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.
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.)
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)×107
. 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.
P.S. I'm so happy to see an APOD where the great Leonardo Orazi has been involved in the making of it!
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