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[llien]

The absence of dark matter from a small patch of sky might appear to be a non-problem, given that astronomers have never directly observed dark matter anywhere. However, most current theories of the universe suggest that everywhere that ordinary matter is found, dark matter ought to be lurking too, making the newly observed galaxy an odd exception. Dark matter's existence is inferred from its gravitational influence on visible objects, which suggests it dominates over ordinary matter by a ratio of 5:1. Some of the clearest evidence comes from tracking stars in the outer regions of galaxies, which consistently appear to be orbiting faster than their escape velocity, the threshold speed at which they ought to break free of the gravitational binds holding them in place and slingshot into space. This suggests there is unseen, but substantial, mass holding stars in orbit. In the Milky Way there is about 30 times more dark matter than normal matter. The latest observations focused on an ultra-diffuse galaxy -- ghostly galaxies that are large but have hardly any stars -- called NGC 1052-DF2. The team tracked the motions of 10 bright star clusters and found that they were traveling way below the velocities expected. The velocities gave an upper estimate for the galactic mass of 400 times lower than expected.The researchers described their discovery in the journal Nature.

Remind me, what that "dark matter" is
Our theories fail to explain a number of phenomena cosmologists observe.
E.g. we can see stars moving at velocities that should allow them to escape, yet they are orbiting.

That's how we got to the idea of "dark matter", something, that apart from gravity, never interacts in detectable ways.

It might feel we have invented magical "matters" instead of accepting that our theories are incomplete, but the thing is, our theory of gravity (general relativity) makes a lot of other predictions on scales of the same order, and they seem to work fine. There are also cases like the Bullet Cluster where the dark matter and ordinary matter components of two galaxies get separated from each other and the dark matter component can be seen by its gravitational lensing effect.

There are at least eleven pieces of evidence for dark matter (of which the galaxy in this story is one, wiki is fast at times )

 

[way more]

But the earth is still roundish, right?

 

[JDB]

But the earth is still roundish, right?

Disks usually are.

 

[ar0s]

Good post, interesting content. Not smart enough to have anything worthwhile to contribute though!

I'm interested in this stuff and listen to a lot of lectures etc. (strongly recommend Science and Futurism with Isaac Arthur) but cannot understand the detailed scientific and math stuff.

What's your opinion Ilien?

 

[a multicultural team of v]

Dark matter to me always felt like a lazy "plug" number to make equations work.

I am pretty firmly on the side of we dont understand what we think we understand, as opposed to the side of magical matter.

 

[way more]

Dark matter to me always felt like a lazy "plug" number to make equations work.

I am pretty firmly on the side of we dont understand what we think we understand, as opposed to the side of magical matter.

We didn't understand what gravity was beyond g = 9.8 m/s/s, for three hundred years. And then a man named Albert Einstein came around with a explanation. And yet we didn't have any evidence of supposed Gravity particles till 2 years ago.

It's all magical matter when talking about fundamental particles. Lazy "plugs" are simply fundamental nuts we can't crack.

 

[a multicultural team of v]

I completely agree. But that argument argues equally for dark matter as it does any other possibility.

Im not trying to say I am right or anything, science is not my profession and I have nothing resembling the proper credentials to make such a case, but this is a topic I have discussed at length with my girlfriend (who is an accomplished scientist, just not in this field), and we've both ended up on the not dark matter side.

Either way, articles like this are great and I'm glad you posted it, and I am looking forward to reading whatever discussion follows.

 

[llien]

But the earth is still roundish, right?

Since you are asking, World Geodtic System 84 (which GPS is using) was created to better reflect the fact that the Earth, in fact, is not a sphere, but an oblate spheroid:

if you pull an old map, say, from WWII times, coordinates you'd read from GPS and the ones on the map would differ by some 20-200 meters.

Oh, and remember that compass always points to Nord Pole? Well, mostly it does, but in in places like Caribbean see it might be off by about 15 degrees.

I'm interested in this stuff and listen to a lot of lectures etc. (strongly recommend Science and Futurism with Isaac Arthur) but cannot understand the detailed scientific and math stuff.

I think while math behind some laws of physics is often terrifyingly complex, one doesn't need understand them, to grasp what laws are about.
If you have questions, don't be shy to ask.

 

[ar0s]

if you pull an old map, say, from WWII times, coordinates you'd read from GPS and the ones on the map would differ by some 20-200 meters.

Oh, and remember that compass always points to Nord Pole? Well, mostly it does, but in in places like Caribbean see it might be off by about 15 degrees.

Can you explain both parts of this in more detail please?

 

[infinitys_7th]

So, is this the first diffuse galaxy to be found to lack dark matter, or is it a common characteristic of them?

If it is common, then you could speculate that dark matter is necessary to star formation.

 

[LordPezix]

Seems right. So much we still don't know, and "plugs" allow us to try make sense of things that we may not fully comprehend yet. Everyone can expect that what we think we know will most undoubtely change continuously throughout human existence.

Besides, once they discover what elementary particle makes up Dark matter, it will no longer be called such and we will again gather new theories and knowledge.

 

[ar0s]

It's interesting how many "plugs" turn out to be true though, such as the Higgs Boson.

 

[llien]

if you pull an old map, say, from WWII times, coordinates you'd read from GPS and the ones on the map would differ by some 20-200 meters.

Oh, and remember that compass always points to Nord Pole? Well, mostly it does, but in in places like Caribbean see it might be off by about 15 degrees.

Can you explain both parts of this in more detail please?

If we'd look at the Earth "from the top" (North Pole) this is where North Magnetic Pole (where compass' North points to) and Geographic North Pole (Earth rotation axis) are:

or (geographic Nord pole is marked with the green arrow and the distance between poles is exaggerated)

(Ignore "Geomagnetic Pole", if you are curious, it is "where the North Magnetic Pole would be, if Earth was a perfect magnet").


So, compass shows us where the magnetic pole is, but we are after geographic pole. In case you are somewhere in Europe (bottom of the map above), we are good, both directions are nearly the same, but it gets worse on the "sides'.

On certified nautical maps you could see marks like this (this one is, apparently, German):

This tells you that as seen from that area on the map, geographic Nord Pole is 5 minutes (one minute is 1/60th of a degree) Westward (actually, counterclockwise) to what you actually have measured.
That the measurement was done in 2010 and that, wait for it, they expect the value to shift 5 minutes clockwise every year.

Magnetic North Pole is moving:

but not only that, but we are pretty sure that Earth's magnetic field had reversed about 40 thousand years ago i (south magnetic pole was on the north pole) and that lasted for about 400 years.

There is no scientific consensus on whether magnetic field reversals are caused by external or internal factors.

 

[caffeware]

Dark matter is a hack. The earth is pear shaped.

 

[strange headache]

It might feel we have invented magical "matters" instead of accepting that our theories are incomplete, but the thing is, our theory of gravity (general relativity) makes a lot of other predictions on scales of the same order, and they seem to work fine.

Could be that dark matter is the modern equivalent of aether, but I don't think so. Theoretical physics and the standard model in particular have become so exact and powerful that most particles are now predicted by their mathematical models. Be it radio waves or the Higgs Boson, most of them were proven to exist in theory before they could be proven empirically.

The reason for that being, is that mathematics isn't merely a language, but it's a method to go from one set of statements to another through logical reasoning. Nobody would invest billions of dollars into something like the Large Hadron Collider, if they wouldn't be convinced by the predictive power of math and its theoretical models. In that sense, no major discovery has proven the basic premises of mathematics to be wrong, they merely added to it (imaginary numbers would be such an example).

Mathematical predictions aren't just a 'hunch', they are the logical consequence derived from a set of premises that are proven to be correct. Hence why stuff like string theory isn't just a crazy idea that some theoretical physicists dreamed up in a fever. If you want to know more about that, I recommend looking into the work of people like Edward Witten, who single-handedly managed to unify string theory:

 

[ar0s]

This tells you that as seen from that area on the map, geographic Nord Pole is 5 minutes (one minute is 1/60th of a degree) Westward (actually, counterclockwise) to what you actually have measured.
That the measurement was done in 2010 and that, wait for it, they expect the value to shift 5 minutes clockwise every year.

Magnetic North Pole is moving:

Fantastic post. Thank you for the response.

It seems to have sped up looking at the modelled and the observed locations. Is this correct (if so, is there any agreement why) or does it just appear that way due to the map?

Out of interest and on another topic, has there been any development in terms of understanding why the speed of light changes in terms of real measurements before it was set as a fixed constant? Could having a flexible speed of light aid in terms of making solutions to physics problems work where currently they do not or does it make no difference either way?

 

[synchronicity]

I am pretty firmly on the side of we dont understand what we think we understand...

That's always a very strong possibility. Look back at our collectively accepted "truths" over time. We know what we know, until we don't.

 

[Kotzen Ducha]

We live in a computer simulation
Anything is possible

This galaxy is probably just a BMP like the grass in Gran Turismo

 

[ar0s]

Is there not some ongoing experiment to work out what resolution the universe is in order to reveal it's true (simulated) nature?

 

[LOLCats]

There is just something there that we don't yet understand.

 

[ickythingz]

The electric universe theory explains all of this AND uses the scientific method to do it. Astronomers need to get it together and start looking beyond what is shoved down your throats in school.

 

[The Sane Psycho]

But the earth is still roundish, right?

Checkmate, science.