STARS SNUFFED in massive galactic whodunit It's generally accepted by astronomers that dark matter makes up roughly 27 per cent of the known Universe – but in a galactic cluster 300 million light years away, that proportion is all skewiff. Simulations carried out by ICRAR (International Centre for Radio Astronomy Research) doctoral student Cameron Yozin using big iron …
If the 'captured' galaxy's gas is pushed out by hot gas in the cluster, the intergalactic space of the cluster is full of hot gas. Where does that hot gas come from, why is it hot and what keeps it hot? Why doesn't the pushed out gas get heated up and join the hot gas collection? Maybe it does and there's a massive cloud of gas diffused throughout the cluster with galaxies hanging around near the 'centre'? Can they see any indications of this?
At some point, wouldn't the gas cool? Then what, new stars someplace else?
I sometimes think, and this is one of them, that this mind-boggling science that we can observe is too overwhelming for us to understand.. then they postulate a theory based on the evidence. Mere mortals, they are not.
Beer because reading the links made my head hurt.
Indeed not.
For the life of me I cannot imagine that Dark Matter exists. I'm convinced that it is gaseous particles, or maybe even small asteroids that orbit galaxies and make up for the "missing matter". After all, we can hardly spot asteroids in our very own Kuiper Belt, and spotting them in the next solar system is simply impossible - so a in a galaxy millions of light-years away it is unconcievable.
But a scientist I am not, and these people are. So if they theorize that Dark Matter and Dark Energy exist, and if their theories hold out, who am I to say they're wrong ? Nobody, that's who.
I still don't understand what Dark Energy is, though. Then again, I can't calculate the inertial mass of my car at 50 km/h and understand what the result means, so . . .
I'd prefer to see some "Dark-Matter/Dark-Energy-in-a-vial" produced by boffins first before I'm convinced it is something that actually exists... Hmmm, perhaps we could try to produce some using appropriately sized Dark Suckers...?
For the life of me I cannot imagine that Dark Matter exists.
Don't see why not. You read about things like pentaquarks here on El Reg on a regular basis. Why is it so hard to conceive of non-baryonic matter made up of a different collection of subatomic particles that result in matter with different properties? We're not talking magic. Just think of dark matter sort of like Linux systems to a Windows admin: same basic building blocks, but being used in a completely different fashion.
I'm convinced that it is gaseous particles, or maybe even small asteroids that orbit galaxies and make up for the "missing matter"
Nope. These would emit light that we could see.
After all, we can hardly spot asteroids in our very own Kuiper Belt
Actually, we're reasonably good at this, given the limitations of the technology to hand. Talk to @plutokiller about how many he's found just in the past few years.
The reason we have trouble is that it's a big ass sky and we have a small ass budget. The primary tool we use for asteroid hunting (Hubble) was never designed for the task. It's slow to turn (shit at tracking anything close by) and has terrible resolution (so kinda crap at focusing on things smaller than stars).
If you wanted to build a modern high end telescope and give it the ability to turn quickly and see in infrared (think an upjumped WISE) you's spot all sorts of awesome stuff. In fact, WISE mark one did see a huge chunk of stuff and we're still picking apart the data from it.
And spotting them in the next solar system is simply impossible
That would be because of the giant ball of fusion that happens to be drowning out the rocks and other things. We can, as a matter of fact, see the interstellar medium and we do have to compensate for it when observing.
Also: the entire mass of a solar system is a mere fraction of the mass of the star. When we calculate what the mass of galaxies "should" be, that's typically included. The problem is that the missing mass is orders of magnitude larger than simply "a bunch of missing planets and asteroids circling the stars".
Questions you didn't ask:
What about rogue planets and brown dwarves?
Glad you asked. This is a growing area of research but the short version is that we can usually actually see these. These live out between the stars so they - believe it or not - count as "galactic dust" as far as we're concerned. They are visible (in aggregate) along with the interstellar medium of the galaxy.
What's more, unless our calculations about solar system formation are wildly off - to the point that we'd need to rewrite physics - there simply can't be enough rogues out there to make up the difference.
I still don't understand what Dark Energy is, though.
Oooooohkay. This is the hard one. Let me try to do this. Apologies for inevitably getting some or all of it wrong.
In the beginning there was nothing, which exploded. And by nothing, of course, I mean everything, but compressed into the most impressive singularity of all time.
Except this wouldn't be a singularity as you understand it. It was "a bunch of baryonic matter shoved into a ball so densely that photons can't escape". Matter didn't exist. Space didn't exist. Not, really, anyways.
But then, all of a sudden, and for no good reason at all, space exploded.
For simplicity's sake I want you to picture the universe as a great big flat circle squished into an impossibly small ball. If you were to unfold that circle and flatten out you would have The Universe in its final, fully extended form. This is The Universe's eventual goal. It was scrunched up so tightly that it is seeking to stretch out a little and get rid of the cramp.
Now, each cubic meter of space to expend energy in order to unfold. This energy comes in the form of two completely different types of energy.
The first type of energy was all released right at the beginning of the universe. The initial collapse of the fundamental singularity caused its emission. At the initial instant of emission it was simply an incomprehensible amount of raw energy occupying an infinitesimal amount of primordial space. This energy would eventually become all matter - dark and baryonic - that we know today.
But the universe was intent on unfolding beyond that mere initial plank space. It continued to expand and as it did so it emitted the second type of energy: dark energy. So far as we can tell, dark energy doesn't interact with the energy that makes up mass in any meaningful way.
In any case, as the universe continued to expand somewhere around 1 usec after the big bang baryogenesis started to occur. The fundamental particles as we understand them formed.
For reasons we don't understand - but which probably mean that either dark energy or dark matter does interact with regular energy on some level - symmetry breaking occurred and the current form of baryonic matter (not baryonic anti-matter) coalesced as the (currently) densest concentrations of energy.
The universe kept right on expanding and that baryonic matter eventually cooled enough that protons and electrons could form atoms and the rest you know from there.
The two odd pieces are symmetry breaking - discussed above - and the variation in universe expansion rates. The initial inflation seems to make perfect sense. The universe sought to unfold and began doing so expeditiously. It then slowed it's expansion for a time and then sped up again.
Some like to think that the gravity of the early universe (it was denser then) slowed the initial expansion. Once past some critical threshold, however, the universe's tendency towards expansion overcame gravity and expansion started accelerating.
The problems with this are A) there's no reason to assume gravity has any sort of effect whatsoever on the universe's desire to expand and B) the universe isn't increasing it's rate of expansion exponentially. (As would be expected if it had overcome some critical threshold.)
The nearest anyone can figure is that the universe is expanding because it damned well wants to, but that it has to expend (or release, like a coiled spring) energy to do so.
I hope that explains things. I am sorry if it doesn't.
I always have read your articles with relish, and this response is simply a delight.
Thank you, Sir, for having given me a recognizable construct with which to apprehend the issue of Dark Energy. I do believe I actually get it now - the Universe unfolding and something has to allow it to unfold. I guess I might have been a bit blindsided by the term "Big Bang" (I am generally not altogether dismayed by Michael Bay films, I must humbly admit). Now I understand why much more intelligent people than me didn't like the term.
In any case, your response is also interesting to me because now I understand that there might be a limit to this "unfolding", which means that, at one point in some undetermined future, the Universe will attain a point of equilibrium and stop expanding. Excuse me while I pick my jaw up from the floor. Science is just bewilderingly exciting, isn't it ?
But, even if the Universe does stop expanding, that will not really stop its Heat Death, now will it ? Or is it remotely possible that this Dark Energy I am beginning to see the outline of in the deep London fog (sorry, couldn't resist) will dissipate into some other form of energy and keep the Universe heated ? Or, after having uncoiled the Universe, is it possible that it contracts everything again to give us the Big Crunch that already has been evoked ?
I'm feeling a bit dizzy now, I guess I'll have to lie down my brain a bit. Watch something with explosions to set it back on track again. The Expendables, maybe. Yeah, that should do the trick.
Sincerely, thank you.
at one point in some undetermined future, the Universe will attain a point of equilibrium and stop expanding
That's one of many interpretations of the data, yes. It seems to be one that more and more scientists are moving towards. A handful think that space - like some sort of elastic - will "snap back" and that whole "big crunch" thing will actually happen.
Others (who are now considered traditionalists, ha!) think space will keep expanding forever, with the force of expansion eventually accelerating past the speed of light (there is a difference between acceleration-driven speed and local timeframe speed which makes this compatible with relativity). At some ????? after this occurs expansion would be so fast that large structures like galaxies, and then stars, planets and even atoms couldn't hold themselves together (the Big Rip).
The former (that the universe will unfold to a maximum extent or eventually collapse) view is held by people who - not to put too fine a point on it - think mcuh of string theory is a whole bunch of hooey. Not that it's all bollocks, mind you, but quite a bit of it. (Brane extrusion is still likely the best reason for our universe to have come into being in the first place.)
The latter people - those who think the universe will continue forever - seem to think the universe will continue expanding forever because that is what it is busy doing now. That the universe changed it mind about how fast it was unfolding in the past seems to be no reason to believe things could ever change again and off they go trying to use maths to prove it. Thus string theory gets more and more silly as they try to beat maths into submission to make it agree.
Basically there are two camps that matter:
1) New space is constantly being created as part of the expansion of the universe and that as a function of this creation there is dark energy. The universe will always create new space (because that's what what it does) and thus the universe is doomed.
2) All the space in the universe was already there to start with, it was just compressed, and the universe is not unfolding to its current size. (Actually, some believe the universe is a multi-dimensional hologram, but let's not get into that as it doesn't really change anything.)
Critical to the debate is the almost anthropic belief of camp 1): that this is the only universe and that it is special. The second group believe that the universe is pedestrian. there are many and instead of being infinite they are popping up all over like sun umbrellas being opened on a beach.
For the universe to expand forever, it basically has to be special. Otherwise it would eventually interact with another universe. Some of us - myself included - believe that the fact symmetry breaking occurred and that expansion changed speeds indicated that our universe has already interacted with other universes (possibly via extra universal forces we don't know - and can't know - anything about.)
Personally, I fall into the latter camp for the simple reason that every time we've thought something about where we lived was "special" we were ultimately proven wrong. There's nothing special about where we live and there's nothing special about us, either.
Thins then changes a "fundamental truth" about what many of us were taught in school: the universe is not infinite. It's just really, really, mind-bogglingly big.
I think we need to award Mr. Pott with a white coat, pipe, and the title of "honorary boffin". He's explained so even I can understand (although it still makes my head hurt).
Well done sir... Since don't have a boffin icon, this will have to do... have a tall cold one and enjoy the rest of the day.
Dark matter is stuff we can't detect directly but that is inferred when we mate current theories with observations.
The simple fact is that dark matter doesn't have to exist for galaxies to rotate the way they do and not tear themselves apart. There are other ways this could work - specifically that our laws and theories describing gravity are not accurate.
Essentially, the reason dark matter is 'needed' is because people are relying on their existing theories of gravity being accurate enough (and we know they are only an approximation) that they can be assumed to hold.
That said, the theories being relied on have been tested time and again and hold wherever they are applied. 'Dark matter' might seem like a huge leap in terms of lavishly proposing extra matter all around the place but it is significantly less of a leap than messing with gravity to explain it.
In terms of what this actually is, it is certain that planets and brown dwarfs and black holes and neutron stars and various other objects we can't directly observe - at least not reliably - are part of the large lump or stuff frequently termed 'dark matter'. This stuff is called 'baryonic dark matter', which translates to: normal stuff that we just can't really see. Specifically, it is stuff made up of protons and neutrons. Electrons are obviously a part of atoms and thus a part of this 'ordinary' dark matter but they are so monumentally out-weighed by their baryonic counterparts that they don't really need to be mentioned.
HOWEVER, even though we can't directly see this type of matter, there are other ways to detect much of it as well as theories and calculations that can be done that impose some kind of upper-limit and the important point is that whatever other objects are put forward as 'dark matter', there still isn't enough to account for observations - when computed with gravity as it is 'understood' currently.
That is where the concept of 'non-baryonic' dark matter comes in.
Once Neutrinos were found to have mass, it was possible that they were the culprits but other measurements and analyses of the structure of the universe strongly suggest that they can't be it alone, though they would certainly form some small component.
In the end, every more 'normal' candidate for the identity of dark matter has been found wanting because if they were responsible, it would mean that those objects are not really what we think they are - as it is would be if neutrinos were found to be the missing matter.
Likewise, dark energy is what we call the unknown stuff that we posit to fill the gap between what we can observe and what we currently know about physics. It is required if we trust our observations and our current theories and both those are on rather solid ground.
Dark matter and dark energy are kind of like the Higgs boson/mechanism.
They are only required if you want to keep your current theories and so some lay-people make out that they are just band-aids, slapped on to make it all work out neatly.
This is a great disservice to the scientists involved and implies that they just don't want to go back and re-think their pet theories. The problem with that notion is that they have rethought those theories. They have theorised and calculated and proposed and experimented and observed and repeated it all numerous times. And the theories work.
However hard it may be to believe concepts of 'dark' matter and energy dominating the universe, it should be understood that if you want to explain the universe without these components then the theories that would have to be thrown out or substantially re-worked to do so are so well supported that that act would be a far greater leap.
In other words, strange, invisible, exotic stuff is actually the most plausible option.
The simple fact is that dark matter doesn't have to exist for galaxies to rotate the way they do and not tear themselves apart. There are other ways this could work - specifically that our laws and theories describing gravity are not accurate.
If you say MOND we can't be friends.
"At some point, wouldn't the gas cool? Then what, new stars someplace else?"
The gas is very diffuse relatively to the densities necessary to form new stars. Also, how do you cool a hot gas in intergalactic space? The only avenue is to radiate the energy away and that takes a very long time.
Nothing that astronomers, physicists, and cosmologists do is beyond the average person. But it takes many years to learn differential geometry, general relativity, functional analysis, group theory, quantum field theory etc. and you can't make a living at it unless you are really good. Most people quite sensibly accept these recent discoveries as a matter of faith, which is unfortunate since science is like democracy, it works best if everyone participates.
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Personally I suspect "dark matter" isn't just one thing. It's a catch-all term for any kind for any matter we can't currently identify, so if/when we do start to identify it, it'll be more like hey X looks like it could account for 45% of the extra mass! ...now the universe is only 15% dark mater. Etc.
I just had a thought (it does happen every now and then and sometimes they're coherent). The basis of Dark Matter is to explain how galaxies move due to the constraints of gravity. While I do believe Dark Matter is a valid theory of why galaxies move the way they do we may also be forgetting that gravity does strange things at the extremes. Hawking has made some wondrous insights into how gravity works (or doesn't) at the event horizon and beyond in black holes, but what is less researched is the possibility that gravity may also act differently at the super macro level. I could be completely wrong and our theories for gravity are 100% accurate, but it wasn't that long ago that Newtonian physics was found to be incomplete by Einstein. And all this is before we even consider the effects of multiple dimensions on space and time as we currently know them. It may even turn out that Dark Matter is dark not because it doesn't reflect light, but because it's actually not part of the observable dimensions of our known universe.
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