Posted on 08/16/2005 7:04:45 PM PDT by LibWhacker
The Milky Way is not a perfect spiral galaxy but instead sports a long bar through its centre, according to new infrared observations from NASA's Spitzer Space Telescope.
Galaxies come in a wide variety of shapes usually thought to be produced by gravitational interactions with nearby objects. Some spiral galaxies look like pinwheels, with their arms curving out from a central bulge, while others have a straight bar at their centres.
Radio telescopes detected gas that hinted at a bar at the heart of the Milky Way in the late 1980s. A decade later, observations with the near infrared survey 2MASS bolstered the case for a bar, but dust in the centre of the galaxy obscured the observations.
Now, astronomers have used Spitzer to peer through that dust at slightly longer wavelengths, observing 30 million stars in the galactic plane in the region around the centre of the galaxy.
They found that the central bar was much longer than previous observations had suggested - reaching about half the distance between the galaxy's centre and our Sun. The bar is estimated to stretch a total of about 27,000 light years from end to end.
"It is a major component of our galaxy and has basically remained hidden until now," says team member Ed Churchwell, an astronomer at the University of Wisconsin in Madison, US. "The fact that it's large means it's going to have a major effect on the dynamics of the inner part of our galaxy."
Bar food
Stars in the spiral arms circle the galaxy in roughly circular orbits. But the old, red stars in the bar appear to be on more elliptical paths that take them more directly towards and away from the galaxy's core, where a colossal black hole is thought to lurk.
"This bar probably does carry matter into the centre of the galaxy and feeds the black hole," Churchwell told New Scientist.
But it is still not clear what the discovery reveals about the Milky Way's past. "I don't think anybody really fully understands how bars are formed," says Churchwell. "What we do know is that it appears there are so many barred galaxies they must be rather stable. Astronomers have to come up with some kind of model that can explain the stability of these structures."
The team will publish its results in an upcoming issue of Astrophysical Journal Letters and has requested more time on Spitzer to study the innermost part of the Milky Way.
That the "others" don't gather at the water hole? Maybe they aren't water based, or more likely they just communicate in some other band, probably something more like laser light than microwaves. And they aren't especially interested in us "primitives" finding them, so they don't waste any effort putting up beacons for us to see at those microwave frequencies. Or any of myriad other reasons they aren't transmitting on the frequencies we are looking for. Heck they could even be using modulation waveforms that our searches are not designed to find.
Yes, thanks, that's what I meant. In fact, SETI can't even say much about the prevalence of civilizations, in general, but only about "technologically advanced" civilizations that happen to be using some kind of radio technology right now, at one or two particular wavelengths, and at sufficient strength to be detected by Arecibo, etc. I've seen lots of other discouraging restrictions on the kind of civilization it would have to be in order for us to detect it. So you're right, the SETI people will have to be careful how they phrase their conclusions. If they find nothing, it doesn't mean nothing is there. But perhaps it'll mean one particular kind of civilization is rare and we'll be able to put upper and lower limits on it. Hey, at least it's something! :-)
This has crossed my mind before too, but how likely is it really that a civilization would build something so big that we'd be able to see it? Even amongst the closest star systems we can't see anything smaller than objects far larger than the Earth itself. Beyond a tiny fraction of the galaxy, we can't see things even as big as Jupiter. Let me put it a different way: how likely do you think it is that humanity will ever build someone big enough that we'd be able to see it now if it were built in another nearby solar system??
Not very likely at all IMHO.
As I mentioned, if the SETI people examined Earth right now by their current protocol, they'd find nothing here. ;^)
This is more than just an amusing irony, BTW. The problem here is that the interference from Earth-based transmissions is so intense that this forces SETI to restrict its search to a frequency not otherwise used. The problem however is that the reason this frequency is not otherwise used is because it's not especially useful. Odds are that if any ET civilizations are out there then they are transmitting on the same frequencies we're transmitting, which we can't search, because we're transmitting on them.......
Doesn't it seem mechanically and visually obviuous that a higher rate of collision would result in a bar galaxy, while more slowly colliding/merging galaxies would result in unbarred galaxies?
The barring effect seems to resemble and suggest a high rate near passby by two near colliding galaxies, such that they "rip" partially past one another, and/or merge while continuing to pass one another by, leaving a sorta 'skid' mark between them, eventually merging but the effects remain of the motion afterward.
now THAT (your post, and it's place in the progression of this thread) brought a real, genuine smile to my face.
It's only too bad that Douglas Adams (may God have mercy upon his soul) turned such a wondrous and beautiful vision < minus the Vogons, though I DID kinda like some of the original captain's poem > into such a depressing and pointless story.
I finished reading the full 5 part trilogy [for the seventh time] about 8 months ago, and I don't think it's in the cards for me to read it again.
Pity, because I DID like his style.
#1: It's a milky white in the sky when you look at it unimpeded by artificial light
#2: Only in recent memory
#3: The sentient creatures that inhabit this planet.
Good gravy, dude, you REALLY have some issues. What are the stars WE look at SUPPOSED to be named? Perhaps something from the "xilnksme wtx lbsxr" (a fearsome and implcable warrior culture that is totally pacifist, once it wins) perhaps?
Get serious, for once.
Go freedom--welcome to Free Republic. In response to your post #102:
Isn't God incredible. Yep. Post a pic of him, please.
Please read the verse below. Thanks.
________________________________________________________________________________
Then Jesus told him, "Because you have seen me, you have believed; blessed are those who have not seen and yet have believed."
John 20:29
No OBSERVABLE life out there! There could be life in a dimension of time/space we don't see....
A bar in the Resteraunt at the end of the Universe.....
MORE COWBELL.
Yes they would.
This is more than just an amusing irony, BTW. The problem here is that the interference from Earth-based transmissions is so intense that this forces SETI to restrict its search to a frequency not otherwise used.
Not true.
The problem however is that the reason this frequency is not otherwise used is because it's not especially useful.
No, the "water hole" frequency band is not utilized because it is so very important to radio astronomers.
Odds are that if any ET civilizations are out there then they are transmitting on the same frequencies we're transmitting, which we can't search, because we're transmitting on them.......
Again, this is not the case.
We haven't even accomplished an all sky survey yet. We are still in our infancy when it comes to SETI.
Physics pretty much dictates a tool biulding civilization will be using radio.
at one or two particular wavelengths,
We are looking at billions.
and at sufficient strength to be detected by Arecibo, etc.
Going to narrowband searches up the odds a bit. :-)
The secret of the Bars will be revealed to man by God, on a need to know basis only.
Scientists remind me of the bacteria in our intestines studying the mysteries of their existance.
SETI (at least the current trend) is searching for extremely narrowband carrier signals that are Doppler shifted due to planetary rotation. The Doppler shift is extremely important since if it is not there, we know the signal is either terrestrial or an artifact of the equipment itself. The other thing that is very important is the two-antenna approach. If two antennas, separated by a thousand miles, were pointed at the same patch of sky, this would not allow a satellite to "spoof" the system. First, the likelihood of it being within the footprint of both antennas are exceedingly small, and the Doppler characteristics between the two antennas would rule it out if such a thing happened.
All that said, I agree with the advances in communications technology can cause a search to be futile for many types of broadcasts. Frequency hopping spread spectrum and the like will make it far harder to detect a tool building species that uses radio (EM).
To be fair to the other side there is another factor in this conjecture. A race is progressing along and figures out that the electromagnetic spectrum is the only real practical method of long-range communications. So high-powered transmitters are built as this technology is in its infancy. As the engineering and science of radio advances, they figure out that tight beam, spread spectrum, synthetic aperture, frequency hopping, etc. are a way of not only saving power, but also bandwidth. So for the first 50 years they have been "bleeding" EM into space across a huge range of frequencies into and ever-increasing sphere of radio noise. However, do to technological advances, this RF that is being bled into space quiets down dramatically.
Now, lets jump a few years. This race has expanded off its initial planet and is exploring the solar system it resides in. (IMHO, star travel still remains firmly in the realm of SiFi) Somehow they have to communicate. So again high power transmitters are employed to accomplish this. Light is not out of the question, however, microwave is easy, cheap, less pointing accuracy requirements, and wont be drowned out by the star. So suddenly this race again is radiating RF into the universe. So according to this scenario, a race can emit RF then grow silent for a time, and then restart emitting RF.
Heck they could even be using modulation waveforms that our searches are not designed to find.
We only look for carrier. Modulation is not an issue.
Coming to DVD September 13th!
(I can't wait!)
Wow! I have a seriously flawed concept of the SETI program. My comments above related to it should be totally disregarded. Time to go do some reading!
Thanks for the correction RA. It's obvious I learned nothing during the brief period I loaned them my computer back in 1999. Sad to think I was one of their first participants..
While I'm at it I think I'll rejoin the quest!
Here is a little more info:
We are quite aware just how far it is "out there". With the speed of light being the fundamental limit for baryonic matter, it will be next to impossible to travel between the stars (at least under our current level of physics knowledge). So the universe may be populated with little isolated bits of intelligence all wondering if any other species are out there.
Just in the past few years we have advanced far enough in our technical prowess to both "announce" to the universe we are here (radio waves) and to receive the same from another species. With that in mind and the speed of light being a constant in a vacuum, the expanding sphere of radio noise heralding our presence has only gone about 60 light years or so. So there may be an entire galactic community out there but our "knock" hasn't yet hit the door so to speak.
(Note: Astronomers use another term for stellar distance that may be not so familiar called the Parsec. A Parsec (parallax-arcsecond) is the distance needed for one astronomical unit (AU) to subtend one second of arc. However for this discussion I will revert to the more familiar “Light Year”)
This also applies in the opposite direction. If there was a radio producing species only 70 light years away and they have had radio only for 50 years, we would have no possible way of detecting them for another 20 years. Expand that out to approximately 100,000 light years (diameter of just our little galaxy) and you begin to see the problem.
While SETI is indeed a long shot, we do have one example of a species that sends signals out into interstellar space: ourselves. This means that intelligent life in the universe is possible and proven. Further, it is possibly detectable if that intelligence uses any form of EM radiation to communicate as we have for years. It is therefore not without merit.
Why EM and not some other means I hear you ask?
There appears to be only four fundamental forces in all of nature; Strong Force, Weak Force, Gravity, and Electromagnetism EM. Both the strong force and Weak force are confined to the nucleus of the atom. Gravity requires prodigious amounts of energy to manipulate, so the only one that appears practical for long distance communication is EM. In an extremely short period of time, we are using EM across the entire spectrum from basically DC to light.
I personally believe for a race to become technologically advanced, it must eventually realize the need for the ability to store and convey information over long distances. Since radio waves (I am including any EM in this such as RADAR, TV, microwave, etc.) are still the best method for accomplishing this, any other race would use/do the same. For about the past 60 years we have been isotropically radiating EM across a huge RF spectrum into outer space. What many SETI systems are looking for is another species that is doing the exact same thing we are; unintentional radiation of EM into outer space.
Even the nearest star (Proxima Centauri), actually a member of a ternary star system, is 4.22 light years away. This is why radio and/or optics (I know some people who are contemplating optical SETI) are the best and at the moment the only way to find other civilizations. The advancing sphere of radio noise radiating from our own planet now encompasses an area more than 120 light years across. There are literally thousands of stars within that volume of space. As we measure the heavens with more precise instrumentation we are finding a plethora of planets orbiting other stars.
A few years ago there were many people who were quite skeptical about the possibility of extra solar planetary systems. Statements were made like "just because there is one known planetary system (ours), it doesn’t mean there are others". It appears now that planetary systems are the norm instead of the exception. I am now hearing the same argument against the possibility of ET. I personally do not "believe" ET is out there. I suspect ET is out there. We are finding the building blocks of life through out the heavens. I also think life is far more tenacious than most people believe. We even find life in the sulfur volcanic vents on this planet.
The other question that periodically comes up is “what about von Neumann probes”?
Two things. First, there may me thousands of races out there, but they are "stuck" just like we are by general relativity. Sigh! Second, the prodigious amount of time it would take to cross the galaxy at sub light speed would possibly prohibit even the most ambitious race from basically spending the money and wasting the precious resources of a local solar system to attempt that feat. Also how long can a machine function and replicate without error entering the picture. Not unlike evolution. :)
And just where in the heck do we look and at what frequency?
Lets start with a bit of a background:
Radio astronomers use temperature to describe the strength of detected radiation. Any body with a temperature above -273 deg C (approximately absolute 0) emits electromagnetic radiation (EM). This thermal radiation isn’t just in the infrared but is exhibited across the entire electromagnetic spectrum. (Note: it will have a greater intensity (peak) at a specific area of the EM spectrum depending on its temperature). For example, bodies at 2000 K (Kelvin), the radiation is primarily in the infrared region and at 10000 K, the radiation is primarily in the visible light region. There is also a direct correlation between temperature and the amount of energy emitted, which is described by Planck’s law.
When the temperature of a body is lowered, two things happen. First, the peak shifts in the direction towards the longer wavelengths and second, it emits less radiation at all wavelengths.
This turns out to be extremely useful. When a radio astronomer looks at a particular point of the sky and says that it has a noise temperature of 1500 K, he/she isn’t declaring how hot the body (nebulae, etc) really is, but is providing a measurement of the strength of the radiation from the source at the observed frequency. For example, radiation from an extra solar body may be heated from a nearby source such as a star. If this body is radiating at a temperature of 500 K, it exhibits the same emissions across all frequencies that a local test source does. The calculated noise figure will be the same across all frequencies. (Note: this does not take into account other sources of radiation such as synchrotron radiation).
So, here’s the rub. Not only does the source that is of interest to the radio astronomer emit thermal radiation but also both the local environment (ground, atmosphere, etc) and the equipment (antenna, amplifiers, cables, receiver, etc) being used to make the measurements. To accurately observe and measure the distant sources, the radio astronomer must subtract all of the local environment and detection equipment noise additions.
In 1963, Arno Penzias and Robert Wilson were working with a horn antenna trying to make it work with as high efficiency as possible for the Telstar project. This antenna was also going to be used for radio astronomy at a later date. They pointed it to a quiet part of the sky and took measurements. When they subtracted all of the known sources of noise, they found approximately 3 K left over. They worked very diligently to eliminate/describe this noise source and were unable to. This mysterious source of noise seemed to be there no matter where they pointed the antenna. What they had discovered was the microwave background produced from the Big Bang. This 3 (closer to 2.7) K microwave background originated approximately 300,000 years after the Big Bang itself had occurred. It has been determined that when these signals originated, the universe had already cooled down to around 3000 K.
So are frequencies radio astronomers use affective for SETI?
There are two real sources of noise that limits the radio astronomer's ability to search for very weak signals. The galactic noise halo interferes with us below 1 GHz and noise due to earth's atmosphere interferes with us above about 10 GHz. This pretty much keeps all SETI searches (at least radio ones) between 1 and 10 GHz. Inside these two frequencies, from about 1.4 to 7 GHz the noise level drops off even further to near the 2.7 Kelvin Cosmic Microwave Background (CMB) that permeates all space. Hydrogen (H) molecules, the most abundant element in the universe, excite and emit (masers) at around the 1.4 GHz frequency (21 cm band) and the hydroxyl (OH) emits at around 1.65 GHz. This is where much of our radio astronomy and SETI research is concentrated. Since H + OH is water, the frequency gap between these two is often called the “Water Hole”.
This is one of the coveted frequencies of radio astronomers; thusly we have international treaties to not broadcast at these frequencies since they would interfere with radio astronomers. So here we are looking for signs of a narrowband signal heralding the fact that intelligent life is not wholly constrained to our tiny little planet at these very frequencies.
Just imagine another tool building species that ends up developing radio and radio astronomy that may also recognizes the importance of this 21cm band. And they also may instigate a SETI search using these same bands such as we do. So here is the question. Would they hear us at those frequencies? They are the very ones that we are not transmitting on at all. I could just see 500 races all looking for each other at the very frequency band that none of them are transmitting on due to the very nature of its importance for the exploration of the universe.
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