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NGC 1365: Majestic Island Universe

Explanation: Barred spiral galaxy NGC 1365 is truly a majestic island universe some 200,000 light-years across. Located a mere 60 million light-years away toward the chemical constellation Fornax, NGC 1365 is a dominant member of the well-studied Fornax galaxy cluster. This impressively sharp color image shows intense star forming regions at the ends of the bar and along the spiral arms, and details of dust lanes cutting across the galaxy's bright core. At the core lies a supermassive black hole. Astronomers think NGC 1365's prominent bar plays a crucial role in the galaxy's evolution, drawing gas and dust into a star-forming maelstrom and ultimately feeding material into the central black hole.

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Nice!










NGC 1365 is an extremely barred two-armed spiral galaxy with very open arms. Hubble class SBc, perhaps?

Not all barred spiral galaxies have open arms. NGC 1300 is another extremely barred two-armed spiral galaxy, but its arms are "held tight to its body". Hubble class SBba, perhaps?

Ann

..."chemical constellation"....???
What does it mean?

APOD Robot wrote:At the core lies a supermassive black hole.

Wikipedia wrote:
In February 2013, observations using the NuSTAR satellite have found out that the central supermassive black hole of NGC 1365, measured to be about 2 million solar masses in mass, is spinning at almost the speed of light.[6]
https://www.nustar.caltech.edu/news/nustar130227

distefanom wrote:..."chemical constellation"....???
What does it mean?

The familiar APOD play on words: Long ago (1756), Fornax was named by French astronomer Nicolas Louis de Lacaille, originally as le Fourneau Chymique (the Chemical Furnace), before being abbreviated to just Fornax.

Very nice shot...

:---[===] *

Is there enough known about barred galaxy development to determine if this is a stable form or if the bars represent a transitional state on its way to a more stable shape?

NCTom wrote:Is there enough known about barred galaxy development to determine if this is a stable form or if the bars represent a transitional state on its way to a more stable shape?

There's been lots of work with increasingly elaborate simulations of galaxy history. Bars can originate as one of the instabilities that disks of gas and stars are subject to; the so-called 2-theta instability that is favored for certain mass distributions (and can be reinforced by a close tidal encounter with another galaxy). A handful of spirals had strong bars 10 billion years ago (an epoch we see at redshift z=2.5); by now, something like 1/3 of spiral galaxies have strong bars, and another 1/3 have small or weak bars. Bars may be long-lasting but are not exactly stable, because their structure allows angular momentum to be transferred from stars closer to the nucleus to those farther out. Eventually the change in stars' locations as their orbits charge can dissolve a bar - one way is into a resonant ring of stars. The handful of disk galaxies with strong rings (such as Hoag's Object) but no accompanying bar may be the aftermath of this process.

In addition, simulations show some circumstances where bars can disappear and reappear, especially for smallish galaxies or when gas is flowing inward from the surroundings.

NCTom wrote:
Is there enough known about barred galaxy development to determine if this is a stable form or if the bars represent a transitional state on its way to a more stable shape?

Linear rotation curves near the center of all spiral galaxies means a constant rotation rate. This situation allows for very stable dynamic systems that are conducive to constant rotation rate structures such as bars.

Very nice! I am curious about the few other more distant galaxies in the picture. 1) to the far left just below center, edge on; 2) the smudge off the left upper arm; 3) the elitical one above and right; and 4) the series of fainter smudges from the right arm proceding from there to the right and up.

NGC 1365 is an excellent visual target - one of my favorites! It's bright, moderately large, and has such a beautiful shape. Well positioned for viewing these days, too.

Is there a book or website that lists the most fascinating characteristics(such as the blackhole rotating at speed of light here) of each of most visible Messiers and NGC objects? Would love to have a recording of these facts I can play as I'm doing outreach with my telescope.

Case wrote:

distefanom wrote:..."chemical constellation"....??? What does it mean?

The familiar APOD play on words: Long ago (1756), Fornax was named by French astronomer Nicolas Louis de Lacaille, originally as le Fourneau Chymique (the Chemical Furnace), before being abbreviated to just Fornax.

That's probably asked every time APOD uses the phrase. In the future, each use should always be hyperlinked to your excellent explanation.

This galaxy is clearly a merger. (A layman's opinion.) The spiral arm that looks like a loop is clearly out of plane with the majority of rotation.
It seems reasonable that each contributor to the merger would have a central black hole, and that these wouldn't necessarily hit head on but would end up orbiting each other, possibly allowing a bar to persist between them for quite some duration.
Michael O'Brien

redmudislander wrote:
This galaxy is clearly a merger. (A layman's opinion.) The spiral arm that looks like a loop is clearly out of plane with the majority of rotation. It seems reasonable that each contributor to the merger would have a central black hole, and that these wouldn't necessarily hit head on but would end up orbiting each other, possibly allowing a bar to persist between them for quite some duration.

You do realize that NGC 1365 is larger than our Milky Way but has a central black hole only half the size of the Milky Way's BH.

Uncle Jeff wrote:

Case wrote:

distefanom wrote:..."chemical constellation"....??? What does it mean?

The familiar APOD play on words: Long ago (1756), Fornax was named by French astronomer Nicolas Louis de Lacaille, originally as le Fourneau Chymique (the Chemical Furnace), before being abbreviated to just Fornax.

That's probably asked every time APOD uses the phrase. In the future, each use should always be hyperlinked to your excellent explanation.

That was a very fine explanation! Dr. Nemiroff can't resist throwing in the more-than-occasional adjective in front of the names of constellations; generally they describe a characteristic of the imaginary source of the constellation name.

NCTom wrote:Is there enough known about barred galaxy development to determine if this is a stable form or if the bars represent a transitional state on its way to a more stable shape?

Many a night, a bar has been my transitional state on my way to a more stable state.
(Sorry, I don't have a serious answer for you, but I couldn't resist.) On the other hand, I wonder what you would count as "transitional" in this context. Lasting less than a billion years? Some steady process of growth or decay, however slow?

Case wrote:

APOD Robot wrote:At the core lies a supermassive black hole.

Wikipedia wrote:
In February 2013, observations using the NuSTAR satellite have found out that the central supermassive black hole of NGC 1365, measured to be about 2 million solar masses in mass, is spinning at almost the speed of light.[6]
https://www.nustar.caltech.edu/news/nustar130227

Fantastic! This leads me to a question. Is it not part of the theory that black holes conserve angular momentum? And is it correct that the black hole will have the same total angular momentum about its central point as the sum of the angular momenta that all of the objects that fell into it had?

MarkBour wrote:This leads me to a question. Is it not part of the theory that black holes conserve angular momentum? And is it correct that the black hole will have the same total angular momentum about its central point as the sum of the angular momenta that all of the objects that fell into it had?

I would think so, that angular momentum would have to be conserved, even in the extreme conditions of a black hole.

Bruce

BDanielMayfield wrote:

MarkBour wrote:
Is it not part of the theory that black holes conserve angular momentum? And is it correct that the black hole will have the same total angular momentum about its central point as the sum of the angular momenta that all of the objects that fell into it had?

I would think so, that angular momentum would have to be conserved, even in the extreme conditions of a black hole.

More or less.

When two black holes merge they first form a rapidly rotating prolate black hole
which radiates circularly polarized gravitational waves containing angular momentum.

neufer wrote:

BDanielMayfield wrote:

MarkBour wrote:
Is it not part of the theory that black holes conserve angular momentum? And is it correct that the black hole will have the same total angular momentum about its central point as the sum of the angular momenta that all of the objects that fell into it had?

I would think so, that angular momentum would have to be conserved, even in the extreme conditions of a black hole.

More or less.

When two black holes merge they first form a rapidly rotating prolate black hole
which radiates circularly polarized gravitational waves containing angular momentum.

Ah, so angular momentum is conserved, but not always in the same place, as when a star’s rotation slows over time since some of its angular momentum is carried off with its stellar wind.

Side point: Since at least most of a black hole’s angular momentum will be retained how can it be that its mass is truly crushed down to a singularly? How can a point with no size possess angular momentum?

Bruce

neufer wrote: ...
When two black holes merge they first form a rapidly rotating prolate black hole
which radiates circularly polarized gravitational waves containing angular momentum.

Yes, mergers present a very complex case in this regard. I'll buy what you're telling me, and so mostly I want to consider the simpler case of one BH with various events of normal matter falling into it. If matter in an accretion disk swirls into a BH, then it will be rotating faster once it has fallen below the event horizon and I assume the BH will spin more and more as a result.

BDanielMayfield wrote:...
Side point: Since at least most of a black hole’s angular momentum will be retained how can it be that its mass is truly crushed down to a singularly? How can a point with no size possess angular momentum?

Bruce

Nice! You read my mind, Bruce. Admitting that a classical view of what is going on here may be inadequate, nevertheless, I imagine matter inside the BH swirling around the central point at a speed approaching c, and then that matter cannot get any closer to the center. Using

• L = mrv

then to conserve angular momentum as r decreased for that matter, v would need to increase.

I can imagine a number of reasons that might be part of the current thinking on this that would get around this problem, but as far as I have imagined black holes so far, this would be a reason that the mass can't get to the center. Surely, this issue of the theory that has been discussed by physicists. Perhaps they agreed with us on this point.

MarkBour wrote:

neufer wrote: ...
When two black holes merge they first form a rapidly rotating prolate black hole
which radiates circularly polarized gravitational waves containing angular momentum.

Yes, mergers present a very complex case in this regard. I'll buy what you're telling me, and so mostly I want to consider the simpler case of one BH with various events of normal matter falling into it. If matter in an accretion disk swirls into a BH, then it will be rotating faster once it has fallen below the event horizon and I assume the BH will spin more and more as a result.

That seems rationally quite sound.

BDanielMayfield wrote:...
Side point: Since at least most of a black hole’s angular momentum will be retained how can it be that its mass is truly crushed down to a singularly? How can a point with no size possess angular momentum?

Bruce

Nice! You read my mind, Bruce. Admitting that a classical view of what is going on here may be inadequate, nevertheless, I imagine matter inside the BH swirling around the central point at a speed approaching c, and then that matter cannot get any closer to the center. Using

• L = mrv

then to conserve angular momentum as r decreased for that matter, v would need to increase.

I can imagine a number of reasons that might be part of the current thinking on this that would get around this problem, but as far as I have imagined black holes so far, this would be a reason that the mass can't get to the center. Surely, this issue of the theory that has been discussed by physicists. Perhaps they agreed with us on this point.

Note however that the reason objects can’t be accelerated to or past c is that the apparent mass increases ... hay wait a minute ... could this factor in to why SMBHs are so dang massive: the relativistic speed of revolution?

It seems to this layman that there is good reason to doubt that singularities really exist at the cores of rotating BHs. Angular momentum is the “hold up” figuratively, but perhaps literally as well.

Bruce

BDanielMayfield wrote:

MarkBour wrote:

BDanielMayfield wrote:
Since at least most of a black hole’s angular momentum will be retained how can it be that its mass is truly crushed down to a singularly? How can a point with no size possess angular momentum?

I can imagine a number of reasons that might be part of the current thinking on this that would get around this problem, but as far as I have imagined black holes so far, this would be a reason that the mass can't get to the center. Surely, this issue of the theory that has been discussed by physicists. Perhaps they agreed with us on this point.

It seems to this layman that there is good reason to doubt that singularities really exist at the cores of rotating BHs. Angular momentum is the “hold up” figuratively, but perhaps literally as well.

• Point singularities DON'T exist in the cores of rotating BHs.
  RING singularities exist in the cores of rotating BHs.

https://en.wikipedia.org/wiki/Kerr_metric#Kerr_black_holes_as_wormholes wrote:

[b][color=#0000FF][size=135]Event horizons and ergospheres of a rotating black hole (spin parameter a=Jc/G/M²=0.99); the ring-singularity is located at the equatorial kink of the inner ergosphere at R=a.[/size][/color][/b]

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<<The Kerr metric or Kerr geometry describes the geometry of empty spacetime around a rotating uncharged axially-symmetric black hole with a spherical event horizon. The Kerr metric is an exact solution of the Einstein field equations of general relativity; these equations are highly non-linear, which makes exact solutions very difficult to find. The Kerr metric is a generalization of the Schwarzschild metric, which was discovered by Karl Schwarzschild in 1915 and which describes the geometry of spacetime around an uncharged, spherically-symmetric, and non-rotating body. The corresponding solution for a charged, spherical, non-rotating body, the Reissner–Nordström metric, was discovered soon afterwards (1916–1918). However, the exact solution for an uncharged, rotating black-hole, the Kerr metric, remained unsolved until 1963, when it was discovered by Roy Kerr. The natural extension to a charged, rotating black-hole, the Kerr–Newman metric, was discovered shortly thereafter in 1965.>>

neufer wrote:Point singularities DON'T exist in the cores of rotating BHs.
RING singularities exist in the cores of rotating BHs.

But it's important to recognize that these are the conclusions of mathematical analyses, taken to limits where our theories may not work. These abstractions are very useful, but we have no clue what a physical singularity (point or ring) really means outside of the math.

Chris Peterson wrote:

neufer wrote:
Point singularities DON'T exist in the cores of rotating BHs.
RING singularities exist in the cores of rotating BHs.

But it's important to recognize that these are the conclusions of mathematical analyses, taken to limits where our theories may not work. These abstractions are very useful, but we have no clue what a physical singularity (point or ring) really means outside of the math.

The point here is that point singularities probably don't exist in the real world.

The cores of black holes and elementary particles consist of strings or sheets or other higher dimensional objects.

neufer wrote:

Chris Peterson wrote:

neufer wrote:
Point singularities DON'T exist in the cores of rotating BHs.
RING singularities exist in the cores of rotating BHs.

But it's important to recognize that these are the conclusions of mathematical analyses, taken to limits where our theories may not work. These abstractions are very useful, but we have no clue what a physical singularity (point or ring) really means outside of the math.

The point here is that point singularities probably don't exist in the real world.

I wouldn't go as far as "probably". We just don't know.

The cores of black holes and elementary particles consist of strings or sheets or other higher dimensional objects.

A conclusion that stems from highly speculative and only marginally scientific ideas. We don't know what the cores of black holes or elementary particles consist of. Maybe the idea of "core" doesn't even apply.