Spinning a black hole as fast as possible

[@Zouzou123gen]

It's one thing to explain research done by others; it's a hugely different feat (IMO) to talk about your own research! I'm sure you have so many things you want to tell us, but you manage to summarize it, explain the rationale, and remain objective about it. Thanks please keep doing this!

[@danleeselman4827]

It has become so institutionalized doing science for money. Science for scientific sake doesn't give you your paycheck.

[@Dave5843-d9m]

How does black hole research make money?

[@djoswald9128]

@@danleeselman4827 “Yes it does. Centripetal force. I still find it hard to believe. Show me galaxies without black 🕳️’s.?.😉.?

[@LeslieShaff-ud1ty]

Zouzou, you have been there, Congrats!

[@jasonbrown9142]

What happens to the ejection matter of the quasars over time where the ejection is perpendicular to the galactic disc? Does this give rise to globular clusters ultimately or are those more a function of galactic collisions? Does the gravity of the galaxy hold onto it or is it ultimately ejected from the galaxy into the void? What are the implications of retro movement versus standard rotation, if any? So many questions…

[@ENDESGA]

This is honestly such an amazing job, Becky and Ricarda! I absolutely love how it's "this is a paper, by me!", because you don't see this too often! Huge congratulations~!

[@FLPhotoCatcher]

Indeed. 👍 But who put Pluto in the list of planets? 🤨

[@AJMansfield1]

2:00 ngl I do genuinely appreciate the clarification that for black holes, spin really does mean a concept related to angular momentum. We're often told that black holes act like "fundamental particles" that only have mass, charge, and spin, but usually the only type of "spin" that a fundamental particle has is this quantum number that has more to do with group theory than macroscopic angular rotations.

[@melanocrisis]

I can't imagine what it feels like to put out literal art and knowledge for the world to see - in a form of research papers. Huge congratulations - you are the real pioneers of humankind.

[@danleeselman4827]

why waste time arguing about the scientific reality between a movie made for entertainment and reality.

[@borisborcic]

Bravo! I opened the comments after watching the video and salient among the intentions of communication collected, was the idea to name this work of Dr Becky's _a powerful model of, or illustration for the name of_ ART. (Now if that's "frame dragging" (of model making) there's an implied conceptual BH to question;)) Would it not make sense btw to split the scope of the name of art and to look for a qualifier to name _the sector of art_ that would here be illustrated? What about "cognitive art" -- it's friends enough to your "...and knowledge"? That's a tame choice. But it precedes the candid question, _can you locate art that would in your opinion be self-evident to call_ "non-cognitive"?_ For a crazy wild alternate choice, "Spin Art"... to promote effort to think of SMBH Spin and of Quantum-Mechanical Spin as forming a wild pair, like say the North and South poles of the Earth -- deeply related but in many regards related by being _particularly_ contrasting. "Spin Art" is also crazy because it's not aligned with the spin _of the name of spin_ where seduction is involved, as it is in art (in principle)... _That_ spin is distinct from the "angular momentum" spin of the name of spin in physics that's here wanted... except perhaps for spin _as evidenced by exotic trajectories of bouncing or flying balls_ -- likely at the linguistic origin. ...this returns me to "frame dragging". Admittedly unique to BH spin (in contrast to QM spin), "frame dragging" is both pure advanced physics and _arguably aligned with the spin of the name of spin where seduction is involved, like in art._

[@reasonerenlightened2456]

it is a preposterous claim in this video that we know the laws of physics inside a black hole therefore we know it is "spinning"

[@FLPhotoCatcher]

Dr Becky and all scientists might have to change their minds about what she says at 10:48. A new study has found evidence of black holes ‘burping’ out matter years after consuming a star... I sense a new video about black holes coming.

[@borisborcic]

@reasonerenlightened2456 no more preposterous than claiming we know there's mass inside the hole and that it therefore has (linear) inertia, and gravity. While rotational inertia (spin) is familiar from usual bodies, rotational gravity (frame dragging) is rather special to bh (although I wouldn't be surprised to learn it can be significant around neutron stars as well).

[@rjblaskiewicz]

There was a moment where you were describing the orientation of the axis of spin and material falling in from the rest of the galaxy where it was entirely plain on your face that you absolutely love your job.

[@manifold1476]

timestamp? svp

[@reasonerenlightened2456]

it is a preposterous claim in this video that we know the laws of physics inside a black hole therefore we know it is "spinning"

[@gurupkaargill2049]

Mam I'm a layman in the field of astrophysics, but i find your lectures on space so fascinating that i couldn't restrain my self from ordering your both books on Amazon, i received those recently, I'm from India, presently I'm reading your book ten things you should know, i hv completed the reading of book on Black Holes, God bless you in all aspects of your life and help you countinue researching and writing about space 🎉🎉

[@azdgariarada]

Hearing about your own research is very exciting. I did a little "hey, I know that author!" as soon as you mentioned your papers.

[@MultiNacnud]

Congratulations on your paper Dr Becky et al. Until now I thought Peter Mandelson was the UK's foremost spin doctor.

[@MauricioA666]

Finally, I got your book thanks to my wife on my birthday. It wasn't easy to get (we live in Colombia), but it is here, and I will read it as soon as possible. Thanks Dr Becky for your great work, and share all your knowledge. Greetings from Rionegro (Antioquia).

[@meslud]

Did you know that Schwarzschild (which is just a German name) literally translated into English means "black shield", so imagine my confusion when I first tried to find out anything about what kind of "shield" a black hole has ^^

[@JarredHarvey-ix4qb]

You have such an impressive flow Detailed, yet succinct. Mature and playful, you'd be such an awesome lecturer

[@martinkellermayr8766]

Great video as always, just one detail I noticed at 5:20, shouldn't the radius of the event horizon get bigger with a more massive black hole?

[@oystercatcher943]

Totally. I think. The equation seems to contradict what Becky said. But great video. I’ll let that go

[@shellbullet0x]

It is my belief that she made an error in her statement. The addition of mass will indeed expand the event horizon, while the addition of angular momentum will have the opposite effect. The accretion disk contains a significant amount of momentum, with a large amount of mass moving at a considerable fraction of the speed of light. Once this spiraling disk crosses The Event Horizon, it continues to spin without stopping suddenly, causing a decrease in radius and an increase in spin. This results in a counter gravity effect, as the centrifugal force of the rapidly spinning disk pulls the mass outward, counteracting the inward pull of gravity. At the center of gravity for this disk, there should be no matter, similar to a CD. If the matter in the disk is uniformly distributed, it would pull equally in all directions outward from the center. When standing on Earth, all the matter pulls you towards it from below, but in the disk, the matter surrounds you if you are at the dead center. Therefore, all the surrounding matter would pull you towards it in a radially distributed manner. As the heavy ring spins faster, its radius increases, causing the matter to spread out and become less dense. This leads to a decrease in the Schwarzschild radius as the ring's radius increases. The only limitation is that objects cannot be accelerated to the speed of light. Therefore, the maximum speed at which the ring can rotate would be 0.9999999 of the speed of light. It is worth noting that the extreme spacetime curvature may contribute to the spin, potentially exceeding the speed of light. If the spacetime curvature is strong enough to trap light, it may have the ability to exert a slight push.

[@MrDlenrek]

Brilliant episode! Love it when you go deep into some of your own research

[@TheAslakVind]

I am so thankful for the with and depth of your videoes, you are truely able to explain without dumbing down. I have a dumb job, and watch your videoes to keep my brain working at full speed.

[@ondrej_hrdina]

The universe is amazing -⁠ thank you so much for trying to find out how it all works. It's a joy to hear about such a fascinating subject from a scientist doing the actual work on it. Not only that, you always explain the essentials really well. Congrats on the papers to everyone who contributed!

[@CydoniaPhysGeekGirl]

I am currently working on something that I hope will explain not just the how but also the why. Very exciting work! Sadly I have several physical health problems standing in my way, delaying my work.

[@CydoniaPhysGeekGirl]

Exploring a new paradigm for dark energy.

[@21palica]

I remember a wonderful example of how the black hole's spin increases as it swallows up material, using a spinning bicycle wheel (representing the black hole) and a hand (representing the spinning material falling inside it). Every time the spinning material hits the surface of the black hole, if it's spinning in the same direction, it will increase the black hole's spin, and vice versa. I am sorry, but I forgot the physicist that was making that wonderfully simple example in the documentary. Congratulation on the paper Dr. Becky! I will be buying your book when it comes out, and can't wait to read it!

[@raydenn6027]

Interesting, very interesting Dr Becky is so good at explaining her passion. I love the bloopers too.

[@azdgariarada]

I'd love to see a video with more in depth information about how you run your simulations of (one presumes, millions of?) galaxies, SMBHs, etc.

[@sophiophile]

Paper titles are in the vid.

[@azdgariarada]

@@sophiophile Did I say I wanted to read a paper? I'm lazy and stupid. I'm not going to try and understand a scientific paper. I want pretty smart science lady to dumb it down for me and spoon feed it to me in easy to digest TV format. Duh! ;-P

[@sophiophile]

@@azdgariarada Fair enough. She has expressed in the past that the simulations+code side of things is not something she is deeply involved with. Maybe an interview with a co-author would be better.

[@vanikaghajanyan7760]

5:28 The Kerr metric is only a particular solution corresponding to a certain distribution of masses in a rotating body. Moreover, this metric contains a trick: when we change only the sign of time or only the sign of the azimuthal angle, the invariance of the metric is violated. This is as it should be, since such transformations are equivalent to changing the direction of rotation, and the nature of the gravitational field depends on the sign of the angular velocity. Obviously, if ar(G), then there is a singularity on the ring with r=0. P.S. About the accretion of matter: the energy of the particle is equal to the derivative of the action in time x(0)/c: and defined in world and proper time: E(0)=с∂S/∂x(0), E=∂S/∂t [momentum p(k)=∂S/∂x(k)]. Then E(0)=E√g(00)=const and E(0) is preserved, and E is not preserved. E=mc^2/√1-v^2/c^2, where in the static case v=dl/dt=-dl/dt√g(00).Thus, when a particle moves in a gravitational field, the energy E(0)=mc^2(√g(00)/√1-v^2/c^2 is preserved. This formula remains valid in the case of a stationary field if, when determining the velocity v, one uses the proper time measured by the clock synchronized along the trajectory of the particle.

[@alexz1104]

So cool to actually see some of your own research featured on the channel. Great job Dr Becky!

[@miles4711]

At 5:23, with more mass (via rotational energy) shouldn't the event horizon grow, given the formula a little beforehand?

[@AKjohndoe]

It is amazing having the person who wrote it, explaining it. Thank you Dr. Becky!

[@davidmarksberry5970]

Great job!! Thank you Dr. Becky!! Using all the big fancy words but string them together in a way that I walk away understanding the basis of the video..🎉🎉🎉

[@malectric]

Thanks

[@jimmagwojo2718]

Thanks for sharing your research Dr Becky a lot of scientists make their work for their peers by explaining this to us like this we feel like we have become your peers too

[@HaniSantosa]

You have small mistake at 3:20: angular momentum should be 2/5 MR^2 ω. The R should be squared.

[@izzygrosof]

5:15 I'm confused by this part - why does having more mass due to spin make the effect horizon shrink? Normally having more mass makes the effect horizon bigger, right?

[@douglaswilkinson5700]

Matter in the accretion disk rotates around the BH. Since angular momentum is conserved this energy spins-up the singularity at the center of the BH. The event horizon spins faster and faster. As it approaches the speed of light the event horizon must *shrink* to prevent it from reaching the speed of light. If the event horizon were to actually reach this speed then the *singularity* would be exposed or *naked.* As I recall the *Cosmic Censorship Hypothesis* states that singularities can never be *naked.*

[@izzygrosof]

This still doesn't make sense - as shown in the figure-skater example, having a smaller radius means faster angular speed for a given angular momentum. Shrinking wouldn't slow things down, expanding would.

[@martixy2]

200 comments I scrolled through for an explanation and you're the only person to bring up this point. Shows you how much of the audience pays attention.

[@dsdy1205]

@@izzygrosof You're treating the black hole as a solid newtonian ball, which does not hold under GR. A 'spinning' black hole drags spacetime along its equator. The result of this is that there is an ellipsoidal volume of spacetime around the black hole called the ergosphere that rotates with it, and this volume of spacetime contains a good part of the black hole's angular momentum. The ergosphere does in fact grow bigger as the black hole's spin parameter grows, which makes intuitive sense.

[@ChthonicJon]

Have I missed something or should the equations at ~3:15 and ~3:40 have R^2 rather than just R ?

[@warrenwormhole]

I've been just short of pulling my hair out on that one. It should be r^2. The dimensional analysis supports this.

[@Joshua-by4qv]

Young brilliant women. And they are here to do the hard work for us. Nothing fascinates me more than cosmology. Keep up the great research.

[@MCsCreations]

Fascinating stuff indeed! Thanks a bunch, dr. Becky! 😃 You guys did a fantastic job, congrats! Stay safe there with your family! 🖖😊

[@noneofyourbusiness5326]

Just to be nitpicky, wouldn't the angular momentum of the Black Hole be slightly smaller than the original star, given that part of the original star has been scattered into the nebula created in the super nova?

[@ivoivanov7407]

Yes, you are completely right, the angular momentum of the black hole is smaller than angular moment of the original star. Rest of the momentum is "carried away" by the matter of the nebulae created by star's collapse.

[@DrakeLarson-js9px]

Dr. Becky cover that in her ice skater example

[@pikmin4743]

awesome! congrats on publishing and thank you for sharing and informing us

[@neoanderson7]

Always a delight to hear from Dr. Becky. Hopefully get some HST time as well as JWST. 🤞

[@DenizenoftheAges]

Amazing. Thanks!

[@Eric-zo8wo]

0:00: 🔬 Two research papers were released on how supermassive black holes grow and spin, with collaboration between an observer and a theorist. 3:29: 🌌 Black holes spin faster when their radius decreases and their angular velocity increases, similar to an ice skater drawing their arms in to spin faster. 6:56: 🔭 Measuring the spin of a supermassive black hole is challenging but can be done by observing the inner edge of the swirling disc of material around the black hole. 10:07: 🌌 Supermassive black holes in galaxies can grow by bringing in material into the accretion disk around them, which can lead to outflows or winds that deposit energy into the surrounding regions of the galaxy, affecting star formation and galaxy evolution. 14:27: ✨ Supermassive black holes in galaxies can have brighter accretion discs due to their faster spinning and more efficient conversion of mass into energy. 17:28: 🔬 Observations suggest that galaxies without mergers have supermassive black holes with higher spins aligned with the galaxy's spin axis, impacting feedback differently. 20:43: 📚 Dr. Becky thanks Brilliant for sponsoring the video and highlights the benefits of interactive learning on the platform. Recap by Tammy AI

[@noneofyourbusiness5326]

I love the explanation of how you measure that spin. You do a wonderful job of talking to us average people.

[@davidpearson3304]

Admittedly most of the stuff on here goes right over my head and I can’t even begin to wrap my arms around it……But….today I actually sort of understood it. 😳🤷🏼‍♂️. Maybe watching Dr B’s videos is starting to sink in.

[@johnmccausland8466]

I always look forward to watching your videos Dr Smethurst. Amazing content.

[@pablotroncosounwin2917]

Congrats, Dr. becky. You've made another masterpiece 👏👏👏 Isn't the assumption that the mass of the original star remains the same when exploding in a supernova? I understand that vast amounts of mass AND energy are spitted out during the collapse.

[@BrookeSimmons]

You're right, the masses aren't exactly the same -- but nevertheless the change in size is so dramatic between star and black hole that even if you only consider the portion of the star that will become a black hole, the collapse still requires a huge spin-up.

[@jessicamorgan3073]

Thanks Drs Becky and Ricarda (and Dr Chris too!). 😊

[@mbdtsmo]

When talking about „spin“ is that the same as the quantum spin in electrons, or more mondane „rotation“ ?

[@OhAncientOne]

Formulas with the descriptions are 🏆 Thanks!

[@martynnewby6298]

Dr Becky. This lecture is finely pitched. It appears undergraduate light. Good. I can watch this with my breakfast and rise from table full and content in body and mind.

[@BHNative]

Happy to have stumbled through, you’re great!

[@dougniergarth]

That answers some of my questions. Thanks!

[@philurbaniak1811]

👍👍 sounds awesome, really interesting ideas!

[@ross077]

Thanks for this great explainer on the geometry of super massive black holes and how they affect their host galaxies Becky. It makes sense in my head and I hope your ongoing research on this subject yields plenty of useful scientific results 👍

[@v4vd]

tysm dr.becky for this lovely insight!

[@artlovepeace42]

Amazing stuff as always and congratulations on writing such great research! Question 🙋‍♂️: Can a black-hole’s spin get “redirected” so much, from a galactic merger, to reverse the black-holes spin? Would it’s spin be able to become the exact opposite of its original spin (a 1 to a -1)?

[@judelekpa2778]

Funny, whenever Dr Becky says something is difficult to... the next statement she makes is there is a way and she then goes on to explain how... Great Job Dr Becky... From Nigeria.

[@kevindoom]

Best one yet Becky

[@gustavderkits8433]

Kudos for getting, not just any skater spinning, but the world record. Well done. Angular momentum is hard for most people to grasp.

[@grayjphys]

great video, love the nail color too!

[@EarlWallaceNYC]

Fantastic explanation. I had to read Wald twice to get the understanding you gave in 10minutes. Nice ! Kudos.

[@j.t.senghas806]

For the formula for angular momentum presented at 3:25, is the radius squared, as you said, or not, as written? Thanks for the concise explanation.

[@richardseymour7162]

The formula as written (not spoken) is correct. I noticed that discrepancy too.

[@warrenwormhole]

written should be r^2, no? @@richardseymour7162

[@martynspooner5822]

And here is me pretending I understand all this and I am busy checking the maths now. ( not really truly) I I do grasp wee bits and I am happy enough with that although admittedly sometimes I feel like I've sneaked into somewhere where I have no right of being but that is what makes it so fun. Thanks for sharing your brilliant work so layman like myself can have a peek.

[@jondor654]

Same here. A word of caution. Not too close to that horizon.

[@martynspooner5822]

@@jondor654 Will keep that in mind. Ps how will I know if I am too close.

[@NathanAkers]

Dr Becky, I learn tons from you. This stuff is fascinating. A couple questions came to mind here that I’ve never thought about, and some feel kinda basic, but here we go: (1) Are there any bodies in space that don’t have a spin? What would happen if they didn’t? Is spin required for gravity? (2) Since matter is being drawn into black holes, and jets of feedback are being expelled, I think that means that space has a lot of matter that’s disconnected from bodies (stars, planets, etc), no? If so, how do we imagine this loose material? Why would it not fill the void of space evenly like gas in a container would? Thanks!!

[@tony52398]

Dr. Becky Is there any theoretical way to map the mass distribution inside a black hole? In my head I’m picturing two black holes merging, the singularities should still be a distance apart even if they are inside the event horizons of the other black hole. By gravitational lensing or some other effect could you understand the mass distributions inside the event horizons?

[@leonais1]

I think Dr Becky made a video about black hole mergers recently? I seem to remember there was no observed data and it was not even certain the black holes merged instead of falling into a binary orbit.

[@lukekowa]

thats a crazily amaZing question can't wait for the answer

[@thomasgade226]

Some hope to measure gravitational waves to use as a "telescope" to view critical data about the merger, particularly at the very end during the so-called "ringdown" right between vibration and silence. That's for two ultradense objects circling rapidly around eachother, many times per second. Then they coalesce into one, while the last wobble fizzles away, hence ringdown.

[@shaunehuolohan5736]

Thankyou Dr Smethurst Amazing I can comprehend this, due to your explanation.

[@PhilMason1972]

I’m going to need to watch this again… got the book now though!!

[@mattslaboratory5996]

Excellent explanation, as always. I also had fun, for a while, trying to decide if you were saying "ion" or "iron," but my clumsy American ears eventually figured it out, I think.

[@FLPhotoCatcher]

When she says "maths" it sounds very much like she is saying "mass". And "mass" is something an astrophysicist often talks about. It is clearer to say "math"... No, an *abbreviation* does not need to be plural.

[@timpointing]

@@FLPhotoCatcher Another clear, unambiguous way to say the word is "mathematics". While it is much longer and may not be one's natural go-to word, there will never be a chance that somebody thought you said "massematics" 😛

[@Yves_Breeze]

@@FLPhotoCatcherAll words are made up, but to the degree that one can speak “correctly”: math is correct in the American dialect and saying maths is correct in the British dialect

[@douglaswilkinson5700]

The British do not pronounce the letter *r* unless it is in word-initial position: they say *kaht* for card (they also devoice the *d* to a *t* in word-final position), *staht* for start, etc.

[@chrischen82]

hey Becky, thaks for your wonderful talk about the spin (and all your other videos). I had a bit trouble undersanding your graphs shown. it would be great to get an explanation for the axis before talking about the gaphs. Have a great time. 🙂 Greatings from Dresden, Germany

[@DouwedeJong]

thanks for explaining. that was super interesting.

[@burnte]

Fantastic book, I bought it in hardback last year and the audio book.

[@nemoniemand9264]

Impressive work!

[@EdmundWChan]

very informative. thank you doc!

[@adriancopping1253]

Thank you Becky 👍

[@RevP369]

Brilliant! As usual, further explanation the unusual.🙏

[@paulgar8]

Great Video, Thank You!

[@CloudhoundCoUk]

Fantastic thank you, Dr Becky.

[@drwaynebuck]

Thank you for the equations. More please!

[@Erik_001]

Love your work. Thanks.

[@malectric]

I'd be interested to know whether there are any deviations from what is expected (considering known/"visible" mass) that could be a result of dark matter being present? I have heard it being hypothesized that supermassive black holes (and galaxies) might not have been able to form without the presence of dark matter. Just love your channel. I think your taking time out to inform people outside academia of your interests and findings is terrific.

[@michaelvalencia3537]

Loved your book!

[@rickrivethead]

Love your Stuff btw!!!

[@JoieVientLeMatin]

I also love your presentation style. It is resulting in me having a growing fascination for astrophysics. So, a quick question from a neophyte in this science - that you probably already covered when I wasn't looking: The time scale over which many of the phenomena being discussed is huge - completely outside anything meaningful to us mere humans. For instance, the period over which black holes have merged. So how do you determine if a black hole has experienced no mergers or many mergers?

[@michaelripley4528]

Your mind is Way faster than your tounge😁 AGU!! Another Great Upload‼️

[@JoJoDo]

3:23 So the radius should be squared here right?

[@louisgiokas2206]

In the bloopers section you talk about the term "maths" (the spell checker in my browser in right now flagging it as incorrect) and how the Americans changed the language. Actually, at the time of American Revolution there was a conscious decision to do so. Something to do with breaking away from the colonizing oppressor. Actually, I lived in the UK for a while and sometimes find myself using terms like maths. Also, my first three cars were small British sportscars. The shop manual for my MGB actually had a glossary of British to American terms. By the way, thanks for sharing your research. It is interesting to see what various KZbinrs, especially on science channels, are doing.

[@Max_Flashheart]

Roy Kerr is from New Zealand and a legend

[@BenWard29]

So is a galaxy just a giant supermassive black hole accretion disk?

[@JosephCrollett]

love how you see through our contractions (butchering) of the English language like black holes compressing(accreting) of close star matter, and then promulgate (burp out) our processed info into the AdS in an effort to define all. Perhaps our attempts at contracting words are similar to the circle of the universe's information from the MULTIPLE SINGULARITIES TO THE SINGULAR PLURALITY. If you see the curve...

[@davydatwood3158]

The first time I encountered the phrase "hard science fiction" was in the afterword of an anthology explaining the science used in the stories. One of the features of this setting was the use of miniature black holes as a form of energy storage - put energy in, black hole spins faster and stores energy; slow black hole down, energy comes out. I don't remember most of the details (and I can't remember either the auth-- wait, in the middle of this sentence the title came back to me). The book is the McAndrews Chronicles by Charles Sheffield. Anyway, I don't remember the details but this video does quite resonate with that memory, so it was very, very engaging. Also: Canadian English is a mix of American and British English and so one could argue that Canadian English is the "best" English because it's subjected the language to a Darwinian contest of survival. From that admittedly nebulous premise, I conclude that although "zed" is correct and "zee" is not, "math" and not "maths" is the best way to truncate "mathematics." (Mostly because "ths" is really hard to say, your tongue is rushing to change position. I suggest that "maths" only persists in the UK because most British accents would actually say "maffs," which is much easier to say than "maths" and also flows better than either "math" or "maff.")

[@andrewsallee6044]

This triggered some new questions for me that I have, so far, not been able to answer: 1. Is the universe spinning? 2. Would that mean that a universal frame of reference is non-inertial? 3. How would an anisotropic universe affect our theories of gravitation? 4. Would a spinning universe replace inflation?

[@Fearls1]

Amazing, thank you Professor!

[@MisterItchy]

I've got a 5-day backlog on my notifications but yours has got to come first!

[@MYBLOODYUSERNAMEFFS]

🤯 that was awesome 😊

[@timwrich5128]

Hi Becky, i have always wondered if gravitational redshift can skew the calculated expansion rate of the universe? How do we know if redshift is from expansion or gravity?

[@RAFAELSILVA-by6dy]

Because the redshift even from the surface of a giant star is small. Especially compared to the redshift from the recession velocity of a distant galaxy.

[@Kane-ib5sn]

the outer-surface of a black-hole/darkened-star, has to spin above the speed of light (locally), in order to expatriate energy - some of it in the form of electromagnetic waves, stretching/dispersing out into gravity waves, as photons collide with other photons moving in opposite direction &spin, same amplitude (destructive interference - which does not actually destroy energy - it causes zero relative motion to the origin of expatriation. since the accumulating wavefront is defined by hooke's law...the wavefront weakens at the square of the distance - becoming a gravity wave). such is the case of a nebula formation, a Black hole / Darkened star may explode, if its core tangential-speed exceeds 'c' (locally). in the greater/grand-scheme, this described phenomenon gave us the Big Bang/Big Spin. that is my interpretation.

[@dmanparttwo]

@DrBecky why does event horizon shrink if BH has extra mass at 5:16 ?

[@trout3212001]

Thanks for another great video. I do have one question. It sounds like you are using the event horizon as the radius of the black hole when calculating angular momentum. I thought the mass was all concentrated at the singularity at the center (at least the maths say that). I realize that would mathematically give infinite angular momentum, but isn't it a big assumption to say that the mass is uniformly distributed throughout the SMBH. Anyway the answer may be in your book, which I am about to reread. Also, I am from the US and I used maths in this comment just to show deference to you 🙂

[@darren8453]

In the same way that it used to be thought that nucleons were of uniform mass, until we figured out how to break them apart into quarks, I suspect we will need better experiments and new theory to get at the mass distribution of a black hole. It's entirely possible that it behaves in a uniform way, or that it's so chaotic with matter and energy sloshing around, that the long-term effect is to appear uniform. Sadly we get no information about any of this, so ... your guess is as good as anyone's 🤷‍♂️

[@garethdean6382]

In the case of a black hole its properties are expressed on its surface, its horizon. So a charged black hole is not expected to have, say, an area of concentrated charge but rather an equal charge across its entire surface. This actually relates to how the hole warps space and the path of anything that would be radiating from its surface. So it doesn't really matter what the internal structure of the hole is, it will 'look' like a uniform rotating sphere. And indeed if the mass distribution *did* matter, then it would allow us to measure something about the inside of a black hole, the apparently immeasurable. It would at the very least be a gateway to new physics.

[@WestOfEarth]

Very clear and concise explanation. I can see the difficulty in correlating accretion spin with bh spin. Sort of like trying to infer the rotation of Venus by measuring the speed of its clouds. I'm curious if bh whose spin axis is perpendicular to the galactic spin axis are the cause of barred galaxy structure?

[@iborgiwc7899]

@Dr. Becky Please do cover the "theoretical" situation where the spin does exceed C, and what happens to the horizons at the convergence point and beyond, particularly in relation to white holes. Please also cover Kip throrns works in this regard. thanks in advance.

[@paulgrosse7631]

Totally right. Keep the 'S' after all, it is plural - there is more than one sum.

[@michaelgian2649]

5:35 the rotational parameter "a" (here called "spin of black hole ") needs be a dimensionless ratio. Would it not be more accurately defined as "J/Mc"?

[@IaIaCthulhuFtagn]

Wouldn't a star lose some of that mass when it goes supernova and explodes expelling both mass and energy out, or does it usually manage to gobble it all back up when it collapses?

[@momund9047]

My world revolves around you. Just afraid that if I pass the event horizon, might not come out of your love❤❤❤❤❤❤❤❤. Love how your nails match your beautiful eyes😊

[@johnallison7608]

Wow! Tour de Force Dr B!!

[@mb1287t]

Good job

[@AndrewDRSWilliamson]

We just love the black holes 🕳 😂. Good luck with your paper!.