APOD: The Long Gas Tail of Spiral Galaxy D100 (2019 Jan 28)

[APOD Robot]

The Long Gas Tail of Spiral Galaxy D100

Explanation: Why is there long red streak attached to this galaxy? The streak is made mostly of glowing hydrogen that has been systematically stripped away as the galaxy moved through the ambient hot gas in a cluster of galaxies. Specifically, the galaxy is spiral galaxy D100, and cluster is the Coma Cluster of galaxies. The red path connects to the center of D100 because the outer gas, gravitationally held less strongly, has already been stripped away by ram pressure. The extended gas tail is about 200,000 light-years long, contains about 400,000 times the mass of our Sun, and stars are forming within it. Galaxy D99, visible to D100's lower left, appears red because it glows primarily from the light of old red stars -- young blue stars can no longer form because D99 has been stripped of its star-forming gas. The featured false-color picture is a digitally enhanced composite of images from Earth-orbiting Hubble and the ground-based Subaru telescope. Studying remarkable systems like this bolsters our understanding of how galaxies evolve in clusters.

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[bystander]

viewtopic.php?t=39114

[Ann]

To me it looks like a jet, being violently ejected by energetic processes in the galaxy's core. Apparently that is not the case. The explanation in the caption is good enough.

APOD Robot wrote:
The red path connects to the center of D100 because the outer gas, gravitationally held less strongly, has already been stripped away by ram pressure.

Ann

[distefanom]

To me it looks like a jet, being violently ejected by energetic processes in the galaxy's core. Apparently that is not the case. The explanation in the caption is good enough.

APOD Robot wrote:
The red path connects to the center of D100 because the outer gas, gravitationally held less strongly, has already been stripped away by ram pressure.

Ann

For me the "Galaxy gas stripping" is new phenomena. How can it happen? Is not so clear to me, If I don't assume the galaxy itself as running inside a "mega -storm" which involves the whole galaxy itself.
in this case, I can imagine that the gas jet should have swirls way more chaotic than what we see here... to me still resemble too much as a jet from an AGN... anyway, is true that the other galaxies are orange-colored a telltale sign of OLD stars

[Ann]

To me it looks like a jet, being violently ejected by energetic processes in the galaxy's core. Apparently that is not the case. The explanation in the caption is good enough.

APOD Robot wrote:
The red path connects to the center of D100 because the outer gas, gravitationally held less strongly, has already been stripped away by ram pressure.

Ann

For me the "Galaxy gas stripping" is new phenomena. How can it happen? Is not so clear to me, If I don't assume the galaxy itself as running inside a "mega -storm" which involves the whole galaxy itself.
in this case, I can imagine that the gas jet should have swirls way more chaotic than what we see here... to me still resemble too much as a jet from an AGN... anyway, is true that the other galaxies are orange-colored a telltale sign of OLD stars

Click to view full size image

Hot intracluster gas. Source:www.astro.ufl.edu

Galaxy ram stripping is a relatively common phenomenon. It occurs when gas-rich galaxies get caught up by the mighty gravity of fairly nearby galaxy clusters. Such clusters are always full of thin, multi-million degree gas, which fills the space between the member galaxies.

Because this gas is so hot, it can only be seen at X-ray wavelengths. The picture at left shows the X-ray-emitting hot intracluster gas in a galaxy cluster.

Click to view full size image

NASA, ESA, and the Hubble Heritage Team

When a spiral galaxy falls into the cluster, pulled there by the cluster's overwhelming gravity, the intracluster gas acts as an "upwind" on the spiral galaxy. The spiral can't hold on to its gas, which is pulled out of it in a long tail. You can see that the galaxy in the picture at right, ESO 137-001, is losing gas from most of its disk.

Click to view full size image

Gas being stripped from the core of galaxy D100 in the Coma Cluster.
NASA, ESA, Hubble, Subaru Telescope, W. Cramer (Yale) et al.,
M. Yagi, J. DePasquale

In the case of spiral galaxy D100 in the Coma Cluster, it has, according to today's caption, already lost the gas in its disk. That makes sense to me. Most of the mass in any large galaxy will be concentrated in its core, and the galaxy'a ability to hold on to its own gas will be greatest in its core.

In galaxy D100, even the gravity of its core is being overwhelmed by the combined gravity of massive galaxies tugging at the gas in its core. The gas in its disk has already been lost, because the galaxy's own "local gravity" is weaker there. Now the rest of the gas is being pulled out of the galaxy in a long narrow "jet" which isn't generated by upheavals in the galaxy's core, just a concentrated source of gas being pulled out of the galaxy in a long narrow string.

It makes sense to me.

Ann

[heehaw]

What a joy to see this image! Fritz Zwicky discovered many decades ago that the galaxies in Coma were moving so fast there must be tons of dark matter there in addition to the galaxies. Surely it must be ionized hydrogen? But X-ray observations discovered the gas that is causing what you see in the picture, and yet its mass is only one percent of what is needed---we still don't know what the rest is: 'dark matter' we call it.

[Tszabeau]

I wonder what becomes of the stars formed within the tail. Will they fall back into D100 or will (have) they become rogues.

[sunson]

Looks like a hot wheeler to me

[Buddy-Oh]

Imagine living in D99, knowing that once your sun burns its fuel, all the others are gone too, and there's nowhere to go.

I remember reading, maybe in Sky and Telescope, and predominantly blue galaxies (intrinsically blue that is, not because of shifting). Wonder what's going on in that case?

[neufer]

High resolution composite image, with Chandra X-ray data in pink and optical data from the Sloan Digital Sky Survey appearing in white and blue.

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Extended (4 Mly) low resolution XMM-Newton X-ray image

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Clues to the Growth of the Colossus in Coma

<<A team of astronomers has discovered enormous arms of hot gas in the Coma cluster of galaxies by using NASA's Chandra X-ray Observatory and ESA's XMM-Newton. These features, which span at least half a million light years, provide insight into how the Coma cluster has grown through mergers of smaller groups and clusters of galaxies to become one of the largest structures in the Universe held together by gravity.

The X-ray emission is from multimillion-degree gas and the optical data shows galaxies in the Coma Cluster, which contain only about 1/6 the mass in hot gas. Only the brightest X-ray emission is shown here, to emphasize the arms, but the hot gas is present over the entire field of view. Researchers think that these arms were most likely formed when smaller galaxy clusters had their gas stripped away by the head wind created by the motion of the cluster through the hot gas.

Coma is an unusual galaxy cluster because it contains not one, but two giant elliptical galaxies near its center. These two giant elliptical galaxies are probably the vestiges from each of the two largest clusters that merged with Coma in the past. The researchers also uncovered other signs of past collisions and mergers in the data.

From their length, and the speed of sound in the hot gas (~1,100 km/s), the newly discovered X-ray arms are estimated to be about 300 million years old, and they appear to have a rather smooth shape. This gives researchers some clues about the conditions of the hot gas in Coma. Most theoretical models expect that mergers between clusters like those in Coma will produce strong turbulence, like ocean water that has been churned by many passing ships. Instead, the smooth shape of these lengthy arms points to a rather calm setting for the hot gas in the Coma cluster, even after many mergers. Large-scale magnetic fields are likely responsible for the small amount of turbulence that is present in Coma.

Two of the arms appear to be connected to a group of galaxies located about two million light years from the center of Coma. One or both of these arms connects to a larger structure seen in the XMM-Newton data, and spans a distance or at least 1.5 million light years. A very thin tail also appears behind one of the galaxies in Coma. This is probably evidence of gas being stripped from a single galaxy, in addition to the groups or clusters that have merged there.

These new results incorporating over 6x days worth of Chandra observing time, appeared in the Sept. 20, 2013, issue of the journal Science.>>

[Avalon]

What happens to the galaxies that fall to the center of the cluster completely stripped of their gases? Do they just snuff out and die, or break up and attract matter from other spent galaxies?

[Wally]

The astronomer should not use the present tense in describing astronomical phenomena. This all happened millions or billions of years ago.

[neufer]

---

The astronomer should not use the present tense in describing astronomical phenomena. This all happened millions or billions of years ago.

Everyone's perception of the outside world lies on the Past Light Cone.

Why limit yourself to just astronomers when criticizing
the observers's nominal definition of present tense

Astronomers discuss events on the Past Light Cone as having occurred in the past only when it's helpful in making a particular point (; e.g., conditions were different back then).

[Boomer12k]

Awesome, and thought provoking... I wonder if the gas will eventually cool and fall into clumps and make new stars and even galaxies one day....hmmmm....
I mean all of the "out gases" of the cluster...not just one galaxy...though that appears to happen in the tails...I mean "much later"...

It is like a "Galactic Comet"...

:---[===] *

[Ann]

What happens to the galaxies that fall to the center of the cluster completely stripped of their gases? Do they just snuff out and die, or break up and attract matter from other spent galaxies?

Click to view full size image

NGC 4921 in the Coma Cluster. NASA, ESA and K. Cook

Click to view full size image

Photo: NASA

Well, first they become "anemic galaxies". They retain their spiral structure, but they lose more and more of their gas. As the gas disappears, the dust lanes become weaker, and fewer and fewer stars can be formed.

Then they become those boring yellow blobs called elliptical galaxies. When they have lost their gas, they lose most of their structure, and the young blue stars turn yellow with age. These galaxies can't make new stars, or at least, their starforming ability is extremely low.

And if they come too close to another galaxy, they may merge with it and "disappear".

Ann

[neufer]

http://asterisk.apod.com/viewtopic.php?f=31&t=39122

[MarkBour]

This explanation, of hot gas stripping away the galaxy's hydrogen, makes little sense to me.
Can I play a bit of a devil's advocate on this one?

The only mental image I can construct for it, would, as distefanom pointed out, result in a more chaotic structure. I would add to that, that I would expect a wider cylinder, and the loss of material out of the "back" should be countered by build-up of material on the "front". Ann's 2nd image, of ESO 137-001, looks more like it. The disk of the galaxy should be bowed, like that of NGC 4402. There should also be bleeding of dust, on a shorter scale. Perhaps imagery in other bandwidths would help make this conclusion more believable.

Why would D100 have a tail and D99 have none? Perhaps you can say "D99 is older, its gas was already stripped and is now no longer visible." If so, where are the stars it left in its wake? There are thousands of galaxies in a Coma Cluster. If this is a "thing", there should be tails like this for quite a few of them. And these tails should bolster the conclusion by all pointing away from the motion of the galaxy from which they emanate. Maybe there is such evidence that has already been gathered. Maybe there is a survey that has just begun. I don't know. I assume that at least for anyone to have believed this hypothesis, this tail is in the opposite direction of D100's motion towards the cluster center. Is there any way to verify that?

A quote from the Hubblesite http://hubblesite.org/image/4285/gallery says: "This can be strong enough to tear galaxies apart, and often results in objects with peculiar, bizarre shapes and features — as seen here." What I'm wondering about is the word "often" in this description. I'd love to see more examples.

[neufer]

This explanation, of hot gas stripping away the galaxy's hydrogen, makes little sense to me. The only mental image I can construct for it, would, as distefanom pointed out, result in a more chaotic structure. I would add to that, that I would expect a wider cylinder, and the loss of material out of the "back" should be countered by build-up of material on the "front".

<<In the massive Coma cluster, this violent gas-loss process occurs in many galaxies. But D100 is unique. Its long, thin tail, for example, extends nearly 200,000 light-years — about the length of two Milky Way galaxies. In addition, the tail is narrow, only 7,000 light-years wide.

“The tail is remarkably well-defined, straight and smooth, and has clear edges. This is a surprise because a tail like this is not seen in most computer simulations,” said Dr. Jeffrey Kenney, also from Yale University. “Most galaxies undergoing this process are more of a mess. The clean edges and filamentary structures of the tail suggest that magnetic fields play a prominent role in shaping it. Computer simulations show that magnetic fields form filaments in the tail’s gas. With no magnetic fields, the tail is more clumpy than filamentary.”>>

Why would D100 have a tail and D99 have none? Perhaps you can say "D99 is older, its gas was already stripped and is now no longer visible." If so, where are the stars it left in its wake?

D99 is older, its gas was already stripped and is now no longer visible.
The stars are like pasties that remain after the gas-stripping is complete.

I assume that at least for anyone to have believed this hypothesis, this tail is in the opposite direction of D100's motion towards the cluster center. Is there any way to verify that?

D100 should attain it's fastest velocity through the densest part of the cluster's hot gas when it is actually at the center of the cluster so I assume that they already know that has yet to reach that point by having located D100 vs-a-vis the center of the cluster.

[neufer]

• https://www.syfy.com/syfywire/how-is-a- ... ipping-dog

[MarkBour]

• https://www.syfy.com/syfywire/how-is-a- ... ipping-dog

Thanks for the reference. The interesting quote from that, for me, would be:

Star formation appears to have ceased in the outer part of D100's disk, but you can still see spiral arms closer in, and that means it still has gas there, closer to the center. Eventually that too will be blown out; the whole process of cleaning out a galaxy takes roughly a billion years.

I didn't really see that in the APOD image at first, but now I do. D100 does indeed look like its outer arms have lost their star-formation, and only the inner 30% or so of the visible radius still appears to have robust star-formation activity. Kind of like hypothermia working its way in to the core! So, that is helpful to believing that this is a gas-stripped tail. I guess it is just much later in the process than what is seen in NGC 137-001. (I wonder if looking further to the left can show any wider, older, remnants of the earlier stages of stripping.)

I have also now found time to skim through an article from The Astrophysical Journal:
https://iopscience.iop.org/article/10.3 ... 357/aa6af5.
It has further persuaded me of the reasonableness of the claims in today's APOD. In addition to many detailed observations of the tail, much like the point made above, they also mentioned that lots of tails have been observed in the Coma cluster, something like "20 and counting".

One of their points is that they believe the galaxy is actually not moving through the intra-cluster medium perpendicular to its plane, which would have been my first guess at looking at the APOD image. Instead, they think it is moving at an angle that is significantly edge-on through the medium, and we are not looking perpendicularly to that tail. An interesting side-point, which I readily accept, is that looking at this tail where it meets the galaxy disk of D100 reveals that the left edge of D100 is the remote edge. That's kind of handy, I think it can sometimes be very hard to tell which is the farther edge.