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Old 2012-07-09, 18:09   Link #1001
C.A.
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Quote:
Originally Posted by Vena View Post
Dark Matter is getting confusing for me. Every few months I see a new report purporting a discovery and then, latter, a new report baffling the pants off of everyone with a discovery that brings to question current dark matter understanding or previous dark matter results. (It was about a year ago when they had the report on two clusters which passed through each other without any of the expected dark matter effects (ie the center of mass was not where it should have been... at all).

Dark matter has been "found" for a while now, though. Wikipedia has an entire chart of observed support.
I think the news just needed an attractive title or that every detection of dark matter is a good discovery.

But I have one burning question I've always wanted to ask: Why can't dark matter just be normal matter like hydrogen and helium which are abundant but spread so thinly that they do not get detected by our instruments?

As far as I know, if telescopes don't point at the right spot for a long enough exposure time, things can skip detection. Or that there are not enough matter or radiation sources to reflect light in the region, stuff can be invisible on various wavelengths.

I always see alot of crazy theories that try to introduce a bunch of whole new particles to describe dark matter.
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Old 2012-07-09, 18:25   Link #1002
mangamuscle
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Quote:
Originally Posted by C.A. View Post
I always see alot of crazy theories that try to introduce a bunch of whole new particles to describe dark matter.
I am far from a physicist, but AFAIK it has to do with the fact that matter and anti-matter were not created in equal proportions after the bing-bang, so enter dark matter as a posible THEORETICAL solution.
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Old 2012-07-09, 18:26   Link #1003
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Even if something is spread extremely thin, with the huge volumes of space, that light has to pass through, a lot of photons would hit some of that thinly spread gas and bounce off it.
And when that happens we get those absorbtion lines, which are easy to detect.

Also, with all the needed mass it would have to account for, it can't be spread that thin.

My understanding is, that with the amount of mass that has to be there for gravity equations to work out, so that our galaxy does not fly apart, we would see it.


I saw some people mention, that if you calculate the galaxy spin with relativity in mind (gravity does not propagate FTL), which makes it a whole lot more complex, then 'dark matter' would not be needed to match our observations. But I have not found any scientific sources on that yet.
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Old 2012-07-09, 22:59   Link #1004
Vena
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Quote:
Originally Posted by C.A. View Post
I think the news just needed an attractive title or that every detection of dark matter is a good discovery.
I hate when they do that, pet peeve.

Quote:
Originally Posted by C.A. View Post
But I have one burning question I've always wanted to ask: Why can't dark matter just be normal matter like hydrogen and helium which are abundant but spread so thinly that they do not get detected by our instruments?
Radiation, normal matter radiates. We use the term dark matter in situations where we observe a high gravitational effect (some sort of warping of expected paths by relativity or such) but no radiation signature for normal matter. To have a noticeable effect on gravity, you'd need a noticeable amount of regular matter yet none is ever observed near where the dislocated center of mass of the system is expected to be by studying the systems under study. No matter how you spread it out, thin and long or a large ball, you'd notice it because you'd had a either a big curtain of radiation or a very large clump of ordinary matter glowing.

There was, however, an article about half a year back that talked about errors in estimation of planets (so regular matter) in our galaxy: Nomad Planets. The research talked about how previous estimations (for our galaxy) of the planet count per star could well have been off by 4 to 5 orders of magnitude (ie we'd have not a few tens of planets per star but hundreds of thousands floating about in loose orbits). I haven't seen any follow up, unfortunately, but these things take time. That said, you could consider these 10000:1 planets to amount to quite a bit of the mass of our galaxy that we'd previously chocked up to Dark Matter.

Then you have releases like this Dark Matter Baffles, that really make the whole enterprise very confusing.
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Old 2012-07-10, 05:21   Link #1005
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Hmmm are you suggesting that undetected nomad planets can make up a large portion of mass and gravity to account for dark matter? Do they not have gravity and give off radiation enough to be detected?

If large undetected planets can account for alot of mass, I'm sure smaller objects like asteroids, dust and even gas spread over huge regions of space can account for significant mass.
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Old 2012-07-10, 06:19   Link #1006
Vena
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Quote:
Originally Posted by C.A. View Post
Hmmm are you suggesting that undetected nomad planets can make up a large portion of mass and gravity to account for dark matter? Do they not have gravity and give off radiation enough to be detected?

If large undetected planets can account for alot of mass, I'm sure smaller objects like asteroids, dust and even gas spread over huge regions of space can account for significant mass.
I'm not expertly versed in astrophysics, so I don't know the particulars of how exactly you miscount up to five orders of magnitude the number of planets per sun in our galaxy (I assume it has to do with the fact that they are all moving on giant orbits, and rather hard to detect when they are not passing a star since their relatively small to the total volume of a galaxy. That's, as far as I'm aware, how its worked in the past for far off star system detection methods. They watch stars for years and wait for awkward shadows that reoccur with some definitive period which are likely planets in an orbit. You can't do the same with nomad planets as they'd have hundreds upon hundreds of years of time for a single orbit, and with their small size they are not exactly things that stick out against the background). That's a lot of mass (assuming the 100,000:1 upper limit on planet:star ratio) and it *may* account for something but we have no idea how large they are and, still, I don't think they'd account for the very large discrepancies between visible matter and calculated mass of our galaxy. Planets are big but they're pretty paltry in size relative to stars. Let's pretend that each nomad planet is roughly the size of the Earth (mass of 5.97E24 kg) and we'll use our sun (even if its a small on at 1.99E30 kg) as a base reference. The mass of the sun is 300,000 times that of the Earth. So if we had a 100,000 more Earth's floating around, we'd roughly have 1/3 the mass of the sun more mass to our solar system. So let's guestimate this over the whole galaxy to mean that we have roughly another 30% of unaccounted for mass over the current visible... which is a big chunk but its not enough, IIRC, by a long shot.

Moreover, dark matter has observable results to it that doesn't fit standard matter. So there's most certainly something exotic out there that isn't just scattered hydrogen, helium, and Li-7.
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Old 2012-07-10, 12:08   Link #1007
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Nomad planets are planets that got ejected from a solar system.

The idea, that those are quite numerous came up recently. They ran a lot of simulations on planets forming around a sun from a dustdisc according to current models. Turned out, that the average number of planets was much higher than expected, but the resulting system would be unstable. It would eject planets into interstellar space until a stable configuration was reached.
This includes gas giants too.

If this was true, then the amount of planets zipping through space while being almost undetectable, should be pretty high.
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Old 2012-07-10, 12:11   Link #1008
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Would not the idea of a large number of dead stars be more reasonable that rogue planets? Not ever star goes supernova. That or Brown Stars that never really ignited.
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Old 2012-07-10, 14:01   Link #1009
C.A.
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Yea I'd think that there would be alot of massive brown dwarfs with extremely weak radiation that makes them extremely hard to detect.

I personally think that the missing mass of dark matter is the result of underestimation from the lack of data and instrument limitations.

I guess I'm just following Occam's Razor, I don't want to think that they are weird particles and mysterious invisible masses.
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Old 2012-07-10, 15:53   Link #1010
Vena
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Quote:
Originally Posted by Dhomochevsky View Post
The idea, that those are quite numerous came up recently. They ran a lot of simulations on planets forming around a sun from a dustdisc according to current models. Turned out, that the average number of planets was much higher than expected, but the resulting system would be unstable. It would eject planets into interstellar space until a stable configuration was reached.
This includes gas giants too.
So they ran simulation tests, neat. I'll dig into this a bit more as I've resparked my interest in astrophysics a bit with these discussions (much to the chagrin of my more useful nanophysics and actual job).

Quote:
Originally Posted by Ithekro View Post
Would not the idea of a large number of dead stars be more reasonable that rogue planets? Not ever star goes supernova. That or Brown Stars that never really ignited.
Very few stars reach supernovae masses, in fact I think of all main sequence stars currently cataloged only >1% are beyond the Chandreskar limit at at >1.4 solar masses, I think. (We'll ignore the dwarf nova and white dwarfs supernovae events because I know little to nothing about them, though I doubt they are very common and I'm almost certain that they require binary systems. )

We'd need better ways of detecting aged brown dwarfs though, to really be able to say how many are floating about unaccounted for...

Quote:
Originally Posted by C.A. View Post
I guess I'm just following Occam's Razor, I don't want to think that they are weird particles and mysterious invisible masses.
There are some observational results, I'm pretty sure, that cannot be answered (as of now) with standard matter. There's some weird stuff out there.
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Old 2012-07-12, 11:36   Link #1011
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FARNBOROUGH: Virgin Galactic takes wraps off LauncherOne:

"Sir Richard Branson stole the show yesterday - swooping in by helicopter and all
but renaming the event the Farnborough space show with a star-studded
presentation of his Virgin Galactic SpaceShip2 and a bold plan to use the system
to slash the cost of launching small satellites."

See:

http://www.flightglobal.com/news/art...herone-374271/


------------------------------------------------------------------------------------------------------

Hubble finds fifth moon orbiting Pluto:

"The Hubble Space Telescope has found yet another moon orbiting what used to
be the last planet in the Solar System.

The moon, the fifth that's been spotted orbiting Pluto, is an irregularly shaped
lump around 6 to 15 miles across and orbits in a plane 58,000 miles around the
dwarf planet. It was spotted in nine images taken with the Hubble's Wide Field
Camera in June and July."

See:

http://www.theregister.co.uk/2012/07...to_moon_fifth/
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Old 2012-07-13, 02:13   Link #1012
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Always giggle when I see news about Pluto, I just can't help but picture a ranting Sailor Pluto bitching about people dissing her rock.
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Old 2012-07-13, 22:01   Link #1013
Pokaru
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Wow, ever since the Hubble went into work, they seem to find more and more stars. If I remember correctly, they already discovered a different moon orbiting Pluto, right? What was it named anyway?
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Old 2012-07-13, 22:36   Link #1014
Ithekro
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I know of Ix and Hydra as two other minor moons of Pluto and Charon.
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Old 2012-07-21, 04:57   Link #1015
LoweGear
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CBS: Drones That May Fly ‘Indefinitely’ Can Be Recharged By Lasers

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Originally Posted by CBS
A recently demonstrated breakthrough in technology may help Unmanned Aerial Systems (UAS), better known as drones, stay airborne for very long periods of time before having to return to Earth.

This development comes at a time when the U.S. government is actively encouraging the domestic use of drones, first by law enforcement, and later, by private concerns.

Lockheed Martin and a company called LaserMotive have been able to keep a drone flying for some 49 hours non-stop, using a ground-based laser to recharge the drone’s on board battery, says Tom Koonce, the project manager for Lockheed Martin, in an interview with KNX1070 Newsradio.
Remote battery recharging via laser.... can't stop thinking of the Impulse Gundam
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Old 2012-07-21, 14:17   Link #1016
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Quote:
Originally Posted by LoweGear View Post
CBS: Drones That May Fly ‘Indefinitely’ Can Be Recharged By Lasers



Remote battery recharging via laser.... can't stop thinking of the Impulse Gundam
When are they going to share this technology with Japan?
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Old 2012-07-22, 22:59   Link #1017
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Scientists create artificial jellyfish from rat's heart

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Old 2012-07-23, 02:56   Link #1018
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Holy mother of god, that is amazing.
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Old 2012-07-23, 06:16   Link #1019
C.A.
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That is technically a nanomachine, I wonder how it gets energy to fuel its movements.

I think in the future, history texts would be calling the 21st century as the 'nano age'.

EDIT: actually I think its still at micro level so it can't be called a nanomachine.
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Ignore gender and kick sexuality to the curb!
I'm a big mecha fan, who keeps playing the SRW series.
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My art album updated 11th May 2013, Science.
Deviant Art: http://ca0001.deviantart.com/
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Old 2012-07-23, 10:23   Link #1020
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Doesn't that mean they transformed an animal's organ into a living being? That's pretty awesome.
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