Starship Asterisk*

BDanielMayfield wrote: ↑Mon Aug 31, 2020 2:45 pm

Chris Peterson wrote: ↑Sun Aug 30, 2020 9:13 pm

BDanielMayfield wrote: ↑Sun Aug 30, 2020 8:51 pm Neil deGrasse Tyson recommends that we "question everything", so whenit makes me wonder. The relative unimportance of supermassive black holes is an opinion Chris has stated in various ways at several times over the years here in this forum. Here at least he makes a claim that can be tested. Stay tuned for the aftermath.

We can't even tell if a galaxy has a supermassive black hole unless it's active. Because it doesn't alter the movement of stars in the core, except for the handful (two so far) of cases where we can use interferometry to actually resolve the inner few parsecs.

That sounds like you might even question the existence of a supermassive black hole at the core of the Milky Way. :shock: Would you care to clarify?

Chris Peterson wrote: ↑Sun Aug 30, 2020 9:13 pm

BDanielMayfield wrote: ↑Sun Aug 30, 2020 8:51 pm Neil deGrasse Tyson recommends that we "question everything", so when

Chris Peterson wrote: ↑Sun Aug 30, 2020 2:33 pm The gravitational influence of a supermassive black hole is not very significant once you are just a few light years away from it.

it makes me wonder. The relative unimportance of supermassive black holes is an opinion Chris has stated in various ways at several times over the years here in this forum. Here at least he makes a claim that can be tested. Stay tuned for the aftermath.

We can't even tell if a galaxy has a supermassive black hole unless it's active. Because it doesn't alter the movement of stars in the core, except for the handful (two so far) of cases where we can use interferometry to actually resolve the inner few parsecs.

BDanielMayfield wrote: ↑Sun Aug 30, 2020 8:51 pm Neil deGrasse Tyson recommends that we "question everything", so when

Chris Peterson wrote: ↑Sun Aug 30, 2020 2:33 pm The gravitational influence of a supermassive black hole is not very significant once you are just a few light years away from it.

it makes me wonder. The relative unimportance of supermassive black holes is an opinion Chris has stated in various ways at several times over the years here in this forum. Here at least he makes a claim that can be tested. Stay tuned for the aftermath.

Chris Peterson wrote: ↑Sun Aug 30, 2020 2:33 pm The gravitational influence of a supermassive black hole is not very significant once you are just a few light years away from it.

JohnD wrote: ↑Sun Aug 30, 2020 11:05 am Excuse me, Chris! My thinking was that we know that binary BHs exits, do orbit each other, and from the LIGO and other observatories do get closer and closer and eventually merge. How likely is it for BHs to come into existence close to each other? Or widely, galactically, seperated, and over time be mutually attracted. You can estimate the timescale better than I can.

But why do you ask those Qs? "Why would a pair of black holes draw stars toward them? Why would they significantly distort a cloud of stars around them that exceeded their own masses by a couple of orders of magnitude?" The answers are obvious: Gravity, and because Supermassive BHs exceed the Sun's mass by millions or billions of times. I assume this is a rhetorical Q, but cannot see the point.

BDanielMayfield wrote: ↑Sun Aug 30, 2020 1:14 pm
While JohnD's befuddlement might remain, at least my being drawn into Idaho's ergosphere is fully explained. (Northern Idaho, I want to go to there. Must plan trip. Soon.)

https://en.wikipedia.org/wiki/Copernican_principle wrote:
In physical cosmology, the Copernican principle states that humans, on the Earth or in the Solar System, are not privileged observers of the universe. Named for Copernican heliocentrism, it is a working assumption that arises from a modified cosmological extension of Copernicus's argument of a moving Earth. In some sense, it is equivalent to the mediocrity principle.

neufer wrote: ↑Sun Aug 30, 2020 12:50 pm

Click to play embedded YouTube video.

JohnD wrote: ↑Sun Aug 30, 2020 11:05 am
Art, I have no doubt in the alternate Earth on the other side of the Sun, but I refer you to Russell's Teapot.

JohnD wrote: ↑Sat Aug 29, 2020 5:44 pm "Our" own Milky Way, Neufer? Oh, of course, you only vacation at Tralfamodore, and that's in our very own Magellanic Cloud! 'Our' galaxy, indeed!

I meant two BHs as cause of a galactic bar, that would, by definition, NOT be at the centre of a galaxy, Chris, but orbiting its centre of mass. Very slowly, as slowly as a galaxy rotates (?). Their interaction would draw matter and stars into that central bar.

As the BHs migrated inwards to eventually merge at the centre, the bar would get shorter, but may remain for some time , after the central cataclysm.

JohnD wrote: ↑Sat Aug 29, 2020 5:44 pm
"Our" own Milky Way, Neufer? Oh, of course, you only vacation at Tralfamodore [sic],
and that's in our very own Magellanic Cloud! 'Our' galaxy, indeed!

• I have dual citizenship for both Titan & Tralfamadore.

https://en.wikipedia.org/wiki/Tralfamadore wrote:
<<In The Sirens of Titan, Tralfamadore is a planet in the Small Magellanic Cloud and the home of a civilization of machines, which dispatches Salo to a distant galaxy with a message for its inhabitants. After a part in his ship breaks, however, Salo is forced to land on Titan, a moon of Saturn, where he befriends Winston Niles Rumfoord. Rumfoord exists in much the same way as the Tralfamadorians of Slaughterhouse-Five, while Salo appears to move in a linear fashion. The translation of Tralfamadore is given by Salo as both all of us and the number 541. The Tralfamadorians were originally developed by super-beings who built them to allow themselves to search for a meaning to their lives. Unable to achieve this task, they eventually asked the machines to do it for them, and upon knowing that they could not be said to have any purpose at all, the precursor race decided to eradicate itself, just to realize that they were not even very good at this, so they used the Tralfamadorians instead to complete the annihilation of their race.>>

JohnD wrote: ↑Sat Aug 29, 2020 5:44 pm
I meant two BHs as cause of a galactic bar, that would, by definition, NOT be at the centre of a galaxy, Chris, but orbiting its centre of mass. Very slowly, as slowly as a galaxy rotates (?). Their interaction would draw matter and stars into that central bar.

Hoyle, Masters, Nichol et al, found that galactic bars were between 3 and 20 kiloparsecs long (10 and 100 ight years), and that of observed galaxies, the higher the red shift (the youngest) the longer the bar. This would correspond with BHs marking the foci of a bar, and their orbits slowly getting smaller with time, presumably due to tidal effects on each other and their surounding matter. https://academic.oup.com/mnras/article/ ... 27/1749219

As the BHs migrated inwards to eventually merge at the centre, the bar would get shorter, but may remain for some time , after the central cataclysm.

https://en.wikipedia.org/wiki/Doppelg%C3%A4nger_(1969_film) wrote:
<<Doppelgänger is a 1969 British science-fiction film. Outside Europe, it was released as Journey to the Far Side of the Sun, the title by which it is now more commonly known. Set in 2069, the film concerns a joint European-NASA mission to investigate a newly-discovered planet that lies opposite Earth on the other side of the Sun. The mission ends in disaster and the death of one of the astronauts, after which his colleague comes to believe that the planet is a mirror image of Earth.>>

Chris Peterson wrote: ↑Sat Aug 29, 2020 2:20 pm
It's not even clear why a pair of black holes in the center of a galaxy would produce an asymmetric structure of stars. The mass of the stars in a galaxy's core hugely outmasses one or two black holes. And the black holes would be orbiting each other, so they wouldn't be maintaining a fixed orientation that you'd probably need to form any structure in the first place. I'd expect the core of a galaxy that contained two black holes to have the same structure that the core of any unbarred galaxy has- spherical.

https://en.wikipedia.org/wiki/Spiral_galaxy wrote:

Exaggerated diagram illustrating Lin and Shu's explanation of spiral arms in terms of slightly elliptical orbits.

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<<The first acceptable theory for the spiral structure was devised by C. C. Lin and Frank Shu in 1964, attempting to explain the large-scale structure of spirals in terms of a small-amplitude wave propagating with fixed angular velocity, that revolves around the galaxy at a speed different from that of the galaxy's gas and stars. They suggested that the spiral arms were manifestations of spiral density waves – they assumed that the stars travel in slightly elliptical orbits, and that the orientations of their orbits is correlated i.e. the ellipses vary in their orientation (one to another) in a smooth way with increasing distance from the galactic center. This is illustrated in the diagram to the right. It is clear that the elliptical orbits come close together in certain areas to give the effect of arms. Stars therefore do not remain forever in the position that we now see them in, but pass through the arms as they travel in their orbits.

The density wave theory also explains a number of other observations that have been made about spiral galaxies. For example, "the ordering of H I clouds and dust bands on the inner edges of spiral arms, the existence of young, massive stars and H II regions throughout the arms, and an abundance of old, red stars in the remainder of the disk". When clouds of gas and dust enter into a density wave and are compressed, the rate of star formation increases as some clouds meet the Jeans criterion, and collapse to form new stars. Since star formation does not happen immediately, the stars are slightly behind the density waves. The hot OB stars that are created ionize the gas of the interstellar medium, and form H II regions. These stars have relatively short lifetimes, however, and expire before fully leaving the density wave. The smaller, redder stars do leave the wave, and become distributed throughout the galactic disk.>>

neufer wrote: ↑Sat Aug 29, 2020 2:10 pm

New view of the Milky Way with four clearly defined and symmetric spiral arms

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JohnD wrote: ↑Fri Aug 28, 2020 10:21 pm
I proposed the same cause (two BHs) for the bar on some galaxies, several APODs ago: viewtopic.php?f=9&t=40902&p=305207&hilit=JohnD#p305207 Post 5 but no one responded. I don't think that is necessary for an 'oblong' galaxy when on seen from the side will look like that, but I still wonder about the bars. Thanks, mine's a double.

:arrow: Do you attribute the bar of our own Milky Way to two BHs :?:

JohnD wrote: ↑Fri Aug 28, 2020 10:21 pm
I proposed the same cause (two BHs) for the bar on some galaxies, several APODs ago: viewtopic.php?f=9&t=40902&p=305207&hilit=JohnD#p305207 Post 5 but no one responded. I don't think that is necessary for an 'oblong' galaxy when on seen from the side will look like that, but I still wonder about the bars. Thanks, mine's a double.

sillyworm 2 wrote: ↑Fri Aug 28, 2020 6:38 pm
THANKS! I was not implying that the event would happen anytime soon.
I was wondering if the oblong center represented there being 2 Black Holes.

• 1) super massive black holes or
  2) the galaxies themselves

sillyworm 2 wrote: ↑Fri Aug 28, 2020 3:35 pm In the reverse B/W image of NGC 3923 the center is oblong.Would this represent the 2 Black Holes on their way to merging?

sillyworm 2 wrote: ↑Fri Aug 28, 2020 3:35 pm
In the reverse B/W image of NGC 3923 the center is oblong.Would this represent the 2 Black Holes on their way to merging?

• If so then then the globular clusters of NGC 3923 are unaware of it.

https://en.wikipedia.org/wiki/NGC_3923 wrote:

elliptical galaxy NGC 3923

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<<NGC 3923 is an elliptical galaxy located in the constellation Hydra. It is located at a distance of circa 90 million light years from Earth, which, given its apparent dimensions, means that NGC 3923 is about 155,000 light years across. NGC 3923 is an example of a shell galaxy where the stars in its halo are arranged in layers. NGC 3923 has up to 42 shells, the highest number among all shell galaxies, and its shells are much more subtle than those of other shell galaxies. The shells of this galaxy are also symmetrical, while other shell galaxies are more skewed. Concentric shells of stars enclosing a galaxy are quite common and are observed in many elliptical galaxies. In fact, every tenth elliptical galaxy exhibits this onion-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop as a consequence of galactic cannibalism, when a larger galaxy ingests a smaller companion. As the two centers approach, they initially oscillate about a common center, and this oscillation ripples outwards forming the shells of stars just as ripples on a pond spread when the surface is disturbed. Based on the velocity dispersion of the globular clusters of NGC 3923 the mass of the supermassive black hole of the galaxy was estimated to be (5.3±2.5)×10⁸ M_☉.

With deep imaging were also detected a stream extending from the core of NGC 3923 and a small elliptical galaxy on its axis, which is a probable progenitor of some the shells. Another stream lies south of the core of NGC 3923, and a hook like structure lies at the northwest.

One supernova has been detected in NGC 3923, SN 2018aoz, a type Ia supernova with peak magnitude 12.7. It was discovered on April 2, 2018.

NGC 3923 is the brightest galaxy in a galaxy group known as the NGC 3923 galaxy group. Within 25 arcminutes from NGC 3923 have been detected seven dwarf elliptical galaxies. NGC 3904 is located 37 arcminutes away. Other galaxies in the group include NGC 3885, ESO 440-27, and ESO440-011. Other nearby galaxies include NGC 3617, NGC 3673, NGC 3717, NGC 3936, and NGC 4105.>>

https://en.wikipedia.org/wiki/Elliptical_galaxy#Evolution wrote:

NGC 3597 is the product of a collision between two galaxies. It is evolving into a giant elliptical galaxy.

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<<It is widely accepted that the merging of smaller galaxies due to gravitational attraction plays a major role in shaping the growth and evolution of elliptical galaxies. Such major galactic mergers are thought to have been more common at early times. Minor galactic mergers involve two galaxies of very different masses, and are not limited to giant ellipticals. The Milky Way galaxy, depending upon an unknown tangential component, is on a four- to five-billion-year collision course with the Andromeda Galaxy. It has been theorized that an elliptical galaxy will result from a merger of the two spirals.

It is believed that black holes may play an important role in limiting the growth of elliptical galaxies in the early universe by inhibiting star formation.

The traditional portrait of elliptical galaxies paints them as galaxies where star formation finished after an initial burst at high-redshift, leaving them to shine with only their aging stars. Elliptical galaxies typically appear yellow-red, which is in contrast to the distinct blue tinge of most spiral galaxies. In spirals, this blue color emanates largely from the young, hot stars in their spiral arms. Very little star formation is thought to occur in elliptical galaxies, because of their lack of gas compared to spiral or irregular galaxies. However, in recent years, evidence has shown that a reasonable proportion (~25%) of early-type (E, ES and S0) galaxies have residual gas reservoirs and low level star-formation.>>

Ann wrote: ↑Fri Aug 28, 2020 7:25 am

johnnydeep wrote: ↑Thu Aug 27, 2020 7:48 pm

Ann wrote: ↑Thu Aug 27, 2020 7:09 pm

What is that blue and strangely rectangular galaxy at right? Oh yes, it's the Large Magellanic Cloud! Photo: Yuri Beletsky.

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How about it's the NGC 474 Galaxy Group version of the Large Magellanic Cloud?

Ann

Though it looks similarly rectangular, this one seems more well-defined and disjoint from the others. And it's also much bluer!

Aha, I found it, and it has a name: PGC 4755 !

From https://www.irida-observatory.org/CCD/N ... otated.jpg

Well done finding out the designation of the blue rectangular galaxy!

However, I'm not sure that PGC 4755 is bluer than the Large Magellanic Cloud. Remember that we are comparing it with the larger galaxies in this field, non of which, not even the blue-looking ring-spiral galaxy NGC 470, is very blue. The color indexes of NGC 470 is, U-B, +0.100, B-V, +0.750. The lower these values are, the bluer is the galaxy. Galaxy colors are always diluted, but NGC 470 is not very blue.

As for the fact that PGC 4755 looks more well-defined than the LMC, remember that PGC 4755 is extremely blurry in the APOD, while the picture that I posted of LMC is sharply defined, so that we can see all the irregularities. The blurriness of PGC 4755 helps smooth out everything but the main features.

My software Guide quotes the PGC catalogue to claim that while the NGC 474 group is about 100 million light-years distant (which is also what the APOD caption reports), the distance to PGC 4755 is about 240 million light-years. I have no idea if you can trust the latter distance estimate, but I guess it is at least possible that PGC 4755 is a background object.

Let me have a go at guessing what kind of a galaxy that PGC 4755 is:

NGC 4631, an edge-on galaxy blue galaxy with a yellow center, and NGC 4656, an edge-on almost completely blue galaxy with a very pale yellowish center. Photo: Mark Hanson.

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Rectangular-shaped galaxy NGC 3628. Photo: Peter Goodhew.

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Take a look at galaxies NGC 4631 and NGC 4656 at left. Both have thick, puffed-up blue disks. NGC 4631 clearly shows off its yellow center (it looks deep orange in the picture I posted), but in NGC 4656 the center is barely yellow.

And take a look at galaxy NGC 3628 at right. This galaxy is not blue at all, but it does have a very rectangular shape.

I think PGC 4755 displays a mixture of those features. I think it has either (and most likely) a thick blue disk full of star formation, or else it might actually have a brilliant blue bar. If the blue feature is a bar, it becomes hard to explain why there is no yellow center. But if the blue feature is a bar, then it becomes much easier to explain the flaring at the edges, because that would simply be the beginnings of a faint ring or faint arms.

The lack of an obvious yellow center is easier to explain if the blue feature is a disk than if it is a bar, but the flaring at the edges becomes problematical. But as you can see in galaxy NGC 3628, flaring at the edges does occur in disk galaxies.

Ann