APOD: Threads of NGC 1947 (2021 Apr 07)

[APOD Robot]

Threads of NGC 1947

Explanation: Found in far southern skies, deep within the boundaries of the constellation Dorado, NGC 1947 is some 40 million light-years away. In silhouette against starlight, obscuring lanes of cosmic dust thread across the peculiar galaxy's bright central regions. Unlike the rotation of stars, gas, and dust tracing the arms of spiral galaxies, the motions of dust and gas don't follow the motions of stars in NGC 1947 though. Their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947 during the last 3 billion years or so of the peculiar galaxy's evolution. With spiky foreground Milky Way stars and even more distant background galaxies scattered through the frame, this sharp Hubble image spans about 25,000 light-years near the center of NGC 1947.

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[Ann]

Cen A. Photo: ESO.

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NGC 1947. Image Credit: ESA/Hubble & NASA, D. Rosario; Acknowledgment: L. Shatz.

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How interesting! NGC 1947 is like a future, "spent" version of active galaxy Cen A!

Both Cen A and NGC 1947 are products of galactic collisions. A small gas-rich galaxy has collided with a larger elliptical galaxy.

In Cen A, the collision probably happened relatively recently. The crash created huge amounts of very thick dark dust and reasonably high levels of star formation (blue stars at upper right and lower left). Cen A also has an active black hole with a jet, probably because the collision has been feeding material into the galactic center. The jet is seen better here.

NGC 1947, by contrast, is "spent". Its dust lanes are thinning like the hairs of a man going bald, and there are no young blue stars associated with the dust lanes.

But we can still see how the dust lanes appear to be "orbiting" around the elliptical galaxy's equator, as if they were rings of Saturn. The dust lanes of NGC 1947 appear to be wind-blown, too, as if they are being drawn out and stretched by the rotation of the elliptical galaxy. The galaxy, or at the very least the dust lanes, seem to be rotating "clockwise".

Another similar galaxy is NGC 1316. But here the dust lanes are more chaotic.

Ann

[orin stepanek]

APOD Their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947

To me it looks like it lost most of it's stars; it's so void and empty; even though their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947! ????????

[neufer]

How interesting! NGC 1947 is like a future, "spent" version of active galaxy Cen A! Both Cen A and NGC 1947 are products of galactic collisions. A small gas-rich galaxy has collided with a larger elliptical galaxy.

In Cen A, the collision probably happened relatively recently. The crash created huge amounts of very thick dark dust and reasonably high levels of star formation (blue stars at upper right and lower left). Cen A also has an active black hole with a jet, probably because the collision has been feeding material into the galactic center. The jet is seen better here.

NGC 1947, by contrast, is "spent". Its dust lanes are thinning like the hairs of a man going bald, and there are no young blue stars associated with the dust lanes. But we can still see how the dust lanes appear to be "orbiting" around the elliptical galaxy's equator, as if they were rings of Saturn. The dust lanes of NGC 1947 appear to be wind-blown, too, as if they are being drawn out and stretched by the rotation of the elliptical galaxy. The galaxy, or at the very least the dust lanes, seem to be rotating "clockwise".

Another similar galaxy is NGC 1316. But here the dust lanes are more chaotic.

Hubble Space Telescope image of polar-ring S0 galaxy NGC 4650A.

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<<A polar-ring galaxy is a type of galaxy in which an outer ring of gas and stars rotates over the poles of the galaxy. These polar rings are thought to form when two galaxies gravitationally interact with each other. One possibility is that a material is tidally stripped from a passing galaxy to produce the polar ring seen in the polar-ring galaxy. The other possibility is that a smaller galaxy collides orthogonally with the plane of rotation of the larger galaxy, with the smaller galaxy effectively forming the polar-ring structure.

The best-known polar-ring galaxies are S0s (lenticular galaxies), but from the physical point of view they are part of a wider category of galaxies, including several ellipticals.

The first four S0 galaxies that were identified as polar-ring galaxies were NGC 2685,NGC 4650A, A 0136 -0801,and ESO 415 -G26. While these galaxies have been extensively studied, many other polar-ring galaxies have since been identified. Polar-ring S0 galaxies may be found around 0.5% of all nearby lenticular galaxies, and it is possible that 5% of lenticular galaxies may have had polar rings at some point during their lifetimes.

The first polar-ring elliptical galaxies were identified in 1978. They were NGC 5128 (Cen A), NGC 5363, NGC 1947 and Cygnus A, while the polar-ring S0 galaxies NGC 2685 and NGC 4650A were at that time indicated as resulting from similar formation processes. Only some years later, when the first observations of the stellar and gas motion of polar-ring elliptical and S0 galaxies were possible with a better spectroscopic technology, the external origin of the gaseous rings was clarified. In addition to the best-known example, NGC 5128 (Cen A), a very regular polar ring elliptical, is NGC 5266.>>

[johnnydeep]

NGC1947potw2051a_1024.jpg

APOD Their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947

To me it looks like it lost most of it's stars; it's so void and empty; even though their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947! ????????

Lost most of its stars? What looks like just a fuzzy white blur is all stars, too small to distinguish individually! I looked for an approximate "number of stars" figure, or even a total mass figure, but came up empty.

[Chris Peterson]

NGC1947potw2051a_1024.jpg

APOD Their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947

To me it looks like it lost most of it's stars; it's so void and empty; even though their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947! :shock: ???????? :roll:

Lost most of its stars? What looks like just a fuzzy white blur is all stars, too small to distinguish individually! I looked for an approximate "number of stars" figure, or even a total mass figure, but came up empty.

Based on measurements of the rotation curve, it has an estimated mass of 2 x 10¹⁰ solar masses. So, a pretty typical spiral galaxy.

[neufer]

To me it looks like it lost most of it's stars; it's so void and empty; even though their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947! ????????

Lost most of its stars? What looks like just a fuzzy white blur is all stars, too small to distinguish individually! I looked for an approximate "number of stars" figure, or even a total mass figure, but came up empty.

Based on measurements of the rotation curve, it has an estimated mass of 2 x 10¹⁰ solar masses.

• Yeah ... but most of that is water weight dark matter mass.

[johnnydeep]

NGC1947potw2051a_1024.jpg



To me it looks like it lost most of it's stars; it's so void and empty; even though their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947! ????????

Lost most of its stars? What looks like just a fuzzy white blur is all stars, too small to distinguish individually! I looked for an approximate "number of stars" figure, or even a total mass figure, but came up empty.

Based on measurements of the rotation curve, it has an estimated mass of 2 x 10¹⁰ solar masses. So, a pretty typical spiral galaxy.

Except that NGC 1947 is thought to be an elliptical that merged with a smaller spiral, yes? "Only" 20 billion solar masses still seems small to me, but I know you've said before that most spiral galaxies are *much* smaller than the familiar Milky Way (400 billion stars / 1.2 trillion solar masses) and Andromeda (1 trillion stars / (also!) 1.2 trillion solar masses) galaxies. I suppose the same is true for ellipticals?

[Chris Peterson]

Lost most of its stars? What looks like just a fuzzy white blur is all stars, too small to distinguish individually! I looked for an approximate "number of stars" figure, or even a total mass figure, but came up empty.

Based on measurements of the rotation curve, it has an estimated mass of 2 x 10¹⁰ solar masses.

• Yeah ... but most of that is water weight dark matter mass.

Sure. But the total mass is still right in the normal range for galaxies like this.

[orin stepanek]

NGC1947potw2051a_1024.jpg

APOD Their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947

To me it looks like it lost most of it's stars; it's so void and empty; even though their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947! ????????

Lost most of its stars? What looks like just a fuzzy white blur is all stars, too small to distinguish individually! I looked for an approximate "number of stars" figure, or even a total mass figure, but came up empty.

Remember; I said looks like!

To me this is what looks like a lot of stars! Maybe it is the way I perceive it!

[johnnydeep]

NGC1947potw2051a_1024.jpg



To me it looks like it lost most of it's stars; it's so void and empty; even though their more complicated disconnected motion suggest this galaxy's visible threads of dust and gas may have come from a donor galaxy, accreted by NGC 1947! ????????

Lost most of its stars? What looks like just a fuzzy white blur is all stars, too small to distinguish individually! I looked for an approximate "number of stars" figure, or even a total mass figure, but came up empty.

Remember; I said looks like!


ngc2841_hstColombari_960.jpg


To me this is what looks like a lot of stars! Maybe it is the way I perceive it!

I get your point, but that one looks like a lot of DUST to me!