing to have a gravitational mass constrained to be somewhere around 1/4 to 1/3 the Mass of the Milky Way, massive enough to induce sloshing by shifting the center of mass of the barycenter of the LMC Milky Way system outside of the galactic center. Thanks to this much higher mass there is also a strong case for the Magellanic streams to be a shock front caused as the LMC's gas halo plows through the Milky Way's much larger gas halo sapping the LMC's momentum. Based on this model the reason only the LMC and SMC retain gas to form stars is that the LMC and it's closest satellite the SMC are the only members of the LMC's retinue protected from ram pressure stripping due to being enclosed within the compressed gas halo.
In this picture the LMC is very much a throwback to the conditions which are thought to have formed most of the Milky Way's true globular clusters during the first few billion years of the Universe. These small primitive galaxies in the modern universe seem to be surprisingly common based on galaxy surveys which is a bit of a mystery of its own but that is outside the scope of this discussion.
Though I guess it probably should also be noted that a fraction of large "Globular clusters" like M32 and Omega Centauri appear to likely be the stripped cores of former galaxies that were cannibalized by the more massive primary galaxy i.e. Andromeda or the Milky Way and are still undergoing the later stages of galactic inspiraling as their dark mass helps hold them together. Evidence for this comes in the form chemically distinct metallicity populations and dynamically inhomogeneous stellar populations with a range of apparent ages.
Another brilliant and informative video… not a physicist, but love everything space, be that science fact or science fiction. A good mind bender is always fun!
But am I the only one who kept having to rewatch bits of that one after getting distracted with the Mission Impossible theme playing in my head every time I saw IMF in that video 😂
Love the delivery and the brightnesses of your humour - oh hang on, is that right? 😅😅😅
Enjoy your videos Dr Becky.
Hey Dr. Becky, speaking of most massive stars, did you see the kurzgesagt video many months back called Blackhole Stars? Would love to know your thoughts on that video and the idea of such stars since black holes are your thing
I studied PDs this semester, the intial maas function fits a poisson distribution right?😊
hiya, Doc! love your channel.....always interesting, informative and pretty easy for this layman's brain to follow. and, i love your bloopers😂 brightnesseses😅 totally agree... "space is hard...words are harder"
TY for explaining the upper limits of great balls of fire.
hello good to learn a bit more from you. as always a pleasure.
Next year the AAT at Siding Spring is having its 50th anniversary. It would be brilliant if they could talk you into coming out for the event.
7:40 the tail of a distribution plotted in logarithmic y axis is a dropping straight line, it cannot be a horizontal asymptote, which would imply it tends to a constant probability, so as many 300 and 400 solar mass starts as there are 200sm stars.
Different levels of brightness. 😊
When a star transitions into a black hole, does the light cut off instantly like a light switch?
Or does it dim into darkness?
Or flutter on and off for a while?
Cuts of instant
@@coast_2coastbecause of the limitation of the speed of light, it can not be instant. The collapse of the star will always be a process, and can never be instant.
@TSteffi So it sort of oscillates through the collapsing process?
Or perhaps a really bright supernova that's slowly fades revealing the black center?
neither....the light is frozen due to infinate time dilation at the horizon..but you will never see that...if you are lucky you might detect a very low frequency radio wave if it gets out.
@@247tubefan In a star that is big enough to become a black hole, the outer layers of the star are fusing atoms on their own. The core, having reached the iron stage, can no longer produce enough energy to resist gravity, and collapses.
That forms a black hole inside the star.
But that is not visible on the outside. Imagine a black hole the size of the sun, inside a star the size of Jupiter's orbit.
The black hole then consumes the rest of the star. But since the material falling in has a long way to fall, and there is still fusion going on around the black hole, that can take months or years.
An intuitive upper bound feels like the ratio of how much force fusion can exert outward vs the force of gravity pushing inward. Do those rates converge? I don't know enough about stellar physics to figure out how the outward fusion pressure scales with mass.
good humor ... nice to find your channel 😁
I'm left with three related questions. First, it appears that theory limits size based on stellar formation. Does it also limit it based on stability or other factors once formed. If you assume that bigger stars can form (by collision or some other process) do we belive they'd function as a stable star?
Second, is there a point at which the gravitational compression from the mass of the star overcomes the outward pressure from the fusion in the core and takes the star straight to some exotic or degenerate state, most likely a black hole. Isn't that one of the theories bouncing around about how early super massive black holes form?
Finally, don't massive stars burn faster? If so wouldn't the short lifetime of these stars explain their observed small population and the lack of observations of of anything beyond a certain limit.
Thanks!
1.) Larger stars are less stable, prone to shedding vast amounts of mass through their solar wind, as well as violently collapsing via pair-instability supernovae, or even directly into black holes.
2.) It's currently unknown whether an object can gain enough mass to collapse into a black hole without passing through a star-like stage; it's difficult to prevent fusion and the energy released from dispersing the mother gas cloud. There *should* be a point where collapse is unavoidable, but we don't know if it's possible to reach that naturally. (And it seems unlikely to be possible in our current universe due to a much lower density of star-forming gas.)
3.) Heavier stars live a shorter time. But not short enough to definitely rule out observing them. A star of 100 solar masses will live 10 million years and with the vast number of stars we can see, we DO expect to see at least a few in the hundreds of solar masses range. It's debatable exactly WHERE the cutoff point is, whether it would be at 1000 solar masses, 500 or 300, but indications are we should be able to see some truly spectacular stars, if they're possible.
This was a video with a lot of brightnessesses.
Do the calculated minimal and/or maximal masses depend upon the composition of the gas cloud?
Yes, due to how it can shed heat energy via radiation. It's expected that the pure H-He clouds in the early universe could more easily form more massive stars.
Cool, Happy Canadian Thanks Giving from, the Pacific West Coast of Canada
There must be an upper limit on the size of a star as black hole formation must have a lowest mass limit that they form at?
I know it's not as simple as that when taking accretion discs into consideration, if the main body of a star itself is just lower than the threshhold of the mass required to collapse directly into a black hole then it could burn off fuel at a same rate or higher than the absorbsion rate from the accretion disc?
The density of the fuel could also play a role in this too, just a few variants to take into account to figure this out.
The range of the variants should be worked out to give best and worst possible case scenarios and look for evidence to work out if any of the conditions that could allow these to come to fruition?!?!
Always be prepared to discover whether these conditions occur but always be prepared to find some that may have conditions unexpected to allow a greater size than predicted?
I like the last part of the video :D
While there is almost certainly some other limit well below this, I can point to *an* upper limit.
There would be a density below which fusion cannot be maintained. I don't think you could reasonably define matter as being part of the star if it is below this density, therefore defining the edge of the star.
For a given density of mass, there is a schwatzchild radius where for a mass at a given density (evenly spread or not), the object can only be defined as a black hole.
Therefore there is a maximum mass, minimally dense, hypothetical star, where adding any more mass within its existing radius would form a black hole, and spreading out the star so that more mass could be added would bring the density too low to sustain fusion and be a star.
What about limits that could kick in AFTER a star firms? Like, if the radiation pressure from fusion blows off the star's outer layers (like Wolf Rayet stars) or instantly starts initiating pair-instability and going supernova the moment they form, or even more extreme yet...if a cloud is too massive to even have time to start fusion before gravity collapses it directly into a black hole?
Also what role if any does metalicity play in how big a star can get?
Brightnissesses, precious!
6:46 - Without being an astrophysicist, I think it's safe to assume that conditions like that would severely limit the possibility for the gas around one forming star to dissipate away, since it would basically immediately be faced with the radiation pressure from another forming star!
Nifty nail polish. Thanks for the talk.
I always figured it would be several proto stars forming alongside or near each other, which then combine to form these much larger stars.
2 or 3 combine and then start eating the other nearby proto stars.
If you have several already quite massive stars that are a dozen or so solar masses and they eat the other stars around them wouldnt that explain how they can get so massive without first starting off their fusion stage?
The only problem with that is that if too many merge into one star they could end up hitting something akin to the Chandra-Sekhar or TOV limits in their core. Which would turn them into neutron stars or black holes respectively. So at what point, in solar masses, does physics prevent something like that happening. If it doesn't, how many of the supernovas we see are actually merging hyper-massive protostars skipping the main-sequence/giant phase and collapsing straight into their degenerative phase.
Which by the way, would be pretty cool.
My favourite sentence coming from people in the fields of science: "We still don´t understand xy very well."
Many scientists (and science communicators) tend to forget that the subjunctive is their faithful companion. Or should be.
chapeau
Dr, would you recommend any intermediate astronomy textbooks that are very good and the most up to date one can find these days?
I have the stellar astrophysics textbook that universities use. It's already out-of-date!
@@douglaswilkinson5700 I know it's terrible. If you study Astronomy and Human Evolution like I do, everything is always out of date within months! ack!
So interesting. I am wondering if there's a limit on how much material can be gathered. I may be making some big errors here as I am not a physicist, but are there specific conditions that are needed to grow stars, density, temperature etc. How far gravity gather material before the star formation begins? Could volumetric measurement show how much material the star gathers? I think from some nebula images you can see a region of emptier space around some stars. Could observation be used to calculate the area of the nebula eaten to make different types of stars?
Purchase a copy of "An Introduction to Stellar Astrophysics" by Francis LeBlanc (Wiley 2010).
Fascinating stuff indeed! Thanks, dr. Becky! 😊
Stay safe there with your family! 🖖😊
This was very interesting, but I'm stuck with questions about that merger scenario. Does the upper limit disappear if mergers are allowed, or is there something that would prevent a merged star from remaining stable above a particular mass level?
It feels like there must be something like Chandrasekhar's limit for non-white-dwarf stars, even for mergers... but it would have to be calculated for the most energetic stars because on how much fusion is going on internally, the composition, etc. would all affect it... and then there's environmental conditions
The more massive a star is, the stronger its stellar wind and the shorter its lifespan. As such ultramassive stars aren't really 'stable' in the way our sun is, but can still exist as an object on human scales. It's believed that the early universe may have had 'quasi-stars' massing millions of times our sun, with black hole cores that eventually formed the centers of galaxies.
Massive stars are weird for example the most massive stars still fusing hydrogen in their cores effectively leave the normal main sequence while still in hydrogen burning because they develop vigorous convective overturning which delivers their fusion products to the surface while also fueling so truly insane stellar winds. The net result is these stars enter a second fully convective regime allowing them to effectively fuse most of the hydrogen that they are made from basically everything that isn't blasted off into space by the extreme stellar winds.
In the case of R136 a1 this stars spectrum at least when I read about it in grad school back in 2019ish indicated it had a probable composition of roughly 60% helium 40% hydrogen with evidence for full CNO catalyzed convective mixing (CNO cycle is a catalytic fusion cycle at high temperatures where carbon nitrogen and oxygen serve as intermediary fusion products converted cyclically to produce a net result of Helium)
Excellent! Stellar astrophysicists admit that R136a1 is fusing hydrogen in its core and by definition that makes it a main sequence star. It's spectral type is listed as WN5h and it's luminosity class should be listed as *V* (WN5hV) but isn't. (Being a main sequence star it is, by definition, a dwarf!)
I didn't think of myself as a fan boy until I watched a recent documentary presented by former astronaut Tim Peake, which featured our beloved Dr Becky. My wife and kids thought I was losing it when I was delightedly exclaiming "It's Dr Becky! Yay!" I got a lot of side-eye...
Is there likely to be a different maximum size limit in different parts of the universe or at different times in the universe's past? And if so, why is it different, and how smoothly does it change over distance and time to what we see nearby?
It is expected that in the early universe, gas clouds made only of hydrogen and helium were better at collapsing into stars, for a few reasons. As such 'Population III' stars, the first to form in the universe, are expected to have contained a lot of very massive stars, up to 250 times the sun's mass. Pollution from heavier elements, as well as a dropping density in the universe, should have quickly reduced this upper bound to near what it (may be) today. Excluding, of course, things like mergers, Thorne-Zitkov objects and the like.
I love this channel - great vid Dr Becky! Though the person helping you to make the graphic at 2:31 showing the plot tending to zero needs to be told what a log scale is :-)
Ngl i was expecting this to be about supermassive stars, quasi-stars, and SMBH seeds. But this was still really interesting
Nice singing voice Dr.!
The upper limit to the size of a star is determined by the metallicity of the solar nebula it forms from with the Eddington limit being the ultimate upper bound on mass.
Very excited to see your new video and can't wait to get and read your book 10:57 "A BRIEF HISTORY OF BLACK HOLEs"
Sorry if I'm repeating a question: but can a star be so massive its local gravity will overwhelm the outward pressure generated by the fusion process and thus cause it to callapse below its Schwarzchild radius?
And a second question that occurs to me is that if the star is massive enough then it's Schawrzchild radius could be at or beyond its surface thus removing the necessity for the star to collapse at all.
I know that we're probably talking galactic masses for the second case, but it's good to start somewhere? 😄
Edit: emoji
"Larson and Starfield" sounds like a '70s band.