Slashdot Mirror
Class of Large But Very Dim Galaxies Discovered (nature.com)
schwit1 writes from a report via Nature: Astronomers have now detected and measured a new class of large but very dim galaxy that previously was not expected to exist. Nature reports: "'[Ultradiffuse]' galaxies came to attention only last year, after Pieter van Dokkum of Yale University in New Haven, Connecticut, and Roberto Abraham of the University of Toronto in Canada built an array of sensitive telephoto lenses named Dragonfly. The astronomers and their colleagues observed the Coma galaxy cluster 101 megaparsecs (330 million light years) away and detected 47 faint smudges. 'They can't be real,' van Dokkum recalls thinking when he first saw the galaxies on his laptop computer. But their distribution in space matched that of the cluster's other galaxies, indicating that they were true members. Since then, hundreds more of these galaxies have turned up in the Coma cluster and elsewhere. Ultradiffuse galaxies are large like the Milky Way -- which is much bigger than most -- but they glow as dimly as mere dwarf galaxies. It's as though a city as big as London emitted as little light as Kalamazoo, Michigan." More significantly, they have now found that these dim galaxies can be as big and as massive as the biggest bright galaxies, suggesting that there are a lot more stars and mass hidden out there and unseen than anyone had previously predicted.
Candlepower output of Kalamazoo, Michigan? And what standard shall we call it?
--sf
Large but very dim, eh? I submit that these galaxies are composed primarily of your momma.
Turns out the more mass you were trying to account for happens to just be more mass you didn't see.
RTFA (and Wikipedia) reveals that the discovery of the galaxies is actually one year old.
What was discovered is that the mass of the brighest one found (1% light of milky way) is the same as the milky way (even if the nature summary talks about weight, tststs). The way they measured it is interesting:
The more massive a galaxy is, the faster its stars move relative to one another. These motions broaden the spectral line through Doppler shifts, [...]. By combining six nights of data, the astronomers found that the stars’ typical movements relative to one another clocked in at 47 kilometres per second.
What I would be interested in is how one is sure that one didn't simply misjudged the distance of the galaxy. If it was 10 times as far away as thought, it would also appear only 1% as bright as expected.
Are there enough if these galaxies to account for the missing mass. I.e not so dark matter?
"Large but dim" - they need someone to be named after. The Donald has boasted about the size of his hands and his, ahem, stuff. The Donald Trump Galaxies is the best name.
1000s Warcraft Gold while you sleep
The whole Dark Matter thing was based on the presumption that there is NO WAY that WE can't see it.
Not at all. The whole dark matter thing was based on the presumption that there is mass that we can't see and this matter that we can't see was called "dark matter".
Others may have read more into it, but the name itself betrays the real, original intent behind describing this matter that we can't see or identify.
I have no problem with your religion until you decide it's reason to deprive others of the truth.
Let's call it Texas!
They are so dim that they are still going to school, billions of years later - they keep failing their exams
I wonder if they are type 3 civilization controlling those Galaxies?
Most theories that attempt to incorporate dark matter treats it like some kind of exotic material that does not obey natural laws.
Not true.
Sheesh, evil *and* a jerk. -- Jade
The Dragonfly array is composed of ten Canon 400mm F2.8 Telephoto lenses. New, they run around $13K each:
http://www.astro.caltech.edu/~ycao/B&ETalks/vandokkum_bne.pdf
There is no direct comparison to Mirror Telescopes, because the Optics are so different. But the Team does compare it to the resolving capabilities of a State-Of-The-Art Coated 46cm F0.89 Refractor... which doesn't exist, and would be horrendously difficult to construct.
This is one very impressive small telescope.
Dark matter is the matter within a galaxy that is not visible/detectable, and still has to be there to explain the speed of outer regions of the galaxy when circling the center. The detection of a dimly lighted galaxy outside of known galaxies doesn't change that, as it won't change the rotation characteristic we observe at wellknown galaxies. It might change some calculation about the structure of super clusters of galaxies though.
Actually this is a much simpler explanation of "the unaccounted" mass the science had strugle with. It so simple that it is very funny.
What's funny is that you think you're incredibly clever, but actually, you have no idea what dark matter is all about.
This discovery - which is actually over a year old - has nothing to do with dark matter.
systemd is Roko's Basilisk.
It's not. There are hree primary motivations for the belief that dark matter must exist:
1) Galactic dynamics. Stars within galaxies are orbiting far too fast given the luminous matter in those galaxies -- far too fast. On the assumption of Newtonian mechanics, we need an overabundance of unobserved matter to matter of around four times, and this needs to be distributed spherically (regardless of the distribution of the galaxy itself). It is simply not possible for that matter to be normal matter; we would see, for instance, frequent microlensing events as the matter passes in front of distant stars. Note that this "dark matter" does not have to literally be dark matter in the form of a particulate matter; it could be anything that replicates the motion of stars within galaxies. MOND, for instance, does an admirable job of fitting practically all (if not all) galaxy rotation curves with a single parameter, which is a bit better than particulate theories can.
2) Cluster dynamics. Galaxies within clusters are *also* orbiting far too fast given the luminous galaxies in the clusters. Here the "microlensing" issue is no longer micro -- galaxies lens rather more visibly. The dark matter distribution is no longer spherical. Note that we have observations, the Bullet Cluster being the most famous, where we can compare the mass distribution as recovered from lensing with the luminous matter and they're in very different places. In this instance, MOND doesn't work -- it breaks down entirely. That does not mean that the "dark matter" must be particulate, but it certainly can't actually be MONDian.
3) Cosmology. Cosmology provides the strongest evidence that something behaving as dark matter has to exist. Cosmological observations tell us that the universe is flat, to within a percent or so. At the same time, we observe the abundances of primordial hydrogen, helium, lithium and the like. These abundances are exquisitely sensitive to the amount of normal matter in the universe. That is, the amount of standard model matter, not just "luminous matter". To fit the observations we're restricted to approximately 5% of the critical density being made up of normal, standard model matter. But to fit observations of the cosmic microwave background and of the large-scale distribution of matter we not only need to be at the critical density but we need around 25%-30% of the universe to be made up of matter that gravitates like normal matter does, and about 70%-75% in something that is beginning to act "anti-gravitationally". That is, entirely independently from galaxy observations, cosmology states we need between four and five times of the matter in the universe in the form of "dark matter". Again, this does not need to be particulate. The conclusions are predicated on a relatively naive interpretation of general relativity. Changing either the theory of gravity, or the way in which it is applied, can change the conclusions, but nothing is especially convincing and in particular little is more convincing than the possible existence of a lightest supersymmetric particle, which would fit observations across all scales.
In each case it's useful to note that the galactic "dark matter" does not in fact have to be from the same source as the cosmological "dark matter". It's also important to note that in all cases its existence is deduced from comparing observations with a model explicitly based on a particular theory. As such, I would advise against taking either "dark" or "matter" as literal descriptions of what's going on. What we can say, with certainty, is that if you relatively naively apply Newtonian mechanics to galaxies or galaxy clusters, and if you relatively naively apply general relativistic dynamics to a universe which is smooth on extremely large scales, you independently come to the same conclusion: something in both cases acts as if there were an invisible distribution of gravitating matter, with an abundance about four or five times that of our normal, well-understood standard model m
Are they aware that the City of London is only one square mile, and where the fuck is Kalamazoo?
Political debates have me rolling my eyes so much I think I got optical whiplash. I should sue. - Foamy The Squirrel
I thought it wasn't just that we can't see it but that it doesn't interact with visible matter in any other way than through gravity for some reason? (Otherwise we should have at least some EM evidence.)
Ezekiel 23:20
Did they check in infrared? Maybe most of the stars are surrounded by Dyson spheres as is what one would expect will happen to our galaxy in a few million years if we don't kill ourselves off first. If so these galaxies should be quite bright in the infrared.
possible. if galaxies with lots of stars are possible and galaxies with some stars are possible then galaxies with few or no stars must also be possible.
Actually, astrophysicists aren't as dumb as you seem to think they are. This has little to do with dark matter and believe it or not, there are actually reasons why astrophysicists don't think dark matter is just dim stars or dust or something else like that. Maybe, just maybe, you might consider that they've thought about it a little more than yourself.
Ha ha ha scientists ha ha ha.
You see.... it's just that our instrumentation didn't detect the presence these GIANT galaxies until now. But, you can rest assured that we've 100% definitely detected and accounted for all the matter *WITHIN* the galaxies that we've err... detected so far! There is NO chance our instrumentation can miss ....any... regular matter within these galaxies - NONE... because to explain away dark matter we'd have to miss something as big a whole galaxy! err.... damn.
"The universe is a pretty big place. If it's just us, seems like an awful waste of space."
- Carl Sagan, Contact
/. Dissent will not be tolerated. Think like us or perish.
Isn't the science behind Dark Matter something that basically does not match the real world? They just hope that it explains away an inconsistency in the overall model. To some scientists, it's really bad science.
No! It's a *SIG*. Keep the Special Interest Groups away! (Con joke!)
Out there as well as here.
I agree, but he does express the general perception that the layman has on dark matter. The crazy theories seem to get into the papers, not surprisingly. I've tried to explain to people, turn out the lights. We are dark matter, and dark matter is all around you. We just have to use indirect methods of observation, which is nothing new to science.
Isn't the science behind Dark Matter something that basically does not match the real world?
It's current theory that doesn't match the real world. Something is missing from it, because we've made observations that don't add up. Dark matter fits pretty well - better than the other theories, I'm pretty sure - but its existence has yet to be proven.
As far as I can tell "science" is doing okay. Maybe some scientists are showing a little too much hubris, giving a little too much credence to the idea of dark matter and not enough to other theories, but how could we actually [i]know[/i] that until it's proven one way or the other?
systemd is Roko's Basilisk.
Oh yeah. Another galaxy discovered. Now what?
. . . high school athletes.
It may very likely also be that "dark matter" tries to explain what was left unexplained from what we can observe and measure, and in doing so, explains things that are a result of other things totally unlike any kind of "matter that doesn't look like matter at all and only interact through gravity" bs. DM is the equivalent of the best Greek models trying to explain elliptical orbits with circles and circles within circles - a kludge that doesn't work.
unfinished: (adj.)
As an engineer, I have to do a lot of unit conversion.
Anyone know how many Kalamazoos are in a London?
And couldn't we just stick with SI units like the Paris?
For a different/new way of understanding the universe see my posts on Quora at Doug Snell Posts/blog or see my youtube videos explaining much about the universe etc... enjoy
https://youtu.be/FOcrsiKmZEI
Doug