Waspie_Dwarf Posted March 11, 2014 #1 Share Posted March 11, 2014 Milky Way amidst a ‘Council of Giants’ We live in a galaxy known as the Milky Way – a vast conglomeration of 300 billion stars, planets whizzing around them, and clouds of gas and dust floating in between. Though it has long been known that the Milky Way and its orbiting companion Andromeda are the dominant members of a small group of galaxies, the Local Group, which is about 3 million light years across, much less was known about our immediate neighbourhood in the universe. Now, a new paper by York University Physics & Astronomy Professor Marshall McCall, published today in the journal Monthly Notices of the Royal Astronomical Society, maps out bright galaxies within 35-million light years of the Earth, offering up an expanded picture of what lies beyond our doorstep. Read more... 2 Link to comment Share on other sites More sharing options...
Taun Posted March 11, 2014 #2 Share Posted March 11, 2014 (edited) Interesting that the local sheet is only 1.5 million LY's "thick"... I wonder if the majority of clusters are like this... I didn't fully understand the comment about the galaxies spinning around "a small circle"... Is this implying that these galaxies are gravitational bound and the whole group is a sort of "system" like our solar system?... Also, is there data to show if the galaxies in question are "in the same plane"?... by that I mean are the equatorial lines in the same plane, or are they "facing" (North/South) in different directions?... Most deep space photography I've seen, shows the galaxies oriented every which direction... It would be interesting to see if this group is more "in step"... I know... lots of questions... But that's the beauty of science... Every answer poses more questions... Edited March 11, 2014 by Taun Link to comment Share on other sites More sharing options...
Waspie_Dwarf Posted March 11, 2014 Author #3 Share Posted March 11, 2014 (edited) Interesting that the local sheet is only 1.5 million LY's "thick"... I wonder if the majority of clusters are like this... Presumably, the final paragraph says this: "Recent surveys of the more distant universe have revealed that galaxies lie in sheets and filaments with large regions of empty space called voids in between," says McCall. "The geometry is like that of a sponge. What the new map reveals is that structure akin to that seen on large scales extends down to the smallest."; I didn't fully understand the comment about the galaxies spinning around "a small circle"... Is this implying that these galaxies are gravitational bound and the whole group is a sort of "system" like our solar system?... Yes, that is exactly what a group or cluster of galaxies is a group bound together by gravity. Also, is there data to show if the galaxies in question are "in the same plane"?. A quick google search for images of galaxies in the Local Group will show you that we see quite a few of them face on, so no, they don't have their poles aligned in the same direction. Edited March 11, 2014 by Waspie_Dwarf 1 Link to comment Share on other sites More sharing options...
Taun Posted March 11, 2014 #4 Share Posted March 11, 2014 Thanks waspie... I know sometimes it can get annoying to have a bunch of easy questions asked, and I do appreciate your taking time to respond... Link to comment Share on other sites More sharing options...
Waspie_Dwarf Posted March 13, 2014 Author #5 Share Posted March 13, 2014 (edited) Thanks waspie... I know sometimes it can get annoying to have a bunch of easy questions asked, and I do appreciate your taking time to respond... I know I sometimes come across as a bit grouchy but I never have a problem with questions. People that are asking questions are people that want to learn, that is something to be admired, not to be cross about. Edited to add: As for the question on the alignment of the galaxies... I had to do the google search to be sure of the answer, so I learnt something new too. Edited March 13, 2014 by Waspie_Dwarf 2 Link to comment Share on other sites More sharing options...
Merc14 Posted March 13, 2014 #6 Share Posted March 13, 2014 I have a question as well. the article states that: McCall says twelve of the fourteen giants in the Local Sheet, including the Milky Way and Andromeda, are "spiral galaxies" which have highly flattened disks in which stars are forming. The remaining two are more puffy "elliptical galaxies", whose stellar bulks were laid down long ago. Does this mean that more ancient galaxies were of the elliptical variety and spiral arm galaxies are a newer formation, an evolved form of galaxy? One possibility I can think of is that maybe the older gaxies had collided with a neighboring galaxy creating the large ellipticals but would that mean the first galaxies formed after the big bang could have been of the spiral type? Link to comment Share on other sites More sharing options...
Waspie_Dwarf Posted March 13, 2014 Author #7 Share Posted March 13, 2014 Does this mean that more ancient galaxies were of the elliptical variety and spiral arm galaxies are a newer formation, an evolved form of galaxy? One possibility I can think of is that maybe the older gaxies had collided with a neighboring galaxy creating the large ellipticals but would that mean the first galaxies formed after the big bang could have been of the spiral type? I don't think that is the case, although I stand to be corrected. The spirals in spiral galaxies are caused by density waves rotating around the galactic centre. These density waves cause nebulae to begin to collapse in on themselves (a process called Jeans instability) and thus cause new stars to be born. The leading edges of the spirals are full of stellar nurseries. Elliptical galaxies lack this density wave and so have far fewer stellar nurseries and thus have an older population of stars. I believe that is what McCall is referring to. 2 Link to comment Share on other sites More sharing options...
Merc14 Posted March 13, 2014 #8 Share Posted March 13, 2014 (edited) I don't think that is the case, although I stand to be corrected. The spirals in spiral galaxies are caused by density waves rotating around the galactic centre. These density waves cause nebulae to begin to collapse in on themselves (a process called Jeans instability) and thus cause new stars to be born. The leading edges of the spirals are full of stellar nurseries. Elliptical galaxies lack this density wave and so have far fewer stellar nurseries and thus have an older population of stars. I believe that is what McCall is referring to. Ok thanks. The oldest Spiral Galaxy found to date is 10.7 billion years old and the universe is approximately 13.8 billion years old so they weren't the first type formed. Possibly it took time for the density waves to form? Edited March 13, 2014 by Merc14 Link to comment Share on other sites More sharing options...
Waspie_Dwarf Posted March 13, 2014 Author #9 Share Posted March 13, 2014 Ok thanks. The oldest Spiral Galaxy found to date is 10.7 billion years old and the universe is approximately 13.8 billion years old so they weren't the first type formed. Possibly it took time for the density waves to form? That would make sense. I have to admit I've never quite got my head around these density waves. Link to comment Share on other sites More sharing options...
Taun Posted March 13, 2014 #10 Share Posted March 13, 2014 (edited) Perhaps the spiral galaxies have stronger black holes in their center, thus imparting a stronger density wave?... Rather like putting an egg beater in a paint can and spinning the handle, eventually the entire liquid mass will spin... Edited March 13, 2014 by Taun Link to comment Share on other sites More sharing options...
Waspie_Dwarf Posted March 13, 2014 Author #11 Share Posted March 13, 2014 Perhaps the spiral galaxies have stronger black holes in their center, thus imparting a stronger density wave?... Rather like putting an egg beater in a paint can and spinning the handle, eventually the entire liquid mass will spin... Some hypotheses suggest that elliptical galaxies were formed by multiple collisions early in the history of the universe. I wonder if this prevented/destroyed any such density waves. Returning to your first post and your question about the orientation of galaxies it seems that they may not be as random as I suggested. Recent results suggest that the orientation of the spin axis of spiral galaxies is not a chance result, but instead they are preferentially aligned along the surface of cosmic voids. That is, spiral galaxies tend to be oriented at a high angle of inclination relative to the large-scale structure of the surroundings. They have been described as lining up like "beads on a string," with their axis of rotation following the filaments around the edges of the voids. Source: wikipedia 1 Link to comment Share on other sites More sharing options...
Taun Posted March 13, 2014 #12 Share Posted March 13, 2014 Thanks waspie... I've always liked this video of the 'beads on a string' aspect of the universe... [media=] [/media] 1 Link to comment Share on other sites More sharing options...
Merc14 Posted March 14, 2014 #13 Share Posted March 14, 2014 Thanks waspie... I've always liked this video of the 'beads on a string' aspect of the universe... [media=] [/media] This video takes my breath away, literally. It is so huge, so beyond comprehension and so awe inspiring that I can only stare stupidly and wonder what is possible in all those galaxies. Thanks for this. 1 Link to comment Share on other sites More sharing options...
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