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Space Science

Nearby Galaxy Surprisingly Young 63

Posted by michael
from the fake-id dept.
Pi_0's don't shower writes "The hubblesite is reporting that a galaxy discovered 70 years ago, I Zwicky 18, has been confirmed to be one of the youngest galaxies in the universe, at only 500 million years old. By contrast, our Milky Way, Andromeda, and most other nearby galaxies are 12 billion years old. This galaxy is the closest newly-formed galaxy, at only 45 million light years away, which has rather interesting implications for galaxy formation."
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Nearby Galaxy Surprisingly Young

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  • Re:Galactic ignition (Score:5, Informative)

    by u19925 (613350) on Thursday December 02, 2004 @08:24PM (#10980948)
    in the beginning everything is assumed to be lumps of gas. due to some intial asymmetry, the otherwise uniform distribution of gas started forming lumps. once the lumps formed, it was a self sustaining chain reaction. as it became more denser, the gravity became strong and pulled gases even close. it still takes time to form the galaxy, because the gravitational collapse produces heat and that regulates the collapse (that is why our sun still shines and not collapsed under its gravity. except that in sun's case, the heat is coming from thermonuclear reaction). once gases start collapsing, they also form small lumps internally. when density of small lumps reaches some critical value we see star formation.

    now the rate at which collapse occurs is difficult to calculate. it is non-linear, too many parameters and depends heavily on initial condition that you start. It may be possible, that these galaxy could produce internal lumps only recently which were dense enough to form stars.
    in the beginning the stars are massive, since thermonuclear reaction is hard to start in "pristine" gas composed of only primordial hydrogen and helium. However, these large stars are also short lived, since they produce heat very fast and consume internal fuel and then they explode and generate heavy elements as by-products, which helps other smaller start formation like our sun.
  • by Teancum (67324) <{ten.orezten} {ta} {gninroh_trebor}> on Friday December 03, 2004 @12:59AM (#10983045) Homepage Journal
    There are a number of ways to do this. Perhaps the #1 way is through what is called a
    Hertzsprung-Russell diagram, named after the two astronomers who came up with this method of classification.

    There are two primary aspects that allow you to plot an individual star on this diagram: Its spectral color (litterally, what color you see the star as) This can be assigned a number as a specific peak color frequency. This also can be interpreted as the temperature of the "surface" of the star. The other axis is the absolute brightness of the star. This is the number of photons you can count in a given period of time relative to how far away it is. For measuring stars in a galaxy, distance measurements can pretty much assume that all of the stars are roughly the same distance away, thus simplifying this task. Close stars will obviously be brighter, but stars like Alpha Centari, an ordinary yellow star, are apparently as bright as Betelguese, a star almost 100 times further away.

    Keep in mind that only until the Hubble telescope was able to resolve the individual stars in this galaxy, this study wasn't able to happen for this particular galaxy... which is why this is now news. Really a neat project on the whole.

    The point here is that young stars fall onto what is called "The Main Sequence". These are stars like our sun that are still mostly converting Hydrogen to Helium as the primary source of nuclear energy. This relationship is quite well defined, and has been observed in not only the Milky Way Galaxy, but in other galaxies where individual stars have been able to be identified.

    Stars that run out of Hydrogen fall into a very different pattern. Like I mentioned with Betelguese (in the constellation Orion), it is much further away but yet just as bright. Also, its color is more Red (in a clear rural sky you can even see this reddish color), which puts it outside of the Main Sequence. That is because (according to current theory) it has run out of Hydrogen and is now in the process of turning Helium into Carbon. This group of stars, known as "Red Giants" play a huge role in determining the age of a galaxy or other group of stars.

    When stars finally run out of Helium, the rest of the elemental transmutation takes place rather quickly, or the fusion simply stops. Without going through the subsequent steps, the star eventually turns into a Super Nova (if there is enough stuff in the star to produce it) and leaves behind a white dwarf or neutron star (for really big stars... black holes are yet more stuff). A white dwarf is quite dim even for its distance, but yet its surface temperature is quite hot. These give yet another very distinctive plot on the HR Diagram.

    So the whole point here is that you can measure the age of a group of stars based on the relative brightness of the stars in that group. Very large stars tend to live very short lifespans because they do a very efficient job of doing the fusion. Small stars (like Wolf 359) will be still doing the hydrogen fusion 20 billion years from now. Over time (and based on considerable observation examples... not just this galaxy in the article but also concrete parallax measurements of close stars to our own as well) you will see fewer and fewer stars on the very blue end of the HR diagram and more and more Red Dwarfs, with white dwarves showing up in increasing numbers as well.

    One other critical tool for measurement is also trying to determine what elements are in the spectra of the stars. Different elements show up in stars and can be measured based on if they are absorbing or emitting light from the surface of the star. Mind you, this doesn't indicate much in terms of what is happening in the center of the star, but rather what is on the surface of the star. The current assumption is that the Universe started out with mainly Hydrogen and Helium, and only very small amounts of other elements. If you find large quantities of other elements in a star (like significant quantities of Iron on the sur
  • by forkazoo (138186) <wrosecrans.gmail@com> on Friday December 03, 2004 @01:04AM (#10983079) Homepage
    Well, science starts with one major assumption. We hope that the laws of physics are the same everywhere. That's not a guarantee, because we have never been outside our solar system, but we have no reason to suspect otherwise.

    So, here on earth, we can do all sorts of laboratory tests. We can figure out under what conditions Hydrogen fuses. We can test the strength of gravity. We can test the way various elements react at various tempuratures and pressures. So, while there isn't a 100% guarantee that we have a good handle on how stellar evolution works in another galaxy, we can be pretty confident that we have a very good handle on it. Accurate to many decimal places.

    Based on what we know about how the elements, we can make some calculations about stellar evolution in general. We can figure out how far away nearby stars are by using parallax while the earth goes around the sun. The nearby stars are the ones we can use to best test our theories, because we can be very very sure how far away they are. Because we know how far away they are, and how bright they appear, we can figure out how bright they actually are (as if they were all the same distance). We can also use spectrography to figure out what elements are giving off the starlight (which we can double check by heating up the elements in a lab and using the same spectroscope). Thankfully, our mathematical models of how bright a star should be with a certain element mixture line up perfectly with what we actually see, so we can safely apply our models to stars so far away that we can't use parallax to measure the brightness.

    So, if you are still with me... We can look at a star, analyse the spectra emitted, and plug it into our mathematical models of stellar evolution. It seems like crazy guessing, and there is certainly some guessing involved, but the theories we use on distant stars have been tested in laboratories, and on nearby stars, with everything being double checked for crazy shit as the tests get farther out.

    Given that this galaxy is so unusual, it is possible that somewhere along the line, we may need to update our models. It's possible our models are just giving us a wrong answer. It's wildly unlikely. But, science is the unending quest for a less-wrong answer. That's the difference between dogma and science. Science will freely admit it is wrong, but it usually turns out to be only slightly so. Dogma just finds ways to explain away new information in terms of the existing dogma, or dismisses it entirely.
  • by Teancum (67324) <{ten.orezten} {ta} {gninroh_trebor}> on Friday December 03, 2004 @02:40AM (#10983584) Homepage Journal
    There are a few astronomical measurements that take place over the course of just a few months or years. Supernova in particular happen in just a matter of a few days, which is where they get their name: They appear in the sky as a "new" (Latin form is "Novo" or "Nova") star that wasn't visible before.

    In 1987 a supernova was extensively sutidied in one of the Magenellic clouds (galaxies very close to our own that are so close that their apparent size takes up a significant portion of the southern hemesphere's sky). Previous sky survey's demonstrated that it was in the Red Dwarf stage of its life, and after the explosion a pulsar was found in the same physical position. That was pretty convincing evidence that at least that portion of stellar evolution is quite accurate, and can still be verified with current measurements.

    Another major scientific measurement took place with the "Eagle Nebula" [wikipedia.org], which is the one that has the really cool columns of gases and has been done as poster you can buy in Wal-Mart and put on T-Shirts. In this case over the course of just a few years you can see stars litterally form right out of the gasses of the nebula. These new stars demonstrate that they are right on the "Main Sequence" after their formation. This certainly was a major plus to confirming these theories.

    There are some suspected stars that are in transition from Main Sequence to Red Giant, but that takes considerably longer to happen.

    With some very recent sky surveys, there have also been some significant confirmation of these theories, if simply from the huge amount of data that simply confirms this information. Keep in mind that many of these theories started out simply as a way to try and come up with a classification system of any kind, and have evloved from there.

    The spectral classification originally started out when a bunch of researchers at Harvard University put star names and coordinates on a bunch of 3" x 5" cards and based on the spectrum lines and measured brightness, they litterally dropped these cards into boxes labeled "A", "B", "C", ect. After some more research the boxes were rearranged by temperature to become "O","B","A","F","G","K","M","R","N","S" ("Oh, Be A Fine Girl, Kiss Me") As can be seen, the original classification was very arbitrary, but based on formal measurements. Our sun is of type "G", and blue stars as type "O".

    We know about spectral lines because we can do that in laboratories here on the Earth. Really quite cool to do as well, and each element puts out its own specrum. I'm sure you've seen a Neon sign with its pink glow, which is exactly what is done with other elements to identify their spectra as well. BTW, this spectra is also critical to understanding the atomic structure of each element, but that is another story to itself.

    The distance measurements are calculated from steallar parallax as the base measurement. We know from several other measurements how far the Earth is away from the Sun, and when the Earth travels around the Sun, stars appear to move relative to each other. This is like taking two photographs a few feet apart and seeing stuff in the background at different angles. Doing this you can directly measure how far away something is from where you are at. This measurement is accurate to about 1000 light years with the Hubble Telescope. Other techniques try to approximate distances based on similar looking stars to ones that are close to us and assuming that stars next to those are probably about the same distance. Obviously that means even further distances are less accurate as you go further away from us. These distance measurements are IMHO very accurate, and their accuracy can be expressed precisely to a certain range of accuracy as well.

    Stellar color is pretty easy, as you just have to have filters at different wavelengths when you take pictures of the stars. That is what gives the color to the photo in this article, and you can
  • Actually, if you would have done your math right you would notice that it was the FLOOD that happened 4400 years ago, not the creation :)
  • by beeplet (735701) <beeplet@gmail.com> on Friday December 03, 2004 @07:37PM (#10992848) Journal
    This is nonsense.

    Straightforward calculations, starting from equations of gas pressure and gravtational attraction, show that any overdense region in a gas cloud, larger than a certain critical mass (called the Jeans mass), will collapse in on itself. It is true that the simplest calculation of the Jeans mass gives 10^5 solar masses, much larger than any star; but if you take into account that a cloud will fragment as it collapses, the Jeans mass becomes much smaller. For typical conditions, the critical mass is ~1/3 the mass of the sun.

    Supernova shocks might help start the process of gravitational collapse, but there is no reason to think 20 or more are necessary.
  • by forkazoo (138186) <wrosecrans.gmail@com> on Friday December 03, 2004 @09:01PM (#10993525) Homepage
    Secondly, I would like to point out that stellar evolution is absolutely impossible. This may sound crazy, but I am willing to back up my statement. In order to create a star (according to evolution), gas must be compressed enough for fusion to take place. The problem with this theory is that gas just can't be compressed that much by anything except (possibly) a bunch of stars blowing up at the same time near each other. Obviously, if you have to loose a bunch of stars to gain a new one, pretty soon, you won't have any stars!

    Ummm, care to share your calculations about how it's impossible for a could of Hydrogen gas to begin fusion due to gravitational compression? Seriously, if you have a gas cloud the size of the sun, it will eventually be attracted to itself, due to gravity, and form into a smaller and smaller cloud, until eventually it is the size of a star. A gas cloud the size and mass of a star means that the center of that cloud is as compressed as the core of a star, and so it is a place where fusion will start happening. No explosions needed, though they can certainly impact the process.

    What *exactly* do you suppose prevents gravity from compressing the gas cloud, making a stellar birth "impossible?"


    Finally, I would like to point out that, by your own definition, evolution is a complete dogma.

    In order to explain the creation of the universe, they have imagined something called the "big bang". By their own definition (read any modern public school textbook), the big bang was caused by the explosion of a dot which either 1 - always existed (the dot is basically god) or 2 - somehow created itself out of nothing (the dot is basically god). I belive that I have proved my point: evolution is a dogma, and will always be a dogma because it is impossible to escape the fact that there is a God! The only reason for coming to the illogical conclusion that the dot is god is that you cannot accept the fact that God is God!

    I can't imagine what would cause one to suppose that thinking a very hot dense gas cloud can start fusion somehow precludes the existence of God. The two questions are quite independant. Frankly, I think there are a lot of cosmologists that have no personal problem with the idea that God created that which went bang in the big bang. It doesn't effect the cosmology in any way.

    My own supposition is that God was sitting around one day, and he wondered to himself, "I wonder if I can microwave a burrito so hot that even I couldn't eat it..." Lacking an answer to this question, God went into an infinite loop, and he exploded from thinking too hard.

    My supposition fits the available evidence as well as supposing that god created the universe, or that there is no God. None of those answers about what was around before the universe effect the laws of physics in any way, because nobody has ever come up with a test or experiment that could demonstrably be effected by what came before the universe.

    While stellar evolution is a Dogma, and it is possible that God created the universe 500 years ago, and just made it look really really old, that's no reason to abandon cosmology.

    BTW, what created God? Isn't it actually simpler to suppose that a point singularity sprang into being one day? God is an extremely complex entity. I find it more difficult to believe that God sprang into being intact and whole and infinitely wise. If anything, God sounds like he requires the "theory of intelligent design" moreso than the universe. :)

This place just isn't big enough for all of us. We've got to find a way off this planet.

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