You may not notice it, but our Milky Way galaxy is cruising along at 630 kilometers (~391 miles) per second. That speed is often attributed to the influence of a single gravitational source. But in a new study, a group of researchers has found that the motions of the Local Group—the cluster of galaxies that includes the Milky Way—are being driven by two primary sources: the previously known and incredibly massive Shapley Supercluster and a newly discovered repeller, which the researchers dub the Dipole Repeller.
Shapley's contribution was already known, but the Dipole Repeller's hadn't been recognized prior to this study.
The researchers plotted the motions of many galaxies in the nearby Universe in a 3D model, using data from the Cosmicflows-2 database. Since the Universe is expanding, most galaxies are moving away from ours, creating a red-shift in the light they emit. But since the researchers were more interested in the other influences on a galaxy's motion, they simply subtracted the expansion's contribution. The resulting plot shows what the motions of galaxies would look like if space wasn't expanding.
The galaxies in that plot all follow different paths—some proceed through the Great Attractor in the middle of the picture, others curve around the periphery, and so on. They all seemed to have a clear destination: the Shapley Supercluster. But they also seem to have a clear origin point: the Dipole Repeller. When the researchers traced the galaxies' paths backwards, they all originate there. It looks a lot like there's something there repelling the galaxies, as if the Repeller and Shapley formed the negative and positive ends of an electrical dipole, and charges were being driven from one to the other.
That's not what's actually happening. Gravity is the dominant force acting on a galaxy, and gravity, unlike electricity, can't repel—it's only an attractive force. So what's going on?
The Dipole Repeller's true identity is probably, well, nothing. It's actually a void with much less mass than the surrounding space. This has the effect of seeming like a repeller because the nearby space has a much denser concentration of matter, creating a gravitational gradient between the two. The low-density void is the only direction from which there's no force pulling on the galaxy, or at least significantly less force than comes from every other direction.
Source:
Journal Reference:
Nature Astronomy, 2017. DOI: 10.1038/s41550-016-0036
Related Stories
A physicist is using a theory he advanced to explain how EmDrive could work to explain how dwarf galaxies can be held together without the requirement of dark matter:
British physicist Dr Mike McCulloch, who previously used quantised inertia to explain how the controversial electromagnetic space propulsion technology EmDrive works, says that he has new evidence showing his theory can also explain galaxy rotation, which is one of physics' biggest mysteries. McCulloch, a lecturer in geomatics at Plymouth University's school of marine science and engineering, says he now has even more evidence that his "new physics theory" about quantised inertia works, and that it makes it possible to explain why galaxies are not ripped apart without using theory of dark matter.
[...] There are 20 dwarf galaxies in existence from Segue-1 (the smallest) to Canes Venatici-1 (the largest), and dark matter is only meant to work by spreading out across a wide distance, but it is still used to explain dwarf galaxies, even though this requires dark matter to be concentrated within these systems, which is implausible. Instead, McCulloch asserts that quantised inertia can be used to explain how galaxies rotate without using dark matter, and he has written a paper that has been accepted by the bi-monthly peer reviewed journal Astrophysics and Space Science.
Reprint of the IBT link here.
From the abstract of Low-acceleration dwarf galaxies as tests of quantised inertia (DOI not yet published):
Dwarf satellite galaxies of the Milky Way appear to be gravitationally bound, but their stars' orbital motion seems too fast to allow this given their visible mass. This is akin to the larger-scale galaxy rotation problem. In this paper, a modification of inertia called quantised inertia or MiHsC (Modied inertia due to a Hubble-scale Casimir effect) which correctly predicts larger galaxy rotations without dark matter is tested on eleven dwarf satellite galaxies of the Milky Way, for which mass and velocity data are available. Quantised inertia slightly outperforms MoND (Modied Newtonian Dynamics) in predicting the velocity dispersion of these systems, and has the fundamental advantage over MoND that it does not need an adjustable parameter.
Previously: Study Casts Doubt on Cosmic Acceleration and Dark Energy
Dark Matter Beats its Latest Challenge
Emergent Gravity and the Dark Universe
Space Race 2.0: China May Already be Testing an EmDrive in Orbit
Milky Way is Not Only Being Pulled—It's Also "Pushed" by a Void
(Score: 4, Insightful) by mhajicek on Sunday February 05 2017, @12:19AM
"The Dipole Repeller's true identity is probably, well, nothing. It's actually a void with much less mass than the surrounding space. This has the effect of seeming like a repeller because the nearby space has a much denser concentration of matter, creating a gravitational gradient between the two. The low-density void is the only direction from which there's no force pulling on the galaxy, or at least significantly less force than comes from every other direction."
So no, it isn't being pushed by the void.
The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek
(Score: 3, Insightful) by wonkey_monkey on Sunday February 05 2017, @01:05AM
So no, it isn't being pushed by the void.
That's why it's in scare quotes in the headline.
systemd is Roko's Basilisk
(Score: 0) by Anonymous Coward on Sunday February 05 2017, @02:10AM
Yeah, subtract the background even though it isn't there. Now there's a signal! Oh, but wait, the signal is an artifact of my processing algorithm. I've certainly confused myself. Quick, let's write a paper before we come to our senses.
(Score: 0) by Anonymous Coward on Sunday February 05 2017, @07:56AM
It just means there's more background than we thought. Need to subtract that too.
(Score: 1, Insightful) by Anonymous Coward on Sunday February 05 2017, @03:26AM
(Score: 2) by AthanasiusKircher on Sunday February 05 2017, @09:11PM
Gravity is never repulsive, but a less attractive force in one direction than all the others behaves indistinguishably from a repulsion. We might distinguish between a pull in one direction and a push in the opposite direction, but in astrophysics, it’s all the same thing: forces and acceleration.
This. I'm astounded that so many people seem to get hung up on this detail in the story. Forces are always relative to a reference frame. In Newtonian physics, we tend to assume an inertial reference frame which has no default "forces" as part of the frame and which isn't accelerating. That's great when you're talking physics 101, but that oversimplification is a bit useless on a cosmic scale.
On the scale of the universe, the "default" state is to be pulled in all directions by gravity. The absence of a pull in some direction is actually an anomaly, which effectively "pushes" you with respect to the default frame of reference (usually taken to be the CMB radiation). If you're designing a system of physics where you assume the absence of net forces is "default," then Newtonian mechanics makes sense, and forces appear to "push" you. But that analogy doesn't survive well when we start talking about gravity in space-time on a cosmic scale.
(Score: 3, Interesting) by RedBear on Sunday February 05 2017, @02:27AM
If one assumes that Mike McCulloch's theory of quantised inertia, a.k.a. MiHsC, a.k.a. horizon mechanics is correct, the figures in this article seem to serve as a perfect demonstration of it. If the theory is true, the article actually has everything backwards. The zero-point field is in fact pushing galaxies out of an area with less mass and pushing them toward an area of greater mass, because mass acts as a shield that blocks the "pressure" from the zero-point field on one side of an object, allowing it to be affected more strongly by the zero-point field pushing on the opposite side. In MiHsC, gravity is an imaginary force similar to centrifugal force. It therefore makes perfect sense that the galaxy paths can be traced back to a "void" in space. It was the existence of the low-density void that got all the movement started.
MiHsC also explains observed galaxy rotation anomalies with impressive accuracy and without the unscientific per-galaxy fudging required by dark matter. I wish more people here would look into it.
http://physicsfromtheedge.blogspot.co.uk/2014/01/mihsc-101.html [blogspot.co.uk]
¯\_ʕ◔.◔ʔ_/¯ LOL. I dunno. I'm just a bear.
... Peace out. Got bear stuff to do. 彡ʕ⌐■.■ʔ
(Score: 2) by Gaaark on Sunday February 05 2017, @02:36AM
THANK YOU!
You have what I was trying to find to link to.
Maybe another confirmation?
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 1, Informative) by Anonymous Coward on Sunday February 05 2017, @05:34AM
(Score: 0) by Anonymous Coward on Sunday February 05 2017, @08:05AM
I'm sure he would but the liberal mainstream physics media is keeping him down so they can get alll thaaat graaaaaaant moneeeey *evil laugh*
(Score: 0) by Anonymous Coward on Sunday February 05 2017, @07:17PM
You can come up with just about any theory and add "dark matter" and "dark energy" to it as needed. It will fit the data.
(Score: 2, Informative) by Anonymous Coward on Monday February 06 2017, @02:13AM
Fritz Zwicky tries to measure the mass of the Coma cluster by using gravitational effects and comes up with a value that’s much larger than the visible matter that is there, and better measurements since his day still have a large discrepancy. Vera Rubin measures the rotation curves of galaxies and find they’re spinning faster than they should. Other astronomers see colliding galaxies and notice that there are gravitational lenses where there is no visible matter. Scientists analysing the cosmic microwave background power spectrum see certain peaks, which cannot be produced by normal matter. Normal matter subjected to the pressures of the early universe will oscillate due to its electromagnetic interaction, but the peaks they see seem to show a type of matter that doesn’t oscillate like that under pressure. That means that there’s a substantial amount of matter out there that interacts only via gravity and possibly the weak interaction.
These aren’t arbitrary fudge factors, and in any case, there is nothing inherently wrong with adding such things into a scientific theory, as long as you can later figure out a way to later characterise the fudge factor more clearly. Around 1900 Antoine Henri Becquerel and Ernest Rutherford discovered that certain radioactive elements emit ‘beta particles’, which they later realised were high energy electrons, and that their emission resulted in the conversion of a neutron into a proton in the atomic nucleus. If this was so, to satisfy conservation of energy, the energy of the emitted electron must have a specific, well-defined value. However, measurements made of the energy of beta decay electrons showed that it could take on an entire spectrum of values, which meant that either beta decay did not obey conservation of energy (terrible) or there was a third particle involved in beta decay that they couldn’t see that was involved (still bad, it was a huge, huge fudge factor). Wolfgang Pauli took up the latter hypothesis in 1930, and suggested that a particle with no or negligible mass, the neutrino, was also produced in beta decay, so it became a neutron emitting an electron and a neutrino, turning into a proton. It took another twenty years for Pauli’s hypothesis to be proven correct by experiments in nuclear reactors to detect neutrinos, and even today, neutrinos still have many mysteries. Incidentally, they are a particle of the sort that satisfies most of the constraints of dark matter. They can only interact via gravity and the weak force. The only problem is there doesn’t seem to be enough neutrinos to account for all of the dark matter.
(Score: 2) by RedBear on Monday February 06 2017, @06:14PM
Thanks! If only the author of the blog was a physics professor in the UK who has already had more than one paper on his theory published in reputable physics journals and is working on having more published. If only it were possible to know this by simply perusing said blog pages for as little as five minutes. How unlucky that he has a blog where no one "important" will ever see this information.
¯\_ʕ◔.◔ʔ_/¯ LOL. I dunno. I'm just a bear.
... Peace out. Got bear stuff to do. 彡ʕ⌐■.■ʔ
(Score: 2) by KritonK on Sunday February 05 2017, @12:15PM
In what frame of reference? Given that velocity is relative, the notion of a galaxy moving at any speed, without mentioning a point of reference, is meaningless. Saying that the galaxy is standing still (with itself as a point of reference) is as valid as saying that the Galaxy moves at a certain speed, with some other part of the universe as a point of reference. If those 630 km/sec are relative to the Shapeley Supercluster, why was it selected as a point of reference? If we pick a random point in the universe and study the motion of galaxies compared to that, I'm sure that we would find some equally fascinating results.
(Score: 1, Informative) by Anonymous Coward on Sunday February 05 2017, @03:48PM
(Score: 3, Informative) by AthanasiusKircher on Sunday February 05 2017, @09:02PM
our Milky Way galaxy is cruising along at 630 kilometers (~391 miles) per second
In what frame of reference?
And yet again, we see tons of questions that could be resolved simply by linking to the original research article [nature.com]. As stated in the first sentence of the abstract, the motion is relative to the cosmic microwave background radiation, which is probably the most common frame of reference when talking about motion of galaxies, etc. on a cosmological scale.
If we pick a random point in the universe and study the motion of galaxies compared to that, I'm sure that we would find some equally fascinating results.
Yeah, the problem with this story is that the motion and assumed frame of reference isn't explained very well, because people (even science reporters) don't seem to understand cosmology very well. The entire universe is in motion, expanding after the Big Bang. The CMB serves as a kind of "frame of reference" that expands at the same general rate as the universe. (See here [stackexchange.com] for some explanation.) Any motion with respect to that reference frame is something that requires some explanation in terms of the the position of bodies around it.
This also kind of explains the use of the term "repulsor" and being "pushed" by the "void" here. The "default" state of a body in the universe is to be pulled on gravitationally in all directions. If these forces are roughly "balanced" by uniform distribution in all directions, we'd move in sync with the CMB reference frame. The Shapeley Supercluster has been proposed as a primary explanation for why the Milky Way appears to be moving with respect to the CMB, but it turns out that the relative velocity is also increased by the absence of mass on the other side. The void in this sense represents a non-uniformity, a kind of anomaly -- hence the idea that it is contributing to "pushing" us.
(Score: 0) by Anonymous Coward on Sunday February 05 2017, @09:11PM
This seems to be the basic idea behind LeSage gravity, which proposes that gravity is an imbalance in "push" forces. EG, the Earth is screening us from a push below, but not above, therefore the net push is downwards.
https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitation [wikipedia.org]