Stories
Slash Boxes
Comments

SoylentNews is people

posted by Fnord666 on Wednesday January 30 2019, @11:37AM   Printer-friendly
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.


Original Submission

 
This discussion has been archived. No new comments can be posted.
Display Options Threshold/Breakthrough Mark All as Read Mark All as Unread
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
  • (Score: 2) by AthanasiusKircher on Wednesday January 30 2019, @07:57PM (1 child)

    by AthanasiusKircher (5291) on Wednesday January 30 2019, @07:57PM (#794220) Journal

    One last thing I'll add after an overlong post: there are lots of theories in science that have long histories of not being directly observed for long periods. As I mentioned in another post, the underlying mechanism for gravity wasn't known for centuries after Newton's theory advanced physics (and some would argue we're still sorting it out), but no one is claiming gravity -- an invisible force acting at a distance -- doesn't exist. The atomic model was essential in advancing modern chemistry out of alchemy, as theories about molecules and chemical equations started to be written when no one had directly observed the existence of molecules or atoms. Electrons were postulated to explain electricity long before the structure of the (still invisible) atom was understood in any detail. Huge theories of electromagnetism were built on it. And when unusual results came along that seemed to conflict with theories (e.g., Rutherford's experiments), they didn't conclude that the unseen atoms and electrons didn't exist -- merely that the properties must be more specific and perhaps different than theorized. I could go on, but hopefully I've made my point.

    Just because you can't observe something directly doesn't mean it's not there, or that you can't create a detailed mathematical model of it that could lead to advancements in science. You're right that the dark matter theory has some problems, though you tend to overstate or misrepresent them -- it's nowhere near as arbitrary a theory as you imply. Perhaps it will turn out to be like phlogiston or the lumeniferous ether, or perhaps it will turn out to be like so many other scientific theories over the years that modeled unseen things and unseen forces and turned out to be broadly correct.

    Starting Score:    1  point
    Karma-Bonus Modifier   +1  

    Total Score:   2  
  • (Score: 2) by Gaaark on Wednesday January 30 2019, @08:24PM

    by Gaaark (41) on Wednesday January 30 2019, @08:24PM (#794229) Journal

    Yet, MAYBE gravity DOESN'T exist, at least not as a folding of space thing: maybe gravity is a PUSH, as in QI, the Unruh waves PUSH objects. A planet blocks the Unruh waves from a certain direction, the waves from the other direction push objects TOWARDS the planet.

    To me, a PUSH makes more sense than a Folding of space... A 'PULL'.

    And where is dark matter not arbitrary? Your other examples had more science behind them than dark matter.

    --
    --- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---