Starship Asterisk*

by **Chris Peterson** » Fri Jul 23, 2010 2:06 pm

Poddy wrote:I have often wondered if the (hubble) pictures are processed somehow to give real perspective (ie depth cueing as it is not in '3D') or if the perspective effect is a fantasy created by the 'false colour' processing?

I'm not sure what "perspective effect" you are seeing. People sometimes see different illusions. There has been no special processing applied to this image (or any HST images I'm aware of) to produce a sense of perspective, and this image doesn't use a false color palette. It was taken through filters that allow its final appearance to reasonably approximate its actual colors, assuming the eye were sensitive enough to see them. In other words, this image shows an object as it really is. But it is a flat image of a 3D object, and determining the 3D structure is difficult, ambiguous, and in places impossible.

by **Poddy** » Fri Jul 23, 2010 9:39 am

I have often wondered if the (hubble) pictures are processed somehow to give real perspective (ie depth cueing as it is not in '3D') or if the perspective effect is a fantasy created by the 'false colour' processing?

by **neufer** » Wed Jul 21, 2010 8:34 pm

mg wrote:So what would happen to an individual on a planet going through this evolution??

Which individual?

by mg » Wed Jul 21, 2010 8:20 pm

So what would happen to an individual on a planet going through this evolution??

by **neufer** » Wed Jul 21, 2010 1:17 am

Don Lund wrote:
What's lost or destroyed in nuclear reactions is not what I'd call matter, but rather nuclear binding energy. Yes, there is a mass equivalent to this energy via E=mc^2, so I suppose it all boils down to how you look at it. Perhaps it just doesn't "matter"...

: Click to view full size image

This isn't a simply question of counting "fundamental particles."

The bound nuclei are legitimate particles of matter
with their own measurable rest masses.

Deuterium, tritium, helium-4 and neutron nuclei all have
measurable rest masses as determined by binding energies.

Fusion of deuterium with tritium creating helium-4,
freeing a neutron, and releasing 17.59 MeV of energy, =>
as an appropriate amount of mass converting to the kinetic
energy of the products, in agreement with E = Δmc²

Hamlet, Prince of Denmark Act 2, Scene 2 wrote:
QUEEN GERTRUDE: More matter, with less Art.

by **bystander** » Wed Jul 21, 2010 12:32 am

Don Lund wrote:How do you edit this stuff, anyway?

Get an account and sign in.

by **Don Lund** » Wed Jul 21, 2010 12:11 am

What's lost or destroyed in nuclear reactions is not what I'd call matter, but rather nucear binding energy. Yes, there is a mass equivalent to this energy via E=mc^2, so I suppose it all boils down to how you look at it. Perhaps it just doesn't "matter"...[/quote]

OOPS! Well, of course, this energy isn't lost or destroyed, just kinda rearranged. How do you edit this stuff, anyway?

by **Don Lund** » Tue Jul 20, 2010 7:08 pm

Chris Peterson wrote:
Don Lund wrote:
rstevenson wrote:"Matter can not be created nor destroyed." (Ignoring nuclear reactions of course.)
Matter is not destroyed in nuclear reactions, the same law applies.
While "matter" isn't strictly defined, I think most physicists are comfortable with the notion that matter may be destroyed in nuclear reactions. That is, "matter" as it is usually defined refers to atoms or subatomic particles that have mass. While matter is equivalent to energy, it is energy in a very specific form, and it can be converted to energy of a different form, essentially losing its "matter" quality. Energy is always conserved, but that doesn't mean matter can't cease to be matter (which is a pretty good definition of "destroyed").

What's lost or destroyed in nuclear reactions is not what I'd call matter, but rather nucear binding energy. Yes, there is a mass equivalent to this energy via E=mc^2, so I suppose it all boils down to how you look at it. Perhaps it just doesn't "matter"...

by **Chris Peterson** » Tue Jul 20, 2010 4:16 am

Don Lund wrote:
rstevenson wrote:"Matter can not be created nor destroyed." (Ignoring nuclear reactions of course.)
Matter is not destroyed in nuclear reactions, the same law applies.

While "matter" isn't strictly defined, I think most physicists are comfortable with the notion that matter may be destroyed in nuclear reactions. That is, "matter" as it is usually defined refers to atoms or subatomic particles that have mass. While matter is equivalent to energy, it is energy in a very specific form, and it can be converted to energy of a different form, essentially losing its "matter" quality. Energy is always conserved, but that doesn't mean matter can't cease to be matter (which is a pretty good definition of "destroyed").

by **Don Lund** » Tue Jul 20, 2010 4:02 am

rstevenson wrote:"Matter can not be created nor destroyed." (Ignoring nuclear reactions of course.)

Matter is not destroyed in nuclear reactions, the same law applies.

by **Chris Peterson** » Mon Jul 19, 2010 5:19 pm

ems57fcva wrote:I will repeat my major concern about this photo, namely the large dusty bridge connecting the two galaxies: It is not predicted by any of the current galaxy collision models!

That is not strictly true. Collision models don't include dust, they only model the motion of stars. There is nothing in the current models that in any way excludes a dusty bridge, and certainly stellar motion not unlike this is seen in simulations. That said, I am not convinced that a dusty bridge between the two galaxy cores even exists. In the absence of three dimensional information, it is difficult or impossible to determine just where the dust lies in relation to the galactic centers.

by **bystander** » Mon Jul 19, 2010 4:45 pm

ems57fcva wrote:I will repeat my major concern about this photo, namely the large dusty bridge connecting the two galaxies: It is not predicted by any of the current galaxy collision models! ...

... A recent APOD (http://apod.nasa.gov/apod/ap100702.html) shows such a leftover bridge.

Simulations certainly show them. See the discussion for APOD 2010 July 02: http://asterisk.apod.com/vie ... 79#p126279
For ems57fcva's discussion on the Antennae Galaxies (APOD 2010 May 07), see: http://asterisk.apod.com/vie ... =9&t=19319

by **ems57fcva** » Mon Jul 19, 2010 4:31 pm

I will repeat my major concern about this photo, namely the large dusty bridge connecting the two galaxies: It is not predicted by any of the current galaxy collision models! They predict only tidal tails. Yet the main tidal tails are heading out to the left and the top of this image, and are almost entirely out of the frame. At the same time, the secondary tidal tails can be seen. For the larger galaxy (NGC 4038) it heads off of the right side of and curves upward. For the smaller galaxy (NGC 4309) it heads downwards and curves to the left.

My suspiscion is that material is being pulled off of both galaxies and into the bridge between them. If this process is strong enough, it will create a new galactic center in what is now the bridge. I suspect that the bridge will then become a bar and that the distorted remnants of the two original galaxies will become spiral arms. The result will be something like NGC1300 (See http://antwrp.gsfc.nasa.gov/apod/ap060827.html).

On the other hand, if the process is not strong enough, it will only leave behind a slender bridge which will get stretch to and past the breaking point over time. A recent APOD (http://apod.nasa.gov/apod/ap100702.html) shows such a leftover bridge.

I am happy to note that my view of how this system may evolve is speculation. However, I repeat that the brdige itself is not predicted by the current models. IMO, that is a serious issue that needs to be dealt with if we are to truly understand how galaxies form, interact, and evolve.

Edward Schaefer

by **Chris Peterson** » Mon Jul 19, 2010 3:02 pm

Ann wrote:I don't quite get what you mean by saying that the Milky Way itself is about the same brightness as these clusters. Obviously our galaxy itself is brighter than any one of the clusters in NGC 4038. Are you saying that any one of the clusters of NGC 4038 would look as faint and diffuse to anyone inside NGC 4038 as the band of the Milky Way looks to us? Are you saying that the brightest clusters of NGC 4038 would be comparable in apparent brightness to the globular clusters that we see in our own galaxy, so that they would at best be faint-looking objects at about fourth magnitude?

Yes to all. The magnitude of extended objects is generally expressed as a brightness integrated over the area. That tells you how much light an object produces, but it doesn't tell you (directly) how bright it appears to the eye. In reality, things made up of tightly clustered stars tend to have similar surface brightnesses. This includes globular clusters and the cores of galaxies. Visually, these are all bright enough to be seen with the naked eye, but none are bright enough to stimulate color vision. Our own Milky Way, the cores of other galaxies, and globular clusters all look similar to our eyes. Sure, there is some variation because of stellar types, but it isn't great- probably not more than a few magnitudes at most. And distance makes no difference- getting closer doesn't make extended objects brighter, just bigger.

So if you were in one of these colliding galaxies, you'd still just see a sky covered with mottled gray marking regions of high stellar density, very similar to the way we see the Milky Way.

Of course, if you were close enough to a cluster to actually resolve individual stars with the eye, it would be impressive. But at that point you aren't seeing an extended object anymore, but just a lot of stars.

by **neufer** » Mon Jul 19, 2010 1:23 pm

Ann wrote:
Chris Peterson wrote:
Ann wrote:Do we really have anything as bright in the Milky Way as the super star clusters of NGC 4038?
Yes, we do. The Milky Way itself is about the same brightness as these clusters, as are most of the globular clusters we see around our own galaxy. From those galaxies, the local globulars will look pretty much the same as our own. If you were very close to them, they would look big, but no brighter than more distant globulars.
I don't quite get what you mean by saying that the Milky Way itself is about the same brightness as these clusters. Obviously our galaxy itself is brighter than any one of the clusters in NGC 4038. Are you saying that any one of the clusters of NGC 4038 would look as faint and diffuse to anyone inside NGC 4038 as the band of the Milky Way looks to us? Are you saying that the brightest clusters of NGC 4038 would be comparable in apparent brightness to the globular clusters that we see in our own galaxy, so that they would at best be faint-looking objects at about fourth magnitude?

I'm not buying that. All our own globular clusters are made of old, relatively faint stars, and they are all very far from us here on Earth. The super clusters of NGC 4038 are not as rich as our globular clusters, but they are made of young stars, some of which are bound to be O-type stars or B-type supergiants, which are very bright and conspicuous. And there may well be some M-type supergiants in there to provide color contrast. If an observer in NGC 4038 was much closer to one of the young super clusters in that galaxy than we are to any of our globular clusters, surely that cluster would look bright and awesome. What if an observer was as close to any of that super clusters as we are to the stars in Orion's Belt? The observer would have a magnificent view indeed, provided, of course, that there was not a lot of dust between the observer and the cluster to obscure the view.

This question is easily resolved by comparing the apparent sizes and
magnitudes of the Antennae Galaxies with say the Andromeda Galaxy:

Code: Select all

From Wikipedia:

_____________         Andromeda         NGC 4039        NGC 4038
---------------------------------------------------------------------
apparent size         190′ × 60′       3′.1 × 1′.6    5′.2 × 3′.1
apparent magnitude       3.44             11.1            11.2

NGC 4039 is indeed about twice as bright as Andromeda!

However, NGC 4038 is only a little more than half as bright
as Andromeda on average due to the dust clouds.

Note: Andromeda is about 3 times brighter than the Magellanic Clouds.

by **Ann** » Mon Jul 19, 2010 6:13 am

Chris Peterson wrote:
Ann wrote:Do we really have anything as bright in the Milky Way as the super star clusters of NGC 4038?
Yes, we do. The Milky Way itself is about the same brightness as these clusters, as are most of the globular clusters we see around our own galaxy. From those galaxies, the local globulars will look pretty much the same as our own. If you were very close to them, they would look big, but no brighter than more distant globulars.

And there would be no color in the sky inside NGC 4038? Sure there would be! There is color in the sky that we can see in the Milky Way, and there would be no less color in NGC 4038.
I've never encountered anybody who reports seeing color in the Milky Way. It is far too dim to trigger photopic vision. Sure you can see color if you make a long exposure, just as you can in other galaxies. But no galaxy, including our own, shows any color (other than gray, of course) to the human eye.

I'm amazed at what you are saying, Chris.

I don't quite get what you mean by saying that the Milky Way itself is about the same brightness as these clusters. Obviously our galaxy itself is brighter than any one of the clusters in NGC 4038. Are you saying that any one of the clusters of NGC 4038 would look as faint and diffuse to anyone inside NGC 4038 as the band of the Milky Way looks to us? Are you saying that the brightest clusters of NGC 4038 would be comparable in apparent brightness to the globular clusters that we see in our own galaxy, so that they would at best be faint-looking objects at about fourth magnitude?

I'm not buying that. All our own globular clusters are made of old, relatively faint stars, and they are all very far from us here on Earth. The super clusters of NGC 4038 are not as rich as our globular clusters, but they are made of young stars, some of which are bound to be O-type stars or B-type supergiants, which are very bright and conspicuous. And there may well be some M-type supergiants in there to provide color contrast. If an observer in NGC 4038 was much closer to one of the young super clusters in that galaxy than we are to any of our globular clusters, surely that cluster would look bright and awesome. What if an observer was as close to any of that super clusters as we are to the stars in Orion's Belt? The observer would have a magnificent view indeed, provided, of course, that there was not a lot of dust between the observer and the cluster to obscure the view.

Perhaps you are saying that the question is moot, since no human-like observer could survive being as close to one of the young super clusters of NGC 4038 as we are to the stars of Orion's Belt?

Ann

by **Chris Peterson** » Sun Jul 18, 2010 11:05 pm

Ann wrote:Do we really have anything as bright in the Milky Way as the super star clusters of NGC 4038?

Yes, we do. The Milky Way itself is about the same brightness as these clusters, as are most of the globular clusters we see around our own galaxy. From those galaxies, the local globulars will look pretty much the same as our own. If you were very close to them, they would look big, but no brighter than more distant globulars.

And there would be no color in the sky inside NGC 4038? Sure there would be! There is color in the sky that we can see in the Milky Way, and there would be no less color in NGC 4038.

I've never encountered anybody who reports seeing color in the Milky Way. It is far too dim to trigger photopic vision. Sure you can see color if you make a long exposure, just as you can in other galaxies. But no galaxy, including our own, shows any color (other than gray, of course) to the human eye.

by **Ann** » Sun Jul 18, 2010 10:46 pm

owlice wrote: If the night sky were different, people would still find patterns and visual relationships between stars, so there would still be asterisms and constellations. The heavens don't impose those on us; we create them out of our own need to find patterns and connect the dots.

Yes, of course people would still se patterns in the sky, even if they lived in an elliptical galaxy. But there would be nothing like the Pleiades in there, probably nothing like the Big Dipper in there, and definitely nothing like Orion in there.

And speaking about Orion, Chris objected to my suggestion that the night sky would look fabulous in NGC 4038 or 4039. He said:

I don't think so. There are still dust clouds that block the view in many directions. Nothing would be brighter than we see in our night sky (except maybe for some stars), and like our sky, almost everything except background structure would be fairly close. There would be no color, and little fine structural detail. Basically, I imagine the sky in a colliding galaxy pair to look something like ours

Yes, there would be dust clouds blocking the view in many directions, but not in all directions. But nothing would be brighter than we see in our night sky? Do we really have anything as bright in the Milky Way as the super star clusters of NGC 4038? If the brightest clusters of NGC 4038 are brighter than anything our galaxy can match, then it goes without saying that it would be possible to see brighter things inside NGC 4038 than we see inside the Milky Way. Also there are very many clusters of very bright stars in NGC 4038 - it's like having ten Orions in the sky instead of one! All right, no, not really, because the really huge clusters are far away from one another, but there are many parts of NGC 4038 that would offer a view of at least one moderately nearby super cluster that would beat Orion many times over.

And there would be no color in the sky inside NGC 4038? Sure there would be! There is color in the sky that we can see in the Milky Way, and there would be no less color in NGC 4038.

So I personally believe that there is a good chance that the night sky for a planet inside NGC 4038 would be quite spectacular, although it is also very possible that the planet would be wrapped in a thick cosmic fog of dust!

Ann

by **neufer** » Sun Jul 18, 2010 10:17 pm

http://www.cita.utoronto.ca/~dubinski/antennae/antennae.html wrote:
Click to view full size image
<<NGC 4038/4039 are perhaps the most famous pair of nearby interacting galaxies known for their symmetrically placed tidal tails resembling insect antennae. N-body simulations of the formation of the Antennae's tidal tails allow us to set limits on the total amount of dark matter in the interacting galaxies. Shown below are two simulations using different amounts of dark matter in the galaxy models. The low mass model only contains 4 times as much mass in dark matter as stars while the high mass model contains 30 times as much dark matter. The low mass model easily produces long tidal tails like the real pair while the high mass model fails, producing only short, stubby features. Simulations using intermediate masses show that long tails only arise when the mass of dark matter is less than 10 times the mass of the stars. >>

by **neufer** » Sun Jul 18, 2010 10:12 pm

Ann wrote:
if you live in either NGC 4038 (the topmost galaxy in today's APOD) or in NGC 4039 (the bottom one)...

While NGC 4039 is indeed the skinny galaxy in today's APOD:

http://antwrp.gsfc.nasa.gov/apod/ap971022.html
http://antwrp.gsfc.nasa.gov/apod/ap970506.html
http://antwrp.gsfc.nasa.gov/apod/ap970602.html

it should be noted that the Wikipedia article mistakenly has NGC 4038 as the skinny galaxy.

by **rstevenson** » Sun Jul 18, 2010 6:16 pm

JosephD wrote:... . simply because of Gravity and the two black holes passing through the Galaxies will destroy a third of all matter in each galaxie while other planets and there systems suffer catastrophy.

"Matter can not be created nor destroyed." (Ignoring nuclear reactions of course. But that's not what you were referring to, I think.)

No such disruption as you describe would occur. There are vast distances between stars, and as Chris has said -- and as you can find out yourself with a very little on-line research -- the galaxies will pass through each other with just gravitic interaction. Disturbance on a galactic scale, yes. We see that in pictures of other galaxies engaged in such a "collision." But nothing like what you've described.

JosephD wrote:Far more distruction is caused then any can realize.

Any but you?

Rob

by **JosephD** » Sun Jul 18, 2010 5:45 pm

It may be true most stars and planets do not collide but the black holes in each Galaxie must wreak havoc as they pass by and through and close to the stars and planets . There must be much destruction and rearanging of every thing .thereby creating a new order to everything.
some thing will pass and others a new genesis will begin. simply because of Gravity and the two black holes passing through the Galaxies will destroy a third of all matter in each galaxie while other planets and there systems suffer catastrophy.
Far more distruction is caused then any can realize.

Joseph

by **JoelN** » Sun Jul 18, 2010 5:41 pm

It would have been nice if the author of the blurb accompanying today's APOD had actually NAMED the two galaxies!!! A decent grasp of English grammar would help as well.

Thank you, Ann, above, for providing fascinating and much-needed follow-up information.

by **Chris Peterson** » Sun Jul 18, 2010 2:29 pm

biddie67 wrote:But what might be the consequences if two stars did happen to collide?

Nobody knows for certain, since stars are not completely understood and no star collision has ever been observed. Most likely you'd end up with a new, larger star. Any planets around either system would almost certainly be ejected from the combined system, or end up in radically different orbits.

Could comet activity increase as gravity tugged in a different direction?

This would almost certainly happen. It is likely that this happens in our own system periodically simply from stars passing fairly nearby (around a light-year or so). Bodies in the Oort cloud are perturbed and some are directed towards the inner system. There may be occasional periods of bombardment from this mechanism.

Could a star pass through a center of gravity "net" because of momentum and then get pulled backwards into a point of balance?

No. If the star has a relative velocity less than the escape velocity of the other, they will simply end up in orbit around each other.

by **biddie67** » Sun Jul 18, 2010 1:36 pm

I think (in my non-technical manner) that whatever cognitive entities might still be living there would be thinking "there go the old neighborhoods". So it would be out with the old star fields and in with the new!!

But what might be the consequences if two stars did happen to collide?

Could comet activity increase as gravity tugged in a different direction?

Could a star pass through a center of gravity "net" because of momentum and then get pulled backwards into a point of balance?

Starship Asterisk*

APOD: The Antennae Galaxies in Collision (2010 Jul 18)

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