Yes they have zero rest mass, but they don't have zero energy. Anything with energy is affected by gravity and causes gravity (mass or energy warp spacetime, and spacetime tell mass/energy how to move).
Our best description of gravity is General Relativity. Within this framework, mass/energy tells spacetime how to warp, and spacetime tells mass/energy how to move. Mass isn't "formed from a concentration of energy," it is a form of energy. Energy can have plenty of different forms, and all of...
Hello Chronos and granpa,
A few comments.
There are two types of GRB's, long bursts and short bursts ( > few seconds and < few seconds respectively). The hypernova model only attempts to explain long GRB bursts. Hypernova are not necessarily stars formed early in the universe ( Chronos had a...
WCOLtd,
Once again, let me warn you, I'm neither a cosmologist nor a general relativity expert. I do astrophysics which (in my case) only requires me to have a peripheral knowledge of such fields.
You're thinking has certain similarities to Einstein's as he was developing his theory of...
WCOLtd,
Here's few comments.
Your close to being on the right track here. Gravity does work against the expansion of the universe (partially described the Hubble constant). However, remember that gravity is a directed force (which causes directed acceleration), not a directed velocity...
WCOLtd,
I'm more of an astrophysicist, but here's my answer anyway.
How fast things are moving away from each other (due to expansion of space) depends on a variety of properties of the mass-energy density in the universe. As it turns out, we think the universe is accelerating due to...
LowlyPion,
That Sciam article is about something else entirely. It's about stars that form really close to the Super Massive Black Hole (SMBH). Here, "really close" means well within the SMBH's sphere of influence. A SMBH's sphere of influence is the volume in which most of the gravitational...
Hi blimkie.k,
Yeah, this is fascinating interesting stuff. I have a comment on this quote.
We haven't proven the existence of a super-massive black hole's (SMBH) anywhere yet, however, we have excellent evidence that there is a SMBH at the center of our galaxy. Mainly, we've been observing...
Dark Energy didn't start playing a role in Cosmic history until roughly ~10 billion years after the big bang. Thus it doesn't have much to say about galaxy evolution (though it is important in the evolution of galactic clusters). As for Dark matter (DM), mmm, it seems like it would play some...
shalayka,
Aren't all these theories alternative theories? That is, don't they seek to replace GR with another theory? Thus aren't they (blatant) attempts to replace (or destroy) GR? Or are you saying that these alternative theories are similar to (or in the same spirit of) GR, thus they...
Hi George,
Last summer I glanced at the paper regarding the strange dark matter ring formed from a line of sight cluster collision. The impression that I got was that the separation between baryonic matter and dark matter isn't quite as established in the "ring" cluster (not really it's name)...
I've recently come across some doubters as to the existence of dark matter. If you find yourself among that group, please read the following article on New Scientist and my comments. Then you can jump on the DM bandwagon with me!
Dark matter and normal matter 'divorce' in cosmic clash...
jnorman,
Why should anyone try to make DM and DE fit into the standard model of particle physics? Clearly they are astronomical evidence for physics beyond the standard model. The standard model clearly is in need of an overhaul (i.e. a new theory must be able to deal with black hole...
hellfire,
Your understanding is correct, except regarding the Gunn-Peterson effect (otherwise known as the Gunn-Peterson trough). The Ly-a forest is so-called because the spectrum of the quasar looks like a forest, a bunch of absorption lines caused by the quasar light being absorbed by...
HallsofIvy,
There are sound waves in space because space is not a vacuum (there's dust and hydrogen and such, even in intergalactic space). The note spoken of is not in the microwave and it's not electromagnetic. You may have thought it's in the microwave because we detected these waves by...