Starship Asterisk*

M106: A Spiral Galaxy with a Strange Center

Explanation: What's happening at the center of spiral galaxy M106? A swirling disk of stars and gas, M106's appearance is dominated by blue spiral arms and red dust lanes near the nucleus, as shown in the featured image. The core of M106 glows brightly in radio waves and X-rays where twin jets have been found running the length of the galaxy. An unusual central glow makes M106 one of the closest examples of the Seyfert class of galaxies, where vast amounts of glowing gas are thought to be falling into a central massive black hole. M106, also designated NGC 4258, is a relatively close 23.5 million light years away, spans 60 thousand light years across, and can be seen with a small telescope towards the constellation of the Hunting Dogs (Canes Venatici).

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

APOD Robot wrote:
M106's appearance is dominated by blue spiral arms and red dust lanes near the nucleus, as shown in the featured image.

The most interesting red features of this galaxy are not the red dust lanes. Rather, they are the jets emanating from close to the center of the galaxy. These jets are twisting, as if they were caught in in a maelstrom of forces, including magnetic ones.

Great image! I love to see all this RGB detail.

Ann

Ann wrote:

APOD Robot wrote:
M106's appearance is dominated by blue spiral arms and red dust lanes near the nucleus, as shown in the featured image.

The most interesting red features of this galaxy are not the red dust lanes. Rather, they are the jets emanating from close to the center of the galaxy. These jets are twisting, as if they were caught in in a maelstrom of forces, including magnetic ones.

Great image! I love to see all this RGB detail.

Ann

Even better is RGB+Ha, which shows the jets/ionized outflow even better! Check this image by R. Jay GaBany. Quite a few other galaxies exhibit nuclear ionized outflow structures such as NGC 3077, NGC 5253 and NGC 5102 to name a few.

Why can't we zoom in closer and see more detail around the 'black hole'?

I have a question about the image. The three large and highly visible stars to the left and lower of the spiral galaxy, each have four reflective rays emanating from them. What causes those rays to be multi-colored? Is that caused by the light of the stars passing thru different gases and do all stars have the same gases surrounding them?

captainwiggins48 wrote:Why can't we zoom in closer and see more detail around the 'black hole'?

At the highest optical resolutions we are capable of, we still can't resolve anything in this galaxy to better than about 10 lightyears or so, and most of what's going on is probably in a smaller region than that.

Dan wrote:I have a question about the image. The three large and highly visible stars to the left and lower of the spiral galaxy, each have four reflective rays emanating from them. What causes those rays to be multi-colored? Is that caused by the light of the stars passing thru different gases and do all stars have the same gases surrounding them?

Those are likely to be diffraction spikes caused by the four arms supporting the secondary mirror in the telescope - they are artifacts of the telescope, not actual 'things'.

APOD should offer these pictures for sale and make it easy with a click on the daily APOD picture to order it.

LonA wrote:APOD should offer these pictures for sale and make it easy with a click on the daily APOD picture to order it.

One of the good things about APOD is that it has no ads and is not commercialized.

But even if this were attempted, it would be an impossible maze of copyright issues and sorting out where the money goes. A lot of people would simply not participate.

Awesome , clear shot... I wonder how many mergers....

:---[===] *

At full magnification, the picture has a number of (mostly vertical) faint streaks running through it. Does anyone know what these are?

Dan wrote:I have a question about the image. The three large and highly visible stars to the left and lower of the spiral galaxy, each have four reflective rays emanating from them. What causes those rays to be multi-colored? Is that caused by the light of the stars passing thru different gases and do all stars have the same gases surrounding them?

Those are diffraction spikes, caused by the absence of light blocked by anything in the telescope's beam - most often, supporting arms for the secondary mirror. 4-part supports are most common, hence the familiar 4-sided pattern (whose orientation reflects the telescope orientation during the imaging observations); in contrast, images from the Keck telescopes show a hexagonal pattern, and refracting telescopes do not show them at all. Noting the color behavior is more subtle - the diffraction phenomenon is wavelength-dependent and comes in multiple orders, each more spread out than the previous one. Some of these stars are bright enough to show many; the radial location of each color around each star matches, but brighter stars show more orders.

Occasionally observers use this effect deliberately; I've seen pictures of the faint companion of Sirius where diffraction spikes were added by putting a mask in front of the telescope aperture, moving the scattered light away from the faint companion; and also seen images taken with a coarse wire grating that created diffraction spikes broken into short segments, allowing a mean position even for stars whose main images were too saturated for accurate measurements. Sometimes one see composite images whose components were obtained with different telescope orientations, so the spikes in each filter are at different angles (Here is an example from Hubble data).

Which image is a mirror and which is real?

The text description for today's picture (2015/02/16) at http://apod.nasa.gov/apod/ap150216.html contains a link to an earlier image of M106 at http://apod.nasa.gov/apod/ap150216.html presented on APOD on 2013/10/03. However, these two versions are mirror images. In today's image , the arms spiral out from center to the left, while the earlier image shows the arms spiraling out to the right.

Assuming that we haven't traveled to the other side of M106 yet and couldn't have taken a picture from there, which image is correct?

EveningStarNM wrote:Assuming that we haven't traveled to the other side of M106 yet and couldn't have taken a picture from there, which image is correct?

Today's is unmirrored.

geckzilla wrote:Today's is unmirrored.

Thank you, geck

NGC3314 wrote: . . . diffraction spikes . . .

Occasionally observers use this effect deliberately; I've seen pictures of the faint companion of Sirius where diffraction spikes were added by putting a mask in front of the telescope aperture, moving the scattered light away from the faint companion; and also seen images taken with a coarse wire grating that created diffraction spikes broken into short segments, allowing a mean position even for stars whose main images were too saturated for accurate measurements. . . .

Thanks, NGC3314. Your brief description here indicates that the diffraction spikes have been used purposefully to improve position measurements. Are diffraction spikes sometimes useful data in other ways? I note that for the large examples here, you can see that the colors in the spikes correspond to the colors of the stars. They are, after all, light from those same stars, spread out a bit. I suppose the beam of the scope may be altering them somewhat, but do they provide any sort of "quick-and-dirty" spectral breakout of the star's light that is useful?

MarkBour wrote:Thanks, NGC3314. Your brief description here indicates that the diffraction spikes have been used purposefully to improve position measurements. Are diffraction spikes sometimes useful data in other ways? I note that for the large examples here, you can see that the colors in the spikes correspond to the colors of the stars. They are, after all, light from those same stars, spread out a bit. I suppose the beam of the scope may be altering them somewhat, but do they provide any sort of "quick-and-dirty" spectral breakout of the star's light that is useful?

I think they mostly just get in the way. Want to look at a planet or a debris disk? Too bad! But if you create a model of the point spread function and then subtract that out of the image you might see something. That's what's happening in this picture. You can see all the black stuff in there where the star used to be. The disks were almost completely hidden before.
(I wasn't going to butt in but I can't help it. I find this topic strangely enjoyable.)

geckzilla wrote:I think they mostly just get in the way. Want to look at a planet or a debris disk? Too bad! But if you create a model of the point spread function and then subtract that out of the image you might see something. That's what's happening in this picture. You can see all the black stuff in there where the star used to be. The disks were almost completely hidden before.
(I wasn't going to butt in but I can't help it. I find this topic strangely enjoyable.)

You can't actually subtract a PSF. The PSF describes what the entire optical system does to a perfect point source. But every point in an extended object generates its own copy of the PSF, and these all overlap in a way that is mathematically impossible to separate. The optical system is a filter, and you can't build an inverse filter. But you can do a clever cheat. If you know something about what the original object might look like, you can essentially make an educated guess and create a synthetic image. Then you apply the PSF to that, and see if you get something that looks like your actual image. Based on the discrepancies, you keep adjusting your input guess until they match. At that point, you have one possible image of what the actual object looks like without the distortions introduced by the optical system. In fact, there are an infinite number of possible solutions, but clever algorithms let us converge on a solution with a high probability of being a good match (but sometimes you get totally bogus results, so care must be taken).

Chris Peterson wrote:You can't actually subtract a PSF. ... In fact, there are an infinite number of possible solutions, but clever algorithms let us converge on a solution with a high probability of being a good match (but sometimes you get totally bogus results, so care must be taken).

Yes, I'm just talking about modeling it for a single source in an image. The folks at STScI even have a handy web-based modeler you can use.
http://www.stsci.edu/hst/observatory/focus/TinyTim

(It's for Hubble, anyway. They've got a preliminary JWST one up too, iirc)