‘Missing Mass’ Found


One of the perplexing problems in modern astronomy is the one of trying to determine the composition and location of the “missing galactic mass”. (The missing mass is matter of which can detect gravitational effects, but which we haven’t been able to see. Dark Matter is part of the missing mass, but there are other sorts that can be out there.) Hence the interest in a recent paper published in the journal Science:

“Astronomers studying dwarf galaxies formed from the debris of a collision of larger galaxies found the dwarfs much more massive than expected, and think the additional material is ‘missing mass’ that theorists said should not be present in this kind of dwarf galaxy

…”Dark matter,” which astronomers can detect only by its gravitational effects, comes, they believe, in two basic forms. One form is the familiar kind of matter seen in stars, planets, and humans — called baryonic matter — that does not emit much light or other type of radiation. The other form, called non-baryonic dark matter, comprises nearly a third of the Universe but its nature is unknown.

…What is the dark matter in the dwarfs? The astronomers don’t believe it is the mysterious non-baryonic type, but rather cold Hydrogen molecules that are extremely difficult to detect.

When the astronomers performed computer models of the collision of NGC 5291 to simulate the formation of the system seen today, the models left the resulting recycled dwarfs with almost no dark matter. These computer models had started off with all the dark matter in the galaxy’s larger halo.

“The result of the computer models means that the additional mass we see in the real dwarfs came from the disks, not the haloes, of the larger galaxies that collided,” Bournaud said. That additional mass, the scientists believe, almost certainly is “normal” baryonic matter, probably cold molecular Hydrogen. “

Now the next question, if this observation and explanation is verified, would be to determine how much of the missing mass is normal matter such as this and how much of it is some sort of exotic, non-baryonic matter. No matter what the ratio, there’s going to be a lot of it. Estimates place the amount of missing mass to be between 90 and 99x the total amount of observed matter in the sky.

Read the rest here: ‘Missing Mass’ Found in Recycled Dwarf Galaxies

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  1. Paul Martin says

    When I read the headline, I was certain that someone had stumbled upon a lost Bach manuscript. I guess you can tell where my head’s at tonight.

  2. ruidh says

    Remembering that some string theorists think that gravity is so weak because the force leaks out through dimensions in addition to our familiar 3 space-like ones, it could very well be that the “dark” or “missing” matter is ordinary matter which is a short distance away through the additional dimensions, but far away if confined to the usual three.

  3. I’m with Paul. Actually when it said “missing *galactic* mass” I thought we’d recovered another section to Eucharistic Prayer C…

  4. Nicholas:
    Does this mean that all the energy spent hunting for weakly interacting massive particles has been for naught–it appears so since hydrogen explains the missing mass. I am sceptical–this looks like too simple a solution.

  5. Chuck, no, not really.
    Dark Matter (or missing mass) is a broad term denoting a number of different actual things. Some of the dark matter consists of things like the brown dwarfs described in the study above. Other, probably more significant amounts are the exotic non-bayronic stuff. Other constituent parts are probably bizarre things we haven’t even begun to imagine.
    If we get a handle on how much of dark matter is made up of brown dwarfs and failed stars, then we can start to get a handle on how much weird stuff we should be looking for.
    (We have some sense of how much dark matter is non-baryonic becuase of the abundance calculations of various particles and elements in the early universe.)

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