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CMNH Frontiers of Astronomy talk summary

From: Tim C.
Sent on: Friday, November 15, 2013 3:47 PM

The presentation last evening by Risa Wenschler at CMNH was interesting and informative, but from talking to some of the group afterward, parts of the talk were a bit confusing or perhaps more detailed than the audience was prepared for.  Therefore, I will try to give a basic capsule summary/explanation of what Risa was talking about!  Hopefully, clear up some of what she said and showed!


Gravity has always been the big kahuna.  We have a pretty good understanding of gravity. Gravity enables us to toss a baseball into the air and reasonably expect the ball to come back down. Gravity also enables clouds of hydrogen gas to condense into balls of fire—i.e. stars!   All good, but there are a couple of phenomena that we observe that gravity fails to explain:


1.        Stars form from the collapse of hydrogen gas clouds. Gravity handles that job nicely.  But galaxies and clusters of galaxies form according to very specific lines and structures (observed), and gravity alone does not seem to be capable to accomplishing this within the time limit of the universe’s existence (appr. 13.8 billion years).  The strength of gravity is dependent upon the mass of the objects doing the gravitational attracting.  The baseball “falls” to Earth because Earth’s mass is great enough to draw the baseball toward it, and that attractive force is stronger than the force with which we tossed the ball upward.  Now, in the case of galaxy clusters, there does not seem to be enough mass in the observed matter (aka Normal Matter or “baryons”)to bring these clusters together into the structures that we now observe through such telescopes as the Hubble!

2.       The stars of spiral galaxies rotate around the center of their galaxy.  Based on the mass that we can see (the Normal Matter), the stars on the outskirts should be rotating at a predicted speed.  Too fast, and they won’t remain as part of the galaxy, but will fly away.  They turn out to be going too fast, but are not flying away. 

The question therefore:  is our knowledge of gravity wrong or is there something else that is enabling galaxy clusters to form and enabling stars on the outskirts of galaxies to orbit the center of galaxy at such a speed and still remain attached to the galaxy?


We think we have a good handle on gravity. Therefore, if our knowledge of gravity is correct, there must be something else adding to the mass of galaxies and galaxy clusters. That something else is what we call Dark Matter.  That is what many folks are looking for (DM does not seem to interact with Normal Matter so if it exists, we have a tough time actually seeing or touching it!).  


What Risa is doing is developing computer simulations that start with a bunch of basic parameters that we know about the early universe and then lets them roll.  Some with Dark Matter included, some not.  So far, those with DM included seem to result in simulated universes that look very much like the actual universe. 


Lots of work still to do, but it would seem that gravity is cool and there is a lot of Dark Matter out there that is making not just galaxy clusters, but US possible! Of all the matter in the universe, it would seem that some 75% is Dark Matter, and only 25% is Normal Matter (us).




This subject requires its own essay, but essentially, the universe is expanding and that expansion is accelerating! We don’t know exactly why, so we are hypothesizing a mysterious energy called Dark Energy (no relation to Dark Matter) that explains what is going on.  Unfortunately, we don’t yet have a good explanation for the DE itself! 


For reference if anyone wishes to learn more, there are many books available, but some of my favorites are EINSTEIN’S TELESCOPE by Evalyn Gates, ATOM by Lawrence Krauss, THE 5% UNIVERSE by Richard Panek, ORIGINS by Neil DeGrasse Tyson, and A UNIVERSE FROM NOTHING by Lawrence Krauss. 


Hope this helps to clear a few things up!




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