Our Universe: Missing, Found, Then Missing Again
Nov 8 at 10:10pm by Aileen
Keeping Up With Astronomy’s Game of Hide-and-Seek
Big astrophysics science news this week that a Big Chunk of the Universe Is Missing - Again. This requires a little background for understanding how it is our universe can be so adept at playing hide-and-seek.
As much as 96% of the mass necessary to account for how our universe is observed to be has been missing for a long time. The mass is necessary to explain the gravity that holds galaxies together, but all the atomic matter we can see in planets, comets, asteroids, assorted space junk, stars and galaxies accounts for just 4% of it. In 1974 astronomer Vera Rubin discovered that instead of following a Newtonian scheme where Mercury travels faster around the sun than Neptune does, almost all stars rotating around a galaxy’s center - at any distance - all travel at the same speed.
There had to be some ‘extra’ source of gravity working in galaxies, but there wasn’t nearly enough mass to account for this anomaly. The choice was between gravity being variable (unthinkable!) or the existence of a great deal of extra mass that we couldn’t see. Scientists jumped on that answer in defense of Newtonian/Einsteinian gravity and gifted us with “Dark Matter.”
They couldn’t come up with likely candidates enough to cover more than about 21% of the necessary extra mass, so they soon came up with some fudges for gravity itself - an “anti-gravity” force called Dark Energy where they could hide the anomalous data. They were up to 4% matter + 21% Dark Matter + 75% Dark Energy. Voilå! Universe explained.
That scientists had no real grasp on what Dark Matter and Dark Energy really are did not particularly upset them, and these have become consensus theory. There are some intriguing alternative theories out there, but none enjoy consensus status and are mostly considered somewhat ‘crackpot’ - aether theories, geometrical theories, and ‘hyper’ theories that include extra large dimensions are generally frowned upon even though some of them actually do attempt to describe the empirical observations without sacrificing 96% of reality to phantom agents.
In 2000, astrophysicists thought the missing matter might be in the form of gas or plasma in the intergalactic medium. Then in 2002 the Chandra space-based telescope seemed to confirm that theory when it discovered 7% of the missing universe.
By 2007 astronomers and astrophysicists were back on the trail, reporting that they’d found hundreds of ‘missing’ black holes hiding in galaxies billions of light years away. Which translates into a finding that billions of years ago there were hundreds of black holes in some galaxies…
“Active, supermassive black holes were everywhere in the early universe,” said Mark Dickinson of the National Optical Astronomy Observatory in Tucson, Ariz. “We had seen the tip of the iceberg before in our search for these objects. Now, we can see the iceberg itself.” Dickinson is a co-author of two new papers appearing in the Nov. 10 issue of the Astrophysical Journal.
Now the new research from the University of Alabama in Huntsville [UAH] informs us that we’re 20% light again even after the discoveries in 2002 and 2005 (and all those black holes discovered just last month). Turns out that a lot of those x-rays supposedly coming from the intergalactic clouds of hot gas are instead probably caused by electrons. Electrons are a lot smaller than atoms, with a lot less mass. Those rivers can’t hold the amount of mass previously attributed to them.
Well, they still have WIMPs [Weakly Interacting Massive Particles] as a candidate for missing matter. Problem with these theoretical beasties is that they’re even less interactive than neutrinos, so much more difficult to detect. In fact, nobody’s ever seen a WIMP or measured any Dark Energy. The term “Dark” in these cases means “We Don’t Know” what the heck it is, or even if it exists at all. But the standard models of how our universe works requires filling in huge (as in 90%) gaps with whatever sounds reasonable right now. The alternative - that our standard models are wrong - is too dire to contemplate.
So anyone interested in the stars - and that’s a lot of us, young and old - should try to keep current on the question of what the “missing” 90% of our universe might be, and where it could be hiding. It’s certainly an entertaining pastime, and never dull!
Links:
Dark Matter the Answer to the “Missing Universe?”
RSS feed for comments on this post · TrackBack URI
Leave a reply