Considering that we can’t see dark matter and have little idea what it is, the notion that we could take its temperature seems preposterous. But new work out of Durham University (UK) points to a way of using visible astronomical sources to draw conclusions about dark matter’s effects in the early universe. Using computer simulations to examine the formation of the first stars, the researchers have applied ‘cold’ and ‘warm’ dark matter models, noting the effects we might expect to see today. These, in turn, should tell us something about how dark matter operates.
Cold, or slow-moving dark matter particles have a particular signature. After the first 100 million years of expansion, dark and more or less uniform, the universe would have begun to witness the birth of structure as dark matter’s gravity drew hydrogen, helium and lithium into the condensations that produced the first stars. In this model, the cold dark matter, clumping into spherical structures, would have produced stars in isolation, one for each dark matter concentration. These are the massive stars that produced the first heavy elements — carbon, oxygen and silicon — necessary for solid planets to emerge.
Warm dark matter is a different beast. Its particles in fast motion, the effect would be to replace the ripple-like spread of cold dark matter with long filaments in which large numbers of stars of differing sizes coalesced out of these strands more or less at the same time. Filaments like these would have been extraordinary structures, some 9000 light years long, according to the researchers, who believe the filaments would have fragmented in spectacular bursts of star formation.
Image: In the authors’ simulations, a gas filament condenses and then fragments to form the first stars. The gas heats as it gets compressed but then becomes cold in the center. The red shading in this image reflects changes in the gas’ temperature. Image copyright: Science.
The massive stars spawned by cold dark matter would have short lifespans that would not allow current observations. Stars formed from warm dark matter, on the other hand, should have varied considerably in mass. “A key question that astronomers often ask,” says Tom Theuns (Durham University),”is ‘where are the descendants of the first stars today’?’ The answer is that, if the dark matter is warm, some of these primordial stars should be lurking around our galaxy.”
That means stars we can observe today could hold valuable clues to star formation and dark matter’s nature. Moreover, collapse of the filaments themselves may have seeded the formation of black holes in the centers of massive galaxies. An exotic and far-ranging theory indeed! The paper is Gao and Theuns, “Lighting the Universe with Filaments,” Science Vol. 317. no. 5844 (14 September, 2007), pp. 1527 – 1530 (abstract).
Off-topic, for sure, but I think this is the best website to find an answer.
Alan Guth speculated that the net energy of the universe may be 0. His argument, as far as I can scope, is that the (positive) energy of the universe plus the equivalent energy in matter = the (negative) energy of gravitation.
In other words, the net energy contained in the universe = 0. (one could argue that it doesn’t exist! :))
Any news/thoughts on this speculation?
Any info (+/-) would be welcome.
I hold a rubber ball in my hand. It contains a huge amount of positively charged particles and also negatively charged particles. However there is an almost equal number of each so there is zero net charge. Does the ball exist? It seems to exist. It even bounces. But then who am I to say? After all the net electrical charge of my body is also zero, so perhaps I don’t exist.
I think, therefore I am…
Hi Ron & Eric
But how many of you are there in quantum copies throughout the Multiverse???
Ron, my aside about non-existence was an attempt at humor.,,
Do you have a response to my query?
And Eric, that quote is incomplete. Transcripts of the event reveal that DesCartes actually said:
“I’ve had too much to drink, I think, therefore I am going to be sick.”
Yes, I noticed the humor which is why I responded in kind. Even so my analogy was pertinent to the question.
If the net energy of the universe is zero it tells us something interesting about its origins and its present large-scale structure. However there is no reason why these separate and equal energy quantities cannot simultaneously exist.
Perhaps another way of looking at it is consider two quantities x and y. When measured they show equal but opposite magnitudes. You would have to combine them in some specific fashion to physically realize the net result. For example, virtual particle creation/destruction out of the vacuum, netting nothing.
Ron S.
Sorry about my rejoinder. I didn’t catch the humor. Text is so dry!
I have been intrigued by Guth’s suggestion since I first encountered it. If my calculus was good enough I might try to solve the triple integral of negative (gravitational) energy -m/r^2 vs. distance from an object of known mass to determine whether it equals the mass energy of the object, but hey i’m only a biologist. (intuitively, it seems that they should be.) I’m not sure that it’s possible, but somebody should attempt it.
After some digging, I have found this statement, which seems to confirm what I asked:
The Higgs Boson vs the Spacetime Metric
John A. Gowan
Revised April, 2007
http://www.people.cornell.edu/pages/jag8/index.html
“… although the gravitational field of a particle may seem to be weak, it extends throughout the Universe, and the negative gravitational energy of a particle is equal in magnitude to its positive rest mass energy …”
Matter energy + gravitational energy = 0.
(It’s only a web article, and I’m not sure that it is valid, but I’m going to assume it is until informed otherwise.)
Large Hadron Collider Could Detect “Unparticles”
Written by Ian O’Neill
Understanding the mysterious dark matter in our universe is paramount to cosmologists. Dark matter and dark energy makes up the vast majority of mass in the observable universe. It influences galaxy rotation, galactic clusters and even holds the answer to our universe’s fate. So, it is unsurprising to hear about some outlandish physics behind the possible structure of this concealed mass. A Harvard scientist has now stepped up the plate, publishing his understanding about dark matter, believing the answer may lie in a type of material that has a mass, but doesn’t behave like a particle. “Unparticles” may also be detected by the high energy particle accelerator, the Large Hadron Detector (LHD) at CERN going online in a few weeks time. High energy physics is about to get stranger than it already is…
Dark matter is theorized to take on many forms, including: neutron stars, weakly interacting massive particles (WIMPs), neutrinos, black holes and massive compact halo objects (MACHOs). It is hard, however, to understand where the majority of mass comes from if you can’t observe it, so much of what we “know” about this dark source of matter and energy will remain theory until we can actually find a way of observing it. Now, we have a chance, not only to observe a form of dark matter, but also to generate it.
Professor Howard Georgi, a Harvard University physicist, wants to share his idea that the “missing mass” of the universe may be held in a type of matter that cannot be explained by the current understanding of physics. The revelation came to him when he was researching what can be expected from the future results of LHC experiments. Beginning with quantum mechanics (as one would expect), he focused on the interactions between sub-atomic particles. Using the “Standard Model”, which describes everything we know and understand about matter in our universe (interactions, symmetry, leptons, bosons etc.), Georgi soon came to a dead end. He then side stepped a basic premise of the standard model: the forces that govern particle interactions act differently at different length scales.
Full unArticle here:
http://www.universetoday.com/2008/01/23/large-hadron-collider-could-detect-unparticles/