APOD: NGC 1365: Majestic Island Universe (2021 Jan 08)

[APOD Robot]

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 Cluster of galaxies. This impressively sharp color image shows the intense, reddish star forming regions near the ends of central bar and along the spiral arms, with details of the obscuring 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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[Ann]

NGC 1365 is, of course, one of the most iconic barred spiral galaxies out there. The only barred spiral more iconic than NGC 1365 would be NGC 1300.

Barred spiral NGC 1365. Photo: Mike Selby, Leonardo Orazi.

Barred spiral NGC 1300. Photo: NASA/ESA/Hubble Team/Kevin M. Gill.

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Both NGC1300 and NGC 1365 have long bars, at the ends of which grand design spiral arms start at almost right angles to the bar. (A grand design spiral has two main long mostly unbroken spiral arms.)

Wikipedia wrote:
Edwin Hubble classified spiral galaxies of this type as "SB" (spiral, barred) in his Hubble sequence and arranged them into sub-categories based on how open the arms of the spiral are. SBa types feature tightly bound arms, while SBc types are at the other extreme and have loosely bound arms. SBb-type galaxies lie in between the two.

Based on what Wikipedia said about open and tightly bound arms, I would expect NGC 1365 to be classified as an SBc galaxy (with open arms) and NGC 1300 as an SBa galaxy (with tightly wound arms). Not so, however.

NGC 1365 is classified as an (R')SBb(s)b galaxy, according to Wikipedia. I don't know what the initial capital R medans, but SBb means that that NGC 1365 has "intermediately tightly wound arms". (The (s) means, I think, that NGC 1365 lacks a ring, and the last 'b' means that NGC 1365 has a second bar, this time in the center of the galaxy.)

NGC 1300, on the other hand, is classified as an (R')SB(s)bc galaxy. That is to say, NGC 1300 is classified as having more open arms than NGC 1365. What???

I guess it might be because the arms of NGC 1365 "meet" "above the center" of NGC 1365. In NGC 1300, by contrast, the ends of the arms "keep pointing outwards".

In any case, the arms of NGC 1365 "rise high" above the center of the galaxy, while in NGC 1300 the arms appear to be "weighed down", so that they are unable to rise much.

The black hole is seen nearly edgewise in this new visualization from NASA.
The turbulent disk of gas around the hole takes on a double-humped appearance.
The black hole’s extreme gravity alters the paths of light coming from different
parts of the disk, producing the warped image.
“What we see depends on our viewing angle,” NASA said.
Image via NASA’s Goddard Space Flight Center/Jeremy Schnittman.

I once read that the mass of a galaxy's black hole determines how open its arms can be. I have absolutely no idea if this is correct.

However, according to Wikipedia, the mass of the black hole of NGC 1365 is 2 million solar masses (which makes it about half as massive as the Milky Way's black hole), whereas the mass of the central black hole of NGC 1300 is given as 7.3(+6.9−3.5)×10⁷M_☉. I take that to mean that the central black hole of NGC 1300 is ~ 73 million solar masses, which is a lot more than the mass of the central black hole of either NGC 1365 or the Milky Way.

Ann

P.S. I'm so happy to see an APOD where the great Leonardo Orazi has been involved in the making of it!

[LMMdT]

Hello, while I see photographs like this I alwasys wonder how this galaxy is seen according to the distance. Supposing the observer is at the outskirts of the galaxy: will he see that bright core covering his sky or will it be just a nebula, a big one indeed, instead? Let's suppose there is no telescope around. Thank you!

[DL MARTIN]

|Can't imagine anyone referring to a galaxy observer as 'he' when Ann is around.

[Chris Peterson]

Hello, while I see photographs like this I alwasys wonder how this galaxy is seen according to the distance. Supposing the observer is at the outskirts of the galaxy: will he see that bright core covering his sky or will it be just a nebula, a big one indeed, instead? Let's suppose there is no telescope around. Thank you!

Our distance from a galaxy doesn't change its appearance. To our eyes, a galaxy seen at 100 magnification through a telescope looks the same as if we were 100 times close without a telescope. Visually, any galaxy will appear as a fuzzy gray object. If we're close, it may span a large angle, as we see with our own galaxy in the band of the Milky Way. Of course, depending on orientation, its structure will be different- a band if seen on edge, a sky filling cloud if seen from above or below. But still just gray fuzz.

[orin stepanek]

To me this galaxy looks as though it has been through an outside disturbance; but I don't see any near galaxies that may have caused it! Who knows in what shape a galaxy may form?

[Chris Peterson]

NGC-1365-RGB-19-DEC-2020_Leo_Mike_1024.jpg


To me this galaxy looks as though it has been through an outside disturbance; but I don't see any near galaxies that may have caused it! Who knows in what shape a galaxy may form? :shock:

I don't think so. This is an almost perfect barred spiral. Spiral galaxies that have interacted with another galaxy almost always lose their symmetry. We don't see that here.

[orin stepanek]

NGC-1365-RGB-19-DEC-2020_Leo_Mike_1024.jpg


To me this galaxy looks as though it has been through an outside disturbance; but I don't see any near galaxies that may have caused it! Who knows in what shape a galaxy may form?

I don't think so. This is an almost perfect barred spiral. Spiral galaxies that have interacted with another galaxy almost always lose their symmetry. We don't see that here.

I'm sure your right; but it is so; (I don't know;) so unusual! It is of coarse JMHO! It is beautiful anyway!

[Leonardo]

....
P.S. I'm so happy to see an APOD where the great Leonardo Orazi has been involved in the making of it!

Thank you so much Ann ... and thank you so much to APOD staff for pubblication.

[saturno2]

Beautiful image

[VictorBorun]

They say NGC 1365 has two bars and an S-shaped pair of arms. I struggle to see it.
1) I see an §-shaped pair of arms
2) the small bright bar looks like an ellips to me or rather like a disk we see at an angle

Rotating and stretching we can reconstruct a face-on view of such a disk (see my attempt at the right).

Has somebody investigated Doppler radial velocities and reconstructed NGC 1365 plane's angle to our line of sight?

[Ann]

They say NGC 1365 has two bars and an S-shaped pair of arms. I struggle to see it.
1) I see an §-shaped pair of arms
2) the small bright bar looks like an ellips to me or rather like a disk we see at an angle

Rotating and stretching we can reconstruct a face-on view of such a disk (see my attempt at the right).

Has somebody investigated Doppler radial velocities and reconstructed NGC 1365 plane's angle to our line of sight?

Victor, I think the "two bars" of NGC 1365 refers to both the long, obvious bar running through the center to the beginning of the spiral arms, and the much shorter bar running through the center of NGC 1365 at an angle to the long bar (I think).

Ann

[VictorBorun]

ok, there are two bars.
neufer says
there is a comfort zone for stable non-smeared structures near the center, due to gravity ~R.

Judging by the arms, this galaxy face on must have looked like this:

[VictorBorun]

There may be gravi-lensed bright points, but supposed lense does not look like centered at the bar:

[Chris Peterson]

There may be gravi-lensed bright points, but supposed lense does not look like centered at the bar:

There is no gravitational lensing here.