APOD: Shell Galaxies in Pisces (2020 Aug 27)

Comments and questions about the APOD on the main view screen.
User avatar
neufer
Vacationer at Tralfamadore
Posts: 17502
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by neufer » Sat Aug 29, 2020 4:05 pm

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.
I assumed that John meant a single asymmetrical located black hole orbiting near the end of the bar structure.

What the sensitivity of spiral structure density waves might be to such a strategically place black hole is unclear. (Some globular clusters are as massive as the Milky Way's central black hole but are not strategically located such that they would affect spiral structure density waves.)

However, I find it hard to believe that such an asymmetrical located black hole would go unnoticed in our own galaxy.
https://en.wikipedia.org/wiki/Spiral_galaxy wrote: <<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.>>
Art Neuendorffer

User avatar
JohnD
Tea Time, Guv! Cheerio!
Posts: 1281
Joined: Wed Feb 16, 2005 2:11 pm
Location: Lancaster, England

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by JohnD » 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.

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.
John

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17502
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by neufer » Sat Aug 29, 2020 6:23 pm

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.
It would be highly improbable for two black holes to be quasi-stable orbiting Doppelgängers of each other
(much less to be playing "ping-pong" with each other with all of those "bar stars").
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.>>
Spiral structure probably has much more to do with dark matter than with black holes.
Art Neuendorffer

User avatar
Chris Peterson
Abominable Snowman
Posts: 15301
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by Chris Peterson » Sat Aug 29, 2020 6:49 pm

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.
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?
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.
Why would they migrate inwards and merge, except perhaps over timescales as great as the age of the universe or longer?
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
JohnD
Tea Time, Guv! Cheerio!
Posts: 1281
Joined: Wed Feb 16, 2005 2:11 pm
Location: Lancaster, England

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by JohnD » 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.

Art, I have no doubt in the alternate Earth on the other side of the Sun, but I refer you to Russell's Teapot.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17502
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by neufer » 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.
Art Neuendorffer

BDanielMayfield
Don't bring me down
Posts: 2490
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by BDanielMayfield » Sun Aug 30, 2020 1:14 pm

neufer wrote:
Sun Aug 30, 2020 12:50 pm
Click to play embedded YouTube video.
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.)

Bruce
Just as zero is not equal to infinity, everything coming from nothing is illogical.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17502
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by neufer » Sun Aug 30, 2020 2:30 pm

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.)
In physical cosmology, the Copernican principle states that Bruce Daniel Mayfield,
in Eastern Idaho, is not yet a privileged observer of the universe until he takes that journey.
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.
Last edited by neufer on Sun Aug 30, 2020 5:38 pm, edited 1 time in total.
Art Neuendorffer

User avatar
Chris Peterson
Abominable Snowman
Posts: 15301
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by Chris Peterson » Sun Aug 30, 2020 2:33 pm

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.
Binary black holes that merge do so because they are very close to each other, rotating so rapidly around their center of mass that they radiate a huge amount of energy in the form of gravitational waves, which is why they come together. A pair of black holes that are hundreds or thousands of parsecs apart will not lose enough energy to come significantly closer for billions or trillions of years. Black holes that are close together are stellar mass black holes that started as binary stars, so did indeed form close together.
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.
It is not rhetorical. There is more gravitational mass at the center of a galaxy from the stars in the central bulge than there is from any supermassive black hole found there. Why don't the stars in the bulge all fall in towards the center? Stars are in orbit. In orbit around the common mass of the galaxy itself, which is far greater than any black holes. The gravitational influence of a supermassive black hole is not very significant once you are just a few light years away from it.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

BDanielMayfield
Don't bring me down
Posts: 2490
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by BDanielMayfield » 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.
Just as zero is not equal to infinity, everything coming from nothing is illogical.

User avatar
Chris Peterson
Abominable Snowman
Posts: 15301
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by Chris Peterson » 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.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
JohnD
Tea Time, Guv! Cheerio!
Posts: 1281
Joined: Wed Feb 16, 2005 2:11 pm
Location: Lancaster, England

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by JohnD » Sun Aug 30, 2020 10:01 pm

I refer the Mayor of Wallace, Idaho, to Bertrand Russell,OM, FRS, philosopher, logician, mathematician, historian, writer, social critic, political activist, and Nobel laureate. Who may be able to refute him. But it's a good joke.

Thank you for your patience, Chris. Further reading finds me NGC 6240, belived to be a merged galaxy, that still has two, or even three active nuclei, believed to be BHs. And it sure don't look like a nice barred galaxy! But of course it may still be all shook up after the merger. Perhaps later?
ngc6240 triple bh.jpg
You do not have the required permissions to view the files attached to this post.

BDanielMayfield
Don't bring me down
Posts: 2490
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by BDanielMayfield » 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 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.
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?
Just as zero is not equal to infinity, everything coming from nothing is illogical.

User avatar
Chris Peterson
Abominable Snowman
Posts: 15301
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by Chris Peterson » Mon Aug 31, 2020 3:30 pm

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?
I don't question it at all. We've observed the one at the center of our own galaxy.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Ann
4725 Å
Posts: 10793
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Shell Galaxies in Pisces (2020 Aug 27)

Post by Ann » Thu Sep 03, 2020 7:18 pm

Dr Becky, an astrophysicist with her own Youtube channel, talks about NGC 474 and shell galaxies.

Click to play embedded YouTube video.
Color Commentator