from the Now-you-see-it-now-you-don't-because-it's-dark? dept.
A galaxy has been found containing no dark matter, but that proves dark matter is real?
A distant galaxy that appears completely devoid of dark matter has baffled astronomers and deepened the mystery of the universe's most elusive substance.
[...] 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 travelling way below the velocities expected. "They basically look like they're standing still," said van Dokkum.
The velocities gave an upper estimate for the galactic mass of 400 times lower than expected. "If there is any dark matter at all, it's very little," van Dokkum explained. "The stars in the galaxy can account for all of the mass, and there doesn't seem to be any room for dark matter."
Paradoxically, the authors said the discovery of a galaxy without dark matter counts as evidence that it probably does exist. A competing explanation for the fast-orbiting stars is that the way gravity drops off with distance has been misunderstood – but if this were the case, all galaxies should follow the same pattern.
https://www.theguardian.com/science/2018/mar/28/galaxy-without-any-dark-matter-baffles-astronomers. The findings are published in the journal Nature.
(Score: 0) by Anonymous Coward on Friday March 30 2018, @10:10PM (8 children)
Do we know if this galaxy features the requisite super-massive black hole at galactic center?
(Score: 3, Informative) by melikamp on Friday March 30 2018, @10:13PM (7 children)
It could also indicate a dense pocket of dark energy.
(Score: 2) by ese002 on Friday March 30 2018, @10:30PM (6 children)
That would require not just a dense pocket of dark energy but that the dark energy nearly balances the dark matter. It's not impossible but those kinds of balancing acts are usually either wildly improbable or mandatory. It is clearly not mandatory because we don't see it elsewhere.
(Score: 0) by Anonymous Coward on Friday March 30 2018, @10:47PM (5 children)
I'd like to see distribution plot of the ratio of estimated dark matter to "regular" matter among a random sample of galaxies. If it's a roughly continuous curve then this particular galaxy could simply be one with a coincidental balance. If there are spikes or sudden drop-offs in the plot, it could imply a variety of things.
If we are dealing with 3 factors (regular matter, dark matter, dark energy) and we can only directly measure 1, interpreting such a curve could be tricky and may await other clues.
(Score: 5, Insightful) by HiThere on Saturday March 31 2018, @06:06AM (4 children)
Actually, we measure two related things:
1) The stars which we see have a mass that we deduce from the spectrum and a few other things and so we think we know their mass, more or less. (This is a lot more definite in multiple star systems.)
2) The orbital speeds of the stars around the galaxy.
We add up the estimated mass of the stars to come up with an estimated mass of visible matter. (A bit of finagling goes on here, because there are planets, comets, dust clouds, etc., but most of the mass is expected to be in stars so it's probably about right.)
We look at the orbital velocities, and calculate the mass of galaxy needed for those speeds to be orbital velocities. Usually there's way too little observable mass. "Dark matter" is "whatever causes stars at a faster velocity to be in orbit". This time they don't need that bugger factor. The easiest answer is that "dark matter" really is matter that we can't detect, but for various cosmological reasons it can't be baryonic matter. (If it's baryonic matter, the amount of Lithium that got produced in the early days is just totally wrong.)
This isn't informal just to be funny. I don't really understand the details, and this is the closest I can come to a real answer to your question.
O, Yes, dark energy. We can't detect that at all on scales as small as a galactic cluster. Sorry. The only way we can detect that is by measuring the apparent speed of the expansion of space-time over areas that are much more loosely bound than a galactic cluster.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 2) by PiMuNu on Saturday March 31 2018, @07:27AM
I think that's a good summary. But it's worth adding that there are other ways to observe the dark matter, like looking at the way light is bent around galaxies by their gravitational field; everything points to gravity being stronger than expected. The best model that fits the data is that there is some extra matter that doesn't emit light at any wavelengths i.e. dark matter.
(Score: 0) by Anonymous Coward on Saturday March 31 2018, @01:42PM (2 children)
It is more correct to say that dark matter is matter we cannot see. We can obviously detect it, otherwise how would we even know it exists? However we can only detect it indirectly through its gravitational effects.
(Score: 3, Interesting) by HiThere on Saturday March 31 2018, @05:08PM
The problem here is "What do you mean 'matter'?". All we know is that *something* is acting on gravity the way matter would. That's something that we usually attribute to matter, but we don't see it, so we're calling it dark matter until we detect something. Or come up with a better explanatory theory.
The thing is, just because is has a name doesn't say much about it. I could take a bagel and name it "hopscotch", but that wouldn't make it jump. All that we really "know" is a perturbation in gravity.
Even that's overstating the case, but here we're starting to get closer to psychology than physics. Just accept that actual knowledge is impossible, and the best we can do is make estimates worth acting on. Normal English usage doesn't map well onto either physics or psychology, but the words we use shape the thoughts we communicate. Within your own mind you've got lots of things that modify the words you use, attached images, feelings, perhaps even sub-text dialogs. Those get stripped off when you talk to someone else. So the Whorfian Hypothesis is true for spoken, and even more written, thoughts, even though the strong form isn't true for personal thought.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 2) by Fluffeh on Wednesday April 04 2018, @11:15PM
Not really. We can see the effects of *something* but it is not anything that we can in fact detect directly - just its symptoms. We can only see the effects that we would associate with more matter. It might be matter we for some reason don't see, it might be that gravity works differently to what we understand - or there might be some completely new physics we haven't scratched at yet.
The things/effects that we can see don't match the formulas we have to explain them.
(Score: 1, Interesting) by Anonymous Coward on Friday March 30 2018, @10:12PM (1 child)
Aliens have mined all the dark matter there to fuel their giant [fill in the blank].
(Score: 2, Funny) by Anonymous Coward on Friday March 30 2018, @10:15PM
Penis.
(What did you expect? This is, after all, the Internet.)
(Score: 4, Funny) by bob_super on Friday March 30 2018, @10:20PM (2 children)
An uncheduled KKK meeting was just held and raised unprecedented funds to accelerate both BFR and SLS development, as well as warp drive and ion thruster tech.
(Score: 0) by Anonymous Coward on Friday March 30 2018, @10:49PM
Orange Matter?
(Score: 2) by RS3 on Friday March 30 2018, @11:24PM
Are they headed to the Cracker Galaxy?
(Score: 0) by Anonymous Coward on Friday March 30 2018, @10:20PM (3 children)
We now have a home for Ethanol Fueled and friends, B Ark at the ready!
(Score: 2) by insanumingenium on Friday March 30 2018, @10:41PM (2 children)
But then where will we put all the hairdressers and telephone sanitizers?
(Score: 0) by Anonymous Coward on Friday March 30 2018, @10:50PM
At this point they are upgraded to the A ark since it was discovered that being only marginally useful to society is massively preferable to those actively trying to destroy it.
(Score: 1) by Ethanol-fueled on Friday March 30 2018, @11:20PM
I'm a farmhand, my job is to clean the horse penises before we collect the samples.
I just needed the money, but those farmers are sick fucks. I ask them why we can't just leave the horses alone and let them breed naturally like the race horse breeders do and they all laugh and make hideous slurping and choking noises before telling me that's "just they way they do it." Their method is pretty convoluted, they use another male horse as a "teaser animal" and then when the stud jumps yank the stud at the last minute over to the side into a pocket-pussy stuffed into the neck-hole of an antique wooden pillory that, the farmers say, held actual negro slaves who had misbehaved centuries earlier. The farmers say that if you stand close enough to it you can still smell the rotten vegetables which were hurled at the slaves' faces during those days.
One of the perks of being White and working on a farm is that you get cushier jobs working with the White farmers. Can't I just go pick vegetables with the Mexicans?
(Score: 1, Informative) by Anonymous Coward on Friday March 30 2018, @10:27PM (7 children)
I'm just waiting for the "modified gravity" folks to come out of the woodwork. :/
"Those scientists trying to explain strange rotation of galaxies by assuming there's something there that we can't see are idiots. We should assume that laws of physics are different instead, that's a much more rational approach!"
News flash, they're both equally insane. (Which, for better or worse, doesn't disqualify either of them.) So please stop the holy wars, it's obnoxious. Thank you.
(Score: 1, Touché) by Anonymous Coward on Friday March 30 2018, @10:29PM
I blame the above screed on a holier than thou user who is ABOVE such holy wars, ummm, infinite loop incoming
(Score: 2) by bob_super on Friday March 30 2018, @10:50PM (5 children)
A bit like keeping on looking for Earth-like life around, it's hard to find surprising that puny humans for assuming that our physics apply to the rest of the universe.
My question, which has never been answered: We're good a physics now, but can anyone prove that our constants do not vary with the millions to billions of years between us and the galaxies we observe ? As the universe expands and changes, is it more rational to think that the laws are invariant, than the opposite?
I'm not an originalist, obviously.
(Score: 3, Insightful) by wonkey_monkey on Friday March 30 2018, @11:06PM
They all seem to be much like our own. We don't see any differences between galaxies 1 billion l.y. away or 10 billion l.y. away that would indicate any changes to the laws of physics over space or time. And if there were changes over space, you'd expect things to be different in different directions, which they aren't.
systemd is Roko's Basilisk
(Score: 1) by khallow on Saturday March 31 2018, @03:54AM (3 children)
No, that's very different. The problem here is that we can see the rest of the universe and thus, the physics of the rest of the universe, but we can't yet see planets with different sorts of life on them.
Because we looked.
(Score: 2) by HiThere on Saturday March 31 2018, @06:10AM (1 child)
That said, only some of the constants can be checked at a distance. But it would take a really weird theory to explain why only the ones we can't check would vary.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 0) by Anonymous Coward on Saturday March 31 2018, @01:48PM
There is a Heisenberg joke in there. Hidden.
(Score: 2) by PiMuNu on Saturday March 31 2018, @07:30AM
I thought there were reasonable "variable speed of light" theories around that conflict with inflation.
https://en.wikipedia.org/wiki/Variable_speed_of_light [wikipedia.org]
(Score: 1, Insightful) by Anonymous Coward on Friday March 30 2018, @10:39PM (6 children)
Let's face it. When we couldn't figure out how EM wave propagate without medium, we came up with "ether". "Dark Matter" is the same shit.
(Score: 0) by Anonymous Coward on Friday March 30 2018, @10:53PM
And yet they named a digital currency after it, shoulda been a big clue ;)
(Score: 3, Funny) by aristarchus on Friday March 30 2018, @10:57PM (1 child)
Don't be bad mouthing the ether, or as we used to call it, the Fifth Element. It has been around longer than you, most likely, and you may need to to come save your insignificant planet from a Big Black Ball of Death.
(Score: 3, Funny) by Hartree on Saturday March 31 2018, @08:56AM
Nah, he's just been breathing the ether 'cause he couldn't score any nitrous oxide.
(Score: 2) by wonkey_monkey on Friday March 30 2018, @11:01PM (2 children)
You've got that completely wrong.
We originally assumed there was an ether because every wave-like phenomenon we were familiar with up until that point had one. Once the requisite evidence showed there could not be an ether, the concept was, with quite some resistance, dropped.
systemd is Roko's Basilisk
(Score: 0) by Anonymous Coward on Friday March 30 2018, @11:21PM (1 child)
Hey, Einstein, read back what you wrote. You write the same shit I wrote, and I am "completely wrong"?! Like you?
(Score: 3, Interesting) by wonkey_monkey on Sunday April 01 2018, @10:56AM
We never had to "figure out how EM wave propagate without medium" because the concept never even occured to anyone. What we had to figure out was how the speed of light could remain constant, and to do that, we had to discard the notion of ether.
We'll discard the notion of dark matter if (and that's a huge if) it ever turns out to be incompatible with observation, but the chances of that - given the existence of the Bullet Cluster and this new discovery - are getting slimmer all the time.
systemd is Roko's Basilisk
(Score: 0) by Anonymous Coward on Friday March 30 2018, @11:55PM (5 children)
I know, I live in the horrible galaxy where SyFy cancelled Dark Matter.
(Score: 3, Touché) by Gaaark on Saturday March 31 2018, @01:12AM (4 children)
And I live in the worse sick feck galaxy where they cancelled FIREFLY!
Firefly for chris-sakes.
Firefly!
Book
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 0) by Anonymous Coward on Saturday March 31 2018, @01:27AM (3 children)
Of course they canceled Firefly and Dark Matter. They need the time slots for Shaknado 6: Jonah's Revenge
(Score: 2) by takyon on Saturday March 31 2018, @01:53AM (2 children)
Shaqnado? Now we might have a hit on our hands.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 0) by Anonymous Coward on Saturday March 31 2018, @10:14AM
So I forgot the 'r'. Spellcheck didn't flag it so how am I supposed to know it was wrong?
(Score: 0) by Anonymous Coward on Saturday March 31 2018, @01:16PM
I'd watch it just to keep him from doing ads for the general and icy-hot. A part of me dies every time I hear his soulless monotone delivery about low rates or back pain.
(Score: 2) by Runaway1956 on Saturday March 31 2018, @02:12AM
The Galaxy S9+ does contain dark matter. The engineers at Samsung have incorporated quantum physics into the dark matter matrix, thus requiring less dark matter to obtain the same results. As for what you people are looking at in the skies: those are the galaxies that have been mined of dark matter, to make your cheapo phones work. Look at your phone. Turn it off. It goes dark when you turn it off? Where did you think manufacturers got that dark from?
(Score: 2) by maxwell demon on Saturday March 31 2018, @09:04AM
It's just that when using the Galaxy Creation Wizard, God forgot to fill out the form field specifying the dark matter content for this galaxy. ;-)
The Tao of math: The numbers you can count are not the real numbers.