No Dark Matter = Proof of Dark Matter?

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We've been failing to detect dark matter for decades but finally the latest failure to detect Dark Matter may have actually proved its existence one of these is true either most of the matter in the universe is invisible and formed by something not explained by modern particle physics or our understanding of gravity is completely broken the debate over which is true has raged for decades but may finally have been resolved in an unlikely way the proof that Dark Matter exists and really is an exotic unknown substance may have come from the discovery of two galaxies that appear to have no dark matter at all today on spacetime journal Club we'll look at the papers that reveal this discovery the effect of dark matter who was first noticed in 1933 when the legendary Swiss astrophysicists Fritz Zwicky noticed that the galaxies in the Coma Cluster were moving too quickly to remain gravitationally bound within that cluster he guessed the presence of Dunkel materia a dark matter invisible to the telescope but whose gravitational effect held the cluster together as with many of his wiki's predictions like the existence of neutron stars and gravitational lensing this wasn't taken seriously until decades later the hunt for dark matter began in earnest after the early 70s when Vera Rubin discovered that the rotation rates of spiral galaxies were too fast given the mass of their visible stars alone they should throw themselves to pieces spinning that quickly that is unless a gravitational force of unseen origin was holding them together since the 1970s generations of astronomers have searched for the origin of dark matter gradually ruling out the possibilities if it were dust or gas we'd see it's obscuring effect on light passing through it if it were dark compact bodies like failed stars or stellar corpses or primordial black holes then we'd see the warping of of more distant stars in their gravitational fields in other words we'd see their gravitational lensing all known particles of the standard model of particle physics have likewise been ruled out if dark matter really is a type of matter then it must be an unknown type generations of experiments to find this particle have also failed to locate the exotic dark matter particle so far this troubled quest has inspired theorists to explore another possibility what if the discrepancies in the orbits within galaxies and clusters is not due to an unknown source of gravity but due to a failure of gravitational theory itself the first such proposal was Mons modified Newtonian dynamics proposed by Mordecai Milgram in the early 80s the idea is the Newton's law of universal gravitation might change between short distances like within the solar system and large distances like entire galaxies and clusters such a proposal doesn't just modify Newton's gravity but also requires modification of Einstein's general relativity over the years various efforts have been made to refine and justify such a modification and new proposals keep popping up like the quantized inertia and dark fluid that last one is something we covered recently but no consistent theory has appeared a few points have come out in favor of the dark matter as mater hypothesis versus the modified gravity schemes there's gravitational lensing the warping of light from more distant objects and due to the gravitational fields of galaxies and clusters this has given us an independent measure of the mass of those objects and those masses were the same as measured from the orbits the Cosmic Microwave Background fluctuations also give us a measurement of the relative amount of dark matter in the early universe compared to atoms once again roughly consistent with what we measure from other methods modified gravity theories had to hard to keep up with the mounting evidence that dark matter looks like actual physical stuff but still we have an impasse astronomers and particle physicists can't find the matter that dark matter is made of while those who would like to overthrow the underlying theory of gravity struggle to make their models fit all the observational evidence but there's one feature common to almost all modified gravity models that could falsify all of them they pin gravity on the baryons they say that most of the gravity in the universe comes from normal stuff like stars and gas in particular the protons and neutrons they contain their baryons that gravity then follows different rules at different distances giving the illusion of there being more baryonic matter than there really is in this scheme baryons on galactic size scales should always produce the effect of dark matter dark matter and baryons should never be observed separately the first piece of evidence that baryons and dark matter can actually be separated came with the bullet cluster this is a pair of clusters that recently collided because galaxies are relatively small compared to the space between the galaxies in these clusters mostly he passed right through each other on the other hand the gas in these clusters collided and ended up left at the location of the collision while the galaxies moved on so where is the dark matter if modified gravity models are correct you'd expect it to be wherever most of the baryons are in this case that's the gas there's about twice as much mass in that trainwreck of gas in the middle compared to the stars in the galaxy clusters on either side the true mass distribution of the bullet cluster was mapped using gravitational lensing this time the warping of life of galaxies behind that cluster it turns out that most of the mass here's a invisible it's not stars or gas but rather dark matter and be it hanging out with the stars and not the gas the Dark Matter also appears to have passed straight through the collision site which is exactly what you'd expect if dark matter is what we think it is some exotic weakly interacting particle but not what you'd expect if dark matter were just a modification of gravity produced by the baryons then the mass should be exactly where we see it hanging out with the gas some modified gravity proposals have claimed they are still consistent with the observation of the bullet cluster so apparently we need more evidence cue the new discovery a galaxy that may have no dark matter whatsoever this weird object is a so-called ultra diffuse galaxy or udg these can be the size of the Milky Way but maybe with 1% of the number of stars sister Milky Way Peter van dokkum and Shani Danieli of Yale University and their team were studying one of these UD G's in the neighborhood of the elliptical galaxy NGC 1052 and this udg is charmingly named and you see 1052 / d f2 but today we're gonna call it fritz to understand how Fritz formed the team measured the motions of stars within that galaxy first some bright lots of stars globular clusters then did a few stars of the rest of the galaxy remember that Ricky and Rubin discovered dark matter in the first place by observing that the velocities were too fast in clusters and in galaxies indicating an unseen source of mass to hold those things together well this team found the velocities were extremely small at least compared to similar you DG's discovered in the past from the stellar orbits they inferred a mass for Fritz of 130 million times that of our Sun although with an error bar of 18 million solar masses the comparison our galaxy has a mess around ten thousand times greater with the vast majority of which is dark matter this was intriguing to determine the ratio of stars to dark matter the team calculates in Fritz's still a mess based on the amount of light received from the galaxy this is actually pretty straightforward because we have an excellent understanding of how much and what type of light stars of different masses produce they got a stellar mass of a hundred million suns that's basically the same mass from the stellar orbits that told the researchers that we don't even need dark matter to account for the mass of this galaxy and most Fritz should have about the same mass in dark matter as it doesn't stars but even that would be bizarre because normally in a galaxy like this the dark matter would outweigh the stars by a factor of 400 the team has since found a second galaxy in the same group that also appears to be missing dark matter and they have several more candidates for which they still need to measure velocities it seems it is possible for a galaxy to be missing dark matter which is an ironically powerful argument in favor of the existence of dark matter if dark matter isn't a substance but rather a modification of the laws of gravity then it shouldn't be possible to separate it from the galaxy yet in this case that seems to be exactly what happened the authors have some ideas of how this could have happened but they emphasize that these are just guesses for the moment perhaps these UD G's form from gas and stars ejected in a past collision with the nearby elliptical galaxies while perhaps that elliptical galaxy once harbored a quasar its central black hole underwent a feeding frenzy that blasted enough gas out of the galaxy to form a new mini galaxy but without the dark matter or perhaps those same quasar winds landed some gas exterior to the elliptical galaxy triggering it to collapse into stars even without the dark matter that would normally be needed to start that process obviously more work is needed to understand these dark metal light galaxies then document team are honored and no doubt many other astronomers will be racing to investigate this weird new class of object hopefully if we can understand how a galaxy can form without dark matter we can learn more about the nature of dark matter itself which be nice I mean it only makes up 80% of all matter in space-time thank you to curiosity stream for supporting PBS Digital Studios curiosity stream is a subscription streaming service that offers documentaries and nonfiction titles from a variety of filmmakers including curiosity stream originals for example you can watch the hunt for dark matter which looks at how CERN and the University of California Santa Barbara are working to uncover just exactly how dark matter works and what it may actually be you can learn more at curiosity stream comm slash space-time so you all seem to have completely understood the holographic universe video on first watch so there's nothing to say here well you fan did request a new video the explanation of the holographic universe explained point taken any further explanations will get their own entire videos today we're just going to use the response section to address your humorous comments and also to show some of the incredible artwork you came up with depicting Roger Penrose dressed as Gandalf with a lightsaber and a TARDIS okay maybe just one science one from Tony face who muses the whole information stored on the surface of a volume idea had got me thinking pick a sphere that encompasses whatever you define of as me so everything about me can be encoded on the outside of that surface could you say that everything I could possibly measure about the outside universe is also encoded on the inside of that same sphere and thus every closed 2d surface in 3d space is essentially a limit of the know ability of one region about the other Tony face consider a career switch this is indeed a reasonable interpretation of the universe beyond our cosmic horizon as a hologram living in the light bill quite reach us trapped at the expanding horizon and that sounds like another entire episode okay to the face mollify shares with us they're tuning in to that video randomly was like Oh bleep I just walked into the final exam without ever going to class so you're saying our videos are like a nightmare to you well at least they're free cook for 20 informs is that while we may feel that we live in a three spatial dimension universe serve up down left right forward back we're actually in a higher dimensional universe of up up down down left right left right B a B a select start that's right you already have all the power-ups you just don't know it bailed agust points out that Roger Penrose is a Time Lord in four-dimensional space but looks like a Jedi in a three-dimensional surface infinitely far away fleam notes that this is a form of Jedi Time Lord duality try RT guys try allottee he's also a wizard as our Roger Penrose fan out reveals here we have a brilliant one from over decks on Twitter I see a soldier of ministereth in the background there but wasn't he Gandalf the White not the gray by the time the fellowshipped reached the tower of watch oh yeah TARDIS he time traveled and also from Twitter we have Steven Halliday's brilliant drawing in which the lightsaber blade is the matrix mathematics of the more penrose conditions truly an elegant weapon for a more civilized age and finally Roger Penrose as dr. Gandalf the White on Shadowfax by David surely no fun is here just wow David I'm gonna just go ahead and replace Ian McKellen with Roger Penrose in my mental image of Gandalf [Music]

Channel: PBS Space Time

Views: 623,573

Rating: 4.9176874 out of 5

Keywords: Space, Outer Space, Physics, Astrophysics, Quantum Mechanics, Space Physics, PBS, Space Time, Time, PBS Space Time, Matt O’Dowd, Astrobiology, Einstein, Einsteinian Physics, General Relativity, Special Relativity, Dark Energy, Dark Matter, Black Holes, The Universe, Math, Science Fiction, Calculus, Maths, Holographic Universe, Holographic Principle, Holography, Holographs, Reality, Consciousness

Id: 5t0jaE--l0Y

Length: 14min 37sec (877 seconds)

Published: Wed Apr 24 2019

Reddit Comments

[u/chillaxinbball]

Quick summary: Finding a lack of evidence of dark matter in certain galaxys means that dark matter is more likely to exist than a modified gravitational model.

[u/0-_1_-0]

Damn, you're quick. I'll beat you guys some day. Catch me on the next video

[u/intrafinesse]

Doesn't Dark matter interact with itself and other particles via gravity?

If so, then if 2 galaxies , each with dark matter, collide then shouldn't some of the dark matter have collided and remained with the dust cloud?