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‘Missing Mass’ Theory Revised

Has ten percent of the mass of the universe disappeared? Not really, but it’s true to say that our assessment of that mass has to be reconsidered, given recent findings on the nature of x-rays emitted from the vast spaces at the heart of galaxy clusters. How we interpret the x-ray data has a great bearing on how we calculate the mass of gases in the galactic clusters, and the mass of the clusters themselves.

The story begins in 2002, when a University of Alabama in Huntsville team studying warm, x-ray emitting gas in galactic clusters reported that it had found large amounts of comparatively low-energy x-rays in addition to higher energy ‘hard’ x-rays. The so-called ‘soft’ x-ray emitting atoms were assumed to exist at a density of one atom per cubic meter, but their cumulative mass was thought to amount to as much as ten percent of that needed to hold galactic clusters together.

But a closer look at data provided by the Chandra X-Ray Observatory, among other instruments, found no emission lines associated with the soft x-rays. Instead of flagging the presence of cooler gas, the energy is now thought to come from the collision of electrons with photons from the cosmic microwave background, converting the photons from low-energy microwaves to high-energy x-rays.

And that’s a problem, for the signal from such electrons would also make up part of the mass of the already observed hard x-rays. Thus our measurements of the gas in galactic clusters may be significantly off. Max Bonamente (UAH) nails the problem:

…the mass of these x-ray emitting clouds is much less than we initially thought it was. A significant portion of what we thought was missing mass turns out to be these ‘relativistic’ electrons.”

In addition, x-rays produced by electrons colliding with photons might mask the emission lines of the hard x-ray energy coming from galaxy clusters, lines which are prominent in iron and other metals. “This is also telling us there is fractionally more iron and other metals than we previously thought,” says Bonamente. “Less mass but more metals.”

The paper is Bonamente, Nevalainen et al., “Soft and Hard X-Ray Excess Emission in Abell 3112 Observed with Chandra,” Astrophysical Journal 668 (October 20, 2007), pp. 796-805 (abstract). So much for what was thought to be ‘missing mass,’ another reason for keeping research into just what holds the universe together on the front line of modern physics.

Comments on this entry are closed.

  • Adam November 3, 2007, 9:37

    Hi Paul

    “New Scientist” this week poses the curious speculation that our Standard Model of particles is just the tip of a much bigger Dark Matter ice-berg composed of ultra-light versions of themselves – some 10^32 “copies” of electrons, quarks and so on. Gia Dvali has come up with this curious idea to solve several puzzles of black holes and the Universe. Specifically: how would particles fit into a tiny primordial black hole?

    I’m yet to read further, but it sounds cool. I’ve always liked the idea that Dark Matter is Shadow Matter with its own particle physics parallel to our own. This new idea is similar, but with some intriguing implications.

  • george scaglione November 3, 2007, 13:29

    adam,just read the above and like it very much.i think we will find that there is so much more to the universe than we ever suspected ! thank you very much, george

  • Adam November 4, 2007, 6:39

    Hi george

    The ArXiv has two papers on the concept by Gia Dvali, perhaps too recent for other physicists to have a proper opinion. Multiplying the particles by 10^32 is a LOT of extra particles interacting – I wonder what it does to the amount of quantum computations that our Universe can do?

    Paul Davies takes Landauer’s idea that physics should be computable by the Universe’s resources and shows that even very small biomolecules (say a chain about 60 amino acids long) are beyond total computation by a computer as powerful as the Universe. He argues that this implies that real emergence is a necessity in our Universe, that reductionism is inherently unphysical in a computational sense.

    So how much bigger molecules can be computed in Dvali’s Universe? I’ll have to work it out.

  • rarchimedes November 6, 2007, 14:35

    What is the relevance of the total quantum computational capacity of the matter in the universe. We do not and will not have access to that capacity in any way, so it is another of those calculations of the number of angels on the head of a pin. The knowledge of the approximate extent and characterization of that matter should be sufficient to keep us out of trouble for at least the next couple of years. With the further realization that the universe is a dynamic place, these attempts to assign some deterministic value to the universe are foolish conceits, meaning absolutely nothing.