APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

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APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby APOD Robot » Wed Dec 07, 2016 5:07 am

Image NGC 4696: Filaments around a Black Hole

Explanation: What's happening at the center of elliptical galaxy NGC 4696? There, long tendrils of gas and dust have been imaged in great detail as shown by this recently released image from the Hubble Space Telescope. These filaments appear to connect to the central region of the galaxy, a region thought occupied by a supermassive black hole. Speculation holds that this black hole pumps out energy that heats surrounding gas, pushes out cooler filaments of gas and dust, and shuts down star formation. Balanced by magnetic fields, these filaments then appear to spiral back in toward and eventually circle the central black hole. NGC 4696 is the largest galaxy in the Centaurus Cluster of Galaxies, located about 150 million light years from Earth. The featured image shows a region about 45,000 light years across.

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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby bystander » Wed Dec 07, 2016 5:38 am

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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby Ann » Wed Dec 07, 2016 6:12 am

This is so interesting! And it touches on a very interesting question - why do elliptical galaxies produce so few stars? And do they produce any new stars at all?

Wikipedia wrote:
Very little star formation is thought to occur in elliptical galaxies, because of their lack of gas compared to spiral or irregular galaxies. However, in recent years, evidence has shown that a reasonable proportion (~25%) of these galaxies have residual gas reservoirs[7] and low level star-formation.[8] Researchers with the Herschel Space Observatory have speculated that the central black holes in elliptical galaxies keep the gas from cooling enough for star formation.


If 25% of elliptical galaxies show obvious star formation, that means that 75% of them do not. What sets the starforming ellipticals off from the non-starforming ones?

NGC 3077. Photo:ESA/Hubble.
Song Huang and Qiu-Sheng Gu wrote:
We find that SFEGs [starforming elliptical galaxies] have relative younger stellar population age, higher metallicity, and lower stellar mass, and that their star formation history can be well described by a recent minor and short starburst superimposed on old stellar component. We also detect 11 E+A galaxies whose stellar population properties are closer to those of quiescent (normal) ellipticals than to star-forming ones. However, from the analysis of their absorption line indices, we note that our E+A galaxies show a significant fraction of intermediate-age stellar populations, remarkably different from the quiescent galaxies. This might suggest an evolutionary link between E+As and star-forming ellipticals.


So the obviously starforming ellipticals are either relatively small, or else they contain whole populations of moderately young stars overall. A good example might be relatively small and elliptical-shaped NGC 3077, a satellite galaxy of M81, which displays a central starburst. If supermassive central black holes play a role in quenching star formation, we should note that most small galaxies have small central black holes, or none at all.

What about dusty filaments? Why do some of them form stars and others do not?

NGC 4696. NASA, ESA, Hubble, A Fabian.
NGC 3597. ESA/Hubble.



















I chose to place the pictures of NGC 4696 and 3597 side by side, because I find their dusty filaments interestingly similar in overall shape. I think, however, that they differ considerably in size. The filaments of NGC 4696 are small and located close to the nucleus of of the galaxy, whereas the filaments of NGC 3597, which is the product of a titanic collision between two galaxies, possibly encircle large volumes of the entire galaxy.

There can be no mistaking the fertile star formation of at least parts of the dusty filaments of NGC 3597, while those of NGC 4696 are literally red and dead. On the other hand, not all of the dusty filaments of NGC 3597 seem to produce new stars. This "limited" star formation ability is in fact typical of dusty filaments. Check out this superb but large (1.2MB) Hubble picture of NGC 3314, processed by André van der Hoeven. NGC 3314 consists of two non-interacting galaxies superimposed on one another as seen from the Earth, and we can judge the stellar content of the spiral arms of the galaxy seen in silhouette against the other one.

2MASX J00482185-2507365 occulting pairs.
NASA, ESA, and The Hubble Heritage Team
In the occulting pair of galaxies known as 2MASX J00482185-2507365, we can see that the smaller galaxy, which has a faintly blue and seemingly staarforming inner disk, seems to sport outer arm fragments that are "all dust". It happens. Besides, this small galaxy is probably close to a supermassive black hole (in its large bully of a galactic neighbor).

Let's return to the question of why the filaments of NGC 4696 are forming no stars at all. The wikipedia link I posted at the beginning of my post suggests that the supermassive black hole prevents star formation here. The caption of today's APOD links heating from the black hole to the influence of magnetic fields to explain the appearance of the the filaments of NGC 4696:

Speculation holds that this black hole pumps out energy that heats surrounding gas, pushes out cooler filaments of gas and dust, and shuts down star formation. Balanced by magnetic fields, these filaments then appear to spiral back in toward and eventually circle the central black hole.


That seems reasonable to me.

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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby Case » Wed Dec 07, 2016 7:21 am

A previous Hubble image of the same galaxy shows that todays APOD displays the bright center of NGC 4696, mostly dimming the outer rims. Thus the galaxy is much larger than a casual visitor might think based on todays image, if you missed the implication of “center” and “central region” in the description.
https://www.spacetelescope.org/news/heic1013/

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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby Ann » Wed Dec 07, 2016 7:35 am

Case wrote:A previous Hubble image of the same galaxy shows that todays APOD displays the bright center of NGC 4696, mostly dimming the outer rims. Thus the galaxy is much larger than a casual visitor might think based on todays image, if you missed the implication of “center” and “central region” in the description.
https://www.spacetelescope.org/news/heic1013/


Interesting, Case. Actually, the inner filaments are larger, in relation to the entire (relatively bright) galaxy, than I thought.

NGC 1316. NASA, ESA, and The Hubble Heritage Team
By the way, it is interesting to compare NGC 4696 with NGC 1316. Both are elliptical galaxies with prominent, non-starforming dust filaments. Actually, NGC 1316, like NGC 4696, has an outer elliptical "body" that is untouched by any (visible) dusty filaments.

To me it seems obvious that the dust filaments of NGC 1316 are the remnants of a past collision, or at least, a past interaction. It could well be that the filaments of NGC 4696 have a similar origin, but perhaps not. The filaments of NGC 1316 seem more scattered and torn than those of NGC 4696. To me, the ones in NGC 4696 appear to be trapped in a magnetic field, which is not so obvious for the ones in NGC 1316.

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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby Boomer12k » Wed Dec 07, 2016 9:12 am

"The COMMA Galaxy..." ,

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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby heehaw » Wed Dec 07, 2016 9:56 am

What a beautiful, exciting, image!

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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby Pipetx » Wed Dec 07, 2016 1:30 pm

I have to read up on black holes. I had assumed that they do NOT pump things out. I need reeducation. :D

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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby Ann » Wed Dec 07, 2016 2:10 pm

Pipetx wrote:I have to read up on black holes. I had assumed that they do NOT pump things out. I need reeducation. :D


Centaurus A. Photo:
ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre);
NASA/CXC/CfA/R.Kraft et al. (X-ray)
They do actually - they emit jets, at least some of them. It's the supermassive black holes of the centers of large elliptical galaxies that typically emit jets, particularly after they have received large helpings of material. That often happens after galactic mergers and interactions, as is the case of Centaurus A, pictured at left. Centaurus A is a collisional product of a relatively large elliptical galaxy and a smaller spiral galaxy, and we still see the prominent, broad dust lane of the spiral galaxy. But it is the supermassive black hole of the elliptical component that has inhibited star formation in the elliptical component, and soon - in a few hundred million years, perhaps - it will snuff out star formation in the remains of the spiral galaxy, too.

Large elliptical galaxies are expected to periodically send enough enough material down their central black holes to make the black holes emit jets. It is the jets that keep the dust and gas in the parent galaxies hot enough and turbulent enough to inhibit star formation.

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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby geckzilla » Wed Dec 07, 2016 2:51 pm

Ann wrote:
Pipetx wrote:I have to read up on black holes. I had assumed that they do NOT pump things out. I need reeducation. :D

They do actually - they emit jets, at least some of them.

To be clear, the relativistic jets are not coming out of the black hole itself. It's just matter that approaches the black hole and then, despite expectations, shoots off either pole instead of falling in. I've never managed to make much sense of this, myself.
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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby Chris Peterson » Wed Dec 07, 2016 3:01 pm

geckzilla wrote:
Ann wrote:
Pipetx wrote:I have to read up on black holes. I had assumed that they do NOT pump things out. I need reeducation. :D

They do actually - they emit jets, at least some of them.

To be clear, the relativistic jets are not coming out of the black hole itself. It's just matter that approaches the black hole and then, despite expectations, shoots off either pole instead of falling in. I've never managed to make much sense of this, myself.

It might be easier to picture if we recognize that the material is not approaching the black hole perpendicularly, but tangentially. It is orbiting the black hole, in a disc, and some gets swept by magnetic fields into jets along the axis of rotation, similarly to how a water spout is swept vertically out of a flat ocean by a circular wind that is parallel to the ocean surface.
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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby neufer » Wed Dec 07, 2016 3:01 pm

APOD Robot wrote:Image NGC 4696: Filaments around a Black Hole

Explanation: What's happening at the center of elliptical galaxy NGC 4696? There, long tendrils of gas and dust have been imaged in great detail as shown by this recently released image from the Hubble Space Telescope. These filaments appear to connect to the central region of the galaxy, a region thought occupied by a supermassive black hole. Speculation holds that this black hole pumps out energy that heats surrounding gas, pushes out cooler filaments of gas and dust, and shuts down star formation. Balanced by magnetic fields, these filaments then appear to spiral back in toward and eventually circle the central black hole. NGC 4696 is the largest galaxy in the Centaurus Cluster of Galaxies, located about 150 million light years from Earth. The featured image shows a region about 45,000 light years across.
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Re: APOD: NGC 4696: Filaments around a Black Hole (2016 Dec 07)

Postby starsurfer » Wed Dec 07, 2016 7:11 pm

Ionized outflows in galaxies are awesome! Shame so many are so small that only professional observatories can image them and then redshift has to be taken into account.

NGC 4696 is one of the dominant galaxies of the Centaurus Galaxy Cluster, check out this deep image.


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