Sorry, but as a professional astronomer (and a regular user of both Arecibo and Parkes), I have to point out that you are off base on most of your comments...
1. Australia is a much better location for SETI since it can see many more stars in the Milky Way than Arecibo can in Puerto Rico -- and for longer portions of time during a day and during the year as a whole. Since the plane of the Milky Way is not aligned with the Earth's equator, an observatory on the equator is _not_ optimal.
2. Local conditions have very little to do with SETI in this radio band (20cm). Observations can be made any time of day -- and even in the middle of thunder storms (although, yes, nearby lightning _does_ add some interference).
3. The stellar density near the Earth is relatively low when looking at the Milky Way as a whole. We live, essentially, on a nice quite side street in the 'burbs.
4. If we don't want to make too many assumptions about where ET is, the best bet is to cover the largest number of stars possible. Since more stars can be seen (because there are _many_ more there) from the southern hemisphere, you have a higher probability of finding ET down there.
As a side note, this is one of the other reasons why the multiple beam thing is so important. You cover 13 times more sky (and therefore 13 times more stars) at a time (or conversely, you can sit on any individual point in the sky 13 times longer without wasting valuable telescope time).
Scott
Re:Not so fast....
on
Quark Stars
·
· Score: 2, Insightful
As for the spectral fits, their main objection to the two component fit (which is required to fit the optical data, BTW) is the lack of pulsations. But there is a ~15% chance of having no pulsations even _with_ a hot spot(s) and a two component blackbody.
If there is no cool BB component, then they are correct that a very small radius is required -- and that could imply a quark star. I don't think this is the most likely answer, though (especially since it doesn't explain the optical data).
As for the distance, I think that the 140pc distance is probably correct. There is a bunch of evidence pointing that way, and at least three people have independently analyzed the HST data and found the larger distance vs. 1 for the smaller....
So in summary, I personally think that there is a two component BB, the hot supplying the x-rays, the cool supplying the optical, and an unfortunate geometry causes the lack of pulsations. This means that RX J1856 is just a normal everyday neutron star...
Not so fast....
on
Quark Stars
·
· Score: 5, Informative
I am one of the authors of a competing paper
on RX J1856 that was published yesterday, as well as a co-discoverer
of the pulsar
in 3C58. In my opinion these results, while definitely a
possibility are certainly very preliminary. And in fact, there
are other possibilities that make quite a bit more sense.
In the case of RX J1856, there is a ~15% chance that the lack of
pulsations (one of the biggest reasons for suspecting a quark star) is
simply the result of an unfortunate emitting geometry or viewing
alignment. Given that there are ~7 objects known that are similar to RX
J1856, having at least one of them in this 15% seems quite
likely to me -- and avoids having to invoke a new form of "star stuff".
As for 3C58, the neutron star cooling problem can be mitigated (but
not completely removed) by assuming a larger age for the supernova
remnant (and therefore the neutron star) -- which expansion
measurements and pulsar timing measurements also suggest.
In other words, there are simpler explanations for the facts.
Although those explanations certainly wouldn't get as much press...
I haven't tried the new Yellow Dog, but a couple weeks ago I installed Debian unstable (closely following Branden Robinson's instructions)
along with Benjamin Herrenschmidts 2.4.18 kernel on my new ibook (600MHz, 384MB, CD-RW/DVD-ROM, Airport wireless) and am extremely impressed about how everything works (all except the modem - which I never use anyways). DVDs (with xine), CD burning, wireless, sound, hardware accelerated 3D, built in ethernet, power management -- all for ~$2000 US. And Linux seems way more snappy than OSX. This is my first Mac, but if they work this well with Linux in the future, it may not be my last...
> Geosync is the most crowded orbital position we have.
> This is the last place you want to be if you are trying to avoid junk.
> Check your facts.
Geosync may be crowded, but the space junk problem is not nearly as severe up there. There are a couple reasons why:
1. The density of small non-trackable debris (i.e. rivets, bolts, metal pieces from booster separation) is _much_ lower than in low-Earth orbit. The small debris causing events happen much lower -- possibly enroute to Geosync.
2. The distribution of relative velocites between spacecraft is much narrower (and hence better for survivability) since the purpose of Geosync is to effectively "park" a spacecraft over a fixed point on the equator. So everything is travelling in pretty much the same direction at the same velocity. In low-Earth orbit there is crap flying every which way.
Sorry, nathanh. Almost all of what you have said has been very accurate. But your aliasing calculation isn't: aliased freqs appear at the _sampling_ rate minus the freq in question, not at the frequency minus the Nyquist as you claim.
Therefore the original poster was correct about his 24kHz signal. It will appear at 44.1k-24k=21kHz.
In my last paragraph I said that "it looks like we have an open (eternally expanding) and flat universe". I shouldn't have said "open", because in Cosmological parlance, that means negative curvature. So just skip that word and continue with "eternally expanding"!
That explanation was pretty close but was slightly incorrect on some important points (I'm finishing my PhD in Astronomy, so have a least _some_ room to speak).
A flat universe (Omega_total = 1) simply describes the geometry of spacetime -- it is flat (i.e. parallel lines do not converge, triangles have 180 degrees). It says absolutely nothing about whether the universe will expand forever or eventually collapse. These bad assumptions are the result of years of astronomy classes that nay-sayed Einstein's Cosmological Constant (his " greatest blunder"). In those days, Omega_total, which equals Omega_cosmo_const + Omega_matter, was thought to equal just Omega_matter -- since Omega_cosmo_const was obviously 0. In that case, if Omega_matter = 1 then you get a universe balanced on the brink between eternal expansion and collapse.
But in the past couple years, numerous groups (the most famous using Type IA supernovae) have shown evidence that Omega_cosmo_const seems to be about 0.65 or so. Add that to the measurements of Omega_matter of about 0.35 and you get Omega_total = 1. The BOOMERANG measurements are simply an independent measurement of this, but this time using the cosmic microwave background -- a very important measurement.
If there is a cosmological constant, but Omega_total = 1, than the universe is flat, but the relative proportions of the two determine whether we get eternal expansion or not.
With current measurements, it looks like we have an open (eternally expanding) and flat universe. This saves (barely) Inflation, and solves a bunch of other Astro problems. Although now we have another big question: If this is real, Where in the hell does the Cosmological Constant come from?
And to imply that "real scientists" don't read it either is totally wrong.
The articles are at just the right level for a technically adept reader to see what's going on in science _outside_ of the readers area of expertise -- stick to peer-reviewed journals and pre-prints for the latest in your own field. And as far as accuracy is concerned, they are written by the preeminent researchers in their respective fields.
I, and many of my "real scientist" friends, believe that SciAm is one of the highest quality magazines out there for the intelligent reader.
in an pseudo-interview with about 6 other students. I asked him if it ever bothered him to be the "Father of the H-Bomb" since his "baby" could be used for such evil and/or immoral purposes.
I thought he was going to jump out of his chair at me.
He got very upset and angrily announced that a scientist's only responsibility is to science. The possible uses of a discovery should not even be considered by the researchers -- that is someone elses business. And because of this, he did not feel even the slightest bit of remorse for his work on the bomb.
And then he upbraided _me_ (since I was on my way to grad school to become a scientist at the time) for thinking that a scientist _should_ worry about the moral implications of his/her work.
Needless to say, I didn't ask any more questions.;)
The reason why this is likely to change a lot of planetary formation theories is due to probabilities. You are absolutely correct that the galaxy is a very big place. And with a couple hundred million stars, if a particular type of system has only a tiny chance of being formed, it probably exists in the galaxy somewhere. That _somewhere_ is the key.
This system is only 44 light-years away. If planetary systems are rare, the chances of there being two such systems (ours and the newly discovered one) within only 44 light-years of one another would be -- pun intended -- astronomical.
Because we found another such system so close to us after looking for only a short amount of time (we have just recently developed the technologies necessary to look for such systems), means that such systems must be very common.
And that is not what conventional theories have been predicting.
The Stephenson Essay is _way_ beyond interesting.
on
Tuesday Quickies
·
· Score: 3
All I have to say is "Wow."
And also: Please re-submit this as its own feature. It deserves to be widely read.
I was truly blown away by this essay -- a huge, rollicking trip through culture, cosmology, computers and the history of the OS. All written in simply amazing prose.
I have never read one of his novels, but I can say that this essay has inspired me to go out and buy _The_Diamond_Age_ and _Snow_Crash_ (and probably _Cryptonomicon_ as soon as its out).
I have recommended it to they small minority of Linux hold-outs I know among my more intelligent friends. This essay shows them with style what they are missing.
Slashdot Mirror
Sorry, but as a professional astronomer (and a regular user of both Arecibo and Parkes), I have to point out that you are off base on most of your comments...
1. Australia is a much better location for SETI since it can see many more stars in the Milky Way than Arecibo can in Puerto Rico -- and for longer portions of time during a day and during the year as a whole. Since the plane of the Milky Way is not aligned with the Earth's equator, an observatory on the equator is _not_ optimal.
2. Local conditions have very little to do with SETI in this radio band (20cm). Observations can be made any time of day -- and even in the middle of thunder storms (although, yes, nearby lightning _does_ add some interference).
3. The stellar density near the Earth is relatively low when looking at the Milky Way as a whole. We live, essentially, on a nice quite side street in the 'burbs.
4. If we don't want to make too many assumptions about where ET is, the best bet is to cover the largest number of stars possible. Since more stars can be seen (because there are _many_ more there) from the southern hemisphere, you have a higher probability of finding ET down there.
As a side note, this is one of the other reasons why the multiple beam thing is so important. You cover 13 times more sky (and therefore 13 times more stars) at a time (or conversely, you can sit on any individual point in the sky 13 times longer without wasting valuable telescope time).
Scott
As for the spectral fits, their main objection to the two component fit (which is required to fit the optical data, BTW) is the lack of pulsations. But there is a ~15% chance of having no pulsations even _with_ a hot spot(s) and a two component blackbody.
If there is no cool BB component, then they are correct that a very small radius is required -- and that could imply a quark star. I don't think this is the most likely answer, though (especially since it doesn't explain the optical data).
As for the distance, I think that the 140pc distance is probably correct. There is a bunch of evidence pointing that way, and at least three people have independently analyzed the HST data and found the larger distance vs. 1 for the smaller....
So in summary, I personally think that there is a two component BB, the hot supplying the x-rays, the cool supplying the optical, and an unfortunate geometry causes the lack of pulsations. This means that RX J1856 is just a normal everyday neutron star...
I am one of the authors of a competing paper on RX J1856 that was published yesterday, as well as a co-discoverer of the pulsar in 3C58. In my opinion these results, while definitely a possibility are certainly very preliminary. And in fact, there are other possibilities that make quite a bit more sense.
In the case of RX J1856, there is a ~15% chance that the lack of pulsations (one of the biggest reasons for suspecting a quark star) is simply the result of an unfortunate emitting geometry or viewing alignment. Given that there are ~7 objects known that are similar to RX J1856, having at least one of them in this 15% seems quite likely to me -- and avoids having to invoke a new form of "star stuff".
As for 3C58, the neutron star cooling problem can be mitigated (but not completely removed) by assuming a larger age for the supernova remnant (and therefore the neutron star) -- which expansion measurements and pulsar timing measurements also suggest.
In other words, there are simpler explanations for the facts. Although those explanations certainly wouldn't get as much press...
I haven't tried the new Yellow Dog, but a couple weeks ago I installed Debian unstable (closely following Branden Robinson's instructions) along with Benjamin Herrenschmidts 2.4.18 kernel on my new ibook (600MHz, 384MB, CD-RW/DVD-ROM, Airport wireless) and am extremely impressed about how everything works (all except the modem - which I never use anyways). DVDs (with xine), CD burning, wireless, sound, hardware accelerated 3D, built in ethernet, power management -- all for ~$2000 US. And Linux seems way more snappy than OSX. This is my first Mac, but if they work this well with Linux in the future, it may not be my last...
> Geosync is the most crowded orbital position we have.
> This is the last place you want to be if you are trying to avoid junk.
> Check your facts.
Geosync may be crowded, but the space junk problem is not nearly as severe up there. There are a couple reasons why:
1. The density of small non-trackable debris (i.e. rivets, bolts, metal pieces from booster separation) is _much_ lower than in low-Earth orbit. The small debris causing events happen much lower -- possibly enroute to Geosync.
2. The distribution of relative velocites between spacecraft is much narrower (and hence better for survivability) since the purpose of Geosync is to effectively "park" a spacecraft over a fixed point on the equator. So everything is travelling in pretty much the same direction at the same velocity. In low-Earth orbit there is crap flying every which way.
Sorry, nathanh. Almost all of what you have said has been very accurate. But your aliasing calculation isn't: aliased freqs appear at the _sampling_ rate minus the freq in question, not at the frequency minus the Nyquist as you claim.
Therefore the original poster was correct about his 24kHz signal. It will appear at 44.1k-24k=21kHz.
http://www.scyld.com/expert/license.html
In my last paragraph I said that "it looks like we have an open (eternally expanding) and flat universe". I shouldn't have said "open", because in Cosmological parlance, that means negative curvature. So just skip that word and continue with "eternally expanding"!
That explanation was pretty close but was slightly incorrect on some important points (I'm finishing my PhD in Astronomy, so have a least _some_ room to speak).
A flat universe (Omega_total = 1) simply describes the geometry of spacetime -- it is flat (i.e. parallel lines do not converge, triangles have 180 degrees). It says absolutely nothing about whether the universe will expand forever or eventually collapse. These bad assumptions are the result of years of astronomy classes that nay-sayed Einstein's Cosmological Constant (his " greatest blunder"). In those days, Omega_total, which equals Omega_cosmo_const + Omega_matter, was thought to equal just Omega_matter -- since Omega_cosmo_const was obviously 0. In that case, if Omega_matter = 1 then you get a universe balanced on the brink between eternal expansion and collapse.
But in the past couple years, numerous groups (the most famous using Type IA supernovae) have shown evidence that Omega_cosmo_const seems to be about 0.65 or so. Add that to the measurements of Omega_matter of about 0.35 and you get Omega_total = 1. The BOOMERANG measurements are simply an independent measurement of this, but this time using the cosmic microwave background -- a very important measurement.
If there is a cosmological constant, but Omega_total = 1, than the universe is flat, but the relative proportions of the two determine whether we get eternal expansion or not.
With current measurements, it looks like we have an open (eternally expanding) and flat universe. This saves (barely) Inflation, and solves a bunch of other Astro problems. Although now we have another big question: If this is real, Where in the hell does the Cosmological Constant come from?
You obviously don't read Scientific American.
And to imply that "real scientists" don't read it either is totally wrong.
The articles are at just the right level for a technically adept reader to see what's going on in science _outside_ of the readers area of expertise -- stick to peer-reviewed journals and pre-prints for the latest in your own field. And as far as accuracy is concerned, they are written by the preeminent researchers in their respective fields.
I, and many of my "real scientist" friends, believe that SciAm is one of the highest quality magazines out there for the intelligent reader.
in an pseudo-interview with about 6 other students. I asked him if it ever bothered him to be the "Father of the H-Bomb" since his "baby" could be used for such evil and/or immoral purposes.
;)
I thought he was going to jump out of his chair at me.
He got very upset and angrily announced that a scientist's only responsibility is to science. The possible uses of a discovery should not even be considered by the researchers -- that is someone elses business. And because of this, he did not feel even the slightest bit of remorse for his work on the bomb.
And then he upbraided _me_ (since I was on my way to grad school to become a scientist at the time) for thinking that a scientist _should_ worry about the moral implications of his/her work.
Needless to say, I didn't ask any more questions.
The reason why this is likely to change a lot of planetary formation theories is due to probabilities. You are absolutely correct that the galaxy is a very big place. And with a couple hundred million stars, if a particular type of system has only a tiny chance of being formed, it probably exists in the galaxy somewhere. That _somewhere_ is the key.
This system is only 44 light-years away. If planetary systems are rare, the chances of there being two such systems (ours and the newly discovered one) within only 44 light-years of one another would be -- pun intended -- astronomical.
Because we found another such system so close to us after looking for only a short amount of time (we have just recently developed the technologies necessary to look for such systems), means that such systems must be very common.
And that is not what conventional theories have been predicting.
All I have to say is "Wow."
And also: Please re-submit this as its own feature. It deserves to be widely read.
I was truly blown away by this essay -- a huge, rollicking trip through culture, cosmology, computers and the history of the OS. All written in simply amazing prose.
I have never read one of his novels, but I can say that this essay has inspired me to go out and buy _The_Diamond_Age_ and _Snow_Crash_ (and probably _Cryptonomicon_ as soon as its out).
I have recommended it to they small minority of Linux hold-outs I know among my more intelligent friends. This essay shows them with style what they are missing.