Captain, dark energy sensor readings show dwarf galaxies orbiting the Milky Way Astronomy teams at the University of Cambridge and America's Fermilab looking for evidence of dark matter have spotted eight (relatively) tiny galaxies orbiting our Milky Way. "DES is finding galaxies so faint that they would have been very difficult to recognize in previous surveys," said Keith Bechtol of the University of …
So, uhhh, they found a bunch of baryonic matter not previously known. That's not dark matter in the esoteric theory sense.
Mebbe we find some systemic measurement errors too - the universe did not used to be expanding toward a big rip.
And before the Page-ists weigh in... I know and accept that science is always a work in progress.
Non-barynoic dark matter is only one candidate for dark matter, old fashioned dust, naked singularities, dust shrouded star nurseries, rogue planets, etc are also likely candidates. There's a hell of a lot of mass to account for, much is dark.
My personal theory is at least one eighth of the unaccounted for mass consists of single missing socks from cloths dryers and missing ball point pens.
>old fashioned dust, naked singularities, dust shrouded star nurseries, rogue planets, etc are also likely candidates.
Really? Those were the first and obvious possibilities and I thought those had been carefully analysed and dismissed years ago. Do you have any references for this assertion?
This is not about dark *matter*. The galaxies were spotted by a telescope designed to search for evidence related to dark *energy*.
These dwarf galaxies have nothing (directly) to do with either dark matter or dark energy. (And being outside the main disk of the galaxy, they wouldn't affect the rotation curves of the inner stars.)
So, is "Dark Matter" or "Dark Energy" some form of matter or energy different to what we already know, or just "Normal" matter and energy we've not yet been able to see due to it being so faint or far away we've not noticed it yet?
I do note with interest that the percentage of "Dark Matter/Energy" we think makes up for the "missing" matter/energy to account for the universe expansion seems to have been downgraded in light of the discovery of more "normal" matter/energy, eg these new dwarf galaxies. Unless there is something special about our galaxy, I suppose we should assume that we are average and that the other 100 billion galaxies also have dwarf galaxies orbiting them. Should we expect the "missing" matter percentage to fall again and have even less "Dark Matter/Energy" to go looking for?
Maybe it's all just normal matter and we simply haven't identified it yet and need better detectors?
After all, the postulation of Dark Matter/Energy is, until some is found, just a "fudge" to account for the lack of observable matter and our idea of how much is needed to drive the observed apparent expansion of the universe.
PS IANAS[cientist] but listen to The Infinite Monkey Cage ;-)
It is true that more "normal" (baryonic) matter has been found as technology has improved, people have thought of more things to look for, etc. But there is a limit to how much more there can be without it being visible in some way (either radiating or blocking electromagnetic radiation).
Note that dark energy and dark matter are hypothesized to explain very different phenomena. The only thing they have in common is the word "dark". In the case of dark matter, it is dark because it doesn't interact with light. In the case of dark energy, it is dark because no one knows what it is.
Dark matter is required to explain the unexpected orbital velocities of stars, gas and dust around galaxies (and galaxies in clusters, and gravitational lensing, and ...). The best explanation so far is simply that there is more mass in galaxies than we can see. It is *possible* that this is actually due to something like gravity not working quite as we think. But the more evidence that is gathered, the more likely it seems that it is some form of matter that doesn't interact electromagnetically (like neutrinos; but not neutrinos - for various reasons).
Dark energy is really a placeholder for whatever is behind the apparent (and unexpected) accelerating expansion of the universe. The simplest way of representing this is to plug an extra energy term into the Einstein Field equations (did I say "simple"?); hence the name. But no one really has any idea if it is some form of energy or something else completely. New physics: yay!
It's about density and stellar population. Globular clusters are really densely packed, despite not having a black hole larger than a few stellar masses. They also tend to be metal poor stars and are much, much, much older.
These dwarf galaxylets are likely to be small stellar nurseries ejected from the Milky Way during a previous collision and are hence metal rich and pretty new. Previous discoveries of similar objects have shown them to be not all that densely packed and roughly in line with the age of the stars in the host galaxy.
Some speculate that these represent stellar nurseries that formed around black holes of a few stellar masses and remained gravitationally bound as their location within the galactic disk was perturbed. As such, when they were ejected they stayed together. By staying together they retained enough gravity (collectively) that they didn't achieve galactic escape velocity but were simply pulled into a wider orbit.
It is probably better not to view these as dwarf galaxies in the traditional sense as they don't have supermassive black holes and aren't remnants of larger galaxies that experienced a collision event. They are - for lack of a better term - larger objects in the Kuiper belt of the Milky Way. Part of it as much as Eris, Haumea, Makemake and Sedna are part of Sol's Kuiper belt, which is a part of our solar system.
There is no hard edge to the galaxy. it doesn't just stop at some arbitrary point. The number of systems and gases peter out with distance, but within the very low density fringed agglomerations appear. These are typically material kicked out from the main body, but there is still enough low density stuff out there - gases, rogue planets, individual systems, etc - that it can keep small clusters of stars young.
I hope that explains how these objects are (most of them, anyways,) likely to be different from the old, dense globular clusters that orbit much farther out.
Post mainly redacted. I really shouldn't post early when still fuzzy-headed.
Trevor, do you by any chance have a link to further data on the subject of the definition of the term galaxy and these interesting new discoveries? Looks like things in that area have passed me by somewhat in the last decade or so.
http://www.fcaglp.unlp.edu.ar/CGGE/Eng/gcdg_obj.html
http://www.gemini.edu/node/247
http://www.phy.duke.edu/~kolena/hou/clusters.htm
http://mydarksky.org/2008/04/04/a-globular-cluster-turns-galaxy/
These provide some basic info for the layman. The best info, however, will be found by searching Google Scholar for articles related to astrophysics classification. Look at dark matter concentration as a means of classification specifically, it's rather interesting.
I take your puny 520Mpixels and raise you 3.2Gpixels! http://www.lsst.org/lsst which coincidentally is to go looking for dark matter using a telescope on a mountain in Chile (the LSST)
So many pixels, so little funding ...
And I agree with Esme - unless they've seen rotational structure or a heavy core, 500 stars does not make even a tiny galaxy.
500 Stars is few but a star cluster is something else (difference based on dispersion and evidence of dark matter). I do not know which galaxy is being referred to but Segue 2 has just 1000 Solar Masses (plus or minus 300 solar masses) worth of stars - it's not like we can count the exact number of stars in another galaxy.
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