Mysterious Radio Bursts Reveal Missing Matter in Cosmos (sciencemag.org) 40
sciencehabit writes: Roughly half of the "normal" matter in the universe -- the stuff that makes up stars, planets, and even us -- exists as mere wisps of material floating in intergalactic space, according to cosmologists. But astronomers had no good way to confirm that, until now. A new study has used fast radio bursts (FRBs) -- powerful millisecondslong pulses of radio waves coming from distant galaxies -- to weigh intergalactic matter, and the results match up with predictions. "Using FRBs as a probe has been an exciting prospect for a while," says astronomer Paul Scholz of the University of Toronto, who was not involved with the work. "Now that we've built up a sample of local FRBs, we're starting to be able to do this. It's certainly exciting." Over the past few decades, cosmologists have compiled an inventory of the stuff that makes up the universe. Some 68% is dark energy, a mysterious force accelerating the universe's expansion. Another 27% is clumps of dark matter that hold galaxies together. Just 5% is so-called normal matter.
Cosmologists know how much normal matter there should be; they can calculate it from how much the big bang should have produced and from the microwave ripple of this cosmic event that still echoes through space. But they can only see about half of it glowing as galaxies and dense gas clouds. The rest, a rarified, intergalactic gas of just one or two atoms in the volume of a typical office room, has been almost impossible to detect. That was until the first FRB burst on the scene in 2007. Because these sporadic blasts are so bright and short, FRBs were originally thought to come from an instrumental glitch, or a source on Earth. (Some early "FRBs" were found to come from a microwave oven at an observatory.) But as detections of FRBs piled up, astronomers realized they were coming from distant corners of the universe. Pinpointing them was difficult because of their rarity: Observers had to be pointing in the exact right direction to catch one, and they wouldn't have time to focus other scopes on the source. These days, telescopes that view large portions of the sky continuously are bagging more FRBs.
Cosmologists know how much normal matter there should be; they can calculate it from how much the big bang should have produced and from the microwave ripple of this cosmic event that still echoes through space. But they can only see about half of it glowing as galaxies and dense gas clouds. The rest, a rarified, intergalactic gas of just one or two atoms in the volume of a typical office room, has been almost impossible to detect. That was until the first FRB burst on the scene in 2007. Because these sporadic blasts are so bright and short, FRBs were originally thought to come from an instrumental glitch, or a source on Earth. (Some early "FRBs" were found to come from a microwave oven at an observatory.) But as detections of FRBs piled up, astronomers realized they were coming from distant corners of the universe. Pinpointing them was difficult because of their rarity: Observers had to be pointing in the exact right direction to catch one, and they wouldn't have time to focus other scopes on the source. These days, telescopes that view large portions of the sky continuously are bagging more FRBs.
Open office or real office? (Score:3)
So...is that a 30x50x12 open office hell room or a 10x10x9 real office like engineers used to have when productivity and/or quality was important?
Re:Open office or real office? (Score:5, Funny)
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Yes, many people feel the freedom from the open office..
as they are currently working from home..
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Nobody uses Open Office anymore, they have all moved to LibreOffice.
Yep, everyone got totally forked.
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Interesting observation (Score:5, Interesting)
That is a really handy way of measuring, if you can determine the distance to the FRB.
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That is a fascinating technique. Thanks for picking out the interesting part.
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Asking because somewhere in here I have to wonder if an FRB - a clump of radio frequencies released at [we assume] the same time - would go through a radio-spectrum equivalent of the red-shift of optical light?
Astronomers have used that doppler effect to calculate distance based on the location of recognized elemental absorption patterns in a light signal from the source. (Hubble's Law, etc
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No, the article states "Low frequencies experience more drag from electrons than high ones, so when the pulse reaches a radio telescope on Earth, low frequencies lag behind." This means that the interference that these electrons provide is NOT uniform across the radio spectrum.
FRB's? (Score:1)
Microwave oven (Score:2)
Sorry, that wasn't two magnetars colliding, I was just heating up my burrito.
sorry stupid question here... but.. (Score:2)
How in heavens name would you KNOW how much matter the big bang produced? Aren't there still a lot of unknown physics from the first 5 min? Do we know how what causes matter at all with certainty? Just checking but seems an odd claim.
Re:sorry stupid question here... but.. (Score:5, Interesting)
The first 5 minutes don't contain unknown physics, we can (and have) replicated those conditions on earth, up past the unification of the electromagnetic and weak forces at 10^{-12} seconds (the "electroweak epoch"), until 10^{-30-several) seconds after t-zero where we'd love to know more. It's the very earliest fractions of a second that have the unknown stuff we're working towards: what happens at the scale where the strong force is also accounted for? (the so-called GUT scale).
So, working this all out is something grad students often do as a homework problem in a 5xxx-level cosmology course. As the universe expands and cools (regular old thermodynamics), the rates at which different stuff in the universe interact/decay are known (we measure it in accelerators). The strongest constraints on "number of baryons" (ie, protons and neutrons) in the universe comes from measuring how much hydrogen vs. helium vs. lithium vs. (etc) there is in the early universe. Too much (or not enough) energy tied up in such "normal" matter (vs. radiation vs. dark matter etc) means the temperatures and densities as a function of time give you different amounts of different elements made as things fuse before it cools off enough that they can't anymore. Compare those calculated ratios to the measured ones, and within error bars, you don't have much room for lots of protons and neutrons without creating a universe composed of very different chemical stuff than the one we have. The "Big Bang Nucleosynthesis" article on wikipedia is actually a pretty good summary if you're curious, and working out just the ratio of hydrogen to helium is something youd do in a Jr/Sr level undergraduate astrophysics course.
Interestingly, one of the largest contributions to the error budget in this calculation is simply the lifetime of a neutron: 881.5±1.5 s (or about 15 minutes). Why? The error bars are comparatively crappy because working with neutrons in a lab is hard. And knowing how fast neutrons are falling apart means you know how many are around to add to protons to make things more complicated than Hydrogen nuclei. So, it's not weird hard physics which limits this calculation: it's something as prosaic as the half life of the second most common baryon in the universe today!
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Thanks I'm a little less ignorant now. I never would have thought to search for those terms. I read the article. Still can't say as I completely understand but some of it make sense. Still this seems like the predicted matter in the universe is being calculated based on observable ratios? How do you go from observable ratios to ' too much matter is missing to hold the universe together so there must be dark energy/ matter'? How do you prove homogeneous distribution ( that seems like a huge leap)? Why c
Re: sorry stupid question here... but.. (Score:2)
There's a(n English) book by German publisher Springer called "Cosmology for the curious" which is *very* well written and can be understood by non-physicists. Amazon link: https://www.amazon.com/Cosmolo... [amazon.com]
(Physicist here, but unrelated to cosmology, and I was able to pretty much read it cover to cover as a bed-time-story, which means it's not as confusing as physics usually is... :-) Hence suitable for non-physicists.)
It's too complicated for me to reproduce, but the answer to the matter ratio essentially
Special relativity (Score:2)
Forget that magic stuff. I would like a good text that really explains Special Relativity.
Einstein himself wrote a layman's explanation but it don't make sense to me. He used a train example in which he walked tediously step by step and then made a giant leap in an "Obviously" which I think was a fudge. (His example had lightening behave like thunder through air, which is exactly wrong.)
Anyway, if you know something then please let me know. But once you start mucking with basic concepts like time and sp
Re: Special relativity (Score:2)
To me, the book above did the trick. They have a good intro to both SR and GR. (There is another very good book on relativity, "Relativity, Gravitation and Cosmology" by Ta-Pei Cheng, published by Oxford Press, which I also have on my desk and probably paved muhc of my way to understanding...).
I don't know which of Einstein's leaps was incredible to you, but for myself, I had to realize first that Special Relativity starts with Maxwell's equations. (That's what I was always told, however I assumed that was
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How in heavens name would you KNOW how much matter the big bang produced? Aren't there still a lot of unknown physics from the first 5 min? Do we know how what causes matter at all with certainty? Just checking but seems an odd claim.
We have a very good photograph from when the universe was 370,000 [wikipedia.org] years old. The technique for figuring out the ratio of energy to matter to dark matter from that isn't obvious, and is worth explaining.
At that time, the dominant forces in the universe were gravity and light pressure. Slightly more dense patches of the universe would contract a little, then "bounce" from the light pressure. This is simple harmonic motion; acoustic waves moving across the universe; the music of the spheres.
So this is much
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> Aren't there still a lot of unknown physics from the first 5 min?
HOW the Laws of Physics just "magically" emerged! /s
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Some of us old-timers still remember "luminiferous aether."
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Except the unicorns and pixie dust _are_ the model. Both have behaviors which are very carefully defined, and the effects of some things which behave exactly like unicorns shows in many places at different scales. We just haven't managed to corral one and send it to the taxidermist for you to mount on your wall yet.
So far, any other magical models do a far worse job of explaining the observables. Doesn't' stop people from coming up with ideas! But, none work as well as your unicorns, so we're stuck with
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A universe where we knew all the answers already would be a pretty boring place.
The universes purported "boringness" has no bearing on the flaws of merits of any model.
Re:Model vs Pixie Dust (Score:4, Informative)
Neil DeGrasse Tyson likes to say that we could call dark matter "Fred" and dark energy "Wilma" because the name of these things may be misleading. And, while general relativity holds up really well, it's possible that at large scales something else is going on, much like Newtonian physics works pretty well for navigating a spaceship out of our solar system, but doesn't work as well for calculating Mercury's orbit.
So it's not exactly correct to say that cosmologists just invented stuff. They put a name to an effect that they can see and measure and described it as well as they could. Dark matter/energy are kind of like placeholders for new maths, new physics, new matter, or some combination of all of the above. We may have an answer for all of it in a couple of years, or it may be the breaking science of 2120. In the meantime, don't get too worked up over what they're called.
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how do we know we can't see it? How do we know it is withing the observable universe? what stops the universe from simply being much larger then observed?
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How do we know this isn't just one big simulation in an alien computer?
How do I know you aren't a cat walking across a keyboard?
There are so many questions.
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how do we know we can't see it?
We don't, but we do know we haven't seen it yet. For Dark Matter, there are a number of promising ideas (WIMPs and Axions in particular), and well-developed experiments trying to see them. Even when these experiments come up empty, each crosses off the list a number of things that must not be what the answer is, or they would have been seen.
How do we know it is withing the observable universe?
We don't. We know that it is affecting the observable universe. The answer could very well be bonus dimensions we don't know about yet. The answer is probably n
How come we can see the Moon? (Score:4, Interesting)
It is a long, long way away. If space was even a tiny bit hazy it would be an invisible blur.
But we can actually see orders of magnitude further, to the beginning of time, 13 billion light years.
For that to happen, space has to be amazingly, stunningly, absolutely, clear. One spec of dust every million kilometers would kill that view.
It has always seemed very odd to me that this is possible. Why would matter clump together so amazingly well that there is (almost) absolutely nothing between galaxies. And very, very little within them.
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Why would matter clump together so amazingly well that there is (almost) absolutely nothing between galaxies. And very, very little within them.
Exactly! Ordinary matter clumps up so well... that it all clumps up: leaving very little left over that's not clumped up. We can see this happening in star forming regions in our galaxy. Very dusty, not transparent, becoming transparent as stuff clumps up (and much of the leftovers are blown away by strong stellar winds from the new stars.)
Why does this happen? Because gravity, even though really weak, is always attractive, and gets stronger as things get closer. F=G m1 * m2 / r^2. That's exactly t
Strung-out in web is half of what ordinary matter (Score:1)