Chandra Discovers "Rivers Of Gravity" That Define Cosmic Landscape

ScienceDaily Magazine ^ | Thursday, August 01, 2002 | Editorial Staff

[RightWhale]

Since these articles started appearing on FR, I have been wondering about the 'rivers of gravity' thing. Still don't know what they are talking about.

[RightOnline]

"In a subsequent announcement, NASA said that they will soon unveil the Mountains of Mashed Potatoes on various planets in the solar system........."

[crystalk]

Imagine by disappointment that this was not about Chandra Levy.

[LibKill]

Again, I call on Physicist to make matters clear for a common man.

I did not know that gravity was subject to remote detection, like X-Rays or Infrared.

Thanks ahead of time, Physicist.

[tet68]

"From the rivers of Gravity,
Where we sat down.
And we wept, when we remembered Orion."

[sheik yerbouty]

Lol!

[Libertarianize the GOP]

.

[Zad]

bump

[RossA]

I don't think this is what these scientists have discovered but gravity is definitely detected remotely. Massive galaxies (probably with black holes) bend light passing near them so we see multiple images of the galaxies behind them. Many examples have been posted on the "astronomy picture of the day" site - a worthwhile site for 2 minutes per day of learning.

[LibKill]

Very good. And I know that light bends around a massive object (please don't expect me to explain why, I could never do the math).

I called upon Physicist because he has a real ability to explain these things to a poor barbaric SOB like me.

[LibKill]

P.S. APOD is one of my favorite sites, every day.

[Moonman62]

Since these articles started appearing on FR, I have been wondering about the 'rivers of gravity' thing. Still don't know what they are talking about.

Maybe they should call it rivers of mass or matter instead, but what the astronomers are seeing is the effect of gravity from the mass. The dark matter in the universe forms a spongy structure similar to bone marrow. The "rivers" they are seeing is the connective fibers, which are so large from our perspective I guess it's appropriate to call them rivers.

[RightWhale]

Okay. I had a mental image of gravity being there already, --potential wells--, in these filaments and attracting dust and gas. Makes more sense this way.

[Physicist]

They don't detect the gravity per se.

There's a certain amount of deduction going on here. Theory (meaning computer simulations) tells them that there should be self-gravitating streams of hot gas between the galaxies.

You can get a taste of what these streams look like and how they form in a couple of simulations I ran using the National Scalable Cluster Project supercomputers here at Penn, using parallel code written by Prof. Paul Bode.

• This animated .gif shows the mass density of a simulated portion of the universe. Black is lowest density, followed by blue, green yellow, red, and finally white as highest density. Later images show later times, when more structure forms due to gravitational attraction. As the movie plays, the universe ages from 50 million to 12.5 billion years. During this time, our simulation volume actually expands by a factor of 40, but this expansion isn't shown.
• Here is another such universe, showing more resolution (WARNING: 7 MB).
• Here is the first frame of that universe, and here is the last frame.

Since they expect the streams to be there, they set about to detect them by looking at the spectra of distant quasars. Since there are so many streams, they reasoned that some quasars must end up behind streams, from our point of view. In that case, the streams will block out part of the light from the obstructed quasars in a characteristic way in the x-ray band. This obstruction is what they have detected.

Note that this doesn't allow them to image the streams themselves; they just see the effect of the streams at a small number of points on the sky. They call them streams because that's what they expected to see. The same data might support the hypothesis that there are big gasseous blobs out there. But either way, the total mass of the gas can be estimated, and it is non-negligible.

[Physicist]

FWIW, I don't think that gravitational lensing plays an important role in this analysis. There's a lot of matter in these streams, but it's not as concentrated--by many orders of magnitude--as it is in a galaxy. What it lacks in density it makes up for in volume, however.

[leadhead]

While Physicist is explaining things to us less experienced, he could also explain the accuracy of these findings. Since, as I understand it, the satellite detects something, converts it to a digital (programmer dictated) equivalent,which is then transmitted to earth and displayed (to the programmers dictates) graphicly.

It seems to all depend on what the programmer expects and programs for, not what may actually be detected.

Just like tomographs are only as good as the base data the programmer works with.

Have I confused everybody as bad as I confused myself ?

The point I'm trying to make is: How good is the interpetive data ?

[pupdog]

Imagine my disappointment that this was not about Chandra Levy

Now there's a statement on our culture.

"Oooh! Oooh! Juicy tidbits about brutal death of some woman I've never met! Yeah...oh, darn. It's just a dumb post about the nature and origins of the universe. BOOOOORINNNNNG."

(Just a joke, no personal jab intended, no purchase necessary, batteries not included)

[LibKill]

Thank you, Physicist.

I count on you for no-BS facts.

If I fail to understand those facts, well that is my failing.