Starship Asterisk*

by **Beyond** » Wed Aug 15, 2012 12:10 am

neufer wrote:Now, however, all bets are off.

All bets are off?? When can i get my money back?

by **neufer** » Tue Aug 14, 2012 9:27 pm

Chris Peterson wrote:
neufer wrote:
One should note that the most distant object that we observe visually or can ever observe visually is the Cosmic Background Radiation which is traveling less than the speed of light.
The distinction is important, because we are not excluded from observing earlier using something other than photons. There is good reason to think that gravity wave telescopes will be a reality in the not too distant future, and they are not limited from peering beyond the ionized wall of the CBR right to the Big Bang itself.

In which case, the most distant object that we observe or can ever observe is some deeper surface corresponding to the end of the inflationary period which is also traveling away from us at less than the speed of light.

Nothing in the foreground of that particular background surface was ever going to travel away from us faster than the speed of light prior to our discovery of our new age of dark energy expansion.

In other words: prior to dark energy expansion, no object's Hubble z could ever exceed infinity.
Objects in the universe were either moving slower than the speed of light or faster than the speed of light; there was no transitioning.

Now, however, all bets are off.

by **Chris Peterson** » Tue Aug 14, 2012 8:42 pm

neufer wrote:One should note that the most distant object that we observe visually or can ever observe visually is the Cosmic Background Radiation which is traveling less than the speed of light.

The distinction is important, because we are not excluded from observing earlier using something other than photons. There is good reason to think that gravity wave telescopes will be a reality in the not too distant future, and they are not limited from peering beyond the ionized wall of the CBR right to the Big Bang itself.

by **neufer** » Tue Aug 14, 2012 8:22 pm

Chris Peterson wrote:
nz1m wrote:
I suspect "A flight through the universe, APOD, Aug 13, shows most of the galaxies moving slower than "c" in relationship to us, the Milky Way, when their photons were first emitted? If so, can we observe "winking out" galaxies as they approach c? Can we plot the galaxies approaching c and predict when they'll disappear?
Cosmologically, all the structures in this video are relatively close; with the most distant having a redshift of 0.15, we're only looking at a maximum light travel time of about 1.8 billion years (comoving distance of 2 billion ly), and a maximum radial expansion speed of about 0.13c - not even significantly relativistic. The edge of the observable universe has a light travel time of 13.7 billion years, and a comoving distance of 47 billion ly.

One should note that the most distant object that we observe visually or can ever observe visually is the Cosmic Background Radiation which is traveling less than the speed of light. In the near future our CBR will constitute a somewhat larger portion of the total Big Bang plasma cloud but it will still be the most distant object that we observe visually and it will not be moving away faster than the speed of light.

Foreground galaxies will form and die but they will only "wink out" at visible wavelengths due to ever higher red shifts (and not because they actually pass c). This is why the James Webb Telescope will be heavily dependent upon infrared observations.

We know now, however, that in the distant future both the CBR and the most distant galaxies will indeed exceed c thanks to the expansion due to dark energy. Only then will distant galaxies "wink out" because they actually pass c.

by **Chris Peterson** » Tue Aug 14, 2012 7:08 pm

nz1m wrote:Eloquent. Thank you. So I suspect "A flight through the universe, APOD, Aug 13, shows most of the galaxies moving slower than "c" in relationship to us, the Milky Way, when their photons were first emitted? If so, can we observe "winking out" galaxies as they approach c? Can we plot the galaxies approaching c and predict when they'll disappear?

Cosmologically, all the structures in this video are relatively close; with the most distant having a redshift of 0.15, we're only looking at a maximum light travel time of about 1.8 billion years (comoving distance of 2 billion ly), and a maximum radial expansion speed of about 0.13c - not even significantly relativistic. The edge of the observable universe has a light travel time of 13.7 billion years, and a comoving distance of 47 billion ly.

by **nz1m** » Tue Aug 14, 2012 6:38 pm

Eloquent. Thank you. So I suspect "A flight through the universe, APOD, Aug 13, shows most of the galaxies moving slower than "c" in relationship to us, the Milky Way, when their photons were first emitted? If so, can we observe "winking out" galaxies as they approach c? Can we plot the galaxies approaching c and predict when they'll disappear?

by **Chris Peterson** » Tue Aug 14, 2012 6:22 pm

nz1m wrote:Please forgive me if I cannot write clearly enough to capture my question in copy. But I'll try. (http://curious.astro.cornell.edu/questi ... number=575) Assuming it's true that a galaxy can travel faster than the speed of light through space [relative to another galaxy]. Let's pretend that galaxy is ours, the Milky Way. Let's then pretend that galaxy B (Andromeda in this example) is also moving through its space at about the speed of light. Isn't it true that if A and B were traveling at diametrically opposite paths from one another then we could never "see" Andromeda? So, Andromeda, though traveling awfully fast, must be moving in relationship to the Milky Way at less than the speed of light?

Parts of space that are very far apart are moving apart at greater than c. Those bits of the Universe are causally disconnected, and cannot influence each other. Colloquially, they are invisible to one another.

Further, that would lend me to suspect that all the galaxies we can observe (both optically and RF) must be traveling at a 'less than the speed of light' in relationship to us, the Milky Way.

More precisely, they were traveling at less than c with respect to us when they emitted the photons we're now detecting. They may now be outside the observable universe, meaning that they are moving away from us at greater than c.

If this is true, then what's all the fuss about dark matter? Wouldn't dark matter (not dark energy) just be galaxies we cannot see because they are in this light speed relativity dance with the Milky Way?

No, because all the stuff that is moving faster than c is far away... so far that the expansion of space has carried it away (you can only exceed c in this way by being carried along in expanding space, since physically accelerating matter to c would require infinite energy). Dark matter is observed in the local universe, where there is not enough expansion to move things away from us anywhere near c (and in galaxies, where there is no expansion of space at all).

by **nz1m** » Tue Aug 14, 2012 5:47 pm

Light Speed Relativity Dance

Please forgive me if I cannot write clearly enough to capture my question in copy. But I'll try. (http://curious.astro.cornell.edu/questi ... number=575) Assuming it's true that a galaxy can travel faster than the speed of light through space [relative to another galaxy]. Let's pretend that galaxy is ours, the Milky Way. Let's then pretend that galaxy B (Andromeda in this example) is also moving through its space at about the speed of light. Isn't it true that if A and B were traveling at diametrically opposite paths from one another then we could never "see" Andromeda? So, Andromeda, though traveling awfully fast, must be moving in relationship to the Milky Way at less than the speed of light?

Further, that would lend me to suspect that all the galaxies we can observe (both optically and RF) must be traveling at a 'less than the speed of light' in relationship to us, the Milky Way.

If this is true, then what's all the fuss about dark matter? Wouldn't dark matter (not dark energy) just be galaxies we cannot see because they are in this light speed relativity dance with the Milky Way?

by **Anthony Barreiro** » Mon Aug 13, 2012 7:18 pm

Regarding the future collision of the Milky Way and Andromeda galaxies, do we know how the galaxies will be oriented as they approach and collide? and where our solar system will be in our galaxy relative to the collision zone? I would think that if you're orbiting a star far from the collision zone, you would only get an interesting light show, rather than anything that would directly affect your daily life.

by **Fafers** » Mon Aug 13, 2012 4:53 pm

"Eventually the two galaxies will converge into one larger spiral galaxy."

I thought that a collision of similar-sized spiral galaxies would result in a larger elliptical galaxy...

by **neufer** » Mon Aug 13, 2012 4:20 am

http://aircraft.desktopnexus.com/wallpaper/45177/ wrote:

.

<<What you see is a bit difficult to explain it is a Wake produced by the fly of a Transporter (Cargo)plane that release some Flares. I think it looks like an abstract Angel watching over the Crew of the plane, Military Planes need very good guardian angels.>> - Desiderare Tim

by **Ann** » Mon Aug 13, 2012 1:19 am

celestekentme wrote:How in the world can they tell us that either Galaxy was a "normal" Galaxy since it has been millions of years since the process started and I seriously doubt there were any Earth based astronomers to see it and record it.

We have very good reasons to believe that NGC 4038 and 4039 started out as two normal galaxies.

If you look at today's APOD, you can see two bright yellow concentrations. These are two galactic nuclei. This is a sure giveaway that we are seeing two galaxies, which in this case are in the process of merging.

You can see that one of the nuclei is half hidden by dust, and there is a huge arch of blue stars forming a semi-circle around this nucleus. The is considerably less dust near the other nucleus, and there are not many blue stars close to that nucleus, either.

This means that one of the galaxies, NGC 4038, was rich in gas and dust, whereas the other galaxy, 4039, was rather gas-poor. It is likely that NGC 4038 had a rather large population of blue stars even before it collided with NGC 4039. However, gas-poor NGC 4039 likely had few blue stars.

NGC 3184. Photo: Robert Gendler.

It is possible that before the collision, NGC 4038 may have looked something like this galaxy, NGC 3184. NGC 3184 has a yellow nucleus and arms that are rich in blue stars. There is probably still a lot of gas left in NGC 3184, which can be used for more star formation.

NGC 2681. Source:
http://skyserver.sdss3.org/dr8/en/tools/places/ngc.asp.

NGC 4039, on the other hand, may possibly have looked more like NGC 2681 before the collision. NGC 2681 is poor in star formation and has only rudimentary arms and a rather yellow disk.

It seems rather certain that the two galaxies that collided to form the Antennae were two disk galaxies, one of which was gas-rich and one of which was gas-poor. The collision triggered a huge amount of star formation in the gas-rich galaxy. The gas-rich galaxy probably also contained a lot of dust, and still more dust was generated by the violence of the collision. Tidal forces also distorted the galaxies.

Ann

by **celestekentme** » Mon Aug 13, 2012 12:20 am

How in the world can they tell us that either Galaxy was a "normal" Galaxy since it has been millions of years since the process started and I seriously doubt there were any Earth based astronomers to see it and record it.

by **Chris Peterson** » Sun Aug 12, 2012 9:54 pm

eltodesukane wrote:I also read a scientific paper saying that within the next 250 million years, plate tectonic will grind to a halt, because of diminishing radioactivity of the Earth, This will cause cooling of the Earth's interior, slowing and stopping plate tectonic, volcanoes, etc. This will cause Earth's magnetic field to vanish, and Earth's atmosphere to be slowly blown away by the solar wind, with no volcano to replenish it.

None of this is true. The isotopes that heat the Earth's interior have half-lives in the range of a billion to ten billion years. The Earth's interior doesn't appear to have cooled more than a few percent since the planet formed. So there will be a liquid core, dynamo, and plate tectonics for billions of years to come (although plate tectonics may start and stop sporadically; it is understood that drift rates can vary significantly over periods of a few hundred million years).

by **eltodesukane** » Sun Aug 12, 2012 8:23 pm

In a few billions years, our galaxy will collide with Andromeda galaxy, and in about 5 billions years the Sun will end it's main sequence star phase to become a giant incinerating Earth.
But other things will happens before that.
I also read a scientific paper saying that within the next 250 million years, plate tectonic will grind to a halt, because of diminishing radioactivity of the Earth, This will cause cooling of the Earth's interior, slowing and stopping plate tectonic, volcanoes, etc. This will cause Earth's magnetic field to vanish, and Earth's atmosphere to be slowly blown away by the solar wind, with no volcano to replenish it. Lack of oxygen will cause animal life to become extinct well before the Sun's life has ended. ( I probably read this in Science some years ago, but I don't have a reference ).
Like Dr. Who said, nothing lasts forever.

====> I add these references, although they do not mention any time scale as short as 250 My:

Lindsay, J.F. and Brasier, M.D., 2002,
Did global tectonics drive early biosphere evolution? Carbon isotope record from 2.6 to 1.9 Ga carbonates of Western Australian basins.
Precambrian Research, 114, 1–34.
http://www.lpi.usra.edu/lpi/lindsay/pap ... ind.com.au

Lindsay, J.F. and Brasier, M.D., 2002,
A comment on tectonics and the future of terrestrial life –– reply.
Precambrian Research, 118, 293–295.
http://yly-mac.gps.caltech.edu/Reprints ... ll2003.pdf

by **eltodesukane** » Sun Aug 12, 2012 8:09 pm

Considering the expansion of the universe, it is usually seen as an expansion of space, but I prefer to view it as a contraction of matter. It may be that those two point of view are exactly equivalent, but maybe they are not.
In any case, whatever the correct interpretation, the actual experimental observations of an accelerating expanding universe can not be denied.
emc is right: "It’s hard to imagine the Universe, period."

by **emc** » Sun Aug 12, 2012 4:42 pm

It’s hard to imagine the Universe, period. I admire the folks that can wrap their heads around cosmology. And I’m glad we have folks capable of such large scale thinking sharing what they formulate. I don’t fully understand why religion came up but in order for Religion and Science to ever merge, paradigm shifts in behavior and thinking are required. I see religion as an ongoing process same as science… ever advancing. This featured galaxy collision shows us how much change occurs when such a large scale event happens. We can easily see the two structures merging. And it's obvious both structures are restructuring. We also like to imagine what they looked like before and after merging. I believe someday we will be able to computer model the universe and run it fast forward and backward. I imagine we will readily see gravity, as Rob says, causing the galactic trajectories and based on what I've learned, we will see in the model that the overall movement of the cosmos is outward.

by **Ann** » Sun Aug 12, 2012 1:27 pm

tannaberton wrote:hard to imagine a universe where everything on a galaxial scale is moving away from each other, yet they intersect. Even galaxies on a concentric circle relative to the center will be driven apart by expansion and as powerful as gravity might be the expansion force seems even more so.A few collisions seem easy to explain but the number claimed by cosmologists is staggering, almost inevitable. are we depending on an easy answer rather than observation?

Like Rob said, science, unlike religion, in an ongoing process where scientists keep making observations and measurements to continually test and refine their theories and find ever better descriptions and explanations of phenomena in the world we live in. If you want one final, unshakable truth about the cosmos once and for all, it might be better to turn to religion rather than to science to find that kind of rock-hard certainty. If you choose that path, however, you will be looking "inwards", examining what seems right to you, rather than be looking "outwards" to learn what the best human observations, measurements and simulations have actually found out about the universe. That's your choice.

What the best human observations of the structure of the universe as well as the best available computer simulations of the structure of the universe - based on the theory that the universe is made of less than 5% ordinary matter, about 25% dark matter and about 70% dark energy - tells us is that the cosmos has a filamentary structure, the cosmic web. Dark energy makes the "holes" in the cosmic web grow bigger. However, it isn't tearing the dense "nodes" of the cosmic web apart. At these nodes, you find clusters of galaxies. Check out this picture by Tony Hallas of the Hercules cluster of galaxies. As you can see, there are several galactic collisions and interactions going on inside this cluster, precisely because this is a part of the universe where the concentration of galaxies is high.

Ann

by **rstevenson** » Sun Aug 12, 2012 12:48 pm

tannaberton wrote:hard to imagine a universe where everything on a galaxial scale is moving away from each other, yet they intersect. Even galaxies on a concentric circle relative to the center will be driven apart by expansion and as powerful as gravity might be the expansion force seems even more so.A few collisions seem easy to explain but the number claimed by cosmologists is staggering, almost inevitable. are we depending on an easy answer rather than observation?

Galaxies occur in clusters and filaments, and are gravitationaly bound within these structures. A particular cluster may be moving away from other clusters due to the expansion of the universe, but within the cluster the galaxies are interacting gravitationally, which is why such "collisions" occur. Another way to look at it is to say that expansion occurs in the empty spaces between the clusters and filaments of galaxies, stretching the filaments and separating the clusters.

As for "are we depending on an easy answer rather than observation?" I think that sort of approach is mostly left to religion. Science tries to create answers out of observations, not the other way around, and there are plenty of observations supporting the current most favoured cosmological theories. Lots of details yet to fill in, of course, but generally scientists have a pretty good idea of why galaxy collisions such as in today's APOD occur: Gravity.

Rob

by **tannaberton** » Sun Aug 12, 2012 12:25 pm

hard to imagine a universe where everything on a galaxial scale is moving away from each other, yet they intersect. Even galaxies on a concentric circle relative to the center will be driven apart by expansion and as powerful as gravity might be the expansion force seems even more so.A few collisions seem easy to explain but the number claimed by cosmologists is staggering, almost inevitable. are we depending on an easy answer rather than observation?

by **bactame** » Sun Aug 12, 2012 10:29 am

Nice Antenna image showing the tumult and the text reminding us that we too will become tumultuous. That is the kind of thing we humans thrive in, under and around; despite the terrible injustice of it all. That is one of the benefits of living in a universe which may drag on for a 100 trillion years or so. Everything no matter how unlikely it is to occur will occur. So keep the faith...you will win the lottery, you will go to heaven and you will meet the girl of your dreams.

by **Tigis** » Sun Aug 12, 2012 9:56 am

I love today's explanation: "this galaxy is having a bad millennium..."

by **henrystar** » Sun Aug 12, 2012 9:48 am

Think what fun their astronomers have!

by **Boomer12k** » Sun Aug 12, 2012 9:04 am

I wonder what that does to a planet with life....you have stars infiltrating the space, changing the gravity, and everything flying every which way...what would that do to the Life Zone of a Galaxy?
Hubble sure takes a might good picture, wonder what my 10" Meade could do in space.

:---[===] *

by **APOD Robot** » Sun Aug 12, 2012 4:20 am

Spiral Galaxy NGC 4038 in Collision

Explanation: This galaxy is having a bad millennium. In fact, the past 100 million years haven't been so good, and probably the next billion or so will be quite tumultuous. Visible on the upper left, NGC 4038 used to be a normal spiral galaxy, minding its own business, until NGC 4039, toward its right, crashed into it. The evolving wreckage, known famously as the Antennae, is pictured above. As gravity restructures each galaxy, clouds of gas slam into each other, bright blue knots of stars form, massive stars form and explode, and brown filaments of dust are strewn about. Eventually the two galaxies will converge into one larger spiral galaxy. Such collisions are not unusual, and even our own Milky Way Galaxy has undergone several in the past and is predicted to collide with our neighboring Andromeda Galaxy in a few billion years. The frames that compose this image were taken by the orbiting Hubble Space Telescope by professional astronomers to better understand galaxy collisions. These frames -- and many other deep space images from Hubble -- have since been made public, allowing an interested amateur to download and process them into this visually stunning composite.

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Starship Asterisk*

APOD: Spiral Galaxy NGC 4038 in Collision (2012 Aug 12)

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