Glad to see CTA featured in your video! A small correction: CTA has better gamma-ray angular resolution not because the array foot print is large in the traditional sense of diffraction-limited telescopes, but because the imaging atmospheric Cherenkov technique has the best angular resolution of any current gamma-ray detection techniques.
Politics have long been set aside at research conferences. Space exploration used to be a special area for cooperation, and I'm sad to see that fall apart (Russia leaving ISS, US refusing to work with China). Science is science, and it's the minimum we can do to work together.
@collindwebb I had the same question. @@TlalocTemporal then perhaps that implies that dark matter annihilation or milli-second pulsars are not only concentrated around the center of the galaxy, but as well distributed along the galactic spiral, which would give a wider spread of GeV excess around 0°/360° ?
Well of course. Why didn’t I think of that 😅😅. Thanks Dr Becky. My 84 year old father in law is a big fan. He does a pretty good job understanding your content, because you do such a good job sharing it with all of us. Thanks.
If a millisecond pulsar exists, then it's rotating once a millisecond. If it rotates once per millisecond, and its circumference is traveling at less than c, then it is less than 95 meters in diameter. And its escape velocity must be so high that a point on its circumference can go around it a thousand times a second without exceeding its escape velocity. This object less than 100 meters in diameter must be so dense that it has an escape velocity that allows something to travel all the way around it in a millisecond. That is more dense than quark stars are theorized to be by a factor of about three hundred. What would something like that be made of?
I don't know how you get the 95 *meters*, that is way too small. Light travels about 300 000 km per second, so 300 km per millisecond. That means a maximum diameter of about 95 *kilometers*.
I’ve been following science my whole life. One thing that is almost universal is that when a new gadget comes online to answer a question or improve resolution, it almost always generates more mysteries than it solves. I will predict this: there will be no resolution to the question of the excess GeV gamma rays. There will be strange excesses that aren’t explained by either model, some coming from completely unexpected directions. And there will be a conviction that more research is necessary.
In the distant future, scientists will study the videos of Dr. Becky and try to prove that she actually existed. Seems too good to be true. I'll vouch for her!😍
Aren't there three possibilities? Millisecond pulsars, dark matter annihilation or a combination of the two - which would be harder to confirm as the data would be neither properly smooth nor as clumped as it would be if the pulsars are solely responsible.
We so need a new metaphor for spin-up when rotating matter collapses. It's like the phrase "building blocks." It's time for another one to keep from overuse.
It's an intuitive explanation that literally anyone whatever their level of physics knowledge can understand and has probably experienced spinning around on a polished floor as a kid. If someone comes up with a BETTER explanation than that, which is highly unlikely, then it's time to switch. The explanation isn't for people who've heard the concept before, it's for people who HAVEN'T, and you absolutely SHOULDN'T fix it to the detriment of the people it's aimed at, to suit the whims of the people who it ISN'T aimed at.
Lost your drink? This is where it starts. Within years you will find yourself staring into the fridge at three AM with a hammer in one hand and a tin of cat food in the other and will be unable to clearly remember the sequence of events that led to this situation. I think I speak from experience. I can't remember.
I've worked developing sensors for high-energy photons. One of our greatest "curses" is Compton Scattering, where even a mono-energetic coherent source will see its spectrum blurred into a distribution of some sort by any intervening material, including the sensor itself! The distribution will be Gaussian if you are lucky, meaning you can then deconvolve the signal. If we subtract out the "model" galactic gammas from the Fermi observations, what is the energy distribution of the residual? Does it fit any known or expected distribution(s)? Or could it be a combination of different distributions, indicating multiple processes contributing to the excess? Subtracting spectra is fraught with error! Doing statistics on the difference of other statistics is not for the faint of heart. However, when done correctly, the results can be truly outstanding. In the case of one of my instruments, a seemingly so-so sensor suddenly became the best in its class due to its great acquisition statistics, which then permitted huge amounts of additional processing to be performed, leading to high-confidence results. In one case, it was a solid *derived* detection of electron-positron annihilation (generating a pair of 511 MeV gammas), which, when coincident in the detector (!!), yielded a 1.022 GeV detection, in an environment where it was not expected. What is Fermi *actually* measuring? Can we infer a more specific source from the "GeV excess"? I'd love to know how much "meat" there is on the bones of those Fermi observations.
@@Steelrat1994 That's sort of my point, what's the range of results their model will produce given the variability of everthing that has had the be measured before being included in the model.
I suspect that they assumed a shape for the curve based on math and then went for a best fit by scaling only. The black line is the result of their best fit.
I would assume that's a fit line. There won't be ertor bars, per se. They probably run a montecarlo style simulation and get a whole suite of lines. The black line is probably the median of the results.
The bigger the telescope, the higher the resolution. I worked in satellite manufacturing and based on the how many satellites are needed for other applications, it could be possible to make a combined "telescope" out of 100s of sensors piggybacking on those satellites. It will propel astronomy into a new age with unparalleled resolution and collection area. Please let me know if you're interested to discuss further. I can email you again with further details. 😊 I have previously sent 2 emails.
Idk man if the problem is that the black line on the graph doesn't fit the purple points... Just move the line up. Seriously though, it looks like the solution should apply everywhere not just at galactic nuclei
You didn’t mention the spectrum of the excess gamma rays. Annihilation of a dark matter particle should exhibit a very narrow peak corresponding to the mass of the particles. If the spectrum is spread out, it’s much less likely caused by dark matter annihilation.
Might depend on the relative speeds of the dark matter particles. Do our models provide insights on the velocities of dark matter particles in concentrations like the galactic center, or in distributions like the galactic halo? Even with improved technology, can we expect to find annihilations event in the galactic halo? Even if we can't see it, there should be plenty of dark matter there.
Dark matter is fun to speculate on. What if dark matter has lower energies at higher velocities. All we'd need to do is change "v squared" to "(c minus v) squared" in the Lorentz contractions of relativity. IDK if that could even work out, but if it's exactly wrong maybe we could apply it to dark energy. It's fun to play with the universe.
An interesting thought is: do the dark matter particles repel each other with something like the nuclear force at close ranges? Gravity pulls them together. If that is all that acted, I would expect a truly massive amount of them meeting each other and destroying each other. If there is a repelling force then the very high velocities at the center of the galaxy can work to smack them together. .... well at least it is interesting to me.
Each particle weighs next to nothing so they don't really notice each other's gravity, at least not on an individual level. They just fly past, and if they're very small (which they are), they almost always miss each other.
@@kensmith5694 this is interesting because they don’t seem to interact with electromagnetic particles so electromagnetic forces don’t act on them We know gravity does and EM doesn’t so honestly it’s a 50-50 shot that nuclear forces do lol For the record I’m not a physicist (yet) so take what I say with a large grain salt
Which also begs the question, wouldn't one see a trail of gamma ray emissions from the path of a rogue star passing through the dark matter cloud around the galaxy? Ideally, if there was a stellar mass black hole that was rogue and outside the galaxy, well good luck detecting it, but that might be one means. It'd accrete dark matter from clouds surrounding the galaxy and those particles would be drawn into an accretion disc of dark matter enough to be detected by eventual annihilation events. Not as high as in the galactic center, but high enough to allow detection from orbital gamma ray telescopes that were looking that way. Of course, ideally, we'd have such large gamma ray telescope arrays in space, where the atmosphere wouldn't interfere, given air's notorious and intense dislike of passing gamma radiation.
Gamma rays are created by matter antimatter annihilation, black holes generate fermions, just more matter than antimatter. The surviving fermions are neutrons in the form of neutron radiation which has minutes before it decays into protons due to beta decay. The free electrons cause some Thompson scattering of the gamma radiation. The more active the galactic nucleus the more fermions thrown free of the black hole. Fermions generated by inactive static black holes are constantly being consumed by the black hole.
A couple of thoughts I have: 1. What if the laws of physics are not homogenous throughout the universe? I know it is not something we could detect or verify, but it might go a long way towards explaining dark matter and dark energy and it would bring into question everything we try to measure at any appreciable distance. 2. Another thing that I haven't heard anything about, but I know it can't be an original thought (and I think you would have something to say about this considering your specialty): We have talked about black holes being at the center of most galaxies and they necessarily contribute to their structure. But what if we are limiting the scales that could exist? What if there are black holes between galaxies that we wouldn't be able to detect (because they would be truly dark since they wouldn't have many stars or other matter around to feed on, and therefore no accretion disk)? And what if these black holes are galaxy sized or even larger? i.e. what if a black hole was not only billions of times bigger than our sun, but instead have masses that exceed the mass of one or more entire galaxies? I think consideration of this might go some distance toward explaining dark matter and dark energy. What do you think? If you think it's enough for a video, then you may want to bring it up in a future Q&A video. I would really like to hear what you might say about these two ideas.
except we can observe atomic spectra everywhere, and those involve h, c, m_e, e, so you're left with G and k. BB radiation has k, h, c so it's pretty uniform from casually separate parts of the sky.
@@DrDeuteron I concede that, but the speed of light is one of the laws of physics that I am talking about may not be the same everywhere. If, say, the speed of light is faster in some places and slower in others, then it would throw off measurements where we assume the speed of light is constant. It sounds like you really know what you're talking about. What did you think of my gargantuan black hole theory?
@@jerrylarch6556 I don't know anything about primordial BH formation. The atomic physics stuff is required grad courses, but how would a giga BH form--rememebr, they are physically tiny and can't eat that much mass in 13.8B years, moreover, accretion disks lead to jets (quasars), which are observable.
The laws of physics (specifically the Lagrangian) being invariant under translation of positions corresponds to (local) conservation of momentum.. I think if the laws differed from place to place, this would allow for local violations of conservation of momentum? I think under GR, uh, it might be that we can take c to be constant across space almost as a definition/convention? Not sure of that though.
5:00 I wanna know about the gamma ray source(s) that is(are) moving in that time lapse shot! Is that a satellite reflecting gamma rays, a moon, or asteroid, something else?
it was only present at the beginning and end of the video and I thought it was pretty quiet and not at all irritating to me. On the real plus side, the voice quality is so much better than last week, sounds really good to me, Dr Becky, well done, whatever you've done with it this week, please just keep doing it! thanks.
Which videos were the ones where Dr. Becky went to that Antimatter Lab and the Grocery (@ 7:35) 🤔😆or were these clips filmed just for this video/spontaneously
Lisa Goodenough must get heartily sick of people joking that she should have been an engineer instead with that name. Which is why I'm not making that joke. 👀
this could also be warm dark matter gavins (GeV) and kevins (KeV). is the 2 left handed serile nuetrino annihilations. warm dark matter could be a proportion of dark matter, even with axions or wimps being the majority of dark matter
I had thought that the prime basis for positing dark matter was that the excess spin speed of galaxies could only be explained by a halo of gravitating particles mostly around the exterior of the visible galaxy. Of course, they could not interact with regular matter and energy as they interact with each other because the dark matter would then shroud all the galaxies from view, or at least obscure them. But this video said that the dark matter is clumped around the center of the galaxies much as ty[ical observable matter is. But would the dark matter then be able to provide the extra spin observed, if it is not a halo as was supposedly needed?
There are many different lines of evidence that point to the existence of dark matter, not just rotation curves. Those are just the easiest to explain, and one of the first to be found.
Observing something directly generally gives you much better data. To use the wind example again, you can see that there are air currents because of their effects on the trees, but you only have a vague sense of where they are and there's a time lag and the unknown stiffness of the branches and twisting of the leaves adds noise to the data that makes it hard to be precise... or you can stick your hand out the window and feel the wind and have a MUCH clearer idea of what's going on. Or you can think of it as trying to guess what an object is by looking at it vs looking at its shadow. Even if you guess from the shadow that it's a teapot, you have no idea what colour it is and no way of finding out.
hmmm - if dm collisions = k dm^2 (i.e. proportional to the square of dm density) and there are certain galactic interactions where the dm density is famously displaced from baryonic matter (aren’t there pairs like a “bullet” galaxy that is punching through another one?), you would expect to see a gamma excess coincident with that displaced dm density, no? … perhaps I should watch the rest of the video
@drbecky I am so confused by the recent excitement over the dark matter stars and the galactic center GeV excess. If the mass of the dark matter particles is in the GeV range, why would we have seen no evidence of this particle at the LHC? Is there something about dark matter particles that would prevent them from forming in the collision types at the LHC? Wouldn't a dark matter particle of that mass need to be taken into account in electroweak calculations to get the right results? If an interaction or decay birthed a GeV ghost particle that only interacted with the weak force, wouldn't we notice thr missing energy?
Have we seen an excess in GeV gamma rays from the Bullet Cluster, that maps the expected distribution of dark matter ? I thought measurements had lead to an unrealistically high annihilation cross-section ?
I'd hesitate, in early days, to claim that we've got a conclusive estimation of our lensing events, so the raised 25° 'gamma-region should/would resolve as rather more numerous & point-countable... Thanks.
big difference btw X and gamma rays is: X-rays are emitted as thermal blackbody radiation (in space, in nukes), but a 1 GeV gamma? That would require 12 Trillion K. That's hotter than quark gluon plasma, so you gotta come up with some kind of mechanism,
There are two important quantities when it comes to dark matter: mass and cross-section (and technically there's cross-section with nucleons and cross-section for self-annihilation). So it's possible that particle colliders may have ruled out that mass range but at higher cross-sections than what's shown here.
How do these new telescope observations plan to cope with an unknown and uneven amount of scatter/absorption by the milky way? Could this cause a smooth distribution to appear lumpy from our viewpoint?
1:43 The Galactic Centre Giga-Electron-Volt Excess is a wicked underground experimental prog-punk-electronica-metal-noise band and it is commonly found in dingy dive bars playing too loud and getting paid in drink tickets.
Can we just admit that the big bang, dark matter, expanding universe, dark energy and all that is unproven and we need to start from scratch. Also, what is the proof that time exists in other than a need for humans to track the changes in the physical universe.
How can we speak of dark matter annihilation when we don’t know what dark matter is ? This is hypothesis on top of hypothesis. Pretty muddy ground I would say.
Optical Telescopes on the moon would be great, and lower gravity means we could build them bigger! But Mars has an atmosphere, and any colonists won't be spending money on conservation getting started,, so we can only expect pollution to start increasing there. The moon is better for location and scenery, and would be way cheaper, but still way to expensive.
Technically, the frequency of light depends on your frame of reference. If we assume relativity is true then for any frequency, there is a reference frame in which a given light source emits light of that frequency. HOWEVER: if we are talking about, like, in the reference frame where the cosmic microwave background is like, balanced, there are two things called the “Schwinger limit” and the “Greisen-Zatsepin-Kuzmin limit” (“GZK limit”). The latter is an energy above which protons with that much kinetic energy in the aforementioned reference frame, are expected to be significantly slowed down over time due to interacting with the microwave background radiation. Of course, that’s for protons, not photons. The Schwinger limit is a value of field strength (in the center of momentum frame) for the electric field beyond which non-linear effects start being significant. I suspect that if you have light at high enough frequency in our frame, then in the center of momentum frame for it and the microwave background radiation going in the opposite direction, it will still have enough field strength that it would interact, and, this could put an effective limit on the frequency? I’m not totally sure though,
interesting. i have just come SpaceTime's shallow dive into the possibility that primordial black holes might be the explanation for dark matter, to this... today is dark matter day, for me at least.
6:20 I hate to ask but... it looks like there's a lot of discrepancies across all the data, with nearly all of it in a positive bias. It almost feels like a 20-50%, and when you put the modelling at 350, the real value looks about 500, that's clearly a proportionate "underestimate" to what's happening across the data.
Normal matter churning around a he black hole at the centre emits high energy radiation usually. Could you let me know how this possibility is ruled out.
7:55 : hm, I would expect that if dark matter particles have antiparticle counterparts they can annihilate with, then, if this annihilation directly produced gamma rays (photons), that would imply that the dark matter particles directly interact with light. Which…, idk, I guess for the particles to work as dark matter, this interaction with photons would have to be pretty weak? Maybe if instead they produced some other pair of particles when they annihilated, and *those* particles then interacted with stuff, maybe one of them annihilating with something, and thereby producing gamma rays?
The production of particles in annihilation reactions isn't due to interacting with photons, it's the energy of the particles being transformed This is the same principle behind the LHC smashing protons together - the exact properties of the proton don't really matter, its just the amount of energy that can be delivered into a region of space in an instant in order for different masses of particles to be generated
Shouldn't 'annihilation' events all have the exact same energy since they all have the same cause -- thus, a very sharp energy peak? But, the video implies that the energy is smeared out. Wouldn't that rule out dark matter particles?
I’m not a particle physicist, but why should dark matter particles annihilate each other if they are their own antiparticle? A counter example of this is the photon which is its own antiparticle, and they absolutely don’t annihilate each other. From a brief google search particles can annihilate each other if one of the quantum numbers that describe them are opposite. E.g. the charge of an electron and a positron. So in the case of dark matter if they all have the same quantum numbers, how can they annihilate? I.e why isn’t this basically like the case of the photon?
Does the spectrum of the gamma rays narrow down possible dark matter models? It seems like it would imply a possible range of masses for dark matter particles for example.
Are the specific frequencies/wavelengths of the gamma rays produced by the annihilation of the black matter particles expected to be identical to that of the millimetre pulsar gamma rays? If they are not, are we unable to distinguish between them due to our current instruments or due to redshift and the distance not being known so that we only observe a distribution of gamma rays over a small spectrum of frequencies?
Oh, and thank you for these youtube clips that allow me a glimpse back into some of the interesting physics that I miss since leaving academia so long ago.
It seems more likely that our prediction was just bad. The shape of the graph is spot on but the values are off. Math error is way more likely than an exotic form of matter that is its own antiparticle.
Ok, but what if your best guess for what antimatter is, already involves it being its own antiparticle for other reasons? The antiparticle of the photon is the photon, so “is its own antiparticle” doesn’t seem all that exotic to me.
hi! if the gamma ray photons are dark matter collisions, what is the mass that's implied and is it a mass that's been ruled out any other way like in an accelerator? would you need to correct for the kinetic energy of the particles or are they not moving fast enough?
![Felix "Unfair" | [Stray Kids : SKZ-PLAYER]](http://i.ytimg.com/vi/Oswujxm2Ag0/mqdefault.jpg)
I enjoy seeing the faces of the different paper authors and contributors when have their work on the screen
Yeah, and it gives a bit of additional "credits", nice touch from becky
Yeah me too, I think it's a nice touch
Glad to see CTA featured in your video! A small correction: CTA has better gamma-ray angular resolution not because the array foot print is large in the traditional sense of diffraction-limited telescopes, but because the imaging atmospheric Cherenkov technique has the best angular resolution of any current gamma-ray detection techniques.
All this gamma ray observing hardware owes a debt to my hiking astronomer friend, Mark Lang.
Embudo forever, Mark.
I am absolutely charmed by Lisa Goodenough's name.
Right? It has GOT to produce so many puns :D
One of the important inventors of lithium ion batteries is John B. Goodenough which is just hilarious.
I think we all know that an excess of gamma rays can lead to too many Hulks.
and Minions.
This is one of those cases where science just works so well together to find meaning for a mystery. Loved the video as always Becky!
Politics have long been set aside at research conferences. Space exploration used to be a special area for cooperation, and I'm sad to see that fall apart (Russia leaving ISS, US refusing to work with China). Science is science, and it's the minimum we can do to work together.
Loved your talk today at UvA, your research is very interesting
Something creating gamma light has to be pretty powerful.
Fascinating subject Dr. Becky, thank you and thanks to Sam too. Love your work.
@ about 6:00 what is the spike at 0/360 coming from? That also looks like it is above expected.
I'd guess the Milly Way in the other direction. It's not a galactic center, but it's still way denser than intergalactic space.
@collindwebb I had the same question.
@@TlalocTemporal then perhaps that implies that dark matter annihilation or milli-second pulsars are not only concentrated around the center of the galaxy, but as well distributed along the galactic spiral, which would give a wider spread of GeV excess around 0°/360° ?
Well of course. Why didn’t I think of that 😅😅. Thanks Dr Becky. My 84 year old father in law is a big fan. He does a pretty good job understanding your content, because you do such a good job sharing it with all of us. Thanks.
In that figure 3, it looks like there’s more gamma rays detected everywhere than expected, not just the peak in the center 6:16
Another interesting talk highlighting a important unresolved question, but this time with prospects of a resolution in the near future.
Thanks for all the info, dr. Becky! 😊
Stay safe there with your family! 🖖😊
Wow I love it when things just fit together like this, it is so cool and exciting
Either explanation is pretty mind blowing honestly
Terrific episode. Thanx 💙🌻💙
If a millisecond pulsar exists, then it's rotating once a millisecond.
If it rotates once per millisecond, and its circumference is traveling at less than c, then it is less than 95 meters in diameter.
And its escape velocity must be so high that a point on its circumference can go around it a thousand times a second without exceeding its escape velocity.
This object less than 100 meters in diameter must be so dense that it has an escape velocity that allows something to travel all the way around it in a millisecond.
That is more dense than quark stars are theorized to be by a factor of about three hundred. What would something like that be made of?
I don't know how you get the 95 *meters*, that is way too small. Light travels about 300 000 km per second, so 300 km per millisecond. That means a maximum diameter of about 95 *kilometers*.
Yosmite is a two hour drive from my home nice to see your sweatshirt
I’ve been following science my whole life. One thing that is almost universal is that when a new gadget comes online to answer a question or improve resolution, it almost always generates more mysteries than it solves.
I will predict this: there will be no resolution to the question of the excess GeV gamma rays. There will be strange excesses that aren’t explained by either model, some coming from completely unexpected directions. And there will be a conviction that more research is necessary.
Very exciting news! I can't wait to see how this turns out.
My guess is milli-second pulsars. Based on absolutely nothing.
We're all armchair scientists here, I bet on the same with the same evidence on hand
An answer to Dark Matter.... that would be very nice tho. It would help us figure out the type of DM detector to focus on.
That's a pretty sensational last statement after the "if", Doc.
16:19 It is called number. Singular and plural are grammatical numbers.
@@JdeBP thank you! I had it on the tip of my tongue.
Great explanation, as always, Dr. Becky! Love your videos!
Gonna have to call it "not so dark matter" going forwards.
What a brilliant video, I have subscribed to you. Fantastic explanation, thank you.
Love the blips at the end of the videos, especially when you see how fleeting Dr. Becky’s attention can be 😂
What a coincidence! MIT Prof. Tracy Slatyer has been visiting IISc and I had so many stimulated discussions with her on this exact topic! 😂
In the distant future, scientists will study the videos of Dr. Becky and try to prove that she actually existed. Seems too good to be true. I'll vouch for her!😍
Thanks Dr. Becky
Loving the Yosemite sweatshirt, Becky! It's a majestic place to visit.
Aren't there three possibilities? Millisecond pulsars, dark matter annihilation or a combination of the two - which would be harder to confirm as the data would be neither properly smooth nor as clumped as it would be if the pulsars are solely responsible.
Congratulations! ❤
We so need a new metaphor for spin-up when rotating matter collapses. It's like the phrase "building blocks." It's time for another one to keep from overuse.
Don’t need to fix what isn’t broken. If the analogy works, adding complexity isn’t smart 👀
It's an intuitive explanation that literally anyone whatever their level of physics knowledge can understand and has probably experienced spinning around on a polished floor as a kid. If someone comes up with a BETTER explanation than that, which is highly unlikely, then it's time to switch. The explanation isn't for people who've heard the concept before, it's for people who HAVEN'T, and you absolutely SHOULDN'T fix it to the detriment of the people it's aimed at, to suit the whims of the people who it ISN'T aimed at.
Lost your drink? This is where it starts.
Within years you will find yourself staring into the fridge at three AM with a hammer in one hand and a tin of cat food in the other and will be unable to clearly remember the sequence of events that led to this situation.
I think I speak from experience. I can't remember.
Love the Yosemite sweat shirt
Thank you Dr. Becky. Almost feel that I understand this after your explanation. (although I know I don't really understand it.)
Great video follow you in Astrophysics
Next time you visit California try Mount Wilson. Technical presentations are frequently performed. I think your contribution would be great.
Cheers from the Pacific West Coast of Canada.
Say hi to Fraser for me
I've worked developing sensors for high-energy photons. One of our greatest "curses" is Compton Scattering, where even a mono-energetic coherent source will see its spectrum blurred into a distribution of some sort by any intervening material, including the sensor itself! The distribution will be Gaussian if you are lucky, meaning you can then deconvolve the signal.
If we subtract out the "model" galactic gammas from the Fermi observations, what is the energy distribution of the residual? Does it fit any known or expected distribution(s)? Or could it be a combination of different distributions, indicating multiple processes contributing to the excess?
Subtracting spectra is fraught with error! Doing statistics on the difference of other statistics is not for the faint of heart. However, when done correctly, the results can be truly outstanding. In the case of one of my instruments, a seemingly so-so sensor suddenly became the best in its class due to its great acquisition statistics, which then permitted huge amounts of additional processing to be performed, leading to high-confidence results. In one case, it was a solid *derived* detection of electron-positron annihilation (generating a pair of 511 MeV gammas), which, when coincident in the detector (!!), yielded a 1.022 GeV detection, in an environment where it was not expected.
What is Fermi *actually* measuring? Can we infer a more specific source from the "GeV excess"? I'd love to know how much "meat" there is on the bones of those Fermi observations.
6:00 What are the error bars on the black line?
None, it's what their model predicts. If that line was within the error bars of the measurements, then there would be no mystery.
@@Steelrat1994 That's sort of my point, what's the range of results their model will produce given the variability of everthing that has had the be measured before being included in the model.
I suspect that they assumed a shape for the curve based on math and then went for a best fit by scaling only. The black line is the result of their best fit.
I would assume that's a fit line. There won't be ertor bars, per se. They probably run a montecarlo style simulation and get a whole suite of lines. The black line is probably the median of the results.
The bigger the telescope, the higher the resolution. I worked in satellite manufacturing and based on the how many satellites are needed for other applications, it could be possible to make a combined "telescope" out of 100s of sensors piggybacking on those satellites. It will propel astronomy into a new age with unparalleled resolution and collection area. Please let me know if you're interested to discuss further. I can email you again with further details. 😊
I have previously sent 2 emails.
Idk man if the problem is that the black line on the graph doesn't fit the purple points...
Just move the line up.
Seriously though, it looks like the solution should apply everywhere not just at galactic nuclei
Interesting, thanks for the info
OMG I used to get nautilus when it was a multimedia data CD with all sorts of articles and movies and audio clips
Just had to comment to say "Goodenough" is an amazing last name
Guessing they've ruled out a sensor/hardware issue on the satellite?
With all this Gamma Ray talk.
I was kinda expecting a Kai Hansen cameo. 🙂
Why not The Incredible Hulk? Why are gamma rays green?
What was the moving object in the gamma ray pictures at 3:49?
The Sun!
I am excited we are getting to the point we're we can resolve key questions about dark matter.
She misled you with that final pitch. If...
You didn’t mention the spectrum of the excess gamma rays. Annihilation of a dark matter particle should exhibit a very narrow peak corresponding to the mass of the particles. If the spectrum is spread out, it’s much less likely caused by dark matter annihilation.
Might depend on the relative speeds of the dark matter particles. Do our models provide insights on the velocities of dark matter particles in concentrations like the galactic center, or in distributions like the galactic halo? Even with improved technology, can we expect to find annihilations event in the galactic halo? Even if we can't see it, there should be plenty of dark matter there.
Dark matter is fun to speculate on. What if dark matter has lower energies at higher velocities. All we'd need to do is change "v squared" to "(c minus v) squared" in the Lorentz contractions of relativity. IDK if that could even work out, but if it's exactly wrong maybe we could apply it to dark energy. It's fun to play with the universe.
An interesting thought is: do the dark matter particles repel each other with something like the nuclear force at close ranges? Gravity pulls them together. If that is all that acted, I would expect a truly massive amount of them meeting each other and destroying each other. If there is a repelling force then the very high velocities at the center of the galaxy can work to smack them together.
.... well at least it is interesting to me.
Each particle weighs next to nothing so they don't really notice each other's gravity, at least not on an individual level. They just fly past, and if they're very small (which they are), they almost always miss each other.
@@kensmith5694 this is interesting because they don’t seem to interact with electromagnetic particles so electromagnetic forces don’t act on them
We know gravity does and EM doesn’t so honestly it’s a 50-50 shot that nuclear forces do lol
For the record I’m not a physicist (yet) so take what I say with a large grain salt
@@karanthakker7434 My bet would be the weak force doesn't and the strong one does. Electromagnetic and weak force unify sort of easily.
@@Hailfire08 I am assuming there are a lot of them. Low odds things happen a lot when you have huge numbers
Which also begs the question, wouldn't one see a trail of gamma ray emissions from the path of a rogue star passing through the dark matter cloud around the galaxy? Ideally, if there was a stellar mass black hole that was rogue and outside the galaxy, well good luck detecting it, but that might be one means. It'd accrete dark matter from clouds surrounding the galaxy and those particles would be drawn into an accretion disc of dark matter enough to be detected by eventual annihilation events. Not as high as in the galactic center, but high enough to allow detection from orbital gamma ray telescopes that were looking that way.
Of course, ideally, we'd have such large gamma ray telescope arrays in space, where the atmosphere wouldn't interfere, given air's notorious and intense dislike of passing gamma radiation.
What the hell is wrong with the comments section
U-tube being u-tube.
Lord of people having no idea and that makes them uncomfortable so they inflict that on us
is it always this bad? seriously!
What do you mean? What sort of thing do you observe in the comments?
They fired the host and replaced her with the producer.
Gamma rays are created by matter antimatter annihilation, black holes generate fermions, just more matter than antimatter. The surviving fermions are neutrons in the form of neutron radiation which has minutes before it decays into protons due to beta decay. The free electrons cause some Thompson scattering of the gamma radiation. The more active the galactic nucleus the more fermions thrown free of the black hole. Fermions generated by inactive static black holes are constantly being consumed by the black hole.
A couple of thoughts I have: 1. What if the laws of physics are not homogenous throughout the universe? I know it is not something we could detect or verify, but it might go a long way towards explaining dark matter and dark energy and it would bring into question everything we try to measure at any appreciable distance. 2. Another thing that I haven't heard anything about, but I know it can't be an original thought (and I think you would have something to say about this considering your specialty): We have talked about black holes being at the center of most galaxies and they necessarily contribute to their structure. But what if we are limiting the scales that could exist? What if there are black holes between galaxies that we wouldn't be able to detect (because they would be truly dark since they wouldn't have many stars or other matter around to feed on, and therefore no accretion disk)? And what if these black holes are galaxy sized or even larger? i.e. what if a black hole was not only billions of times bigger than our sun, but instead have masses that exceed the mass of one or more entire galaxies? I think consideration of this might go some distance toward explaining dark matter and dark energy. What do you think? If you think it's enough for a video, then you may want to bring it up in a future Q&A video. I would really like to hear what you might say about these two ideas.
except we can observe atomic spectra everywhere, and those involve h, c, m_e, e, so you're left with G and k. BB radiation has k, h, c so it's pretty uniform from casually separate parts of the sky.
@@DrDeuteron I concede that, but the speed of light is one of the laws of physics that I am talking about may not be the same everywhere. If, say, the speed of light is faster in some places and slower in others, then it would throw off measurements where we assume the speed of light is constant. It sounds like you really know what you're talking about. What did you think of my gargantuan black hole theory?
@@jerrylarch6556 I don't know anything about primordial BH formation. The atomic physics stuff is required grad courses, but how would a giga BH form--rememebr, they are physically tiny and can't eat that much mass in 13.8B years, moreover, accretion disks lead to jets (quasars), which are observable.
The laws of physics (specifically the Lagrangian) being invariant under translation of positions corresponds to (local) conservation of momentum..
I think if the laws differed from place to place, this would allow for local violations of conservation of momentum?
I think under GR, uh, it might be that we can take c to be constant across space almost as a definition/convention? Not sure of that though.
5:00 I wanna know about the gamma ray source(s) that is(are) moving in that time lapse shot! Is that a satellite reflecting gamma rays, a moon, or asteroid, something else?
Interpreted the situation as the decompression of particles (Galaxy size collection)
Long-time viewer: I don't mind the new music, but I thought it was a bit loud in terms of balance, for what it's worth.
it was only present at the beginning and end of the video and I thought it was pretty quiet and not at all irritating to me. On the real plus side, the voice quality is so much better than last week, sounds really good to me, Dr Becky, well done, whatever you've done with it this week, please just keep doing it! thanks.
Your GeV Excess chart shows an excess in the center as well as to the left and right extremes. Could this be some kind of measurement distortion?
Which videos were the ones where Dr. Becky went to that Antimatter Lab and the Grocery (@ 7:35) 🤔😆or were these clips filmed just for this video/spontaneously
Where is the cat? You teased us with your cat for the last few months. I want to see him/her.
Lisa Goodenough must get heartily sick of people joking that she should have been an engineer instead with that name. Which is why I'm not making that joke. 👀
Funny enough, the Dutch, Westerbork astronomers, made quite the discovery regarding the billions of years old flashes of lights from neutron stars..
this could also be warm dark matter gavins (GeV) and kevins (KeV). is the 2 left handed serile nuetrino annihilations. warm dark matter could be a proportion of dark matter, even with axions or wimps being the majority of dark matter
I had thought that the prime basis for positing dark matter was that the excess spin speed of galaxies could only be explained by a halo of gravitating particles mostly around the exterior of the visible galaxy. Of course, they could not interact with regular matter and energy as they interact with each other because the dark matter would then shroud all the galaxies from view, or at least obscure them. But this video said that the dark matter is clumped around the center of the galaxies much as ty[ical observable matter is. But would the dark matter then be able to provide the extra spin observed, if it is not a halo as was supposedly needed?
There are many different lines of evidence that point to the existence of dark matter, not just rotation curves. Those are just the easiest to explain, and one of the first to be found.
Does it matter if we detect dark matter directly or indirectly? Surely the only important question is what is it exactly.
Observing something directly generally gives you much better data. To use the wind example again, you can see that there are air currents because of their effects on the trees, but you only have a vague sense of where they are and there's a time lag and the unknown stiffness of the branches and twisting of the leaves adds noise to the data that makes it hard to be precise... or you can stick your hand out the window and feel the wind and have a MUCH clearer idea of what's going on.
Or you can think of it as trying to guess what an object is by looking at it vs looking at its shadow. Even if you guess from the shadow that it's a teapot, you have no idea what colour it is and no way of finding out.
hmmm - if dm collisions = k dm^2 (i.e. proportional to the square of dm density) and there are certain galactic interactions where the dm density is famously displaced from baryonic matter (aren’t there pairs like a “bullet” galaxy that is punching through another one?), you would expect to see a gamma excess coincident with that displaced dm density, no? … perhaps I should watch the rest of the video
Special Request:
Yearly Compilation of Bloopers
What's the source that moves in an arc at the top from right to left?
@drbecky I am so confused by the recent excitement over the dark matter stars and the galactic center GeV excess. If the mass of the dark matter particles is in the GeV range, why would we have seen no evidence of this particle at the LHC? Is there something about dark matter particles that would prevent them from forming in the collision types at the LHC? Wouldn't a dark matter particle of that mass need to be taken into account in electroweak calculations to get the right results? If an interaction or decay birthed a GeV ghost particle that only interacted with the weak force, wouldn't we notice thr missing energy?
Have we seen an excess in GeV gamma rays from the Bullet Cluster, that maps the expected distribution of dark matter ? I thought measurements had lead to an unrealistically high annihilation cross-section ?
I'd hesitate, in early days, to claim that we've got a conclusive estimation of our lensing events, so the raised 25° 'gamma-region should/would resolve as rather more numerous & point-countable...
Thanks.
big difference btw X and gamma rays is: X-rays are emitted as thermal blackbody radiation (in space, in nukes), but a 1 GeV gamma? That would require 12 Trillion K. That's hotter than quark gluon plasma, so you gotta come up with some kind of mechanism,
At 9:50, the mass of the dark matter particle is estimated at 7-10 Gev. Hasn't this been ruled out by experiments in partile colliders?
Easy enough to look up
There are two important quantities when it comes to dark matter: mass and cross-section (and technically there's cross-section with nucleons and cross-section for self-annihilation). So it's possible that particle colliders may have ruled out that mass range but at higher cross-sections than what's shown here.
How do these new telescope observations plan to cope with an unknown and uneven amount of scatter/absorption by the milky way? Could this cause a smooth distribution to appear lumpy from our viewpoint?
1:43
The Galactic Centre Giga-Electron-Volt Excess is a wicked underground experimental prog-punk-electronica-metal-noise band and it is commonly found in dingy dive bars playing too loud and getting paid in drink tickets.
Can we just admit that the big bang, dark matter, expanding universe, dark energy and all that is unproven and we need to start from scratch. Also, what is the proof that time exists in other than a need for humans to track the changes in the physical universe.
How can we speak of dark matter annihilation when we don’t know what dark matter is ? This is hypothesis on top of hypothesis. Pretty muddy ground I would say.
We don't know which thing dark matter is, but we know several things it could be. Exploring different options is how you get to a better understanding
It involves a hypothesis about the kind of thing dark matter is.
@drdca8263 to elaborate, one of the kinds of things we know it probably is based on process of elimination
can you please do a video on Quantized Inertia? All this talk about Dark Matter, MOND, but no video on QI?
Dr. Becky - serious question. What if we put telescopes on Mars or the Moon where there is no atmosphere? can we get better images?
Optical
Telescopes on the moon would be great, and lower gravity means we could build them bigger! But Mars has an atmosphere, and any colonists won't be spending money on conservation getting started,, so we can only expect pollution to start increasing there. The moon is better for location and scenery, and would be way cheaper, but still way to expensive.
Is there a maximum possible frequency of light? Planck-length wavelength? Something to do with opacity of space?
Technically, the frequency of light depends on your frame of reference. If we assume relativity is true then for any frequency, there is a reference frame in which a given light source emits light of that frequency.
HOWEVER: if we are talking about, like, in the reference frame where the cosmic microwave background is like, balanced,
there are two things called the “Schwinger limit” and the “Greisen-Zatsepin-Kuzmin limit” (“GZK limit”).
The latter is an energy above which protons with that much kinetic energy in the aforementioned reference frame, are expected to be significantly slowed down over time due to interacting with the microwave background radiation.
Of course, that’s for protons, not photons.
The Schwinger limit is a value of field strength (in the center of momentum frame) for the electric field beyond which non-linear effects start being significant.
I suspect that if you have light at high enough frequency in our frame, then in the center of momentum frame for it and the microwave background radiation going in the opposite direction, it will still have enough field strength that it would interact, and, this could put an effective limit on the frequency?
I’m not totally sure though,
interesting.
i have just come SpaceTime's shallow dive into the possibility
that primordial black holes might be the explanation for dark matter,
to this...
today is dark matter day, for me at least.
What interaction mediates the dark matter annihilation?
6:20 I hate to ask but... it looks like there's a lot of discrepancies across all the data, with nearly all of it in a positive bias. It almost feels like a 20-50%, and when you put the modelling at 350, the real value looks about 500, that's clearly a proportionate "underestimate" to what's happening across the data.
0:43 Clearly dark matter is Element Zero. 😃
I'm Commander Shepard, and this is my favourite comment 😁
Normal matter churning around a he black hole at the centre emits high energy radiation usually. Could you let me know how this possibility is ruled out.
Sagittarius A* isn't very active, so it can't explain these gamma rays
7:55 : hm, I would expect that if dark matter particles have antiparticle counterparts they can annihilate with, then, if this annihilation directly produced gamma rays (photons), that would imply that the dark matter particles directly interact with light.
Which…,
idk, I guess for the particles to work as dark matter, this interaction with photons would have to be pretty weak?
Maybe if instead they produced some other pair of particles when they annihilated, and *those* particles then interacted with stuff, maybe one of them annihilating with something, and thereby producing gamma rays?
The production of particles in annihilation reactions isn't due to interacting with photons, it's the energy of the particles being transformed
This is the same principle behind the LHC smashing protons together - the exact properties of the proton don't really matter, its just the amount of energy that can be delivered into a region of space in an instant in order for different masses of particles to be generated
Shouldn't 'annihilation' events all have the exact same energy since they all have the same cause -- thus, a very sharp energy peak? But, the video implies that the energy is smeared out. Wouldn't that rule out dark matter particles?
I’m not a particle physicist, but why should dark matter particles annihilate each other if they are their own antiparticle? A counter example of this is the photon which is its own antiparticle, and they absolutely don’t annihilate each other.
From a brief google search particles can annihilate each other if one of the quantum numbers that describe them are opposite. E.g. the charge of an electron and a positron. So in the case of dark matter if they all have the same quantum numbers, how can they annihilate? I.e why isn’t this basically like the case of the photon?
Does the spectrum of the gamma rays narrow down possible dark matter models? It seems like it would imply a possible range of masses for dark matter particles for example.
Extragalactic sources are excluded as an explanation? This could be also i.e. big galaxy cluster hidden by our Galxy nuclei.
Are the specific frequencies/wavelengths of the gamma rays produced by the annihilation of the black matter particles expected to be identical to that of the millimetre pulsar gamma rays? If they are not, are we unable to distinguish between them due to our current instruments or due to redshift and the distance not being known so that we only observe a distribution of gamma rays over a small spectrum of frequencies?
Oh, and thank you for these youtube clips that allow me a glimpse back into some of the interesting physics that I miss since leaving academia so long ago.
Didn't we get an excess from the AMS II as well supporting the DM origin of the excesses?
It seems more likely that our prediction was just bad. The shape of the graph is spot on but the values are off. Math error is way more likely than an exotic form of matter that is its own antiparticle.
Right? 6:20 . It looks like the measures are 20-50% above prediction for most of the data, including the center.
Ok, but what if your best guess for what antimatter is, already involves it being its own antiparticle for other reasons?
The antiparticle of the photon is the photon, so “is its own antiparticle” doesn’t seem all that exotic to me.
It's neither. It's strangelet decay.
did you ever find that drink :D i do that all the time.
hi! if the gamma ray photons are dark matter collisions, what is the mass that's implied and is it a mass that's been ruled out any other way like in an accelerator? would you need to correct for the kinetic energy of the particles or are they not moving fast enough?
the obvious answer is M = 500 MeV, which is way to high for thermal doppler shifts to be a problem.
Do particles that are their own antimatter ever spontaneously annihilate? If not, why should they annihilate on contact with another?
Conservation laws that are broken if one decays vs not if two annihilate
the heliospheric current sheet scales up. the galactic current sheet! nothing to do with dark matter.
Incidentally, I've subscribed to _Nautilus_ starting with issue 1. Still am.