APOD: Messier 106 (2011 Mar 19)

[APOD Robot]

Messier 106

Explanation: Close to the Great Bear (Ursa Major) and surrounded by the stars of the Hunting Dogs (Canes Venatici), this celestial wonder was discovered in 1781 by the metric French astronomer Pierre Mechain. Later, it was added to the catalog of his friend and colleague Charles Messier as M106. Modern deep telescopic views reveal it to be an island universe -- a spiral galaxy around 30 thousand light-years across located only about 21 million light-years beyond the stars of the Milky Way. Along with a bright central core, this colorful composite image highlights youthful blue star clusters and reddish stellar nurseries tracing the galaxy's spiral arms. It also shows off remarkable reddish jets of glowing hydrogen gas. In addition to small companion galaxy NGC 4248 (bottom right) background galaxies can be found scattered throughout the frame. M106 (aka NGC 4258) is a nearby example of the Seyfert class of active galaxies, seen across the spectrum from radio to x-rays. Active galaxies are believed to be powered by matter falling into a massive central black hole.

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[Beyond]

WOW! A Galaxy that lives up to It's name. It sure looks Great in the colorful composit image. I give it two thumbs up! It's all i have.

[B]

the reddish jets of hydrogen gas appear to be falling into galaxy core above and below plain of galaxy. what this may mean is that more than one spiral orientation is involved - secondary spiral structures consisting of molecular gas and dust can form on a different plain due to intense gravitation attraction by galaxy core.

[mexhunter]

WOW!!! excellent work of R. Jay Gabany.
Greetings
César

[Axel]

the reddish jets of hydrogen gas appear to be falling into galaxy core above and below plain of galaxy. what this may mean is that more than one spiral orientation is involved - secondary spiral structures consisting of molecular gas and dust can form on a different plain due to intense gravitation attraction by galaxy core.

If you look at the multiple-wavelength image of M106 in Wikipedia you can see that different orientations are involved.

[Axel]

The red spiral arms (said to contain stellar nurseries) seem to be evenly spaced. There are three and they seem roughly 1/3rd of a circle apart. Is this so?

[biddie67]

Are black holes considered to have one "entry port" for pulling matter in or more than one entry port?

Could there be an "exit port" for "waste" or excess energy?

Could the direction of matter being pulled into a black hole affect the direction of rotation of the galaxy's spiral arms or vice-versa?

[Chris Peterson]

Are black holes considered to have one "entry port" for pulling matter in or more than one entry port?

Could there be an "exit port" for "waste" or excess energy?

Nothing exits a black hole, and generally, very little enters.

Could the direction of matter being pulled into a black hole affect the direction of rotation of the galaxy's spiral arms or vice-versa?

No. The central black hole of a galaxy has little gravitational effect on the galaxy as a whole. That's because it has a mass of only a few million suns, while the central stellar mass of a typical spiral galaxy is hundreds of millions or billions of suns. Dynamically, the galaxy will behave the same whether or not there is a central black hole.

[Axel]

The red spiral arms (said to contain stellar nurseries) seem to be evenly spaced. There are three and they seem roughly 1/3rd of a circle apart. Is this so?

I meant three main red arms. I know it's not a perfectly neat picture, but the trend seems clear enough. And besides whether it's true for M106, I wonder if this is often observed.

[Ann]

The red spiral arms (said to contain stellar nurseries) seem to be evenly spaced. There are three and they seem roughly 1/3rd of a circle apart. Is this so?

I meant three main red arms. I know it's not a perfectly neat picture, but the trend seems clear enough. And besides whether it's true for M106, I wonder if this is often observed.

I'm not exactly sure what you mean by three red arms.

Please note that the red color of hydrogen alpha emission has been enhanced in today's beautiful image of M106. 900 minutes of H-alpha exposure went into the making of the image, whereas the normal Red, Green and Blue exposures only got 740 minutes put together. Therefore the H-alpha emitting red nebulae look very bright in this image, and they seem to dominate much of the inner part of the galaxy. If there had been no H-alpha exposure at all, the arms would only have displayed small patches of red nebulae, and the hydrogen alpha jets emanating from the center of the galaxy would have been barely visible.

What this means is that M106 doesn't have three red arms. Personally I would describe it as a galaxy with two starforming rings, an inner, incomplete ring of star formation and an outer, more complete ring. The galaxy also has two jets of ionized red hydrogen gas emanating from its center. These jets don't contain any star formation.

I would compare M106 with M82, which is violently emitting ionized red hydrogen gas from its center:

Click to view full size image

M82 is expelling much more hydrogen from its center than M106 is doing, so the galaxies are not fully comparable. Also the causes of the outflows are probably different, since the jets of M106 appear to be driven by the galaxy's central black hole, whereas in M82's case the outflows appear to be caused by a central starburst. In both cases, however, the red gas streaming out of the galactic centers doesn't contain any star formation.

As for galaxies having three starforming arms, the only example I can think of off hand is Messier 99. Here is an image which was made without any special H-alpha exposure, and the emission nebulae look quite pale: http://www.robgendlerastropics.com/M99JM.jpg

Please note, however, that M99 contains much more star formation and many more and larger emission nebulae than M106.

Ann

[knight]

Sorry guys. This is far too extreme colorized. I don't like it.

[Chris Peterson]

Please note that the red color of hydrogen alpha emission has been enhanced in today's beautiful image of M106. 900 minutes of H-alpha exposure went into the making of the image, whereas the normal Red, Green and Blue exposures only got 740 minutes put together. Therefore the H-alpha emitting red nebulae look very bright in this image, and they seem to dominate much of the inner part of the galaxy.

This is partly true, but you need to be careful when comparing exposures with narrow band filters.

The Ha filter used has a 5nm pass band; the red filter has a 60nm pass band. So the red channel contains more than three times the signal of the Ha channel, even with the latter's longer exposure (probably more, given the spectral response of the CCD). And of course, the red channel also contains a good deal of the Ha signal itself. Certainly the Ha regions are enhanced by including the Ha filtered data, but not as much as the exposure time alone might suggest. The enhancement is largely a matter of processing; a much shorter Ha exposure would have given a similar image, but the noise in that channel would have been higher, making it less aesthetic.

Because narrow band filters reject so much of the total light, very long exposures are always required simply to provided good S/N. A galaxy like this is much brighter in continuum energy than in atomic emissions, which is actually why you don't see nearly as much Ha in an ordinary RGB image. Not because you haven't collected it, but because it is washed out by the continuum.

[orin stepanek]

Sorry guys. This is far too extreme colorized. I don't like it.

Art wise I don't like it either; but information wise it makes a point about star formation. Artistically I do like this rendering better.

Click to view full size image

[garry]

In the APOD we are told that "active galaxies are powered by black holes" If they are then why is a galaxy a flat disk? Then in a reply by Chris we are told they are not needed. So, who is right? How can you tell if a galaxy has a black hole or not?
What about rotation? Clockwise or anti clockwise? We really don't know very much do we?

[Chris Peterson]

In the APOD we are told that "active galaxies are powered by black holes" If they are then why is a galaxy a flat disk?

Not all galaxies are flat discs. But a disc is a natural state for a high angular momentum system to evolve into.

Then in a reply by Chris we are told they are not needed.

What isn't needed?

How can you tell if a galaxy has a black hole or not?

You can't, always. In a few cases with fairly close galaxies, it is possible to observe the orbital characteristics of stars at the very center (and we can do this with our own galaxy, too). Otherwise, the presence of a central black hole is generally inferred in the case of active galaxies, where you have jets or some sort of high energy emissions.

What about rotation? Clockwise or anti clockwise? We really don't know very much do we?

I think we know quite a lot. But what about rotation? Certainly, the direction of rotation is physically meaningless, since it is determined only by the direction we happen to view it from.

[jgabany]

The red spiral arms (said to contain stellar nurseries) seem to be evenly spaced. There are three and they seem roughly 1/3rd of a circle apart. Is this so?

I meant three main red arms. I know it's not a perfectly neat picture, but the trend seems clear enough. And besides whether it's true for M106, I wonder if this is often observed.

Hello Axel:

The red structures expanding from the center of this galaxy aren't spiral arms. These structures were formed by high energy jets emanating from M106's active 40 million solar mass central super-massive black hole.

Instead of being oriented at right angle to the plane of M106, the black hole's jets are tilted at a low inclination causing them to pierce the galaxy's disk and surrounding halo.

As the jets pass through regions of dust and gas, they create an expanding cocoon of shock waves that heats the surrounding material causing it to release radiation in optical wavelengths. So, the image does not depict the jets, themselves, because they are not visible in optical wavelengths. Instead, the picture displays the shock waves created by the jets. This is similar to seeing foot prints left in snow.

The curvature and fraying seen at the extremities of the shock wave features represents previous trajectories of the jet due to past precession. Precession is a change in the orientation of the rotation axis of a spinning object. For example, the wobble of a spinning top.

I hope this makes sense.

Jay