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The hypothesis of dark matter has proved incredibly successful in explaining the overall large scale structure of the universe and in interactions on the level of galactic clusters, which competing hypotheses such as modified gravity have failed to adequately explain. However, on the relatively smaller scales of individual galaxies, hypothesising dark matter shows some problems. In a paper recently accepted for publication in Physical Review Letters, astronomers Stacy McGaugh and Federico Lelli of Case Western Reserve University, and Jim Schombert of the University of Oregon, have made observations of 153 different galaxies with a wide variety of shapes, masses, sizes and amounts of gas. They have found a strong relationship between how quickly the galaxy rotates and the presence of normal (baryonic) matter alone. From an article on Case Western Reserve University's Daily:
[...] A team led by Case Western Reserve University researchers has found a significant new relationship in spiral and irregular galaxies: the acceleration observed in rotation curves tightly correlates with the gravitational acceleration expected from the visible mass only.
"If you measure the distribution of star light, you know the rotation curve, and vice versa," said Stacy McGaugh, chair of the Department of Astronomy at Case Western Reserve and lead author of the research.
The finding is consistent among 153 spiral and irregular galaxies, ranging from giant to dwarf, those with massive central bulges or none at all. It is also consistent among those galaxies comprised of mostly stars or mostly gas.
[...] "Galaxy rotation curves have traditionally been explained via an ad hoc hypothesis: that galaxies are surrounded by dark matter," said David Merritt, professor of physics and astronomy at the Rochester Institute of Technology, who was not involved in the research. "The relation discovered by McGaugh et al. is a serious, and possibly fatal, challenge to this hypothesis, since it shows that rotation curves are precisely determined by the distribution of the normal matter alone. Nothing in the standard cosmological model predicts this, and it is almost impossible to imagine how that model could be modified to explain it, without discarding the dark matter hypothesis completely."
[...] Arthur Kosowsky, professor of physics and astronomy at the University of Pittsburgh, was not involved but reviewed the research.
"The standard model of cosmology is remarkably successful at explaining just about everything we observe in the universe," Kosowsky said. "But if there is a single observation which keeps me awake at night worrying that we might have something essentially wrong, this is it."
Additional coverage and commentary by Ethan Siegel and Brian Koberlain. It seems that the universe has just thrown us yet another curve ball. This kind of correlation is just the sort of thing that modified gravity such as MOND and TeVeS predict. However, they fail miserably in explaining the large scale structure and evolution of the universe, which the dark matter explains admirably.
(Score: 3, Informative) by tangomargarine on Friday September 30 2016, @07:16PM
You're probably thinking of Voyager 1, not Pioneer 1, if you're talking about the farthest manmade thing from Earth.
With a bit of googling I'm getting ~126 AUs out. One AU is from Earth to the sun.
93 million miles = 1 AU
Voyager is 11.7 billion miles
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 3, Informative) by turgid on Friday September 30 2016, @07:58PM
What's really cool is that you can see the comms to the spacecraft in realtime [nasa.gov] -- Voyager 1:-)
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 1) by nitehawk214 on Friday September 30 2016, @09:44PM
Currently transmitting at 159 bytes/second.
I didn't know comcast could communicate in deep space.
"Don't you ever miss the days when you used to be nostalgic?" -Loiosh
(Score: 0) by Anonymous Coward on Saturday October 01 2016, @04:17AM
The speed is a bit too fast for it to be comcast, but the lag is about right.
(Score: 1) by In hydraulis on Friday October 07 2016, @01:54PM
No, he means Pioneer.
https://en.wikipedia.org/wiki/Pioneer_anomaly [wikipedia.org]
(Score: 2) by tangomargarine on Friday October 07 2016, @02:44PM
Except it says communication with the Pioneers was lost in 2003. The Voyagers are expected to still have limited functionality (including communications) until at least 2020.
2020 Start shutdown of science instruments (as of October 18, 2010 the order is undecided but the Low-Energy Charged Particles, Cosmic Ray Subsystem, Magnetometer, and Plasma Wave Subsystem instruments are expected to still be operating)[82]
2025–2030 Will no longer be able to power any single instrument.
- Wikipedia [wikipedia.org]
Suzanne Dodd, the Voyager project manager at NASA's Jet Propulsion Laboratory, says the Voyager spacecraft are powered by a couple of nuclear reactors sitting on the back of the probe, but they will soon run out of steam. "The nuclear power sources lose about 4 watts of power a year," she says. At this rate, Dodd says, Voyager should have enough power to communicate with Earth until 2022 or maybe 2025.
- Popular Mechanics [popularmechanics.com]
Although I believe it's inaccurate to refer to the RTGs [wikipedia.org] as "reactors." They just feed off the heat produced by the nuclear material sitting there and gradually decaying.
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by tangomargarine on Friday October 07 2016, @02:53PM
Saying the "reactors" will "run out of steam" is particularly wince-worthy since there's no steam involved in the process, unlike real nuclear reactors.
Apparently the RTGs themselves last surprisingly well vis-a-vis power generation: it's the thermocouples degrading that will cause the probe to die first. In 2011 with fresh thermocouples it would've been at 76% power; with the initial ones it's only at 57%.
https://en.wikipedia.org/wiki/Voyager_program#Power [wikipedia.org]
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"