APOD: NGC 1365: Majestic Island Universe (2010 Aug 20)

[neufer]

From a link in the APOD, Fornax galaxy cluster (thanks owlice),
it is apparent that there is a lot of interaction within the cluster.
But I still don't know why NGC 1365 looks so unsettled.

Perhaps it is that dense cloud of gas passing right in front of the nucleus.
(It is as disorienting as an Escher drawing.)

Credit: X-ray: NASA/CXC/CfA/INAF/Risaliti Optical: ESO/VLT

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<<Chandra observations of the galaxy NGC 1365 have captured a remarkable eclipse of the supermassive black hole at its center. A dense cloud of gas passed in front of the black hole, which blocked high-energy X-rays from material close to the black hole. This serendipitous alignment allowed astronomers to measure the size of the disk of material around the black hole, a relatively tiny structure on galactic scales. The Chandra image (shown in the inset) contains a bright X-ray source in the middle, which reveals the position of the supermassive black hole. An optical view of the galaxy from the European Southern Observatory's Very Large Telescope shows the context of the Chandra data.

NGC 1365 contains a so-called active galactic nucleus, or AGN. Scientists believe that the black hole at the center of the AGN is fed by a steady stream of material, presumably in the form of a disk. Material just about to fall into a black hole should be heated to millions of degrees before passing over the event horizon, or point of no return. The process causes the disk of gas around the central black hole in NGC 1365 to produce copious X-rays, but the structure is much too small to resolve directly with a telescope. However, astronomers were able to measure the disk's size by observing how long it took for the black hole to go in and out of the eclipse. This was revealed during a series of observations of NGC 1365 obtained every two days over a period of two weeks in April 2006. During five of the observations, high-energy X-rays from the central X-ray source were visible, but in the second one -- corresponding to the eclipse -- they were not.>>

[neufer]

Does anyone know how far 200,000 lightyears is?? I'd like to know...

A light-year, also light year or lightyear, (symbol: ly) is a unit of length, equal to just under 10 trillion kilometres (10¹⁶ metres, 10 petametres or 6 trillion miles). As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in a vacuum in one Julian year.

So, multiply that by 200,000 ... 2*10²¹ meters or 1.2*10²¹ miles.

Bystander means, of course: 1.2*10¹⁸ miles; or to be more precise: 1.112*10²¹ smoots

• 1 light year = 5.56*10¹⁵ smoots

1 smoot = 170.18 cm

Click to view full size image

<<The smoot is a nonstandard unit of length created as part of an MIT fraternity prank. It is named after Oliver R. Smoot, a fraternity pledge to Lambda Chi Alpha, who in October 1958 lay on the Harvard Bridge (between Boston and Cambridge, Massachusetts), and was used by his fraternity brothers to measure the length of the bridge.

One smoot is equal to Oliver Smoot's height at the time of the prank (five feet and seven inches ~1.70 m). The bridge's length was measured to be 364.4 smoots (620.1 m) plus or minus one ear, with the "plus or minus" intended to express uncertainty of measurement. Over the years the "or minus" portion has gone astray in many citations, including the markings at the site itself, but has now been enshrined in stone by Smoot's college class.

To implement his use as a measuring unit, Oliver Smoot repeatedly lay down on the bridge, let his companions mark his new position in chalk or paint, and then got up again. Eventually, he tired from all this exercise and was carried thereafter by the fraternity brothers to each new position. Markings typically appear every 10 smoots, but additional marks appear at other numbers in between. For example, the 70-smoot mark is omitted in favor of a mark for 69. The 182.2-smoot mark is accompanied by the words "Halfway to Hell" and an arrow pointing towards MIT. Each class also paints a special mark for their graduating year.

Oliver Smoot graduated from MIT with the class of 1962, became a lawyer, and later became chairman of the American National Standards Institute (ANSI) and president of the International Organization for Standardization (ISO). He is the cousin of Nobel Prize winner George Smoot. The prank's fiftieth anniversary was commemorated on October 4, 2008, as Smoot Celebration Day at MIT.

NPR interview of Oliver Smoot

People walking across the bridge today can see painted markings indicating how many smoots there are from where the sidewalk begins on the Boston river bank. The marks are repainted each semester by the incoming associate member class (similar to pledge class) of Lambda Chi Alpha. The markings have become well-accepted by the public, to the degree that during the bridge renovations that occurred in the 1980s, the Cambridge Police department requested that the markings be maintained, since they had become useful for identifying the location of accidents on the bridge. The renovators went one better, by scoring the concrete surface of the sidewalk on the bridge at 5 foot 7 inch intervals, instead of the conventional six feet.

Google Calculator also incorporates smoots, which it reckons at exactly 67 inches (1.7018 meters). Google also uses the smoot as an optional unit of measurement in their Google Earth software.>>

[ems57fcva]

This galaxy looks perturbed. The spiral arms are far from symmetrical and there are shadow arms off to the right. Is there another galaxy close by with which this one is interacting?

Bystander - I think that you have made a very profound observation. I think that this is a case where there are two galaxies that are interacting very strongly. To make matters more interesting, I think that the remnants of the two galaxies are on each side of the central bar of NGC 1365

Here is my take on this galaxy: This is a galactic merger in the later stages of the merger. This is an Antennae galaxies type of situation, but much more evolved, and evolved in a direction that the theorists don't expect and cannot yet model. It appears to me that when the central so-called black holes of two galaxies get close enough, material started boiling off of both of them and into the space between them, forming a bridge. I suspect that what is boiling off is largely dark matter, but it is dragging a fair amount of gas and dust along with it. Indeed, you can see columns of dust and gas being drawn into a whirlpool at the center of the bar.

In any case, if enough material goes into the bridge, if starts forming a new galactic center, with a new "black hole" of its own. This change in the mass distribution of the system keeps the galaxies from just plain sweeping past each other, and also lowers the gravitational gradient for the original central objects (if I may call them "objects" instead of "black holes" now), and so permits even more material to flow out of them. If this process is allowed to proceed long enough, you get something like NGC 1365. If instead the configuration is such that only a limited amount of material is drawn into the bridge before the galaxies move away from each other, that the result will be a narrow bridge connecting the centers of the galaxies for a while. The July 2, 2010 APOD (http://antwrp.gsfc.nasa.gov/apod/ap100702.html) is an example of this alternate outcome.

So here is what I see in more detail. There is a central bar connecting the remnants of two smaller galaxies, with each galaxy becoming a spiral arm for the unified galaxy. The primary arm of each side was the primary tidal tail for one of the original galaxies. The secondary arm on each side was the secondary tidal tail, now twisted around so that it is parallel to the primary tidal tail as the arms have come to rotate around the new central object. The central bar is a new central bulge, into which gas and dust are still being drawn. The primary source of matter for the new central object is the remnants of the old central objects, located at either end of the bar, where the primary and secondary tidal tails meet.

I admit that this idea raises a lot of questions, but it is what I have been seeing in my mind's eye for some time now.

EMS

[Ann]

Certainly interactions is the most important reason for distorted galaxy shapes. Personally I really like this picture of the Hercules Cluster, which shows how interaction has distorted the shapes of several elliptical or lenticular galaxies.

Click to view full size image

I'm posting this image as a link as well, in case it gets too small when it's posted here as an image.

http://unigalactic.com/images/Space/The ... laxies.jpg

But it is my impression that gas-rich galaxies are relatively often disturbed for no obviously discernible reason. Perhaps all the gas that the galaxies contain is enough in itself to disturb them?

NGC 6946 is a good example of a galaxy with a high gas content, very many supernovae and an assymetric shape.



Ann

[DavidLeodis]

Lovely picture.

I like the question mark area near to the bottom of the lower spiral arm. I wonder what the question is

[DavidLeodis]

Why can't we just name galaxies, instead of numbering them? We named the Andromeda Galaxy And our own The Milky Way galaxy. Is it that we are afraid of the alien life forms in other galaxies? Same way with stars. I think it would be easier if Stars didn't have numbers but names.

FS

there are billions and billions of galaxies and each has billions and billions of stars! Naming them all would be quite a feat! other galaxies do have names though; like the Whirlpool and the Sombrero for example.

In the Wikipedia entry under 'Galaxy' it states "There are probably more than 170 billion galaxies in the observable universe". That's quite a lot, though I would not be surprised if there are more!

[Henning Makholm]

In the Wikipedia entry under 'Galaxy' it states "There are probably more than 170 billion galaxies in the observable universe". That's quite a lot, though I would not be surprised if there are more! :)

It would be very surprising if there were "more than 170 billion galaxies" without there also being more than "more than 170 billion" of them.

[DavidLeodis]

In the Wikipedia entry under 'Galaxy' it states "There are probably more than 170 billion galaxies in the observable universe". That's quite a lot, though I would not be surprised if there are more!

It would be very surprising if there were "more than 170 billion galaxies" without there also being more than "more than 170 billion" of them.

Oh you are are being clever aren't you! Anyway, the entry does state "probably more" so that allows me to state that I would not be surprised if there were more.