Your explanation makes sense; I couldn't see the alternate explanation for the selective dimming -- and now that there is one, I retract my accusation. (Moderators, please mod root post down.)
With 6:00 as the point nearest us and 12:00 as the point diametrically opposed through the galactic nucleus--there's a bright one at 7:30, lower part of the dust disk. There's also a bunch on the top of the disk, between 2:00 and 5:00. (And they're all foreground stars, so they're not really associated with the disk).
If you compare the other stars in the image, it's pretty clear that it's not a resolution artifact.
There are a number of missing stars -- look more carefully at the disk. There's a bright one on the left and a smattering on the right. And yes, I realize that ESO is not HST.
There's a number of stars in the foreground that are missing -- presumably, they prettied up the disk a bit to make it more photogenic. (Compare to this ESO shot and you'll see what I mean.) I'm always disappointed when NASA has to bend the truth -- even just a little bit.
(I posted this on metafilter, but it bears a mention on slashdot.)
I did a quick back-of-the-envelope calculation last month when I saw a piece about this in Science. There's no way that a mere 22% change in dilation can't double your acuity; the pinhole effect isn't *that* strong. So I'd bet that most of the improvement has to come from "accommodation" or some other effect.
Been a long time since I looked at the specs, but:
* I think it's 200 GeV/nucleon.
* I believe that the volume is the same order of magnitude of the nucleus itself -- probably a few times larger than a nucleus.
* I don't know. A very short time, no doubt.
* It decayed by condensing into ordinary hadrons, just as steam condenses into liquid water. Lots of energy was shed by the creation of extra matter.
* Between condensation and mass-energy conversion, you get ordinary matter -- baryons, mesons, leptons, and the force carriers. (And, presumbably, other beyond-SM particles that we don't know about yet.)
Neutrinos are weakly interacting and they've got mass, but they're not a real candidate for exotic dark matter. (There are two types of dark matter: baryonic, which is about 4% of the "stuff" in the universe and exotic, which is about 23% of the stuff. [The remainder is dark energy.])
Because of oscillation measurements of neutrinos, of CMB fluctuations, and of galaxy clusters, scientists have concluded that neutrinos make up only about 0.5% of the stuff in the universe. This is as much matter as is in the visible stars and galaxies, but it's not enough to account for exotic dark matter.
Um... can you point me to an experiment that's reached breakeven? The closest I know of is a late '90s claim by JT-60 that claimed a "breakeven equivalent" -- basically, they said if they had run the machine in a different configuration, they should have had breakeven. (Read: they didn't reach breakeven in the experiment they ran.)
AFAIK, we haven't gotten more energy out than we put in yet, much less "long since gotten past" that point.
ICF was never principally for power generation; it was a weapons-lab project with energy thrown in as an afterthought to make it look like it had peaceful purposes. The big ICF facility in the states, NIF, is just coming online now... and the future of ICF will have nothing to do with what happens with ITER.
Boiled water. Ever put olive oil on top of water you're going to put spaghetti in? It degasses pretty thoroughly before it hits a rolling boil, but the oil remains on top and doesn't emulsify even when it hits a boil.
On the other hand, I don't think the definition of darkmatter is fine as it stands.... You hope that dark matter are not really "dark", i.e. you can see it via some interaction with non-dark matter. If you find it, then they are not "dark".
That's true, and your definition is consistent. However I prefer the definition of "dark" as being something that doesn't interact via em radiation, which means I'd have to coin a new word for something that doesn't interact except via gravity... maybe "sterile." But then I'd have to rename the sterile neutrino. *sigh* Maybe your definition is for the best. *grin*
In a maximally boring universe, dark matter is just that, dark and completely undetectable except through gravity.
Yeah, that would suck.:) But even maximally boring has to be pretty interesting. Not only do you need a new particle and extend the SM that way, you also have to extend it to explain how you can get a matter-antimatter asymmetry without any contribution from the weak sector.
Astronomy/astophysics pays my bills, and I can tell you that 4.4% of baryons from WMAP really means anything that is known in particle physics as quarks, leptons, blah blah blah.
Sorry; I'm afraid you're wrong. Neutrinos, which are leptons, are not in that 4.4%. They constitute an additional 0.5% or so on top of the baryonic fraction.
"baryons" (in the 4.4% of WMAP) is classified as matter that is not "dark". "Non-dark" means it interacts with other stuff and itself beyond just pure gravitation. That includes "radiation", which is stuff that behaves relativistically, and include things like photons, neutrinos,a nd perhaps other relics.
I can't believe this, because according to your definition, all the leading candidates for exotic dark matter like WIMPs and axions aren't dark. That doesn't make any sense at all. I'm willing to accept that astronomers are sloppy with their nomenclature, but not that sloppy.
First, he said baryons, not baryonic matter -- you will never hear any astronomer call a lepton a baryon.
Second, technically, even in astronomy, baryonic matter is only the nuclei -- the leptons are counted separately, though they're unimportant masswise, as you mentioned. Here's why.
There are several ways of computing the amount of and types of matter in the universe. One of the most important is examining primordial gas clouds and looking at the relative abundances of hydrogen, helium, and lithium and their various isotopes. This tells us about the era of nucleosynthesis -- the time 3 seconds to 3 minutes after the big bang when the temperature and pressure of the universe was enough to induce nuclear fusion. After 3 minutes, this process ended and froze the ratios of primordial elements.
By looking at those ratios, scientists could figure out the abundance of those nuclei -- the nuclei, not the leptons, which don't affect the ratios at all. From this, they can figure out the density of nuclear matter in the universe, which is related to a quantity known as omega sub b. This number is thought to be about 4.5% from measurements of the elements in those gas clouds -- and MAP confirmed this by a different method. But this baryonic fraction does not have anything to do with the leptonic component of matter... including electrons and neutrinos.
So, when astronomers say that they have shown that 4.4% of the universe is made up of baryonic matter, they really mean baryons. It just so happens that there are pesky leptons hanging around the baryonic matter, too.
Not quite. There are two types of dark matter. Some is made up of baryons -- it's part of the 4.4%. The rest is not made up of baryons, nor is a significant part of it made up of the leptons we know of. That's "exotic dark matter."
Nope. Baryons are the heavy particles made up of three quarks. Leptons are light particles that are themselves fundamental particles. In between are mesons, made of a quark and antiquark.
... about what this mysterious technology is, other than it's some form of signal processing. (Geez, what an advance!) And the quotes don't make me too confident that this is real:
"This technology allows you to double the resolution of the sonar at any given distance.
"If you're looking for a mine at 400 metres, the picture you get would be as clear as if it was 200 metres away."
Um... wouldn't that be quadrupling the resolution?
... it's appalling. Every image that comes through the NASA PR machine winds up on their site. And surprise, surprise, almost all the images come from NASA; nothing from ESO, nothing from DASI or CBI... almost all of it is NASA stuff, made up or not.
When Space.com was younger, it had its offices in NASA's HQ building. Seems like they haven't gotten any more independent as they got older.
I say we find a way to make it profitable. Everyone knows that once there's money to be made development takes off (no pun intended). Maybe NASA should consider bringing tourists into space just for the extra revenue!
Yeah, right. Do you have any idea how much the ISS costs? $100 billion. Each shuttle flight costs $400 million. Even a Soyuz costs $100 million, and the Russians take a tourist only when they have an unused seat on the flight.
At the current going rate of $10 million a tourist (and $10 million tourists are pretty rare), you'd need to get 10 in every Soyuz (capacity 3) and 40 in every Shuttle (capacity 7) to break even on launch costs alone. Then throw in the cost of the space station... ha, ha. Profitable -- not in this lifetime. But then again, since "everyone knows" that there's money to be made, these numbers *must* be wrong.
IIRC, the publication of the g-2 results was in 2001 and 2002. There's probably a third release coming, where they release the mu-plus results, too.
When it comes down to it, the g-2 stuff is just a three-sigma deviation from the standard model -- interesting, and better than most other three-sigma results out there, but not definitive. The neutrino results, first at Super-K, SNO, and K2K, and now at KamLAND, are pretty much definitive.
Besides, the g-2 result and the neutrino results each require different modifications to the standard model; the latter requires supersymmetry or some extension of the model, whereas the former requires the assumption of mass in existing particles.
10^54 ergs would resolve a lot of the difficulty, but I thought that SNs couldn't produce anything much more than 10^51 or so ergs; anything significantly greater than that is a "hypernova" and is thought to have a different origin. (Or that the SN is beamed, which gives the illusion of higher energies.)
Even so, I'm still confused about the companion, as the system's binding energy is probably rather less than its kinetic energy.
1) The black hole has a companion star, so wouldn't a kick of that magnitude tear it away from its companion and preclude it from acquiring another until it slows?
2) Even ignoring the mass of the companion, the estimates are that the BH is about 7 solar masses.
That means that the BH has acquired a kinetic energy of 1/2 * 7 * (2^30 kg) * (10^5 m/s)^2 = about 10^41 J of energy, which is about 1/1000 of the energy of the SN explosion (10^51 erg = 10^44 J). To me, that seems like an exceedingly large fraction of a roughly isotropic explosion converted into motion. It gets even worse if you throw in the mass of the companion.
Anyone have any insights into how this can happen?
Very nice and informative post. Case closed. I hope this company goes the way of ZeoSync, which claimed to have universal lossless compression. (They seem to have fallen off the face of the earth.)
As for 90% vs 84%, my calculation was nothing more complicated than 1 - (0.5)^(0.5/0.15), so I obviously defer to the numbers of an expert.:)
And as for other outrage on the internet, Bob Park's What's New column at www.aps.org mentioned it, which is always the kiss of death. But it's been pretty quiet other than one thread in a physics-related newsgroup, as far as I can tell.
Slashdot Mirror
Your explanation makes sense; I couldn't see the alternate explanation for the selective dimming -- and now that there is one, I retract my accusation. (Moderators, please mod root post down.)
If you compare the other stars in the image, it's pretty clear that it's not a resolution artifact.
There are a number of missing stars -- look more carefully at the disk. There's a bright one on the left and a smattering on the right. And yes, I realize that ESO is not HST.
(I posted this on metafilter, but it bears a mention on slashdot.)
I did a quick back-of-the-envelope calculation last month when I saw a piece about this in Science. There's no way that a mere 22% change in dilation can't double your acuity; the pinhole effect isn't *that* strong. So I'd bet that most of the improvement has to come from "accommodation" or some other effect.
* I think it's 200 GeV/nucleon.
* I believe that the volume is the same order of magnitude of the nucleus itself -- probably a few times larger than a nucleus.
* I don't know. A very short time, no doubt.
* It decayed by condensing into ordinary hadrons, just as steam condenses into liquid water. Lots of energy was shed by the creation of extra matter.
* Between condensation and mass-energy conversion, you get ordinary matter -- baryons, mesons, leptons, and the force carriers. (And, presumbably, other beyond-SM particles that we don't know about yet.)
Because of oscillation measurements of neutrinos, of CMB fluctuations, and of galaxy clusters, scientists have concluded that neutrinos make up only about 0.5% of the stuff in the universe. This is as much matter as is in the visible stars and galaxies, but it's not enough to account for exotic dark matter.
(MACHOs are thought to be baryonic dark matter.)
AFAIK, we haven't gotten more energy out than we put in yet, much less "long since gotten past" that point.
ICF was never principally for power generation; it was a weapons-lab project with energy thrown in as an afterthought to make it look like it had peaceful purposes. The big ICF facility in the states, NIF, is just coming online now... and the future of ICF will have nothing to do with what happens with ITER.
Boiled water. Ever put olive oil on top of water you're going to put spaghetti in? It degasses pretty thoroughly before it hits a rolling boil, but the oil remains on top and doesn't emulsify even when it hits a boil.
That's true, and your definition is consistent. However I prefer the definition of "dark" as being something that doesn't interact via em radiation, which means I'd have to coin a new word for something that doesn't interact except via gravity... maybe "sterile." But then I'd have to rename the sterile neutrino. *sigh* Maybe your definition is for the best. *grin*
In a maximally boring universe, dark matter is just that, dark and completely undetectable except through gravity.
Yeah, that would suck. :) But even maximally boring has to be pretty interesting. Not only do you need a new particle and extend the SM that way, you also have to extend it to explain how you can get a matter-antimatter asymmetry without any contribution from the weak sector.
Sorry; I'm afraid you're wrong. Neutrinos, which are leptons, are not in that 4.4%. They constitute an additional 0.5% or so on top of the baryonic fraction.
"baryons" (in the 4.4% of WMAP) is classified as matter that is not "dark". "Non-dark" means it interacts with other stuff and itself beyond just pure gravitation. That includes "radiation", which is stuff that behaves relativistically, and include things like photons, neutrinos,a nd perhaps other relics.
I can't believe this, because according to your definition, all the leading candidates for exotic dark matter like WIMPs and axions aren't dark. That doesn't make any sense at all. I'm willing to accept that astronomers are sloppy with their nomenclature, but not that sloppy.
Second, technically, even in astronomy, baryonic matter is only the nuclei -- the leptons are counted separately, though they're unimportant masswise, as you mentioned. Here's why.
There are several ways of computing the amount of and types of matter in the universe. One of the most important is examining primordial gas clouds and looking at the relative abundances of hydrogen, helium, and lithium and their various isotopes. This tells us about the era of nucleosynthesis -- the time 3 seconds to 3 minutes after the big bang when the temperature and pressure of the universe was enough to induce nuclear fusion. After 3 minutes, this process ended and froze the ratios of primordial elements.
By looking at those ratios, scientists could figure out the abundance of those nuclei -- the nuclei, not the leptons, which don't affect the ratios at all. From this, they can figure out the density of nuclear matter in the universe, which is related to a quantity known as omega sub b. This number is thought to be about 4.5% from measurements of the elements in those gas clouds -- and MAP confirmed this by a different method. But this baryonic fraction does not have anything to do with the leptonic component of matter... including electrons and neutrinos.
So, when astronomers say that they have shown that 4.4% of the universe is made up of baryonic matter, they really mean baryons. It just so happens that there are pesky leptons hanging around the baryonic matter, too.
Not quite. There are two types of dark matter. Some is made up of baryons -- it's part of the 4.4%. The rest is not made up of baryons, nor is a significant part of it made up of the leptons we know of. That's "exotic dark matter."
Nope. Baryons are the heavy particles made up of three quarks. Leptons are light particles that are themselves fundamental particles. In between are mesons, made of a quark and antiquark.
"This technology allows you to double the resolution of the sonar at any given distance.
"If you're looking for a mine at 400 metres, the picture you get would be as clear as if it was 200 metres away."
Um... wouldn't that be quadrupling the resolution?
here, here, and here.
None. I think the total mass energy is less than a thousandth of a Joule.
When Space.com was younger, it had its offices in NASA's HQ building. Seems like they haven't gotten any more independent as they got older.
Yeah, right. Do you have any idea how much the ISS costs? $100 billion. Each shuttle flight costs $400 million. Even a Soyuz costs $100 million, and the Russians take a tourist only when they have an unused seat on the flight.
At the current going rate of $10 million a tourist (and $10 million tourists are pretty rare), you'd need to get 10 in every Soyuz (capacity 3) and 40 in every Shuttle (capacity 7) to break even on launch costs alone. Then throw in the cost of the space station... ha, ha. Profitable -- not in this lifetime. But then again, since "everyone knows" that there's money to be made, these numbers *must* be wrong.
Neutrinos require mass assumption; g-2 requires supersymmetry or other extension.
When it comes down to it, the g-2 stuff is just a three-sigma deviation from the standard model -- interesting, and better than most other three-sigma results out there, but not definitive. The neutrino results, first at Super-K, SNO, and K2K, and now at KamLAND, are pretty much definitive.
Besides, the g-2 result and the neutrino results each require different modifications to the standard model; the latter requires supersymmetry or some extension of the model, whereas the former requires the assumption of mass in existing particles.
Even so, I'm still confused about the companion, as the system's binding energy is probably rather less than its kinetic energy.
1) The black hole has a companion star, so wouldn't a kick of that magnitude tear it away from its companion and preclude it from acquiring another until it slows?
2) Even ignoring the mass of the companion, the estimates are that the BH is about 7 solar masses. That means that the BH has acquired a kinetic energy of 1/2 * 7 * (2^30 kg) * (10^5 m/s)^2 = about 10^41 J of energy, which is about 1/1000 of the energy of the SN explosion (10^51 erg = 10^44 J). To me, that seems like an exceedingly large fraction of a roughly isotropic explosion converted into motion. It gets even worse if you throw in the mass of the companion.
Anyone have any insights into how this can happen?
As for 90% vs 84%, my calculation was nothing more complicated than 1 - (0.5)^(0.5/0.15), so I obviously defer to the numbers of an expert. :)
And as for other outrage on the internet, Bob Park's What's New column at www.aps.org mentioned it, which is always the kiss of death. But it's been pretty quiet other than one thread in a physics-related newsgroup, as far as I can tell.