Home sweet home. In the vicinity of the sun, our Milky Way galaxy seems to contain no dark matter, one team of astronomers claims.
Credit: Serge Brunier/NASA
Posted on 04/19/2012 9:54:03 PM PDT by neverdem
If a new study is true, then the search for dark matter just got a lot weirder. Our little corner of the Milky Way contains no observable concentration of the mysterious stuff whose gravity binds the galaxy, claims one team of astronomers. That finding would present a major problem for models of how galaxies form and may undermine the whole notion of dark matter, the researchers claim. But some scientists doubt the reliability of the team's method for measuring the elusive substance.
"This is not just some piddling little detail," says Frederic Hessman, an astronomer at the University of Göttingen in Germany who was not involved in the work. "If this is right, it turns everything totally upside-down." But that's a big if, says Julio Navarro, an astrophysicist at the University of Victoria in Canada: "The argument is provocative, but it remains inconclusive, in my opinion."
According to standard cosmology, we should be swimming in dark matter. Measurements of the afterglow of the big bang—the so-called cosmic microwave background—and of the distribution of the galaxies suggest that 85% of all matter in the universe is dark matter. What's more, decades of astronomical observations show that the stars within galaxies swirl about faster than they could if only the gravity of the others stars were holding them in. In fact, the speed with which the sun goes around the center of our galaxy suggests that dark matter ought to be about as abundant as ordinary matter at our distance from the galactic center, about 27,000 light-years.
But that's not what Christian Moni Bidin, an astronomer at the University of Concepción in Chile, and colleagues find. Using data gathered with several telescopes, they studied old stars called red giants in a cylindrical region a couple of light-years wide and extending 13,000 light-years above the plane of the galaxy. Treating the stars a bit like atoms in a gas, researchers assumed that they were trapped in the gravitational "well" of the galaxy. So by studying distributions of the stars' speeds in three dimensions, they could deduce the well's shape and hence the total distribution of mass from both dark and ordinary matter along the cylinder. Subtracting the distribution of ordinary matter as determined from star counts would then reveal the distribution of dark matter.
When Moni Bidin and colleagues did the analysis, however, they found that no dark matter was needed to explain the stars' speeds. The researchers had expected to detect a complicated mass distribution with a contribution from the galaxy's disk of stars and gas and the presumably spherical "halo" of dark matter surrounding the disk. Instead, they found that the disk alone neatly explained their data(PDF FReebie), as they report in a paper in press at The Astrophysical Journal.
The data don't disprove the existence of dark matter, Moni Bidin is quick to say. Astrophysicists still need the stuff to explain the speed of the stars in the galaxy. However, the data do suggest that there isn't any dark matter in our neck of the woods. "We're not saying that there isn't any dark matter," Moni Bidin says. "We're just saying that there isn't any dark matter here."
But that could lead to a major problem with the whole idea of dark matter. For example, one way to explain why there is no dark matter 27,000 light-years from the center of the Milky Way would be to assume it's all in one tall cigar-shaped lump that sticks through the center of the galaxy. But simulations show that such a shape for the halo is unlikely, Moni Bidin says.
Another possibility is that dark matter is made not of "cold," massive particles moving very slowly, but rather of "warm," lightweight particles moving much faster. In that case, the galactic halo would be larger and more uniform, producing an even and therefore undetectable background, Hessman says. But that inference would fly in the face of standard cosmology, which assumes that galaxies start to form as cold dark matter starts to condense in massive clumps. "Basically," Hessman says, "the cosmologists should say, 'Oh my God!' because you're taking away the one thing that makes everything work and they're going to have to go back to square one."
Or not. The new result may say more about the method than the distribution of dark matter, Navarro says. To get that distribution, at each position in space Moni Bidin and colleagues must subtract one large quantity (the amount of ordinary matter) from another large quantity (the amount of total mass) to get a small quantity. That process is likely to suffer from large uncertainties, Navarro says. "I applaud them for trying," he says. "I just don't think this method will ever give a conclusive answer." Moni Bidin says the method is robust and that larger surveys to come will pin down the dark matter distribution more precisely.
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Dark matter has gone missing because it doesn’t matter.
It’s not matter.
It’s momentum.
P=MV
Momentum is what it takes to balance out the Lorentz equations.
It takes various forms, the one we hear about most is the neutrino.
Y’all read it here first...
I just could never see dark matter.
Big Dark Matter is hoarding it to drive up the price.
“We can’t afford a situation where dark matter speculators can reap millions while millions of American families get the short end of the stick. That’s not the way the market should work.”
Hell no. It can’t be iffen it’s DARK.
Bush stole it. ALL.
The Milky Way Is Racist!Paging Rev Al and Rev Jesse.
You need a blacklight to see it.
“...whose gravity binds the galaxy...”
I thought the “Force” is what “...Binds the Galaxy Together...” - At least that’s what Obi-Wan said in Star Wars IV!
That's what happens when you put it in the clothes dryer. If they should ever find it, they'll probably solve the mystery of the missing socks too.......
—
Successors (principally the James Webb) will finally be canceled to fund muslim outreach. Hubble telescope doomed without shuttle to repair it - sometime between 2019-2032. At which time, China will determine what the US does or does not launch into LEO.
Expect these things to happen in Obama’s second term - or in his third, but definitely by his fourth term when space will be something which happens in other countries and in the US will be the distance from one ear to the other.
USA enters space with a bang, but goes out silently - not even with a whimper.
It’s the Romulans. They’re cloaking everything.
If Obama gets his third term, he better not parade down Pennsylvania avenue.
It’s funny when they say there is simply no room for God in creation, yet they hop from theory to theory struggling to explain the basics of the observable universe.
I have always believed that there is a spiritual, unobservable counterpart to what is visible.
What is truly funny is the lack of understanding of how science actually works. Without the self-corrections by proposing and testing new theories, the assumptions made cannot be relied upon as bearing truth. But for science's openness to testing and re-evaluation, we'd still be considering anaesthesia as the work of the Devil intended to nullify God's punishment in the form of pain, and burning witches at the stake or drowning them.
This is a common modern canard.
The scientific method relies on the moderate realism of the Middle Ages —particularly the promulgation of the dogma of “creation from nothing,” from which a direct line can be drawn through Buridan to Newton.
It’s not coincidental that so many great scientists were clerics.
The Origin of Science
columbia.edu/cu/augustine/a/science_origin.html
The Time Argument is a big problem for those citing the "something from nothing" canard. For God to even perform the first act of anything, Time has to pre-exist God, so that there is meaning in that act of God separating it from the prevailing configuration. Lawrence Krauss has an amazing lecture on this First Cause topic:
For God to even perform the first act of anything, Time has to pre-exist God, so that there is meaning in that act of God separating it from the prevailing configuration.I don't get why Time has to pre-exist God. I'm not sure I understand what that would even mean.
Besides that, even if it's somehow true and not reversed (God pre-existed time), how do you know one way or another with enough certainty to make such a statement as "Time has to pre-exist God"?
What is your authority for making that statement? You state it as if its an axiom, not the result of a chain of logical reasoning, so you must have an authority for that axiom. What is it? (Just curious.)
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