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goenitz
2015-Jul-03, 11:10 PM
http://msutoday.msu.edu/news/2015/were-not-alone-but-the-universe-may-be-less-crowded-than-we-think/


Interesting article,

Apparently , the Universe has fewer galaxies than previously believed. While I'm trying to figure out the specific implications, what I don't quite understand is:

Does the Universe now contain less visible matter than previously thought, in effect overturning the current Lamda CDM model?

or

Does this simply mean that the primordial gas in the early Universe simply did not coalesce into galaxies as much as we thought?

Hopefully, someone here can make more sense out of this.

antoniseb
2015-Jul-04, 11:59 AM
... Does the Universe now contain less visible matter than previously thought, in effect overturning the current Lamda CDM model?

or

Does this simply mean that the primordial gas in the early Universe simply did not coalesce into galaxies as much as we thought?
The article is about an observation about how when star-forming happened vigorously enough for us to see. It doesn't impact LCDM. It will be interesting to see if the James Webb Space Telescope sees it any differently. This could be about the onset of star forming in small galaxies, or it could be about reionization lifting the haze. Keep in mind this is only about small faint galaxies. The big galaxies are just numerous as models predict.

Noclevername
2015-Jul-04, 12:40 PM
There may be far fewer galaxies further out in the universe then might be expected,

(grinds teeth)

goenitz
2015-Jul-04, 12:49 PM
The article is about an observation about how when star-forming happened vigorously enough for us to see. It doesn't impact LCDM. It will be interesting to see if the James Webb Space Telescope sees it any differently. This could be about the onset of star forming in small galaxies, or it could be about reionization lifting the haze. Keep in mind this is only about small faint galaxies. The big galaxies are just numerous as models predict.

OK got it. So, in effect, the title of the article is slightly misleading. I was under the impression that by not being able to see those galaxies, it implied that the matter making them up simply wasn't there, making the Universe an "emptier place."

Jens
2015-Jul-04, 12:54 PM
(grinds teeth)

Yeah, somebody kneads too tel MSU a bout that. It mite effect they're reputation. :)

Noclevername
2015-Jul-04, 01:42 PM
What was the theoretical basis for thinking that the dim galaxies were far more numerous?

Ken G
2015-Jul-04, 02:36 PM
Also bear in mind that most of the baryonic matter in the universe is in the form of ionized gas in between galaxies, not the galaxies themselves. So even reducing the number of galaxies would not alter cosmology, as long as the matter between galaxies wasn't affected.

goenitz
2015-Jul-04, 03:36 PM
Also bear in mind that most of the baryonic matter in the universe is in the form of ionized gas in between galaxies, not the galaxies themselves. So even reducing the number of galaxies would not alter cosmology, as long as the matter between galaxies wasn't affected.

So in effect, the amount of intergalactic gas in the distant Universe just increased if these findings are accurate.

Noclevername
2015-Jul-05, 10:33 PM
So in effect, the amount of intergalactic gas in the distant Universe just increased if these findings are accurate.

Very slightly.

Jerry
2015-Jul-05, 10:55 PM
I call this a 'hedge' paper. The authors did not say there are fewer small galaxies, what they said is:
The team simulated thousands of galaxies at a time, including the galaxies’ interactions through gravity or radiation.

The simulated galaxies were consistent with observed distant galaxies at the bright end of the distribution – in other words, those that have been discovered and confirmed. The simulations didn’t, however, reveal an exponentially growing number of faint galaxies, as has been previously predicted.(my bold)

In other words, past predictions based upon current theories include 'hundreds to thousands' of small galaxies will be found with additional scope power. This SIMULATION uses current cosmology and predicts far fewer small galaxies will be found.

So, whatever the James Webb telescope discovers, (many/few small galaxies in the distant past) there is a paper sitting-on-the-shelf that will cover it - no surprises, no new physics required.

Noclevername
2015-Jul-06, 12:39 AM
Why was it previously thought that the number of faint galaxies were exponentially greater than visible galaxies?

antoniseb
2015-Jul-06, 01:10 AM
A lot of computer models of the early universe show about a hundred dwarf galaxies for every conglomeration that eventually gets to be a Milky Way sized galaxy. So far we've seen about 30 around the Milky Way, but expect that some more may be out there but that they will be nearly starless clouds of dark matter.