APOD: A View Toward M106 (2017 Jul 07)

[APOD Robot]

A View Toward M106

Explanation: Big, bright, beautiful spiral, Messier 106 dominates this cosmic vista. The two degree wide telescopic field of view looks toward the well-trained constellation Canes Venatici, near the handle of the Big Dipper. Also known as NGC 4258, M106 is about 80,000 light-years across and 23.5 million light-years away, the largest member of the Canes II galaxy group. For a far away galaxy, the distance to M106 is well-known in part because it can be directly measured by tracking this galaxy's remarkable maser, or microwave laser emission. Very rare but naturally occuring, the maser emission is produced by water molecules in molecular clouds orbiting its active galactic nucleus. Another prominent spiral galaxy on the scene, viewed nearly edge-on, is NGC 4217 below and right of M106. The distance to NGC 4217 is much less well-known, estimated to be about 60 million light-years.

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[Boomer12k]

Great looking image...

:---[===] *

[Ann]

I'm always glad to see a galaxy image as the APOD, and today's widefield portrait of M106 is fine and interesting!

I would have liked to know more about the image itself, how it was made, but I couldn't find out. The link, telescopic field of view, leads to Facebook, and since I don't have Facebook, I'm not allowed to read it. So I'm going to have to guess.

I think that today's APOD is an RGB image, made from individual exposures through red, green and blue filters.

Click to view full size image

M106 with an extra pair of arms, reddish in color and made of ionized gas.
Photo: R Jay GaBany.

It seems clear that no Hα filter has been used for the APOD. Such a filter would have highlighted pink emission nebulas in M106, sites of recent and ongoing star formation. We may also have been able to see the "extra pair of arms" of M106, arms purely made of gas, energized by the active black hole of M106.

I have to wonder if the "extra arms" of M16 are in any way similar to the reddish filaments of active spiral galaxy M77 or the even more prominent reddish filaments of active elliptical galaxy NGC 1275.

Click to view full size image

The Orion Nebula. Its reddish color is impossible to see through a telescope.
Photo: Bill Schoening, KPNO 4m telescope.

A picture like today's APOD gives a "true" portrait of M106 and its neighbors. This is what the galaxy would look like to our eyes, if we retained the same "relative color vision" but had eyes that were many times more sensitive to light and color than they actually are. If our "relative color vision" remained the same, but got sharper, we wouldn't see the reddish filaments of M106. They are too faint, compared with the starlight of M106, and our eyes are comparatively insensitive to their red light.

Today's APOD is a reminder of the fact that a lot of modern astrophotography shows us details that our eyes could never see. It is in fact humanly impossible to see the pink color of emission nebulas with our eyes, because our eyes are too insensitive to their deep red light. Today's APOD is an idealized version of the "visible universe" to us.

Finally, note the one blue object in the picture, a star near small-looking galaxy NGC 4217 at 5 o'clock. The blue star is HD 106420, a B8V star with a color index as blue as -0.125 ± 0.013. The absence of any other strikingly blue objects in the field is a reminder how rare these blue stars really are - and in reality they are a lot rarer than a picture can show us, because these blue-hot stars are typically bright and conspicuous. By contrast, there are lots and lots of small red and yellow stars that are too faint for us to notice.

Ann

[Péter Feltóti]

Dear Ann!

Thank you for writting such a detailed post about my image. I'm happy that you are interested in the details of makeing it. It was made by a guided 200/800 Newton scope and a DSLR modified camera, wich means that only the IR filter is changed to a wider one in order to be sensitive to H alpha emission. Since the camera has bayer mask, there were no separate color filter images, but indeed it is a pure RGB image. By the way, 204 pieces of 5 minute individual raw images had been stacked to eliminate noise.
Also I appreciate that you very well summareized my motivation in astrophotography: to give an idealized or "true" vision of our Univerze.

If you have questions, feel free to ask.

Thank you

[MikeODay]

Congratulations Peter and very well deserved. This is a lovely clean and natural looking image that, as well as the beautifully rendered main targets, reveals more and more as one zooms in to see the multitudes of 'tiny' galaxies and colourful stars in this rich region of the sky. Well done.

[Chris Peterson]

Today's APOD is a reminder of the fact that a lot of modern astrophotography shows us details that our eyes could never see. It is in fact humanly impossible to see the pink color of emission nebulas with our eyes, because our eyes are too insensitive to their deep red light.

"Impossible" may be a bit extreme. In fact, there are credible reports by experienced observers of visually detecting the red of Ha in a few bright sources like the Orion nebula.

All the same, it's certainly true that even the simplest imaging equipment (a point-and-shoot camera with an exposure of a few seconds) will show far more than our eyes are capable of seeing.

[neufer]

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[b][color=#0000FF]In this composite image of spiral galaxy M106 (NGC 4258), optical data from the Digitized Sky Survey is shown as yellow, radio data from the Very Large Array appears as purple, X-ray data from Chandra is coded blue, and infrared data from the Spitzer Space Telescope appears red. Two anomalous arms, which aren't visible at optical wavelengths, appear as purple and blue emission.[/color][/b]

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Amateur astronomer Robert Gendler retrieved archival Hubble images of M 106 to assemble a mosaic of the centre of the galaxy. He then used his own and fellow astrophotographer Jay GaBany’s observations of M 106 to combine with the Hubble data in areas where there was less coverage, and finally, to fill in the holes and gaps where no Hubble data existed. The centre of the galaxy is composed almost entirely of Hubble data taken by the Advanced Camera for Surveys, Wide Field Camera 3, and Wide Field and Planetary Camera 2 detectors. The outer spiral arms are predominantly HST data colourised with ground-based data taken by Gendler’s and GaBany’s 12.5-inch and 20-inch telescopes, located in New Mexico.

<<Messier 106 is one of the brightest and nearest spiral galaxies to our own. Despite its appearance, which looks much like countless other galaxies, Messier 106 hides a number of secrets. At its heart, as in most spiral galaxies, is a supermassive black hole, but this one is particularly active. Unlike the black hole at the centre of the Milky Way, which pulls in wisps of gas only occasionally, Messier 106’s black hole is actively gobbling up material. As the gas spirals towards the [1.6 AU wide] black hole, it heats up and emits powerful radiation. Part of the emission [within one light year of the black hole] is produced by a process that is somewhat similar to that in a laser - although here the process produces bright microwave radiation. As well as this microwave emission from Messier 106’s heart, the galaxy has another startling feature - instead of two spiral arms, it appears to have four. Although the second pair of arms can be seen in visible light images as ghostly wisps of gas they are even more prominent in observations made outside of the visible spectrum, such as those using X-ray or radio waves. Unlike the normal arms, these two extra arms are made up of hot gas rather than stars, and their origin remained unexplained until recently. Astronomers think that these, like the microwave emission from the galactic centre, are caused by the black hole at Messier 106’s heart, and so are a totally different phenomenon from the galaxy’s normal, star-filled arms. The extra arms appear to be an indirect result of jets of material produced by the violent churning of matter around the black hole. As these jets travel through the galactic matter they disrupt and heat up the surrounding gas, which in turn excites the denser gas in the galactic plane and causes it to glow brightly. This denser gas closer to the centre of the galaxy is tightly-bound, and so the arms appear to be straight. However, the looser disc gas further out is blown above or below the disc in the opposite direction from the jet, so that the gas curves out of the disc — producing the arching red arms seen here. Despite carrying his name, Messier 106 was neither discovered nor catalogued by the renowned 18th century astronomer Charles Messier. Discovered by his assistant, Pierre Méchain, the galaxy was never added to the catalogue in his lifetime. Along with six other objects discovered but not logged by the pair, Messier 106 was posthumously added to the Messier catalogue in the 20th century.

Lasers work when light stimulates emission of more light from a cloud of excited gas, with the original light in effect being amplified (the word laser is an acronym for light amplification by the stimulated emission of radiation). The centre of M106 harbours a similar phenomenon called a maser (short for microwave amplification by the stimulated emission of radiation), in which microwave radiation, which is at longer wavelengths than visible light, is emitted. Note that unlike man-made lasers, which are designed to produce a narrow beam, astronomical masers shine in all directions.>>

[Ferran_Bosch]

Should be full of IFN....in fact it is appreciated quite well....

[MarkBour]

... Finally, note the one blue object in the picture, a star near small-looking galaxy NGC 4217 at 5 o'clock. The blue star is HD 106420, a B8V star with a color index as blue as -0.125 ± 0.013. The absence of any other strikingly blue objects in the field is a reminder how rare these blue stars really are ... Ann

Thanks for pointing that out. I really like the contrast there among the three stars that are visually near each other. They appear white(ish), red, and blue to my eye.

But it appears to me that there are also some serious blue patches in M106 in the image as well (?)

The link in the "Image Credit" goes to a blog of Mr. Feltoti's, which is very nice (and has some of the data).

[Ann]

... Finally, note the one blue object in the picture, a star near small-looking galaxy NGC 4217 at 5 o'clock. The blue star is HD 106420, a B8V star with a color index as blue as -0.125 ± 0.013. The absence of any other strikingly blue objects in the field is a reminder how rare these blue stars really are ... Ann

Thanks for pointing that out. I really like the contrast there among the three stars that are visually near each other. They appear white(ish), red, and blue to my eye.

I should have pointed out the very orange star next to the blue one, too. Just like the blue star, the orange one is unique in the field because of its color. My software has very little information about it, but I would guess, because of its color, that it is a M-type giant. M-type stars are not always very much more orange than the common-as-dirt early K-type giants, but they are very much more infrared. Peter Feltoti mentioned an IR filter in his reply to me, which is why I think that the orange star is an infrared-bright M-type giant. These stars are quite rare. M-type dwarfs are terribly common, but they are so faint that they will not show up in the field of any "normal" galaxy image (unless a nearby one happens to position itself right next to a galaxy imaged by Hubble).

I should point out that the orange star in the field of M106 might be a K5III star, similar to Aldebaran, rather than a M-type giant. They are (very) orange in color, but not at all as infrared as M-type giants.

But it appears to me that there are also some serious blue patches in M106 in the image as well (?)

Click to view full size image

M100 with blue star formation in dust lanes. Photo: Salvatore Grasso.

Oh, sure! But here we're seeing star formation in dust lanes in M106. That is a very common phenomenon in spiral galaxies - indeed, you will be hard pressed to find to find any bona fide spiral galaxy that doesn't have any blue patches at all in any of its dust lanes.

Click to view full size image

B-type stars of the Sco-Cen association.
Photo: Akira Fuji.

The stars that color (some) dust lanes blue are (relatively) numerous and typically much brighter than the surrounding stars. Take a look at the picture at right, which shows the Sco-Cen association of young stars. As you can see, the field is dominated by blue stars. Most of them are about 400 light-years away, and almost all of them are B-type stars. The brightest of them are up to 3,000 times as bright as the Sun in visual light. Seen from space, their combined light would form a "blue patch". (Note one orange star at lower right. That is Gacrux of constellation Crux, and it is, interestingly, an M-type giant. It does not belong to the Sco-Cen association, because it is only 90 light-years away. Also note a really bright white star at six o'clock. That is the most nearby star of them all from our vantage point, Alpha Centauri, four light-years away!)

The link in the "Image Credit" goes to a blog of Mr. Feltoti's, which is very nice (and has some of the data).

Thanks, I'll check it out!

Ann

[MarkBour]

And thank you, Ann, for the additional guidance!