Starship Asterisk*

Ann wrote:I have two nitpicks, though. In today's APOD, the surface brightness of M33 appears to be about equal to the surface brightness of M31, the Andromeda galaxy. That is not the case, because Andomeda is much brighter.

Also, the stellar content of these two galaxies appears to be quite similar. But Andromeda has a huge population of old yellow stars, and comparatively few young blue stars. For M33, the situation is the opposite. The yellow bulge of M33 is relatively faint and comparatively star-poor, but its arms are bursting with a rich population of young blue stars.

wonderboy wrote:
this image got me thinking about dark matter. if you grab a squishy ball (dark matter in this example) and squash it between each hand (representing each galaxy) then the ball will displace accordingly on both sides. If dark matter exists then surely it should be similarly displaced by the two galaxies approaching one another?

http://en.wikipedia.org/wiki/Dark_matter wrote:

[b][color=#0000FF]Isolated balls of dark matter sent [u]off to the sides[/u] of interacting galactic pairs[/color][/b]

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<<The most direct observational evidence to date for dark matter is in a system known as the Bullet Cluster. In most regions of the universe, dark matter and visible material are found together, as expected because of their mutual gravitational attraction. In the Bullet Cluster, a collision between two galaxy clusters appears to have caused a separation of dark matter and baryonic matter. X-ray observations show that much of the baryonic matter (in the form of 10⁷–10⁸ Kelvin gas, or plasma) in the system is concentrated in the center of the system. Electromagnetic interactions between passing gas particles caused them to slow down and settle near the point of impact. However, weak gravitational lensing observations of the same system show that much of the mass resides outside of the central region of baryonic gas. Because dark matter does not interact by electromagnetic forces, it would not have been slowed in the same way as the X-ray visible gas, so the dark matter components of the two clusters passed through each other without slowing down substantially. This accounts for the separation. Unlike the galactic rotation curves, this evidence for dark matter is independent of the details of Newtonian gravity, so it is claimed to be direct evidence of the existence of dark matter. Another galaxy cluster, known as the Train Wreck Cluster/Abell 520, appears to have an unusually massive and dark core containing few of the cluster's galaxies, which presents problems for standard dark matter models.>>

http://en.wikipedia.org/wiki/NGC_404 wrote:

[b][color=#0000FF]NGC 404 by Hubble Space Telescope; 1.68′ view[/color][/b]

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<<NGC 404 is a galaxy located about 10 million light years away in the constellation Andromeda. It was discovered by William Herschel in 1784, and is visible through small telescopes. NGC 404 lies just beyond the Local Group but does not appear gravitationally bound to it. It is notable for being within 7 arc-minutes of second magnitude star Mirach, making it a difficult target to observe or photograph and granting it the nickname "Mirach's Ghost".

NGC 404 is a very isolated dwarf lenticular galaxy, a bit more luminous and smaller than the Small Magellanic Cloud and unlike many other early-type galaxies is very rich in neutral hydrogen, most of it concentrated on a pair of large rings around it. It also has star formation both on its center and on its outermost regions, albeit at a low level

Both the outer gas disk and its star formation are assumed to have been triggered by one or several mergers with smaller galaxies roughly 1 billion years ago and it has been proposed NGC 404 is a former spiral galaxy that was transformed into a lenticular one by that event.

NGC 404 contains a low-ionization nuclear emission-line region (LINER), a type of region that is characterized by spectral line emission from weakly ionized atoms. A nuclear star cluster is also present as well as -likely- a supermassive black hole, with a mass of several tens of thousands solar masses.

At least two techniques have been used to measure distances to NGC 404. The infrared surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to NGC 404 using this technique in 2003 is 9.9 ± 0.5 Mly. However, NGC 404 is close enough that red supergiants can be imaged as individual stars. The light from these stars and knowledge of how they should compare to nearby stars within the Milky Way galaxy allows for direct measurement of the distance to the galaxy. This method is referred to as the tip of the red giant branch (TRGB) method. The estimated distance to NGC 404 using this technique is 10.0 ± 1.2 Mly. Averaged together, these distance measurements give a distance estimate of 10.0 ± 0.7 Mly.

http://en.wikipedia.org/wiki/Beta_Andromedae wrote:

[b][color=#0000FF]Mirach's Ghost (NGC 404) 7 arc-minutes from Mirach[/color][/b]

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<<Beta Andromedae (β Andromedae) has an average apparent visual magnitude of 2.05, which makes it the brightest star in Andromeda. Based upon parallax measurements, it is located at a distance of roughly 197 light-years from Earth. The apparent magnitude of this star is reduced by 0.06 from extinction caused by the gas and dust along the line of sight.

Beta Andromedae is a red giant with a stellar classification of M0 III. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It is suspected of being a semiregular variable star whose apparent visual magnitude varies from +2.01 to +2.10. At this stage of the star's evolution, the outer envelope has expanded to around 100 times the size of the Sun. It is radiating 1,995 times the luminosity of the Sun at an effective temperature of 3,842 K.

The name Mirach, and its variations, such as Mirac, Mirar, Mirath, Mirax, etc. come from the star's description in the Alfonsine Tables of 1521 as super mizar. Here, mirat is a corruption of the Arabic ميزر mīzar "girdle", which appeared in a Latin translation of the Almagest. This word refers to Mirach's position at the left hip of the princess Andromeda. Medieval astronomers writing in Arabic called β Andromedae Janb al-Musalsalah (English: The Side of the Chained (Lady)).>>

Geckzilla wrote:
If everything in astronomical processing was left at its natural brightness, a lot of things would either get lost in flat white bright spots or disappear into blackness.

Ann wrote:

Geckzilla wrote:
If everything in astronomical processing was left at its natural brightness, a lot of things would either get lost in flat white bright spots or disappear into blackness.

I agree. I believe that most large or moderately large spiral galaxies have bulges and/or central parts that are much brighter than the spiral arms. Compare, for example, this ESO picture of apparently bright-armed spiral galaxy M100 (with a burnt-out center) with this ESO picture where M100 is seen to have a brilliant center but faint arms and an even fainter disk. (There is a supernova in there, too.) Or compare it with this picture where the center of M100 is not burnt out, but the arms are moderately bright anyway. I like the last picture a lot, but I'm not sure it gives us a good idea of how bright the center of M100 is compared with the arms.

As for the Andromeda galaxy, take a look at this picture which shows the brilliant bulge of M31, but the arms can hardly be seen at all. I believe that this picture gives you a good idea of what M31 looks like visually.

What about M33? In this picture, the bulge is brighter than the arms, but the difference is rather small. Also the overall color of M33 is neutral or slightly blue, whereas the dominant color of M31 is clearly yellow. This is obvious from the B-V indexes of these galaxies: 0.950 for Andromeda (considerably yellower than the Sun) versus 0.550 for M33 (bluer than the Sun).

Also M31 is about two magnitudes brighter visually than M33, and it also has a higher surface brightness, particularly if we compare the two galaxies' central parts.

So the overall colors and brightnesses of these two galaxies have been tweaked in opposite directions to produce this image. The result is a dramatic, delightfully symmetric image. It is clear from the image that M33 is smaller than M31, so the picture still tells us a very important fact about these two "islands of stars".

Ann

Anthony Barreiro wrote:I didn't take Ann's comments as any sort of negative criticism, either. On the contrary, she offered positive comments on the picture. And I don't think you need to process your own astronomical images to have opinions about pictures you see. I've never painted an oil painting, but when I go to the museum I have opinions about the pictures I see.

Although they look far apart, M31 and M33 are locked in a mutual gravitational embrace. Radio astronomers have found indications of a bridge of neutral hydrogen gas that could connect the two, evidence of a closer encounter in the past. Based on measurements, gravitational simulations currently predict that the Milky Way, M31, and M33 will all undergo mutual close encounters and potentially mergers, billions of years in the future.

walker1001 wrote:We are told here

Although they look far apart, M31 and M33 are locked in a mutual gravitational embrace. Radio astronomers have found indications of a bridge of neutral hydrogen gas that could connect the two, evidence of a closer encounter in the past. Based on measurements, gravitational simulations currently predict that the Milky Way, M31, and M33 will all undergo mutual close encounters and potentially mergers, billions of years in the future.

And we are told this sort of thing many times. (See yesterday 25th September 2013, among others)

Yet it is accepted that ALL galaxies are flying away from us and each other at ever increasing speed and will disappear into deep infinity.

When I ask why some will interact and perhaps join up when "ALL are flying away from each other", the short answer I get is that Gravity-does-it. Why does gravity do it in some cases and not"all" is not answered. Surely all matter exerts gravity on all other matter. But why are there local galaxy clusters and superclusters if everything is moving away from everything else as evidenced by their red shifts? If gravity is doing it then how can they be flying away from each otherand forming clusters? Can you have it both ways? Am I missing something?

Can someone point me to links to articles that might clear the clusters of fog in my brain? This is a matter of utmost gravity.

walker1001 wrote:Yet it is accepted that ALL galaxies are flying away from us and each other at ever increasing speed and will disappear into deep infinity.

walker1001 wrote:When I ask why some will interact and perhaps join up when "ALL are flying away from each other", the short answer I get is that Gravity-does-it. Why does gravity do it in some cases and not"all" is not answered.

geckzilla wrote:Blown out, not burnt out. It makes no sense to me to compare the "color" of the Sun (or any star) to the dynamic range of both tone and hue to an entire galaxy. What is the point of that, anyway? I could understand comparing galaxies to galaxies but galaxies to the Sun? I don't get it.

geckzilla wrote:But a galaxy is not an average of all the light of its stars.

geckzilla wrote:

Anthony Barreiro wrote:I didn't take Ann's comments as any sort of negative criticism, either. On the contrary, she offered positive comments on the picture. And I don't think you need to process your own astronomical images to have opinions about pictures you see. I've never painted an oil painting, but when I go to the museum I have opinions about the pictures I see.

Of course, but you'd have a lot more insight if you did do oil painting. And you'd probably want to be familiar with oil painting technique before criticizing someone else's technique at length. I find Ann's comments to be strangely biased toward her well-known affection for the color blue and for how she thinks certain objects should be perceived. It bothers me a lot because of the large volume of verbose comments with certain esoteric terms that could cause the average reader to mistake her superficial opinions as being more deeply qualified.

starsurfer wrote:I like that Ann offers us what's in her mind, so many people lack the courage to speak what they feel.

geckzilla wrote:

starsurfer wrote:
I like that Ann offers us what's in her mind, so many people lack the courage to speak what they feel.

The number of crackpots I ban from the forum tell me otherwise...

http://en.wikipedia.org/wiki/Crank_%28person%29 wrote:
<<"Crank" is a pejorative term used for a person who holds an unshakable belief that most of his or her contemporaries consider to be false. Common synonyms for "crank" include crackpot and kook. A crank belief is so wildly at variance with those commonly held as to be ludicrous. Cranks characteristically dismiss all evidence or arguments which contradict their own unconventional beliefs, making rational debate a futile task, and rendering them impervious to facts, evidence, and rational inference. A crank differs from a fAnnatic in that the subject of the fAnnatics obsession is either not necessarily widely regarded as wrong or not necessarily a "fringe" belief.

Although a crank's beliefs seem ridiculous to experts in the field, cranks are sometimes very successful in convincing non-experts of their views. A famous example is the Indiana Pi Bill where a state legislature nearly wrote into law a crank result in geometry.

The second book of the mathematician and popular author Martin Gardner was a study of crank beliefs, Fads and Fallacies in the Name of Science. More recently, the mathematician Underwood Dudley has written a series of books on mathematical cranks, including The Trisectors, Mathematical Cranks, and Numerology: Or, What Pythagoras Wrought. And in a 1992 UseNet post, the mathematician John Baez humorously proposed a checklist, the Crackpot index, intended to diagnose cranky beliefs regarding contemporary physics.[2]

According to these authors, virtually universal characteristics of cranks include:

• Cranks overestimate their own knowledge and ability, and underestimate that of acknowledged experts.
  
  Cranks insist that their alleged discoveries are urgently important.
  
  Cranks rarely, if ever, acknowledge any error, no matter how trivial.
  
  Cranks love to talk about their own beliefs, often in inappropriate social situations, but they tend to be bad listeners, being uninterested in anyone else's experience or opinions.