Why can't LIGO detect mergers of supermassive black holes?
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- Äas pĆidĂĄn 8. 06. 2024
- LIGO detects ripples of gravitational waves, so why can't it detect the biggest ripples? To learn more on the foundations of scientific thinking head to brilliant.org/drbecky
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đ©đœâđ» 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 - VÄda a technologie
"We're in Earth mode now, not astrophysics mode" - new favorite Dr. Becky quote :D
lol xd
Distortion of frames of reference like that remind me of when I was studying geology in college. I was getting used to thinking in millions of years as my base unit of time and the eco-people were running around complaining about how plastics will still be around, basically unchanged, when my grandchildren were around (so, like 2 generations... 30years?). I had to stop myself from looking around and saying "well, so will that rock". I had totally lost track of human timescales while studying geologic time scales.
I'm the 5th grade gifted teacher and I talk about this stuff a lot during science! I have several kids who love and watch your videos at home and then we have physics talk at school.. this was the best AND EASIEST breakdown of LIGO I've ever seen.. It makes so much more sense. Thanks!
Are you a gifted teacher, or a teacher of gifted 5th graders?
@@j.w.8663 Why not both? :p
Well, only teacher of 5th grade gifted children would make sense from the context I'd say. Gifted children is the preferred term for children of high achievement in school / high IQ
It isn't in the curriculum. Why would you teach this?
@@sleepingwarrior4618 (Dr. Becky, please excuse Anthony here; he's a flat earther.)
Forces (including gravity) _are_ part of the 5th grade _general_ curriculum. Several of Mr. Dixon's gifted students-exceptional curiosity and intelligence-watch Dr. Becky's videos at home and apparently he engages these students' questions and interest. That's great!
One of my students chose these two gravitational wave detectors as her topic for a science paper she wrote recently; it came completely out of the blue and I had no idea that she even knew about them or was interested in astrophysics. Great to see you covering it, I'll share this video with her to inspire her some more!
Dr. Becky, the way you explain things is awesome. You can present the information in a way that someone without an astrophysics degree, (read - me), can understand. Well done.
The way Dr Backy explains it even makes it easier to understand for someone with a physics degree đ€.
Itâs confusing for everyone. No worries, bud. đ
@@thefourshowflip I resemble that remark, although my university physics was very long time ago a little after the first claims of gravity wave detection.
@@776281
Thatâs about the time I started upper division (3rd year) courses. đ€
Iâd be very interested to hear how LISA plans to keep spacecraft precisely half a wavelength of light offset over time. I know we have computers now to manage station-keeping, but thatâs a crazy amount of precision!
Seems like an impossible feat. Maybe they have a solution to track the distance? Maybe something like interference can be used to measure small changes simultaneously with the gravitational wave measurements?
Yeah, seems like they must have some way of compensating for offsets.
I was thinking the same thing. Plus how will they adjust for micrometeors striking the spacecraft. Most satellites wouldn't care, But this one needs ultra precision.
It's complicated -- I just read the concept on the LISA website and only grasp pieces of it -- but one very cool aspect of the mission is that the spacecraft each contains a "free fall" mass within it (i.e. it's not touching the spacecraft), and it's these masses that are in carefully configured stable orbits around the Sun, and the spacecraft (which are subject to thermal variations, and other effects that cause their orbits to wander) actively maintain their position around the masses. This allows the interferometry lasers to very accurately measures the distances between those masses unimpeded by any vibrations and wanderings, using techniques that are well established but are way too advanced for me to explain or understand!
There has already been a LISA Pathfinder mission which was successfully used as a test bed for new technology involved.
To start, the reference mirrors are mounted to "proof masses" and not the spacecraft itself. The spacecraft floats around the proof masses with a tunnel passing to the exterior through which the light can pass.
The proof masses are set in specific orbits around the Sun. The spacecraft floating around them prevents them from being disturbed by dust, solar radiation, and the like so that they will maintain their relative positions exactly (see Newton's first law).
The outer spacecraft will be disturbed but by using a set of position sensors (capacitive if I remember correctly) these will be detected relative the proof mass and corrected for.
So just like light or electromagnetic wave telescopes have a measurement range, LIGOs also have a measurement range for gravitational waves.
Yes. Sort of like antennas and radio waves. For FM radio (100 MHz, 3 meters wavelength) we have efficient, tuned antennas. For AM radio (1 MHz, 300 meters wavelength) any antenna you can actually build is too small to be very efficient.
@@michael.a.covington Actually efficient AM radio _transmitter_ antennas were built and they used to be the highest human constructions on Earth (see: en.wikipedia.org/wiki/Warsaw_radio_mast). But what might be (barely) practical for the transmitter was completely unpractical for radio receivers.
How do they know, at LIGO, that a black hole merger is the cause of their signal?
@@tabamal
If it was mergers of stars, we'd see significant amounts of radiation coming from the location of said merger.
@@TheMathias95 is LIGO directional?
I love your expressive nature. I am an introvert so learn a lot from programs like yours.
yeah I liked this video
Yeah I love her hotness too⊠I mean, expressive nature
I learned naught, naught, naught, ... naught.
Dr. Smethurst You are a joy to watch the enthusiasm you display in your information and presentation is a perk for sure. Keep up the great work.
LIGOâs engineering alone should have earned a Nobel.
I had no idea how a gravity wave detector worked before this. I have admire how the simple the concept of the detector is.
Amazing video, love your way of making scientific concepts tangible and easy to follow!
LISA is such an incredibly cool project. I hope I'm around to see it happen.
Space interferometry is the future. Iâm pumped.
I likely won't be. It's been such a great time to be alive for science, though!
It's nice to hear you sing at the end!
As per usual, a beautiful breakdown, Smethurst. Your ability to so effectively summarize technical material for us laypersons clearly demonstrates your understanding of the subject. Thanks! #keeplookinup
For some reason the issue with the too large wavelength of SMB mergers reminded me of Pratchett and Gaiman's Good Omens:
It might, or might not, have helped Anathema get a clear view of things if she'd been allowed to spot the very obvious reason why she couldn't see Adam's aura.
It was for the same reason that people in Trafalgar Square can't see England.
These Bloopers Reels you do it the end of the videos are awesome and priceless!!
I LOVE them⊠đđŒđđ€đŒ
Hi Dr. Becky! We saw you while watching PBS Nova s48 e18, Universe Revealed: Black Holes. Was a surprise Becky appearance we weren't expecting! Cheers!
I love those outtakes at the end!
So love the bloopers but wow this was a super short video this week.
I subscribed to your channel back when you only had about 8,000 subscribers and now that youâre totally famous I just want to tell you how happy I am that you havenât changed. Your intelligence and down to earth personality makes you one of my favorite channels.
Another amazingly concise explanation of something complicated!
Good morning from Canada Dr.Becky. I never knew you had such a wonderful singing voice, thank you for sharing it.
Great video with very clear explanation! I just want to thank you for that.
Well done. You made it simple enough that even I can understand. Thanks.
Thank you for breaking this down, Dr. Becky. I'd wondered about the supermassive black hole merger measurements! This explains it!
Awesome video Dr. Becky.
Thank you. You explained it so well. I hadnât understood that before
Thank you Dr. Becky, another wonderful video! It's also worth mentioning nature's detector which are pulsars and how Pulsar Timing Arrays detect the GWB and all other exotic sources :)
Very interesting!
(looking forward to hearing more about it)
Kind of early? Also tysm for the video dr.becky! I have been waiting for your upload for SO long
Love this channel!!! The Dr is awesome!!!!
This is a very interesting and impressive presentation, Dr. Becky. Thank you for your knowledge and expertise. This is far more interesting than the science and astronomy classes of the early 70's--80's classes that I remember. You are a inspiration to all females who want to pursue astrophysics or astronomy.
Nice explanation. Thank you.
A bundle of great info in this upload Becks.
Have to admit that it doesnât have much of an impact right now but the predicted gains when the space version of LIGO comes online itâll be very useful. What the info will give us Iâve no idea but it WILL be cool. đđđ
Thank you for the superb explanation of how LIGO works. It's the best I've heard because I think I actually understand it now.
Yeah I wish other explainors had her clarity
The gravitational wave song in the outtakes. So amazing.
Nicely done Becky, thank you!
What a fantastic video! Really amazing.
Thanks Dr Becky.
That was a good, clear explanation. I didn't know that about LIGO.
I love how well you can present such topics in ways non-scientists can follow =)
What practical applications can we attain (if any) from what the detection of these waves shows us?
I am just mesmerised by your knowledge and beauty â€ïžâ€ïž
Good day, Dr Becky video!
Cool Dr Becky! TFS, GB :)
Watching your videos helps me feel closer to my late uncle, who was an astrophysicist. Thank you for what you do Dr. Becky, and how you put it, so even us normies can understand. I appreciate what you do more than I can actually. So thank you
BRILLIANT! I understand now how LIGO works. Thanks Beky
I love space, but you make it even more lovable. May I suggest a video idea for the future?! A dedicated video where you explain the effects of gravity on time & space. How would it affect life expectancy if we were to live on Mars. Is space/time fabric quantum in nature and leading theories of what it may be! Thank you Becky!
Could be pretty easy to adjust, because of the setup, LIGO. Just a pair of headphones tapped into the detector, then adjust one of the reflectors ever so slightly, until no sound is heard. Like my cousin did with his satellite setup. He had no signal measuring device, so he put the TV on full blast, set the decoder to MTV (it was that long ago). Left a door open and went up to the roof to semi-randomly adjust the dish. When he heard Tina Turner, he tightened the bolts and was done.
I was just reading about LIGO a few days ago in Emily Levesque's book. Very intereesting alright.
That new LISA project sounds really exciting too. Off to read about it now.
I just found this channel the other day, and Iâm certainly glad I did. Iâve always been fascinated by space time, gravity, black holes etc. While Iâm not cool enough to hold a degree in astrophysics (let alone from Oxford), for some inexplicable reason, the effects of gravity on all things including light and space time just makes perfect sense to me. So, itâs nice to learn these things from someone who IS cool enough to hold a doctorate in astrophysics⊠from Oxford. Lol.
Well explained!!
Could you do a video about the Heliosphere? Why itâs there, what it does, what if it wasnât there, and what space is like beyond it? I could research it myself (and I plan to!) but I love the way you explain things and make it all make sense :)
@6:06 "on the piddly side".. one of sir patrick moore's favourite sayings i believeđ€
I was kind of hoping you would have have talked about the Final Parsec Problem.
In case you wondered why the length of the arms needs to be in the range of the wavelength⊠imagine youâre on a ship. A very looong wave is not causing any noticeable tilting because it just lifts the entire ship up and down. On the other hand, very short waves donât tilt your ship either, because your ship sits on top of many waves that average out. Itâs only a certain range inbetween where you get the effect of the wave lifting parts of your ship and thus tilt it. Hope this helps!
Oh wow, I had never heard of LISA. That is super cool!
Great explanation, as always, for those that don't typically follow this stuff. I really need to call attention to those sweet dance moves though!!!
Great information! I had always wondered about how LIGO could measure such a small disruption in space/time with our current technology. Electronics just are not fast enough to time light waves, and this setup is an amazing way to get around those limitations.
This leads me to one question that could be really cool to cover on a video. Since you mentioned how much more powerful the gravitational waves were in closer proximity to the merger, what would a person experience if close to a merger of 2 supermassive black holes?
look up spaghetification.
@@00BillyTorontoBill I wasn't speaking of being torn apart by the black holes gravity, but only the effect of the gravity waves if one was actually close enough to feel them.
INterestingly, i was listening to the FQXi podcast recently when they were talking about the new system of Optical Lattice clocks, which will have accuracy several orders of magnitude better timekeeping accuracy that the current caesium clocks in usage today. I note that one particular use for these has been mentioned for gravitational wave detection astronomy. But also may have uses in investigating quantum events, at the other end of the scale.
Will be interesting to see how this will impinge on the burgeoning world of gravitational wave astronomy.
Ohhh, that's really neat. Keeping a stopwatch for the giant wavelengths by measuring the teeny tiny wavelengths. Living in the future is pretty cool, I just wish I could call the past and tell me about it. And also which stocks to buy.
LISA will take the notion of distance dating to a new level.
Is distance dating a new COVID thing?
It will be like a love triangle
@@nickt9467
6 feet
@@Bassotronics hahaha
Itâs a threesome!
This was very good.
This is awesome and so accessible. Thanks Becky. Would love you to do a Reacts To video of Professor Brian Cox's new Universe series. I'm no expert so I'd love to hear the science behind all the claims he makes as hard fact. Plus the visuals are AWESOME! :)
Hello Dr. Becky! What size would a detector be to detect gravitational waves from the big bang? And are there any plans for one?
How does this BRILLIANT woman NOT have a 1million subs??
She's getting there -- it takes time when you trying to communicate real science and not trying to sensationalize everything.
I've been reading Janna Levin's book "Black Hole Blues" about LIGO. Fascinating.
Hmmm... I have a question, Dr. Becky. Changing the wavelength of the light used in Ligo... Would it change anything?
Hello Dear Doctor Becky.
Please go there and make great videos.
But till that time, thank you so much for this.
Good job Becky
It would have been good to comment on the MAGIS-100 and MAGIS-1000 experiments planned at Fermilab. According to Don Lincoln's video they are said to have the potential to see the gravitational waves before the merger of the black holes and/or neutrons stars that LIGO can see and should also see the merger of much larger black holes. I had heard of the European plans and the Fermilab plans, but I have never seen someone discusses all three gravitational wave detectors and puts everything into context.
Thanks for another fab video, Br.Becky.
Just one question, does doppler shift apply to gravitational waves?
Thanks đ
That's a great question! I hope Dr. Becky answers it!
I hope Dr. Becky chimes in too, but for the impatients, yes, every wave that moves at c speed experiments redshift. The details... Dr., help!!
A propagating wave (gravitational or electromagnetic) doesn't have an inherent frequency, nor a wavelength, both are entirely dependent on the reference from of the observer, so: yes.
2:08 Dr Becky gets all noughty.
Hi Dr. Becky, could you please make a video on Pulsar Timing Array?
I didn't realize that the 4 kilometer distance for the LIGO was about the wavelength of the gravitational waves, but that makes perfect sense. Detecting much longer wavelengths with three spacecraft is pretty impressive in scope....The engineering challenges have got to be insane. I hope they manage to pull that one off.
How would one go about keeping these three separate antenna's synced to each other across such a vast distance? And would de laser's divergence be a problem with them being so far apart?
The interference 'hack' of LIGO is one of my favourite things in recent science. I'm a musican turned engineer, and it still astonishes me how we when playing music, can play in tune, down extremely small differences in frequency, despite just using our ears. Then we can also marvel at strobe tuners, (the most accurate), that using the same pheonomenon as LIGO. Essemtially. we can make an extremely sensitie tuner by having one part of the display flicker at the frequency desired, and the other at the frequency recorded. By matching these, they stop interfering, and you're in tune.
very clearly explained. Its cool how the distance is adjusted so one arm of LIGO is exactly 1/2 wavelength longer than the other so there is no signal when no gravitational waves are present. What i didn't understand: Why can't LIGO detect mergers of supermassive black holes? I guess they also make spacetime stretch and contract so that the distances along LIGO's two arms vary. You said it had to do with the wavelengths which are much larger. Is it because the amount of stretching over that distance is far too small to cause a significant shift in the synching of the two waves? I.e. the amplitude of the gravitational wave reaches its maximum extent at a much greater distance (like millions of km instead of 4 km)? A visual aide would be super helpful to understand the concept.
I love this Becky
Jamming Dr. Becky, is the BEST.
Oh my god, a doctor Becky video earlier than usual thanks alot because I am from India and I used to wait till late night to see the video but today I can see it rn
Thanks again and the video is osmđđđđ€đ€
@Bobb Grimley my profound apologies for the greatest mistake mankind has ever made.
I am sorry and thanks alot for informing me
Truth be told , Nothing hit better than hearing you say "BRILLIANT" .đđđđ
The noise canceling headphone explanation makes me wonder if that's how the Kiowa Warrior helicopter does it.
You can still hear the helicopter, but all directionality of the sound is distorted / dispersed so that it sounds like it's coming from all around you.
And, by the time you spot the bubble, it would already be too late. Not only do they have visual eyes on you, they've had you on thermal long before then.
Training with them in the Army it was always a matter of I'm glad they're on our side. đ
I decided to click on your Toenail Moon t-shirt link on Spring hoping you had that in sticker form. The Galaxy in her eyes stickers are wonderful but I would also want a Toenail Moon sticker.
I would put them with my trust in science sticker
There's something I don't understand. If the laser interferometer can detect changes in space smaller than one proton, doesn't that mean that the mirrors need to be positioned also with a proton-sized precision? Also, with such small distances, doesn't quantum mechanics have anything to say?
Veritasium did a video with the LIGO director a couple of years ago that goes into this factor further than Dr. Becky had time for
From my understanding of laser interferometry (used commercially, part of my professional experience), the following applies.
As Becky explained, the light is split into two paths. When those two path are retro-reflected and re-combined, the constructive/destructive interference of the light waves creates an intensity. We never bothered to precisely set the differential paths as whatever is the baseline intensity can be arbitrarily set to "zero", but Becky states that LIGO did this and I have no reason to doubt this.
Then, as the intensity of light changes as a function of the path length change, the increment of distance measured is proportional to the wavelength of the monochromatic) light and variation in intensity.
The more precisely and reliably you can measure the change in intensity; the more accurately you can measure the distance.
Legless Legolas is gonna be my new gamer tag.
Looking forward to your video on the first detection of a super massive black hole merger come 2036 đ
Can you talk about the pursal timing array method to detect supermassive black hole merge? What is the principle of this method? And can you show the results until now and future of this method?
a counterintuitive and interesting fact!
How does something like LIGO get calibrated? Do they use high amplitude, short wavelength lasers? Getting any measurements correct accurate to 1E-16 just seems so terribly difficult. All so fascinating⊠thanks Dr Becky!
suggestion for next video subject: space topology and other source of gravity waves like voids, wormholes etc and how do you know or sure LIGO really dedect something ? any evidence exist about dedection results related gravity waves or something else ?
Well, as long as I watch your videos I won't over estimate my own brilliance. đ LISA sounds so amazingly clever, it makes me understand what a drudge I am.
With love and thanks, to Dr Becky.,. For the great presentation of head đ€Ż bending, scientific information. That you concisely pass on, so as us lesser mortals can take it. in ,đđŒđ€đȘđđŒđđŒâ€ïžđïž
There is one thing that not many videos that show the operation of LIGO mention when explaining the principle:
The animation nicely shows how the light can either cancel out or amplify, depending on the path length the light has taken. With half a wavelength of variation you get between zero (cancelling out) and full brightness.
However, the wavelength of light is of the order of 10^-7 m (hundreds of nanometer) while the measured changes are of the order of 10^-15 m as explained in the video.
So there is no such thing as half a wavelength of change! It is more like 10^-8 wavelength of change. That means the differences in light will be minute, and not so easy to measure as one would think watching the animation...
Oh, the best part is the part the bloopers :D
7:25 that's definitelly a nod to Matt from PBS Spacetime.
So how far apart and how many of these interferometer-satellites would one need to build up a 1080p image of the ripples produced by the super massive black hole at the centre of our galaxy?
Given the level of accuracy required and the lack of any kind of friction/air resistance, would things such as space dust, micro meteorites, solar wind etc, pose an issue for keeping the 3 separate craft the correct distance apart?
There is a upper and lower bound to waves. Electromagnetic waves and also compression waves ("gravitational"/sound). You can't get a shorter wavelength than a Planck meter. And you can't have waves with a wavelength that's larger than the universe. Meaning some stuff just doesn't work.
You can also describe a wave in frequency, not wavelength. But you can't go shorter than the Planck second or longer than the lifetime of the universe.
"destructive" interference is a flawed concept. Energy cannot be destroyed. So the energy of those "interfering" waves still goes somewhere.
Amazing video and alsoEasy to understand, thanks black-hole queen đ
2:00: Dr. Becky is a noughty, noughty girl.
Also, the thing about the different measurements of blackholes is that itâs not intrinsically âgravityâ that we see disturbed but the distribution of velocity mass. Bigger black holes diffuse less space when they co-merge because they can only occupy a certain amount of space smaller blackholes actually become larger as a result of co-mergency, bigger black holes just become more denseâŠ