US Lab Models Galaxy Cluster Merger 89
astroengine writes "The scales are mind-boggling and the physics is cutting edge, so how do you go about simulating the collision of two galactic clusters? Using some of the most powerful computers in the world, researchers at Argonne National Laboratory, the Flash Center at the University of Chicago and the Harvard-Smithsonian Center for Astrophysics have done just that."
Hopelessly confused by dark matter. (Score:3, Interesting)
I'm confused by "As the two clouds of dark matter inside each cluster can only interact gravitationally"
If dark matter can interact gravitationally wouldn't this mysterious crap just accumulate in the gravity wells of massive objects like stars or even the earth the same way planets collect rocks and dust around them?
Especially since everyone seems to be saying that dark matter so outnumbers normal stuff wouldn't a significant portion of the total mass that contributes to gravity of our own sun and earth be from dark matter?
I don't doubt that dark matter contributes to gravity but to say that it has an effect in a way that would suggest it have "mass" is one of those moments where I go searching to find out what I don't understand this time because that makes no sense. If dark matter acted as "stuff" that had mass then surely it would clump!!
Photons are massless but they have energy and therefore contribute to the gravity field even though they are not effected by gravity in the same way a massive object would be...the only effect is travling thru the pit created in the metric by the presence of "stuff".
Please if there is anyone who can help me make sense of this I would be eternally grateful.
Re:Does this qualify as a big bang? (Score:5, Interesting)
No. Sound is the vibration of air molecules, so when you speak or drop something, it creates compression waves that travel through the air and vibrate your eardrum, which in turn creates waves in the fluid of your cochlea that stimulate hair cells connected to the acoustic nerve. Since outer space has (almost) no air, these waves have no medium on which to travel, and sound as we know it does not happen.
Well, yes and no. There's no sound in space that a human could hear -- especially over the deafening roar of their blood boiling in the near-vacuum of space -- but there is a tremendous amount of diffuse gas and dust in galaxies and galaxy clusters, through which compression waves travel, albeit very weakly and slowly. If you were to observe those waves, then you could convert that data into an audio waveform in the range of human hearing. I may be misremembering, but I seem to recall that a group of researchers did precisely that with the (vastly smaller, nearer, and more easily observable) waves of gas being propelled outward by the pulsar at the heart of the Crab Nebula.
And yes, I know that really stretches the human notion of sound, but objects the size of galaxy clusters stretch most of our petty human notions, so it only seems fair.