APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 3550
Joined: Fri Dec 04, 2009 3:27 am

APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by APOD Robot » Sun Feb 21, 2016 5:11 am

Image M82: Galaxy with a Supergalactic Wind

Explanation: What's lighting up the Cigar Galaxy? M82, as this irregular galaxy is also known, was stirred up by a recent pass near large spiral galaxy M81. This doesn't fully explain the source of the red-glowing outwardly expanding gas, however. Evidence indicates that this gas is being driven out by the combined emerging particle winds of many stars, together creating a galactic superwind. The featured photographic mosaic highlights a specific color of red light strongly emitted by ionized hydrogen gas, showing detailed filaments of this gas. The filaments extend for over 10,000 light years. The 12-million light-year distant Cigar Galaxy is the brightest galaxy in the sky in infrared light, and can be seen in visible light with a small telescope towards the constellation of the Great Bear (Ursa Major).

<< Previous APOD This Day in APOD Next APOD >>
[/b]

User avatar
Ann
4725 Å
Posts: 9519
Joined: Sat May 29, 2010 5:33 am

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Ann » Sun Feb 21, 2016 5:47 am

The central region of the nearby Cigar Galaxy.
Credit: Josh Marvil (NM Tech/NRAO), Bill Saxton (NRAO/AUI/NSF), NASA
The galactic superwind of M82 is certainly fascinating. Personally I'm even more fascinated by the central starburst that causes the galactic superwind. The picture at left is my favorite portrait of this starburst. It is a radio image, made with the Karl G. Jansky Very Large Array (VLA). The bright white sources are both newborn stars, massive mature stars blowing ferocious winds, and supernova remnants.

Ann
Color Commentator

antibius
Asternaut
Posts: 1
Joined: Sun Feb 21, 2016 7:07 pm

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by antibius » Sun Feb 21, 2016 7:23 pm

Suspect that the 'red expanding gas' is the remnants of a phenomenon within our own galaxy. What has atronomers thinking that it eminates from M82 and not simply in viewing line.

User avatar
Ann
4725 Å
Posts: 9519
Joined: Sat May 29, 2010 5:33 am

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Ann » Sun Feb 21, 2016 7:36 pm

antibius wrote:Suspect that the 'red expanding gas' is the remnants of a phenomenon within our own galaxy. What has atronomers thinking that it eminates from M82 and not simply in viewing line.
M81 and M82.
Photo: André van der Hoeven, Neil Fleming, Michael van Doorn.
The ionized and therefore red hydrogen gas most definitely emanates from M82, as this widefield image makes abundantly clear.

My previous post shows the central starburst of M82. It is this starburst, which has produced large numbers of massive stars with strong stellar winds, as well as very many central supernovas that pack enormous kinetic energy, that drives gas out of M82 at its poles and ionizes it.

The red gas of M82 has nothing whatsoever to do with our own galaxy.

Ann
Color Commentator

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15976
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by neufer » Sun Feb 21, 2016 10:06 pm

Suspect that the 'red expanding fluid' is the remnants of a phenomenon within a Sam Peckinpah movie.
Art Neuendorffer

User avatar
Chris Peterson
Abominable Snowman
Posts: 14362
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Chris Peterson » Mon Feb 22, 2016 1:02 am

antibius wrote:Suspect that the 'red expanding gas' is the remnants of a phenomenon within our own galaxy. What has atronomers thinking that it eminates from M82 and not simply in viewing line.
The red gas is ionized hydrogen. Ionizing it requires an energy source. If this were a local phenomenon, we'd see one or more hot stars doing that (as we do in many nebula). No stars here; the galaxy is the only plausible source of ionizing radiation.

Also, given that this is an unusual phenomenon, we can be pretty sure that it has been examined spectroscopically, in part to determine the speed of the material. That means that the average redshift of the gas will have been compared with the redshift of M82 (which is quite high for a nearby galaxy). If the two were different, as we'd expect if they were unrelated, that would be known and in need of explaining.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
MarkBour
Subtle Signal
Posts: 894
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by MarkBour » Mon Feb 22, 2016 1:45 am

neufer wrote:Suspect that the 'red expanding fluid' is the remnants of a phenomenon within a Sam Peckinpah movie.
WildBunchAd.jpg
Seriously, though, the APOD image is beautifully revealing. And thanks for the added info and images, Ann.

Would it be reasonable to think this intense starburst region is caused by the same overall phenomenon that was discussed here with another recent APOD ... that M82 is a smaller galaxy with a good stock of gas that had not yet been "used", and the larger M81 galaxy's gravitational interaction with it ignited this starburst?
You do not have the required permissions to view the files attached to this post.
Mark Goldfain

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15976
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by neufer » Mon Feb 22, 2016 4:15 am

MarkBour wrote:
Would it be reasonable to think this intense starburst region is caused by the same overall phenomenon that was discussed here with another recent APOD ... that M82 is a smaller galaxy with a good stock of gas that had not yet been "used", and the larger M81 galaxy's gravitational interaction with it ignited this starburst?
  • A tidal interaction that came too late and stayed too long :?:
https://en.wikipedia.org/wiki/Messier_82 wrote:
<<Recently, M82 has undergone at least one tidal encounter with M81 resulting in a large amount of gas being funneled into the galaxy's core over the last 200 Myr. The most recent such encounter is thought to have happened around 200-500 Myr ago and resulted in a concentrated starburst together with a corresponding marked peak in the cluster age distribution.

Oddly enough, stars in M82's disk seem to have been formed in a burst 500 million years ago, leaving its disk littered with hundreds of clusters with properties similar to globular clusters (but younger), and stopped 100 million years ago with no star formation taking place in this galaxy outside the central starburst and, at low levels since 1 billion years ago, on its halo. A suggestion to explain those features is that M82 was previously a low surface brightness galaxy where star formation was triggered due to interactions with its giant neighbor.

A low-surface-brightness galaxy, or LSB galaxy, is a diffuse galaxy with a surface brightness that, when viewed from Earth, is at least one magnitude lower than the ambient night sky. Most LSBs are dwarf galaxies, and most of their baryonic matter is in the form of neutral gaseous hydrogen, rather than stars. They appear to have over 95% of their mass as non-baryonic dark matter. There appears to be no supernova activity in these galaxies.

In comparison to the more well-studied high-surface-brightness galaxies, LSBs are mainly isolated field galaxies, found in regions devoid of other galaxies. In their past, they had fewer tidal interactions or mergers with other galaxies, which could have triggered enhanced star formation. This is an explanation for the small stellar content.>>
Art Neuendorffer

User avatar
Ann
4725 Å
Posts: 9519
Joined: Sat May 29, 2010 5:33 am

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Ann » Mon Feb 22, 2016 6:37 am

MarkBour wrote:
Would it be reasonable to think this intense starburst region is caused by the same overall phenomenon that was discussed here with another recent APOD ... that M82 is a smaller galaxy with a good stock of gas that had not yet been "used", and the larger M81 galaxy's gravitational interaction with it ignited this starburst?
Interesting question, Mark.

As the quote Neufer inserted in his post shows, M82 is believed to have been a low surface brightness galaxy before it started interacting with its larger neighbour, M81. So yes, M82 would have had a lot of unused gas that could be converted into stars.

I would like to add, however, that I think that much of that gas has now been used up and converted into stars, certainly in the disk of M82.
Wikipedia wrote:
Oddly enough, stars in M82's disk seem to have been formed in a burst 500 million years ago, leaving its disk littered with hundreds of clusters with properties similar to globular clusters (but younger), and stopped 100 million years ago with no star formation taking place in this galaxy outside the central starburst and, at low levels since 1 billion years ago, on its halo.
That massive starburst in the disk of M82 that started 500 million years ago and ended 100 million years ago has left the disk of M82 very bright and somewhat (but not very) bluish in color.
Wikipedia wrote:
M82 was previously believed to be an irregular galaxy. In 2005, however, two symmetric spiral arms were discovered in near-infrared (NIR) images of M82. The arms were detected by subtracting an axisymmetric exponential disk from the NIR images. Even though the arms were detected in NIR images, they are bluer than the disk. The arms were previously missed due to M82's high disk surface brightness
Due to all its recent star formation, M82 is a very bright galaxy for its size and mass.
Wikipedia wrote:
Messier 82 (also known as NGC 3034, Cigar Galaxy or M82) is a starburst galaxy about 12 million light-years away in the constellation Ursa Major and a member of the M81 Group. It is about five times more luminous than the whole Milky Way and has a center one hundred times more luminous than our galaxy's center.
For all its brightness, I believe that M82 is considerably smaller than the Milky Way.
The Casual Sky Observer's Guide wrote:
Although smaller than the Milky Way, M82 is in reality five times as bright.
I see the brightness of M82's disk, coupled with the complete lack of star formation in the disk, as a strong sign that huge amounts of gas has recently been converted into stars in the disk, but that the available gas has now been mostly used up. Alternatively, and perhaps more likely, the available gas in the disk is turbulent and too hot to form stars at present.

There are several examples of galaxies whose disks are devoid of star formation, but star formation can be seen in its center.
Universe Today wrote:
Most galaxies are throughout the universe are happenin’ places, with all sorts of raucous star formation going on. But for a nearby, small spiral galaxy, the star-making party is almost over. In this latest Hubble release, astronomers were surprised to find that star-formation activities in the outer regions of NGC 2976 are fizzling out, and any celebrating is confined to a few die-hard partygoers huddled in the galaxy’s inner region.








I know all about star formation fizzling out in all my outer regions and leaving me with a star forming central migraine, says NGC 4314. M64, the Blackeye Galaxy, agrees.

Ann
Color Commentator

User avatar
MarkBour
Subtle Signal
Posts: 894
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by MarkBour » Mon Feb 22, 2016 6:58 am

Wow, that starburst core of M82 is sooo active, it boggles my mind.
https://en.wikipedia.org/wiki/Messier_82
In 2005, the Hubble Space Telescope revealed 197 young massive clusters in the starburst core. The average mass of these clusters is around 200,000 solar masses, hence the starburst core is a very energetic and high-density environment. Throughout the galaxy's center, young stars are being born 10 times faster than they are inside our entire Milky Way Galaxy.
... supernovae within the clumps which occur at a rate of about one every ten years.
I would vote we re-label it the Exploding Cigar Galaxy.
( https://upload.wikimedia.org/wikipedia/ ... t_1963.jpg )
Mark Goldfain

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15976
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by neufer » Mon Feb 22, 2016 12:48 pm

We three kings, of orient are
trying to smoke a rubber cigar.
It was loaded,
it exploded!
Now we are seeing stars!
Art Neuendorffer

User avatar
Ann
4725 Å
Posts: 9519
Joined: Sat May 29, 2010 5:33 am

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Ann » Mon Feb 22, 2016 8:35 pm

Chris Peterson wrote:
antibius wrote:Suspect that the 'red expanding gas' is the remnants of a phenomenon within our own galaxy. What has atronomers thinking that it eminates from M82 and not simply in viewing line.
The red gas is ionized hydrogen. Ionizing it requires an energy source. If this were a local phenomenon, we'd see one or more hot stars doing that (as we do in many nebula). No stars here; the galaxy is the only plausible source of ionizing radiation.

Also, given that this is an unusual phenomenon, we can be pretty sure that it has been examined spectroscopically, in part to determine the speed of the material. That means that the average redshift of the gas will have been compared with the redshift of M82 (which is quite high for a nearby galaxy). If the two were different, as we'd expect if they were unrelated, that would be known and in need of explaining.
Good points there, Chris.
Starburst dwarf galaxy I Zwicky 18.
Credit: NASA, ESA, and A. Aloisi (ESA & STScI)
But to me, the outflows of M82 are more than unusual. They are not exactly unique, because tiny dwarf galaxy I Zwicky 18 is surrounded by a galaxy-sized nebula of ionized and ejected hydrogen. (Note that the image at left is a false color one: the blue nebula is really red.)

But I Zwicky 18 is so tiny that it isn't really comparable to M82. Note that you can almost count the individual stars of I Zwicky 18, and even more so in its galactic companion, which must be responsible for turning on such a magnificent starburst in I Zwicky 18. M82, on the other hand, is "way bigger than its stars". Take a look at this 1 217,36 KB Hubble image of M82. You can indeed see bright spots in the disk of M82 (those are likely young globular clusters), but mostly the disk is just suffused with a pale aqua-colored featureless glow.
M106. Image credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA),
and R. Gendler (for the Hubble Heritage Team)





There is one other galaxy that has big red outflows of ionized gas, and that is M106.

But again, there is a big difference between M106 and M82. M106 is a much bigger galaxy than M82, and its ionized red gas outflows are much fainter. They are also collimated like jets and seem to turn like water from a sprinkler.

So the nature of the red outflows of M106 is clearly different from the outflows of M82. If the amazing rose-colored explosive gaseous debris emanating from the center of M82 is not unique, it is not not far from being that special.



Ann
Color Commentator

User avatar
Ann
4725 Å
Posts: 9519
Joined: Sat May 29, 2010 5:33 am

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Ann » Tue Feb 23, 2016 9:31 pm

Here is another core starburst galaxy with gaseous and dusty central outflows, NGC 1808.

I love this 1 156,54 KB SSRO image of NGC 1808, too. What I love about it is that its colors are brilliant. You can compare the magenta-pink color of the obvious Ha nebulas in the disk of NGC 1808 with the color of the central outflows and see that the colors are not the same. Rather than being Ha-red, the outflows are dust-orange. So again, this galaxy is not like M82, but it is similar enough to be of interest.

Ann
Color Commentator

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15976
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by neufer » Tue Feb 23, 2016 10:34 pm

Ann wrote:
You can compare the magenta-pink color of the obvious Ha nebulas in the disk of NGC 1808 with the color of the central outflows and see that the colors are not the same. Rather than being Ha-red, the outflows are dust-orange.
https://en.wikipedia.org/wiki/Seyfert_galaxy#Type_1.2.2C_1.5.2C_1.8_and_1.9_Seyfert_galaxies wrote: <<[NGC 1808 is a Seyfert galaxy located in the constellation Columba.] In 1981, Donald Osterbrock introduced the notations Seyfert 1.5, 1.8 and 1.9, where the subclasses are based on the optical appearance of the spectrum, with the numerically larger subclasses having weaker broad-line components relative to the narrow lines. For example, Type 1.9 only shows a broad component in the Hα [656 nm] line, and not in higher order Balmer lines. In Type 1.8, very weak broad lines can be detected in the Hβ [486 nm] lines as well as Hα, even if they are very weak compared to the Hα.

In Type 1.5, the strength of the Hα [656 nm] and Hβ [486 nm] lines are comparable.>>
Art Neuendorffer

User avatar
Ann
4725 Å
Posts: 9519
Joined: Sat May 29, 2010 5:33 am

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Ann » Wed Feb 24, 2016 6:38 am

ESO Messenger wrote:

NGC 1808 is a beautiful spiral galaxy located in the southern sky at a distance of more than 10 Mpc. The peculiarity of its nudear region has first been mentioned by Morgan (1958) who identified numerous, extremely brilliant, smaIl nuclei in the central region which he called "hot spots". A real-color image of this most interesting and unusual central region has been presented in The Messenger by VBron-Cetty & Vbron (1983). This image nicely demonstrates the presence of several very blue 'hot spots", corresponding to bright H I1 regions, and of a reddish nucleus which shows spectroscopic evidence for the presence of Seyfert activity (Vdron-Cetty & VBmn 1985).

An additional peculiarity of this complex central region was noted in 1968 by Burbidge & Burbidge. They found that NGC 1808 "contains an unusual amount of dust [in the disk] and some curious dust lanes which look almost radial in form". These prominent dust filaments which seem to emerge from the nuclear region are best seen on optical short exposures of NGC 1808, e.g., those given by Laustsen et al. (1987) or Tarenghi (1990) In a previous issue of the Messenger. Whereas in 1970 Arp & Bertola already speculated "that these lanes represent the passage of compact bodies outwards from the nucleus", we now have observational evidence that they are indeed connected with the outflow of neutral and ionized gas into the halo of NGC 1808 (Koribalski et at. 1992a, Phillips 1992). Also new is the discovery of a fast rotating torus of cold gas very near to the centre which has been revealed using HI absorption measurements against the extended radio continuum emission (Koribalski et al. 1992b).

The far-infrared (FIR) luminosity of NGC 1808 is with .= 2 101° Lg quite high, similar to NGC 253 and M 82.
I take this to mean that the outflows from the center of NGC 1808 are mostly dusty in character, but they also contain both neutral and ionized gas.

We should also note that NGC 1808 is similar to M82 in its high far infrared brightness, which is again a sign of copious amounts of dust. But while the ouflows of M82 are dominated by Ha, the outflows of NGC 1808 are dominated by dust.

But thank you for providing that interesting bit of info about Seyfert galaxies, Art. NGC 1808 is indeed a Seyfert galaxy, and its outflows are probably affected by what type of Seyfert galaxy it is.

Ann
Color Commentator

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15976
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by neufer » Wed Feb 24, 2016 2:01 pm

Ann wrote:
We should also note that NGC 1808 is similar to M82 in its high far infrared brightness, which is again a sign of copious amounts of dust. But while the ouflows of M82 are dominated by Ha, the outflows of NGC 1808 are dominated by dust.

But thank you for providing that interesting bit of info about Seyfert galaxies, Art. NGC 1808 is indeed a Seyfert galaxy, and its outflows are probably affected by what type of Seyfert galaxy it is.
Dust may indeed account for the primary color difference between the outflows of NGC 1808 & M82.

But I am curious why our blue loving color commentator invariably refers to Balmer line hydrogen purely in terms of the Red Hα [656 nm] line while totally ignoring possible subtle color contributions from higher order Balmer lines such as Blue Hβ [486 nm], Indigo Hγ [434 nm] & Violet H-δ [410 nm].
https://en.wikipedia.org/wiki/Balmer_series wrote: <<The Balmer series is particularly useful in astronomy because the Balmer lines appear in numerous stellar objects due to the abundance of hydrogen in the universe, and therefore are commonly seen and relatively strong compared to lines from other elements.

The spectral classification of stars, which is primarily a determination of surface temperature, is based on the relative strength of spectral lines, and the Balmer series in particular are very important. Other characteristics of a star that can be determined by close analysis of its spectrum include surface gravity (related to physical size) and composition.

Because the Balmer lines are commonly seen in the spectra of various objects, they are often used to determine radial velocities due to doppler shifting of the Balmer lines. This has important uses all over astronomy, from detecting binary stars, exoplanets, compact objects such as neutron stars and black holes (by the motion of hydrogen in accretion disks around them), identifying groups of objects with similar motions and presumably origins (moving groups, star clusters, galaxy clusters, and debris from collisions), determining distances (actually redshifts) of galaxies or quasars, and identifying unfamiliar objects by analysis of their spectrum.

Balmer lines can appear as absorption or emission lines in a spectrum, depending on the nature of the object observed. In stars, the Balmer lines are usually seen in absorption, and they are "strongest" in stars with a surface temperature of about 10,000 kelvin (spectral type A). In the spectra of most spiral and irregular galaxies, AGNs, H II regions and planetary nebulae, the Balmer lines are emission lines.

In stellar spectra, the H-epsilon line (transition 7-2) is often mixed in with another absorption line caused by ionized calcium known by astronomers as "H" (the original designation given by Fraunhofer). That is, H-epsilon's wavelength is quite close to CaH at 396.847 nm, and cannot be resolved in low resolution spectra. The H-zeta line (transition 8-2) is similarly mixed in with a neutral helium line seen in hot stars.>>
Art Neuendorffer

User avatar
Ann
4725 Å
Posts: 9519
Joined: Sat May 29, 2010 5:33 am

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Ann » Wed Feb 24, 2016 9:28 pm

Art wrote:
But I am curious why our blue loving color commentator invariably refers to Balmer line hydrogen purely in terms of the Red Hα [656 nm] line while totally ignoring possible subtle color contributions from higher order Balmer lines such as Blue Hβ [486 nm], Indigo Hγ [434 nm] & Violet H-δ [410 nm].
Good question. The answer is probably that stars are strongly colored to me, and I have seen their colors. My vivid memories of my own perception of star colors, as I observed stars through a telescope, are what I use to judge the truthfulness of the colors of astrophotographies. I judge those images by my own memories, so that I either agree or disagree with what those photographs show me.

But when it comes to nebulas, I have no direct experience of colors in them at all, apart from the Trapezium region of the Orion Nebula, which looked greenish to me. But that's it. I haven't seen color in any other nebulas.

That's why I trust color images when it comes to nebulas. I have looked at great numbers of RGB images, and if I trust their star colors, I also generally trust their nebula colors. In those images where I trust the star colors, normal emission nebulas (like, say, the Lagoon Nebula) invariably look mostly reddish-pink or magenta-colored, sometimes with a touch of violet. (Admittedly their brightest parts should not necessarily look pink, but rather pale yellowish.) Dust-reddened nebulas, like NGC 6357, have had their blue and violet Balmer lines scattered away, and look very red. This 1 897,39 KB image of NGC 3603 and 3576 by Michael Sidonio shows one example of a reddened and one example of a mostly unreddened nebula apparently side by side.

To me, nebulas are colored only in photographs, while stars are colored in real life. I go by the nebula colors I see in photographs where the star colors seem "true". That's why I think of hydrogen emission nebulas as pink or even red.

Ann
Color Commentator

User avatar
geckzilla
Ocular Digitator
Posts: 8964
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by geckzilla » Wed Feb 24, 2016 10:15 pm

Ann wrote:To me, nebulas are colored only in photographs, while stars are colored in real life. I go by the nebula colors I see in photographs where the star colors seem "true". That's why I think of hydrogen emission nebulas as pink or even red.
This theory gets completely blown out of the water when an astrophotographer uses wideband RGB filters so that the stars look natural and then adds an H-alpha filter over the top. Any references you are using that utilize narrowband filters such as the H-alpha filter are going to be strongly biased in the direction of that filter.
Just call me "geck" because "zilla" is like a last name.

User avatar
Ann
4725 Å
Posts: 9519
Joined: Sat May 29, 2010 5:33 am

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Ann » Wed Feb 24, 2016 10:22 pm

geckzilla wrote:
Ann wrote:To me, nebulas are colored only in photographs, while stars are colored in real life. I go by the nebula colors I see in photographs where the star colors seem "true". That's why I think of hydrogen emission nebulas as pink or even red.
This theory gets completely blown out of the water when an astrophotographer uses wideband RGB filters so that the stars look natural and then adds an H-alpha filter over the top. Any references you are using that utilize narrowband filters such as the H-alpha filter are going to be strongly biased in the direction of that filter.
I realize that.
David Malin used only RGB photo, not Ha. In his astrophotography, emission nebulas almost invariably looked red or pink. So here is David Malin's version of NGC 3603 and 3576, with no Ha filter.

Ann
Color Commentator

User avatar
geckzilla
Ocular Digitator
Posts: 8964
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by geckzilla » Wed Feb 24, 2016 10:29 pm

Ann wrote:
geckzilla wrote:
Ann wrote:To me, nebulas are colored only in photographs, while stars are colored in real life. I go by the nebula colors I see in photographs where the star colors seem "true". That's why I think of hydrogen emission nebulas as pink or even red.
This theory gets completely blown out of the water when an astrophotographer uses wideband RGB filters so that the stars look natural and then adds an H-alpha filter over the top. Any references you are using that utilize narrowband filters such as the H-alpha filter are going to be strongly biased in the direction of that filter.
I realize that.

David Malin used only RGB photo, not Ha. In his astrophotography, emission nebulas almost invariably looked red or pink.
But not only pink or red. The colors of a nebula are much more nuanced without the forcing most astrophotographers do to get them to be glaringly red and magenta. There are varying shades of red, pink, gray, brown, purple, and white, depending on which nebula we're talking about and how complex its composition is.
Just call me "geck" because "zilla" is like a last name.

User avatar
Ann
4725 Å
Posts: 9519
Joined: Sat May 29, 2010 5:33 am

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Ann » Thu Feb 25, 2016 6:28 am

geckzilla wrote:
Ann wrote:
geckzilla wrote: This theory gets completely blown out of the water when an astrophotographer uses wideband RGB filters so that the stars look natural and then adds an H-alpha filter over the top. Any references you are using that utilize narrowband filters such as the H-alpha filter are going to be strongly biased in the direction of that filter.
I realize that.

David Malin used only RGB photo, not Ha. In his astrophotography, emission nebulas almost invariably looked red or pink.
But not only pink or red. The colors of a nebula are much more nuanced without the forcing most astrophotographers do to get them to be glaringly red and magenta. There are varying shades of red, pink, gray, brown, purple, and white, depending on which nebula we're talking about and how complex its composition is.
Absolutely. And some parts of emission nebulas frankly aren't red or pink. The Trapezium region is not red or pink, but yellow, because of the presence of quite a lot of green OIII which, along with Ha, makes the region yellow. To me it looked green. I don't believe that the Hourglass Nebula in the Lagoon Nebula is pink, either. And the Flaming Star Nebula in Auriga is not all red and pink, but bluish too, which some astrophotographers ignore. Indeed, not all emission nebulas are the same color. Several planetary nebulas are mostly greenish, and some lack hydrogen altogether and are all green. I still wonder about Hanny's Voorwerp. Is it really all green? Is that possible? A really large nebula like that?

Nevertheless, I think of emission nebulas as red or pink. Calling a typical emission nebula red is so much easier for me than calling swollen evolved stars red. To me the California Nebula is so very much redder than Betelgeuse.

Ann
Color Commentator

User avatar
geckzilla
Ocular Digitator
Posts: 8964
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by geckzilla » Thu Feb 25, 2016 9:16 am

The point of this is that you are drawing conclusions based on color yet again which aren't necessarily true. M82's outflows are being viewed edge on while NGC1808 is viewed facing nearly toward us. I wish I had a wideband red filter from Hubble so I could show how crazily its outflows have been emphasized over the years. I've got wideband green and blue filters I can look at on their own and get a pretty good idea of how unsaturated the clouds really are. I think they could be more properly described as being a kind of dull lavender with some parts a little redder, others a little bluer, and some nearly colorless.
Just call me "geck" because "zilla" is like a last name.

User avatar
Ann
4725 Å
Posts: 9519
Joined: Sat May 29, 2010 5:33 am

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by Ann » Thu Feb 25, 2016 9:55 am

geckzilla wrote:The point of this is that you are drawing conclusions based on color yet again which aren't necessarily true. M82's outflows are being viewed edge on while NGC1808 is viewed facing nearly toward us. I wish I had a wideband red filter from Hubble so I could show how crazily its outflows have been emphasized over the years. I've got wideband green and blue filters I can look at on their own and get a pretty good idea of how unsaturated the clouds really are. I think they could be more properly described as being a kind of dull lavender with some parts a little redder, others a little bluer, and some nearly colorless.
Oh yes, I believe you. I have been interested in astronomy for so many years and looked at color pictures of astronomical objects for so many years that I am very well aware that Ha filters are used extremely frequently these days to enhance the brightness and color of the red Ha emission very much.

I remember what M82 used to look like before the Ha filters. Something like this. Or something like this.

I would love to see that RGB Hubble image of M82 if there was that red wideband filter! And I would love to see a more direct comparison between the outflows of M82 and BGC 1808, using the best scientific methods.

Ann
Color Commentator

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15976
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: M82: Galaxy with a Supergalactic Wind (2016 Feb 21)

Post by neufer » Thu Feb 25, 2016 2:21 pm

Ann wrote:
geckzilla wrote:
The point of this is that you are drawing conclusions based on color yet again which aren't necessarily true. M82's outflows are being viewed edge on while NGC1808 is viewed facing nearly toward us. I wish I had a wideband red filter from Hubble so I could show how crazily its outflows have been emphasized over the years. I've got wideband green and blue filters I can look at on their own and get a pretty good idea of how unsaturated the clouds really are. I think they could be more properly described as being a kind of dull lavender with some parts a little redder, others a little bluer, and some nearly colorless.
I would love to see that RGB Hubble image of M82 if there was that red wideband filter! And I would love to see a more direct comparison between the outflows of M82 and BGC 1808, using the best scientific methods.
https://en.wikipedia.org/wiki/Bad_Girls_Club wrote:
<<Bad Girls Club (abbreviated BGC) is an American reality television series [that] focuses on the altercations and physical confrontations of seven highly aggressive, quarrelsome, and unruly women. They are introduced to the show based on their capacity to be a "charismatic, tough chick.">>
Art Neuendorffer