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from the mini-halos-are-for-really-small-angels dept.
Missing Galaxies? Now There's Too Many:
Gaze skyward from the Southern Hemisphere and it's hard to miss the Large Magellanic Cloud. The fact that it looks like one of the Milky Way's spiral arms, albeit smaller, reveals that it's a small galaxy roughly 30,000 light-years across with a few billion stars. Indeed, any small telescope will show that it's scattered with glowing nebulae that are punctured by dark dollops of dust.
And it isn't the only satellite galaxy that slowly swirls around the Milky Way. By 1999, astronomers had detected a dozen companions, many of them invisible to the unaided eye. But at that time, computer simulations of the evolution of the universe had predicted that the Milky Way's neighborhood should be bustling with activity — hosting not a dozen, but thousands, of tiny companions. So where were the missing satellites?
That astronomical riddle went on to bedevil astronomers for nearly two decades. Researchers came up with a number of potential explanations. Some involved speculative new ideas about how galaxies evolve. Others proposed the existence of exotic forms of dark matter — the mysterious substance that makes up 84 percent of the matter in the universe.
But within the past few years something strange happened. New surveys allowed astronomers to find more satellite galaxies that had previously been hidden. At the same time, updated computer simulations predicted the existence of far fewer galaxies than their predecessors did.
In fact, the estimates of galaxy numbers from observational studies and from theoretical simulations converged so quickly that they ended up overshooting each other. Whereas in the early 2000s astronomers worried that there were too few satellites, by 2018 there appeared to be too many. The missing satellites problem had been turned inside out.
The story dives into ultra faint dwarf galaxies, dark matter halos, mini-halos, tiny little ghost galaxies, as well as computer simulations of the Milky Way galaxy having different results depending on whether they were based on dark matter or on our everyday baryonic matter.
But [University of California, Irvine astronomer James] Bullock and his colleagues didn't merely outline the problem, they also proposed a solution. Simulations have long suggested that lots of dark-matter mini-halos formed around the Milky Way. But astronomers argued that these halos didn't form galaxies. There's a threshold, the argument went, below which these halos simply didn't have enough gravity to hold on to the gas necessary to form stars. They were thus star-free and invisible.
For nearly 20 years, astronomers thought that threshold for the mass of a dark-matter halo that could form a galaxy rested around 500 million times the mass of the sun. But Bullock's team suspects that it's much lower, around 30 million times the mass of the sun.
If such small globs of dark matter can grab onto enough ordinary matter to create stars (and thus galaxies), then simulations start to match observations. Indeed, Bullock's team was able to model galaxies that are eerily real. Not only do the numbers of simulated mini-halos match the numbers that are predicted by observations, but the shapes of the galaxies' orbits even look like the ones we have already detected.
(Score: 2, Flamebait) by jmorris on Wednesday January 30 2019, @06:29PM (3 children)
The models were certain the North Pole would be ice free years ago. Last I looked the ice is steadfastly refusing to conform to the model.
Tell me, what could possibly discredit your faith? If the weather is warm, Global Warming! We are having a cold spell, Climate Change! If we have hurricanes it is due to Warming, if we run a few years without any that is Climate Change. More rain, less rain, both mean the same thing, another confirmation. It is exactly like belief in God, if your kid gets cancer it is God's Will. If the kid recovers it is a Miracle. Tell me how one would disprove AGW Theory? Because that is how Science works, make a testable hypothesis, then test it and grade it pass/fail.
(Score: 3, Touché) by bob_super on Wednesday January 30 2019, @07:14PM (2 children)
It's easy to disprove. Just get rid of all data collection, and destroy all historical records. That may require providing all humans with mandatory medication to make sure nobody remembers what the climate used to be like and how fast the patterns are changing.
Also, killing all the bugs and plants which are migrating north (south down-under) because the new long-term patterns allow their survival.
And go get the Antarctic shelves to avoid future coring, and move them to replace the melting glaciers.
Peace of cake.
A lot easier than making you admit that maybe there is a change happening, and maybe not all scientists around the world are commie pinko taliban eager to destroy your way of life by pointing out that some of us use on average three times more energy than other people with as many freedoms...
(Score: 0) by Anonymous Coward on Thursday January 31 2019, @02:51AM
Ask the Romans about the climate.
(Score: 0) by Anonymous Coward on Thursday January 31 2019, @03:00AM
The parent talked about specific failures of the models. It seems you are satisfied that the models predicted "change". The climate is always changing... so "predicting" this should not impress anyone.