Galaxy evolution and supermassive black holes. Warning: potentially educational
Galaxy evolution and supermassive black holes. Warning: potentially educational |
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Message boards : SETI@home Staff Blog : Galaxy evolution and supermassive black holes. Warning: potentially educational
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Eric Korpela  Volunteer moderator Project administrator Project developer Project scientist  Send message Joined: 3 Apr 99 Posts: 998 Credit: 5,844,050 RAC: 6,191  | |
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You never know what's going to show up in your inbox. Today, out of nowhere, someone sent me a question about the relationship between elliptical and spiral galaxies and whether one turns into the other. Since it's a good question and the response shows the interrelatedness of different parts of astronomy, I figured I'd post the response. ... if the energy levels of [stars in] elliptical galaxies were generally higher than those of a spiral galaxies, could ellipticals "decay" to become spirals? Here's my answer: We do think about galaxies in terms of energy, but a better analogy might be temperature. An elliptical galaxy is "hot", all the stars are orbiting in random directions the way atoms in a hot gas move. A spiral is "cold", with most of the stars orbiting in the same direction at roughly the same speed. In the current epoch, galaxies tend to evolve from "cold" to "hot." When galaxies merge, the energy of the collision tends to go toward randomizing the orbits of the stars, and so you will probably end up with an elliptical galaxy after you've had a bunch of mergers. The centers of dense galaxy clusters tend to contain giant elliptical galaxies that are probably the result of mergers of hundreds of galaxies. These processes are often the subject of supercomputer modeling efforts. If the Milkyway and the Andromeda galaxy merge, the result will probably be an elliptical galaxy. It's harder for galaxies to evolve the other direction, because it's hard to get rid of the accumulated energy. An atom with an electron in a high energy level can emit a photon in order to get rid of the energy, but the only thing a galaxy can emit in order to get rid of excess energy is stars. And they do emit stars, but it's hard to put very much energy into a single star so the process is fairly slow. It's similar to evaporation. In an evaporating liquid, the fast moving atoms in the liquid can escape, which removes energy from the liquid, causing it to cool. In an elliptical galaxy, if three or more stars make a close approach to one another, one of the stars might get accelerated to high speed, while the remaining ones slow down. If the fast star is fast enough, it might be moving at a speed greater than the galaxy's escape velocity. If it escapes, it'll take its kinetic energy with it, which will "cool" the galaxy slightly. Because the remaining stars aren't moving as quickly the galaxy will shrink slightly. Because this process requires close approaches between stars, it happens most quickly where the stars are the closest together, which is in the center of the galaxy (the core). This causes the core to lose energy rapidly, which causes it to shrink, and if the remaining stars get close enough together, you might form a supermassive black hole. We do tend to find supermassive black holes in the centers of most every galaxy large, and this may be how they form. Given enough time (hundreds or thousands of times the current age of the universe), you'll probably end up with a large fraction of the stars having fallen into the black hole, and the rest scattered throughout intergalactic space. ____________  | |
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One good question always inspires another! | |
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Eric Korpela Volunteer moderator Project administrator Project developer Project scientist Send message Joined: 3 Apr 99 Posts: 998 Credit: 5,844,050 RAC: 6,191 | |
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Ellipical galaxies have been stripped of all of their gas and dust, so there is little or no new star formation in them. The stars they contain tend to be old and faint. Since (we think) planet formation requires a high abundance of heavy elements that are made in stars, whether there are planets depends on how long ago the gas and dust was stripped. | |
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Q. IF - when one is in 'Space' - why is it that one cannot 'judge' Distance? > an 'object' may well be quite a distance away from the viewer - as opposed to the Fact that it may well be quite close Why [?] is this [?] ____________  BOINC Wiki . . .Science Status Page . . . | |
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And if planets are necessary for life, that would make spiral galaxies a better place to look. You seem to be in agreement that the search for life can be narrowed down by eliminating "Less likely" places where life might exist. In this case, the spiral might be a better place to focus the SETI@home search. Using this same logic, could SETI@home narrow its search by eliminating data recorded from Hugh chunks of the sky. Using Matt and Jeff's new NitPicker data and the information in the Hipparcos Star Catalog that you have installed on the SETI servers, you could narrow the search. Am i correct in saying that ALL the data recorded from the whole sky at Arecibo is turned into work units? That means that 95% of the work units are data recorded from parts of the sky with massively distant stars and Galaxy's that any signal would be too faint to detect. There would also be Hugh amounts of data from blank or almost empty parts of the sky. Could we use the information in the Hipparcos Star Catalog to narrow the search to stars and Galaxy's that might be more likely candidates? Looking at this as an optimist, Contained within the data recorded in the last 10 years are radio transmissions by other intelligent life, but we don't know how strong the signals are and we don't know what frequency they are transmitted on. We also don't know where in the sky the strongest signals are coming from. We need to take the data we have and look closer at the data. Narrow the search and look for fainter signals coming from stars and Galaxy's much closer to home. Who wrote the cosmological book that says that aliens must transmit at 1.42 GHz?. Yes, the hydrogen line is a defined mathematical line in the spectrum, but the spectrum is wide and holds the key to finding what we are looking for. John. ____________    | |
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I'll give a shot at an explanation for this... The way distances are judged optically is through the process of triangulation. The human mind (and animals' too) does this by forming a mental triangle between the view of an object from one eye vs the view from the other eye, and getting a more or less accurate distance result. Accuracy from triangulation is increased by having a larger angle between the object and view-1/view-2. Unfortunately (or perhaps not), the Human head can only be so large and there is a limit to the size of that angle...the distance between the two eyes. As objects get farther away from the viewer, the angle between the object and each of the viewer's eyes decreases. At some point it becomes so small it is effectively zero. At that point, the only way to judge distances is to make a guess as to how big something is and estimate based on that guess...not very accurate. The guess is more accurate if you have an object of a known size nearby to the target object and can compare relative sizes. In space, this is not possible. Most of us have been in a situation where we look at a scene and think that there is this huge object way far away from us...until we realize that the object is actually much smaller and closer than we originally thought. This happens with airplanes, birds, and flying saucers all the time (just kidding about the flying saucers...). HTH. | |
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By not scanning those empty parts of the sky, would we be eliminating the possibility of receiving a signal from a probe launched by a civilization seeking to make contact? I'm thinking there is the possibility that another lifeform might be seeking contact in a more proactive way than relying on intercepting stray radio broadcasts from a homeworld. | |
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By not scanning those empty parts of the sky, would we be eliminating the possibility of receiving a signal... Indeed so. However, note that the search task is infinite to do a completely thorough search (assuming our universe to be infinite). We have limited capability and limited resources to make any search and so only the best of what can be done at the moment is being done. Also, that 'best' relies on various guesses and assumptions. There has long been hopes of getting data from the Parkes radio telescope in Australia to give coverage of the southern skies. I guess no grants and no progress for that one so far... Keep searchin', Martin ____________ Mandriva Linux A user friendly OS! See new freedom Mageia2 The Future is what We make IT (GPLv3) | |
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Robert & ML1, | |
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And another point, | |
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Eric Korpela Volunteer moderator Project administrator Project developer Project scientist Send message Joined: 3 Apr 99 Posts: 998 Credit: 5,844,050 RAC: 6,191 | |
Hi Byron, Haven't heard from you in a while. Hope you're doing well. Dan is heavily involved with the instrumentation for the ATA. Whether that is code depends on where you draw the lines. I'd call it code, but Dan (coming from an electrical engineering background) might disagree. My contribution to that has been minuscule thus far. Eric ____________ | |
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Applying this theory to SETI@home, i am suggesting that so far SETI@home has detected nothing. So yes, ET could well be signalling us right now from 100,000 light years away, but we have no way of detecting it. Not to confuse the issue with facts, but if ET is signaling us "right now" and they're signaling using Radio (since SETI@Home is looking for radio signals) and they're 100,000 light years away, the signal won't get here for 100,000 years. As we earthlings have evolved, we've gone from blasting "I Love Lucy" all over the galaxy to increasingly controlled emissions, and to a large extent, have installed great ruddy networks of coax and fiber to carry what used to go through the air. Seems like we need to find a civilization "x" light years away, that was at the proper period in their technological evolution "x" years ago to be beaming "I Love Lintilla" to the stars. Still, what if we found that signal? ____________ | |
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I'm not confused Ned, I'm aware of the speed of light. So it must be taken for granted that anything we measure in electromagnetic spectrum has a time lag proportional to its distance from earth. I also don't think the simple science concept behind SETI@home has changed, even though human science has progressed. SETI@home is looking at the radio wave part of the spectrum, but its only looking for something around the hydrogen line at 1420 MHz. If (100,000 years ago Ned) ET is broadcasting to us at 100.00 FM, 100 MHz, your favourite radio station, SETI@home won't pick it up. One thousand years from now, we as humans will still know that simple radio waves travel well in space and its still going to be a good way to detect other intelligent life. (Yes, its very complex to listen for ET in the lower wave lengths because of Human RFI). So my suggestion is focusing on a much smaller, and more specific targeted part of the sky and broadening the search algorithms. Think about this, the earth is spinning, so Arecibo is only ever "Flashing momentarily" past any single part of the sky as it records. So even if we get 50 recordings from one spot in the sky over 10 years, the recordings for that spot on the sky are still minuscule. Kepler is looking at one small densely populated, targeted part of the sky continuously for 4 years straight, with out blinking. SETI@home does not need to look at one spot for 4 years, but the concept should be similar, targeted searches. After 10 years searching, we don't call it a day and say there is no ET when all we have measured was a quick flash past the whole sky. No, instead this project evolves and learns from the current zero result. When NASA took loads of images with Hubble, did NASA call it a day and say there are no planets out there because Hubble did not see them? No, they had a zero result for planets, they evolved the science and progressed. They built Kepler, the first of several steps to finding biological life on another planet. And thanks Byron, its interesting to see the SETI Institute, and the ATA, both ET projects, are publishing science papers about real science. I bet the NSF will look very kindly on these scientists when it comes to funding. It goes to show you that you can look for ET and get NSF funding if your clever. Byron its also worth noting the hugh emphasis on the seti institute website on "Educating Kids" and "Kids Science". The NSF just love that stuff, they love to see scientists educating Kids, they throw money at that kind of stuff. Just a few pages of "Kids" science and the NSF are happy campers.(I would be glad to volunteer to prepare some kids science pages if needed (Eric, PM me if you need)). John. ____________ | |
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Arecibo is much more "steerable" than you'd think, but the problem isn't the ability (or inability) to control the telescope from a technical standpoint. It's organizational. The data for SETI@Home comes from SERENDIP. The basic idea there is that the cost of time where you control the telescope is expensive, so instead of demanding control of the telescope, you stick another receiver at the feed and go along for the ride while someone else pays to control the telescope. SETI@Home gets signals from the ALFA receiver, which was built by a consortium to spread costs. Listening at 100 MHz would require a different receiver, with a different feed antenna (the dish at Arecibo would be fine, just the resonant elements at the feed itself). So, as with many things, there is a difference between what you'd like to do, and what you can do. 1420 MHz was chosen because it's a quiet spot in the radio spectrum, at least observed from here. When tuning around looking for a place to transmit, you look for a quiet spot -- the noisy spots take a lot more transmit power to get above the noise. Is that the best spot? Who knows. ____________ | |
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Hello, I typed in Black Holes and this is the thread that i found. | |
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Message boards : SETI@home Staff Blog : Galaxy evolution and supermassive black holes. Warning: potentially educational
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