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M95: Spiral Galaxy with an Inner Ring

Explanation: Why do some spiral galaxies have a ring around the center? First and foremost, M95 is one of the closer examples of a big and beautiful barred spiral galaxy. Visible in the featured combination of images from Hubble and several ground based telescopes are sprawling spiral arms delineated by open clusters of bright blue stars, lanes of dark dust, the diffuse glow of billions of faint stars, and a short bar across the galaxy center. What intrigues many astronomers, however, is the circumnuclear ring around the galaxy center visible just outside the central bar. Although the long term stability of this ring remains a topic of research, observations indicate its present brightness is at least enhanced by transient bursts of star formation. M95, also known as NGC 3351, spans about 50,000 light-years, lies about 30 million light years away, and can be seen with a small telescope toward the constellation of the Lion (Leo).

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Ring, Bar? Where exactly?
You better gave an indication (e.g. in red dots when waving the mouse over the photograph) of - the bar and of - the ring. I easily see two rings: a ringlike structure in the very center if the galaxy, and the stucture with blue enclosing the yellow part of the galaxy. I have no idea what is really the bar. Please repeat the photograph!
There are many structures you mention in photographs, that I don't recognise. You had better marked them.
When you mention "horsehead" or so, i am not sure I recognise them. You had better marked them.

I am thinking it was a smaller galaxy with a merger...now settling down...the older stars are yellow and in the center area, right? Then new younger stars and star formation kind of "homogenized the mix"...the greater concentration of gravity was buttressed in the ring...you can still see some of the more yellow ARMS of the previous population.

Our own galaxy has Population 1 and Population 2 sections...right?

:---[===] *

emanueldewitt wrote: ↑Wed May 29, 2019 4:35 am Ring, Bar? Where exactly?
You better gave an indication (e.g. in red dots when waving the mouse over the photograph) of - the bar and of - the ring. I easily see two rings: a ringlike structure in the very center if the galaxy, and the stucture with blue enclosing the yellow part of the galaxy. I have no idea what is really the bar. Please repeat the photograph!
There are many structures you mention in photographs, that I don't recognise. You had better marked them.
When you mention "horsehead" or so, i am not sure I recognise them. You had better marked them.

Robert Gendler and Roberto Colombari have processed data from NASA/ESA/Hubble/ESO and produced today's APOD. I don't know what data was available to them, because that depends on what filters were used on the Hubble Telescope to photograph this galaxy.

But consider the picture at left, which is a NASA/ESA/Hubble image. If you visit this page, you can see that M95 has been imaged by Hubble through five filters: 275 nm (UV), 336 nm (also UV), 438 nm (blue, but mapped as cyan in the picture at left), 555 nm (green) and 814 nm (infrared).

One filter that is missing is 656 nm for hydrogen alpha. The fact that the 656 nm hydrogen alpha filter is missing makes it harder to produce pink nebulas in the final image. Bear in mind, too, that M95 is not forming very many new stars. There are certainly pink nebulas in this galaxy, but they are not all that numerous and definitely not all that big. (Correction: They may well be numerous, but they are certainly not big. Unless, possibly, there are some big ones in the inner ring.)

Note in the NASA/ESA/Hubble picture at left that there are many hot and blue stars in the inner ring. As you can see, the dusty bar, running from the outer to the inner ring of M95, is also quite obvious. But please note in today's APOD that one half of this bar is much more visible than the other.

Ann

The text says that the width of M85 is 50000 light years. M95 was also featured in APOD on 22/Mar/2012 (https://apod.nasa.gov/apod/ap120322.html). That text mentions the width as 75000 light years. This image also includes supernova SN 2012aw. The very first entry of M95 in APOD was on 14/Mar/2007 (https://apod.nasa.gov/apod/ap070314.html). That text gives the width as 50000 light years.

Ann wrote: ↑Wed May 29, 2019 5:26 am Ring, Bar? Where exactly?
..."Note in the NASA/ESA/Hubble picture at left that there are many hot and blue stars in the inner ring. As you can see, the dusty bar, running from the outer to the inner ring of M95, is also quite obvious. But please note in today's APOD that one half of this bar is much more visible than the other."
Ann

I think, the inner ring system is in rotation at right angles to the inner bar? So it would be obvious that the arm closer to us is darker resp. better visible than the one facing away from us, which is covered by more stars "dust"?

it would be interesting to know, if such galaxies form ring systems, where the inner ring has over-turned, resp. the ring is the result of a counter-rotation?

Beautiful Galaxy! I don't claim to know what caused it to have such a ring; But i like it!

As I've noticed, many if not most center-galaxy bars are not just a straight bar, but include a bit of a trailing ring fragment at each end. Is this what appears to be a full ring?

emanueldewitt wrote: ↑Wed May 29, 2019 4:35 am Ring, Bar? Where exactly?
You better gave an indication (e.g. in red dots when waving the mouse over the photograph) of - the bar and of - the ring. I easily see two rings: a ringlike structure in the very center if the galaxy, and the stucture with blue enclosing the yellow part of the galaxy. I have no idea what is really the bar....

Not sure I've got this right, but here are the structures I see. The pale circle is what I think is the outer ring, with the small black oval representing the inner ring. The ragged blue oval is where I think the bar is --- it's a hard to distinguish bright oblong area. (The bright circular area would be the central bulge of the galaxy.) Ann suggests the bar is the pair of stretched out dust lanes, which are slightly rotated away from the bar I'm indicating.
Hope this helps,

Rob

rstevenson wrote: ↑Wed May 29, 2019 1:53 pm

emanueldewitt wrote: ↑Wed May 29, 2019 4:35 am Ring, Bar? Where exactly?
You better gave an indication (e.g. in red dots when waving the mouse over the photograph) of - the bar and of - the ring. I easily see two rings: a ringlike structure in the very center if the galaxy, and the stucture with blue enclosing the yellow part of the galaxy. I have no idea what is really the bar....

Not sure I've got this right, but here are the structures I see. The pale circle is what I think is the outer ring, with the small black oval representing the inner ring. The ragged blue oval is where I think the bar is --- it's a hard to distinguish bright oblong area. (The bright circular area would be the central bulge of the galaxy.) Ann suggests the bar is the pair of stretched out dust lanes, which are slightly rotated away from the bar I'm indicating.

M95 central area.jpg

Hope this helps,

Rob

No, you are right that the bar is the thick yellow structure running like a huge fat pillar straight across the yellow center and sort of preventing the ring from "collapsing"! The dust lanes themselves are not bars, but most bars do have dust lanes.

At left you can see a picture of barred galaxy NGC 1365. The elongated central yellow structure is the bar. Note the dust lanes.

Ann

rstevenson wrote: ↑Wed May 29, 2019 1:53 pm

---

Not sure I've got this right, but here are the structures I see. The pale circle is what I think is the outer ring, with the small black oval representing the inner ring. The ragged blue oval is where I think the bar is --- it's a hard to distinguish bright oblong area. (The bright circular area would be the central bulge of the galaxy.) Ann suggests the bar is the pair of stretched out dust lanes, which are slightly rotated away from the bar I'm indicating.

Your "pale circle is what I think is the outer ring" is probably what
is called a circumnuclear "inner" ring lying just outside the central bar:

https://www.flickr.com/photos/geckzilla ... otostream/
https://apod.nasa.gov/apod/ap991212.html

Your "small black oval representing the inner ring" is probably what is called a "nuclear ring":

https://apod.nasa.gov/apod/ap170710.html

My gosh, it looks like a radioactive hurricane.

I am also curious..is the inner ring perpendicular to the bar? Like a napkin ring?

Hubblesite wrote:

In a landmark study of more than 2,000 spiral galaxies, Hubble has found clear evidence that majestic barred spirals—galaxies
that show a distinctive bar-shaped structure of stars and gas that slice across their nuclei—were far less common 7 billion years
ago than they are today.
...
Galactic bars develop when stellar orbits in a spiral galaxy become unstable and deviate from a circular path. The tiny elongations
in the stars’ orbits grow and get locked into place, forming a bar. The bar becomes even more pronounced as it collects more and
more stars in elliptical orbits. Eventually, a high fraction of the stars in the galaxy’s inner region join the bar. This process has been
demonstrated repeatedly with computer-based simulations.

It is not clear, however, what makes stellar orbits become unstable and go on to form bars. One of the more well-accepted theories is that this happens through the interaction of stars in a galaxy with a differentially rotating disk—when a galaxy rotates not as a solid body, but with the inside rotating slightly faster than the outside. In galaxies with stars moving in a Keplerian fashion—like the planets in our solar system where the nearest to the Sun revolve the fastest—passing interactions with other stars can leave stellar orbits unstable.

Ann

Edit: I know I should have used img3 for the caption of the picture I posted, but I have never been able to figure out how to do img3. When I try to see how the rest of you do it by quoting your posts, your posts look so cluttered that my mind sort of shuts down.

sillyworm 2 wrote: ↑Thu May 30, 2019 12:00 am I am also curious..is the inner ring perpendicular to the bar? Like a napkin ring?

I don't think so. If you look at the napkins with napkin rings in the picture at right, you can see that the napkins look like elongated structures with a "band" running in the opposite direction across them in the middle, like a bow tie.

The nuclear ring of a barred galaxy does not look like a bow tie. What you have in the center of many barred galaxies is a ring, not a vertical band. So nuclear rings are not like napkin rings.

Ann

May be it's helpful to take a closer look to the inner ring...

Source: Hubble WFPC2

In your post, AVAO, we can see the two dust lanes feeding gas into the nuclear ring. One of the dust lanes "hits the ring" at about 7 o'clock(ish), and the other one is hitting the ring at about 12 o'clock. One dust lane is "coming in from the lower left", and the other is "coming in from the upper right".

In this post, you can very clearly see the two dust lanes feeding gas and dust into the nuclear ring of NGC 1512.

What happens in the nuclear ring is that gas is being fed and compressed from two directions, fuelling star birth. Why doesn't the gas fall straight into the black hole that is certainly there at the center of any large galaxy? All I can say is that in any stable feature, such as a nuclear ring, the material that makes it up must be in orbit around the massive central object. That is what is happening in the Solar system, after all: the Earth isn't falling into the Sun, and neither is any of the other planets, because we are all orbiting the Sun. In the case of the nuclear rings of galaxies, new gas being fed into the ring is captured by the ring and prevented from falling (straight) into the black hole. I'm not saying that some of the gas might not wind up there eventually!


Finally, take a look at two barred spiral galaxies that have run out of gas. One of them, NGC 4314, still has a little bit of gas near its center, and it still has two short dust lanes leading gas into its nuclear ring, fuelling fresh star birth there and creating one single splash of color in the entire galaxy. But NGC 936 has run out of gas altogether, leaving the galaxy "red and dead".



You can still recognize the major features of these two galaxies. There is a bright round central object where a huge number of stars are in orbit around a black hole. You can clearly see the bar of both galaxies, and you can make out the outer ring outside the bar. In NGC 4314, you can see two long elegant but "dead" (non-starforming) spiral arms. In NGC 936, every trace of spiral arms is gone, and there is only a featureless disk.

Why are the main features of the two galaxies (apart form the nuclear ring of NGC 4314) not the same color, if they are both made up of old stars? It is because they have been photographed through different filters and the images have been processed and mapped differently. Both galaxies are completely dominated by old stars, but there is still a little gasp of gas and blue fire left in NGC 4314.

Ann

sillyworm 2 wrote: ↑Thu May 30, 2019 12:00 am I am also curious..is the inner ring perpendicular to the bar? Like a napkin ring?

You are at least half right. The nuclear ring does seem to be inclined to the outer ring, which appears to be almost perfectly face on.

Ann