The second peak depends on the sound speed, which depends on the temperature and density of ONLY THE BARYONIC matter. It is a true acoustic peak, and so depends on how fast sound waves travel, which is not something affected by the non-baryonic matter. The number you get is completely consistent with the number you get from the light element abundances and big bang nucleosynthesis theory.
The universe is almost certainly exactly flat. Flatness is expected from inflation, but, more tellingingly, is the fact that if it weren't exactly flat (to within 40 orders of magnitude), it shouldn't be close to anything flat today.
Yes, right, neutrinos can only contribute a tiny amount.
Similar to galactic rotation curves, galaxy velocities in clusters are too high without large amounts of dark matter.
The best evidence at this stage probably comes from the microwave background acoustic peaks. The amplitudes of the second and third peaks depend on the amount of baryonic matter (second peak) and the total amount of matter (third peak), and indicate about six times as much non-bayonic matter as baryonic matter. We still don't know what it is, but know how much there is to two significant figures.
I've alerady linked to it already in this thread, but I'll do it again because it is a very nice pedagogical website about these results. Check out Wayne Hu's webapages.
There's some information from the public WMAP webpage here. You might also look at Wayne Hu's excellent webpages here. Start with the intructory materials and move up from there. It has only been in the last couple of years that we've been finally confident about the values of the cosmological parameters and that the universal geometry is flat. The dark matter and dark energy both are still confusing, to be sure, but the picture of the fundamental nature (age, curvature, etc.) of the universe is pretty solid at this point.
I've read the scientific abstract now. They've indeed got something interesting here. There ought to be a substantial galaxy here to be seen, and they've looked hard for it down to a sufficiently faint level, and don't see it. Pretty cool!
It's a very well supported hypothesis based on empirical evidence. The only viable alternative would be that we have gravity very, very wrong on large scales, and the evidence is against that. On the other hand, the evidence for non-baryonic dark matter comes from a number of areas, not just galactic motions. One form of non-baryonic dark matter you probably know something about is the neutrino, which apparently does have a tiny mass based on recent experiments demonstrating oscillations, but other considerations indicate that neutrinos are far from the dominant type of dark matter. Thirty years ago, your level of skepticism would have been appropriate. To experts in the field today, it's a no-brainer. What the stuff actually is, however, is still largeley unknown.
Yeah, but Hawking radiation is negligible in big black holes, and not something astronomers observe. Radiation associated with massive astronomical black holes is completely dominated by surrounding accretion processes.
That's right. Observations of our own Milky Way galaxy, which we have good limits on the normal baryonic dark matter, is dominated gravitationally by something more exotic, and a lot of it. The best limits on the amount of baryonic matter and non-baryonic matter in the universe come from WMAP. There's about six times as much non-baryonic dark matter out there as there is normal stuff. These results are well supported by many other observatoins (e.g., light element abundances, galactic rotation curves, cluster mass estimates, etc.).
There is both baryonic and non-baryonic dark matter. Astronomers distinguish between the two types, and try to study/understand both. We don't know what the major non-baryonic dark matter is, but we know some of its properties (how it clumps on various scales), and we know it doesn't readily interact with baryonic matter. There are candidate particles. Neutrinos apparently have a mass, and likely make up a small fraction of it, but for the most part, no, we don't know what it is.
No, hey, that's pretty good analysis based on the scant information in the article. I'd need more to be sure myself. Presumably they've done very deep imaging and think they ought to have seen the stars in a galaxy of this mass, if they were there, and don't. But this is a relatively low mass for a galaxy, and such dwarf galaxies are notoriously difficult to make out. There are some good people at Cardiff, and if they're making a fuss out of this they've probably got a pretty good case, but I'd want to read the refereed journal article to better understand the limits.
You're last point is off the mark, however. Our best estimates for the universal mass density don't depend on optical observations at all (rather microwave background), and are very robust against missing faint/dark matter. The closed universe/collapse model, based on our current best understanding is dead, dead, dead. Only something very surprising about the time evolution of dark energy would seem to be able to alter this conclusion.
There is both baryonic and non-baryonic dark matter. Astronomers worry about understanding both. HI isn't bad because it emits 21 cm radiation (although very weakly), but things like black holes, low-mass dwarf stars, cool white dwarfs and neutron stars, all count toward dark matter. There is a lot more non-baryonic dark matter, absolutely, and it dominates galaxy masses and is indeed the primary thing of interest here.
To me, a flat is a flat is a flat. There's no information there from the source (ideally). So it may be pointed toward Earth, but you're not SEEING Earth (e.g., focusing).
The optical CCDs just oversaturate immediately. The UV-sensitive MAMA detectors would actually be destroyed. Hundreds of man hours (at a minimum) are spent checking for bright targets when they are in use.
Hubble is no good for looking at the Earth because it's too bright. It would flood and destroy the detectors! We always have to do bright object checks and are restricted with how close we can look at bright objects. They made one exception to look at the moon once, but I believe they had to do some tricky things to manage that.
Some astronomers at the Space Telescope Science Institute told me about unidentified people from the government coming to see them in the early 1990s. Hubble was having problems with a wobble when moving between light and shadow, and they were making progress in reducing it. I was told these people answered no questions, only asked them. Sounded like they had their own version of Hubble, pointed Earthward. Duh. Don't know its capabilities, but I'm sure it's pretty good.
How many piano tuners are there in Chicago? This is an example Fermi used to use. Yes, maybe you could go out and measure this, using the "job" field in tax returns, the yellow pages, etc., but you can also get an idea of the number by figuring out how many people live in Chicago. How many of those people on average have pianos? How often do they need tuning? How fast can they be tuned? You have a pretty good idea (or he did anyway) of the answers to those individual questions, you can put an estimate on the number without actually making a direct measurement. Some problems in science can be tackled this way, and it's a type of reasoning scientists ought to be able to use well.
I don't know all the details myself, but the article focuses on SWIFT, which is designed to monitor the whole sky for bright gamma ray bursts. It just went up itself in November, although there are other satelites up with similar (but worse) capability). Gamma ray bursts go off about once a day, give or take, and spacecraft like SWIFT detect them, point toward them and localize them, then relay that information to ground-based telescopes for follow-up at other wavelenghts. So some of your analysis is right, but some of your assumptions are wrong.
It's funny that gamma ray bursts were first discovered by the military who wanted to watch for nuclear weapons. This was in the early 1970s, maybe a bit earlier. They went batshit when these previously unknown bursts started setting off alarms on a regular basis.
Actually, it's more complicated. Yes, the radiation/heating would not be uniform, but the bigger killer would be from the destruction of chemicals like ozone in the upper atmosphere that protects us from the sun's radiation. The details are kind of complicated, and depends on exact distances, fluxes, and spectral energy distrubution. And atmospheric science.
I guess I've observed there too many times for such a joke to be funny. Lick Observatory is named after James Lick who funded the establishment of the Observatory back in the 1890s. It's an interesting place -- the first observatory put on a mountaintop (it was originally going to be in downtown San Francisco, imagine that). His ashes are kept in a memorial under the 36 inch refractor.
It's a spectacularly pretty location, overlooking the bay, and the old observatory portion is all marble and brass, 19th century elegance. I got married there and the reception was great (band, catered dinner, and the 36 inch refractor was available for guest viewing).
The road to Lick from San Jose is a very twisty 19 miles. The mules, originally used to haul material there, wouldn't go up more than a six degree incline, so it's switchback city. This also makes it a popular road for bicyclists. I used to be annoyed with them, since I had to go there semi-regularly for work and often drove while sleepy. I imagined I'd come around a corner and have a tired rider at zero speed in the middle of the lane. They paid me back though one time. I was sitting in the dining room eating breakfast one afternoon, and these two riders and a car pulled up. The car driver switched off to ride a bike, and she stepped in front of the window and stripped out of all her clothes while the milk dripped off my spoon, caught halfway to my mouth. Good times.
The Drake equation IS an equation. That's the right term for it in science, hard or soft. The number of technological civilizations in the galaxy we can communicate with is equal to the product of the probabilites/numbers on the other side of the equal sign. Just because some of those numbers/probabilites are uncertain does not stop it from being an equation. For instance, it isn't a proportionality or an approximation (unless you actually start pluggin in approximate numbers). And I wouldn't say that the term equation is a "title." You're reading too much into this.
These sort of estimation games are really valuable in lots of branches of science and often lead to insight. Enrico Fermi used to do this all the time, which is especially relvant since his "Fermi Paradox" about how it's strange we haven't encountered alien intelligences is the same sort of thing that Drake formalized.
Sure, the Drake equation is but a structured guess, but it is a handy way of organizing the important terms and quantifying each and how certain they are. I got to have dinner with Frank Drake a few years ago at Lick Observatory, which was pretty cool.
At the risk of belaboring the point, I wanted to mention how important Toomre and Toomre's galaxy simulations were in the early 1970s. We could see interacting galaxies out there, with long drawn out tails of stars, that looked really strange. It wasn't until they did numerical simulations with many stars moving according to gravity that we could really be sure we understood what was going on. These simulations produced the same sort of odd features very naturally, the result of gravitational tidal forces. It wasn't a waste of time at all, and really the only way to make progress on the problem.
You're missing something. The work is trying to explain a rather tight relationship between the masses of the central black holes and the masses of the stars in the galaxies. The black hole is always about 1/1000 of the galaxy mass. Why 1/1000? Why not 1/100 or 1/10000? Why so steady for ALL galaxies? It's THAT observation that makes this research of interest, because they've apparently found a quantitative way to explain this fundamental relationship.
Simulations are a valuable area of investigation in most modern sciences, including astronomy. It's a very reasonable approach and complementary to observation. Basically, think of it as an expression of a theory, that makes specific predictions that can be tested against observation. Their simulation, based on some assumptions and our current physical understanding, has to match observations or we know they did something wrong. To the extent the simulation matches observations, and continues to pass observational tests, we gain confidence that the assumptions and physics actually reflect reality. It's just a lot more complicated than a one line equation like Newton's Law of Gravitation. Yeah, you should scrutinize the number of variables and suspect the conclusions, but it's science and can be tested and improved.
To go to your analogy, if economics/people were as predictable as matter and energy, their simulation might show how millionaires arise in a population based on initial conditions, at least statistically. They could make a prediction for how many millionaires appear in the population over the next decade, and if the prediction was borne out, you might think they'd figured out something worthwhile.
As I understand it Hawking radiation is completely negligible from supermassive black holes. I would imagine that the event horizon scale is so large compared to anything really freaky that the distortion doesn't make that much of a difference.
This is just a simple calculation based on the distance to the galactic center and the given absolute magnitude. You work it out in a couple of lines of math. This is for my non-major course and doesn't involve MHD simulations!!!
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The second peak depends on the sound speed, which depends on the temperature and density of ONLY THE BARYONIC matter. It is a true acoustic peak, and so depends on how fast sound waves travel, which is not something affected by the non-baryonic matter. The number you get is completely consistent with the number you get from the light element abundances and big bang nucleosynthesis theory.
The universe is almost certainly exactly flat. Flatness is expected from inflation, but, more tellingingly, is the fact that if it weren't exactly flat (to within 40 orders of magnitude), it shouldn't be close to anything flat today.
Yes, right, neutrinos can only contribute a tiny amount.
Similar to galactic rotation curves, galaxy velocities in clusters are too high without large amounts of dark matter.
The best evidence at this stage probably comes from the microwave background acoustic peaks. The amplitudes of the second and third peaks depend on the amount of baryonic matter (second peak) and the total amount of matter (third peak), and indicate about six times as much non-bayonic matter as baryonic matter. We still don't know what it is, but know how much there is to two significant figures.
I've alerady linked to it already in this thread, but I'll do it again because it is a very nice pedagogical website about these results. Check out Wayne Hu's webapages.
There's some information from the public WMAP webpage here. You might also look at Wayne Hu's excellent webpages here. Start with the intructory materials and move up from there. It has only been in the last couple of years that we've been finally confident about the values of the cosmological parameters and that the universal geometry is flat. The dark matter and dark energy both are still confusing, to be sure, but the picture of the fundamental nature (age, curvature, etc.) of the universe is pretty solid at this point.
I've read the scientific abstract now. They've indeed got something interesting here. There ought to be a substantial galaxy here to be seen, and they've looked hard for it down to a sufficiently faint level, and don't see it. Pretty cool!
It's a very well supported hypothesis based on empirical evidence. The only viable alternative would be that we have gravity very, very wrong on large scales, and the evidence is against that. On the other hand, the evidence for non-baryonic dark matter comes from a number of areas, not just galactic motions. One form of non-baryonic dark matter you probably know something about is the neutrino, which apparently does have a tiny mass based on recent experiments demonstrating oscillations, but other considerations indicate that neutrinos are far from the dominant type of dark matter. Thirty years ago, your level of skepticism would have been appropriate. To experts in the field today, it's a no-brainer. What the stuff actually is, however, is still largeley unknown.
Yeah, but Hawking radiation is negligible in big black holes, and not something astronomers observe. Radiation associated with massive astronomical black holes is completely dominated by surrounding accretion processes.
That's right. Observations of our own Milky Way galaxy, which we have good limits on the normal baryonic dark matter, is dominated gravitationally by something more exotic, and a lot of it. The best limits on the amount of baryonic matter and non-baryonic matter in the universe come from WMAP. There's about six times as much non-baryonic dark matter out there as there is normal stuff. These results are well supported by many other observatoins (e.g., light element abundances, galactic rotation curves, cluster mass estimates, etc.).
There is both baryonic and non-baryonic dark matter. Astronomers distinguish between the two types, and try to study/understand both. We don't know what the major non-baryonic dark matter is, but we know some of its properties (how it clumps on various scales), and we know it doesn't readily interact with baryonic matter. There are candidate particles. Neutrinos apparently have a mass, and likely make up a small fraction of it, but for the most part, no, we don't know what it is.
No, hey, that's pretty good analysis based on the scant information in the article. I'd need more to be sure myself. Presumably they've done very deep imaging and think they ought to have seen the stars in a galaxy of this mass, if they were there, and don't. But this is a relatively low mass for a galaxy, and such dwarf galaxies are notoriously difficult to make out. There are some good people at Cardiff, and if they're making a fuss out of this they've probably got a pretty good case, but I'd want to read the refereed journal article to better understand the limits.
You're last point is off the mark, however. Our best estimates for the universal mass density don't depend on optical observations at all (rather microwave background), and are very robust against missing faint/dark matter. The closed universe/collapse model, based on our current best understanding is dead, dead, dead. Only something very surprising about the time evolution of dark energy would seem to be able to alter this conclusion.
There is both baryonic and non-baryonic dark matter. Astronomers worry about understanding both. HI isn't bad because it emits 21 cm radiation (although very weakly), but things like black holes, low-mass dwarf stars, cool white dwarfs and neutron stars, all count toward dark matter. There is a lot more non-baryonic dark matter, absolutely, and it dominates galaxy masses and is indeed the primary thing of interest here.
To me, a flat is a flat is a flat. There's no information there from the source (ideally). So it may be pointed toward Earth, but you're not SEEING Earth (e.g., focusing).
The optical CCDs just oversaturate immediately. The UV-sensitive MAMA detectors would actually be destroyed. Hundreds of man hours (at a minimum) are spent checking for bright targets when they are in use.
Earth flats are not at all the same thing as looking at the Earth directly.
UV-sensitive MAMA detectors would be destroyed. CCDs would saturate rapidly.
Hubble is no good for looking at the Earth because it's too bright. It would flood and destroy the detectors! We always have to do bright object checks and are restricted with how close we can look at bright objects. They made one exception to look at the moon once, but I believe they had to do some tricky things to manage that.
Some astronomers at the Space Telescope Science Institute told me about unidentified people from the government coming to see them in the early 1990s. Hubble was having problems with a wobble when moving between light and shadow, and they were making progress in reducing it. I was told these people answered no questions, only asked them. Sounded like they had their own version of Hubble, pointed Earthward. Duh. Don't know its capabilities, but I'm sure it's pretty good.
How many piano tuners are there in Chicago? This is an example Fermi used to use. Yes, maybe you could go out and measure this, using the "job" field in tax returns, the yellow pages, etc., but you can also get an idea of the number by figuring out how many people live in Chicago. How many of those people on average have pianos? How often do they need tuning? How fast can they be tuned? You have a pretty good idea (or he did anyway) of the answers to those individual questions, you can put an estimate on the number without actually making a direct measurement. Some problems in science can be tackled this way, and it's a type of reasoning scientists ought to be able to use well.
I don't know all the details myself, but the article focuses on SWIFT, which is designed to monitor the whole sky for bright gamma ray bursts. It just went up itself in November, although there are other satelites up with similar (but worse) capability). Gamma ray bursts go off about once a day, give or take, and spacecraft like SWIFT detect them, point toward them and localize them, then relay that information to ground-based telescopes for follow-up at other wavelenghts. So some of your analysis is right, but some of your assumptions are wrong.
It's funny that gamma ray bursts were first discovered by the military who wanted to watch for nuclear weapons. This was in the early 1970s, maybe a bit earlier. They went batshit when these previously unknown bursts started setting off alarms on a regular basis.
Actually, it's more complicated. Yes, the radiation/heating would not be uniform, but the bigger killer would be from the destruction of chemicals like ozone in the upper atmosphere that protects us from the sun's radiation. The details are kind of complicated, and depends on exact distances, fluxes, and spectral energy distrubution. And atmospheric science.
Yeah, excuse me, big science nit-picker tonight.
???
I guess I've observed there too many times for such a joke to be funny. Lick Observatory is named after James Lick who funded the establishment of the Observatory back in the 1890s. It's an interesting place -- the first observatory put on a mountaintop (it was originally going to be in downtown San Francisco, imagine that). His ashes are kept in a memorial under the 36 inch refractor.
It's a spectacularly pretty location, overlooking the bay, and the old observatory portion is all marble and brass, 19th century elegance. I got married there and the reception was great (band, catered dinner, and the 36 inch refractor was available for guest viewing).
The road to Lick from San Jose is a very twisty 19 miles. The mules, originally used to haul material there, wouldn't go up more than a six degree incline, so it's switchback city. This also makes it a popular road for bicyclists. I used to be annoyed with them, since I had to go there semi-regularly for work and often drove while sleepy. I imagined I'd come around a corner and have a tired rider at zero speed in the middle of the lane. They paid me back though one time. I was sitting in the dining room eating breakfast one afternoon, and these two riders and a car pulled up. The car driver switched off to ride a bike, and she stepped in front of the window and stripped out of all her clothes while the milk dripped off my spoon, caught halfway to my mouth. Good times.
The Drake equation IS an equation. That's the right term for it in science, hard or soft. The number of technological civilizations in the galaxy we can communicate with is equal to the product of the probabilites/numbers on the other side of the equal sign. Just because some of those numbers/probabilites are uncertain does not stop it from being an equation. For instance, it isn't a proportionality or an approximation (unless you actually start pluggin in approximate numbers). And I wouldn't say that the term equation is a "title." You're reading too much into this.
These sort of estimation games are really valuable in lots of branches of science and often lead to insight. Enrico Fermi used to do this all the time, which is especially relvant since his "Fermi Paradox" about how it's strange we haven't encountered alien intelligences is the same sort of thing that Drake formalized.
Sure, the Drake equation is but a structured guess, but it is a handy way of organizing the important terms and quantifying each and how certain they are. I got to have dinner with Frank Drake a few years ago at Lick Observatory, which was pretty cool.
At the risk of belaboring the point, I wanted to mention how important Toomre and Toomre's galaxy simulations were in the early 1970s. We could see interacting galaxies out there, with long drawn out tails of stars, that looked really strange. It wasn't until they did numerical simulations with many stars moving according to gravity that we could really be sure we understood what was going on. These simulations produced the same sort of odd features very naturally, the result of gravitational tidal forces. It wasn't a waste of time at all, and really the only way to make progress on the problem.
You're missing something. The work is trying to explain a rather tight relationship between the masses of the central black holes and the masses of the stars in the galaxies. The black hole is always about 1/1000 of the galaxy mass. Why 1/1000? Why not 1/100 or 1/10000? Why so steady for ALL galaxies? It's THAT observation that makes this research of interest, because they've apparently found a quantitative way to explain this fundamental relationship.
Simulations are a valuable area of investigation in most modern sciences, including astronomy. It's a very reasonable approach and complementary to observation. Basically, think of it as an expression of a theory, that makes specific predictions that can be tested against observation. Their simulation, based on some assumptions and our current physical understanding, has to match observations or we know they did something wrong. To the extent the simulation matches observations, and continues to pass observational tests, we gain confidence that the assumptions and physics actually reflect reality. It's just a lot more complicated than a one line equation like Newton's Law of Gravitation. Yeah, you should scrutinize the number of variables and suspect the conclusions, but it's science and can be tested and improved.
To go to your analogy, if economics/people were as predictable as matter and energy, their simulation might show how millionaires arise in a population based on initial conditions, at least statistically. They could make a prediction for how many millionaires appear in the population over the next decade, and if the prediction was borne out, you might think they'd figured out something worthwhile.
As I understand it Hawking radiation is completely negligible from supermassive black holes. I would imagine that the event horizon scale is so large compared to anything really freaky that the distortion doesn't make that much of a difference.
This is just a simple calculation based on the distance to the galactic center and the given absolute magnitude. You work it out in a couple of lines of math. This is for my non-major course and doesn't involve MHD simulations!!!