APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

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APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by APOD Robot » Tue Nov 12, 2019 5:05 am

Image NGC 3717: A Nearly Sideways Spiral Galaxy

Explanation: Some spiral galaxies are seen nearly sideways. Most bright stars in spiral galaxies swirl around the center in a disk, and seen from the side, this disk can be appear quite thin. Some spiral galaxies appear even thinner than NGC 3717, which is actually seen tilted just a bit. Spiral galaxies form disks because the original gas collided with itself and cooled as it fell inward. Planets may orbit in disks for similar reasons. The featured image by the Hubble Space Telescope shows a light-colored central bulge composed of older stars beyond filaments of orbiting dark brown dust. NGC 3717 spans about 100,000 light years and lies about 60 million light years away toward the constellation of the Water Snake (Hydra).

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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by shaileshs » Tue Nov 12, 2019 6:41 am

There's a mention of another (thinner) galaxy - https://apod.nasa.gov/apod/ap141105.html It's not only thin but more interestingly it lacks dust (dust lanes/patches) which we are used to see+imagine in most galaxies. I wonder, what's the reason for lack of dust lanes/patches in such galaxies ? Is it normal or rare/unusual (based on info about known galaxies) ? Thanks in advance for all comments and answers.

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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by Ann » Tue Nov 12, 2019 7:26 am

Well, today's APOD makes me want to post a million pictures of sideways galaxies! :D Let's begin with NGC 3717 itself:

NGC 3717. ESA/Hubble & NASA, Processing: D. Rosario.
NGC 3717 in widefield image. Photo: Warren Keller.

























Note how broad and dominant the NGC 3717 central dust really is. Also note how red the overall color of this galaxy is. Its B-V index is +1.04, which is very red indeed for a spiral galaxy. The Hubble picture does show us some whitish-looking (dust-reddened) star clusters in NGC 3717 along the upper edge of the dust lane. We can also see som "free-floating" little groups of blue stars above the dust lane. The U-B index of NGC 3717 is +0.450, pretty red, but blue enough to allow the presence of some young blue clusters.

An interesting aspect of the dust lane is that it appears to be "double", as if it consisted of two dark relatively thin dust lanes with a broad, lighter swathe in between. Note the peanut shaped bulge of NGC 3717, suggesting that this is a barred galaxy.

M104. Vicent Peris (OAUV / PTeam), MAST, STScI, AURA, NASA

A very iconic edge-on spiral galaxy is M104. Note how thin the dust lane of M104 is, compared with NGC 3717. There are suggestions of young stars in parts of the dust lane, but if so, these younger stars are most likely not very young and not numerous. The B-V index of M14 is +0.98, less red than NGC 3717, but the U-B index of M104 is +538, redder than NGC 3717.



NGC 891. ESA/Hubble & NASA
Acknowledgement: Nick Rose









NGC 4631. NASA & ESA.









A relatively nearby example of an edge-on galaxy is NGC 891. The Hubble picture of it clearly shows us star formation in the dust lane itself. Note that the dust lane is thinner than the dust lane of NGC 3717 but broader than the dust lane of M104. The dust lane is also somewhat "messy" and full of smoking "chimneys", suggesting it has been disrupted by the forces supernova explosions. The B-V index of NGC 891 is +0.88, and the U-B index is +0.27. Both values are bluer than either NGC 3717 or M104, clearly demonstrating higher levels of star formation in NGC 891 than in the other two galaxies.

Bluer still, however, much bluer, is the edge-on galaxy NGC 4631. The dust lane is practically bursting with new stars, and the dust lane is almost torn to pieces by the forces of star formation. The B-V index of NGC 4631 is +0.56. I haven't been able to find out what its U-B index is, but I'll venture a guess that it is actually negative.

So the amount of star formation in a spiral galaxy will have a large impact on the shape of its central dust lane.

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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by Ann » Tue Nov 12, 2019 8:02 am

shaileshs wrote:
Tue Nov 12, 2019 6:41 am
There's a mention of another (thinner) galaxy - https://apod.nasa.gov/apod/ap141105.html It's not only thin but more interestingly it lacks dust (dust lanes/patches) which we are used to see+imagine in most galaxies. I wonder, what's the reason for lack of dust lanes/patches in such galaxies ? Is it normal or rare/unusual (based on info about known galaxies) ? Thanks in advance for all comments and answers.
NGC 4762. ESA/Hubble & NASA
NGC 4762. David W. Hogg, Michael Blanton, and the Sloan Digital Sky Survey.




















Interesting example, shaileshs. As I said in my previous post, the amount of star formation in a spiral galaxy has a tremendous impact on the shape of its central dust lane.

However, NGC 4762 clearly lacks a dust lane altogether, and it is not a spiral galaxy but a lenticular one. But what is that thin, bright line? How was it formed?

In my amateur opinion, this bright line is made up of stars only, and it might be the remains of a small starforming inner disk of NGC 4762. The star formation ended long ago, and the dust is gone, but there are still a lot of stars in there.

M64. Photo: Andrea Tamanti.
The inner part of M64. NASA and the Hubble Heritage Team (AURA/STScI),
S. Smartt (IoA) & D. Richstone (U. Michigan) et al.






















To imagine what NGC 4762 may have once looked like, consider galaxy M64, NGC 4826. As you can see, this galaxy has a very small but "thick" inner disk with some star formation, and a large fairly "thin" outer disk.


NGC 4314. Photo: Bruce Pipes.
There are other examples of galaxies that have lost all gas and star formation ability except in a small disk near its center. A very interesting example is NGC 4314. In Bruce Pipes' great picture of NGC 4314, you can see several components of this galaxy: A relatively substantial bulge and a straight and thick bar, a rather flimsy outer ring and spiral structure, and a tiny inner starforming blue ring around a yellow core.

In my opinion, we can be sure that NGC 4314 formed many stars in the past. There was a time when this galaxy had a lot of gas and dust and a lot of new star formation. But NGC 4314 ran out of dust and gas everywhere except in a small region near its center. All of the rest of the galaxy has the same uniform color (really yellowish rather than gray), and to me, it is easy to imagine a time when star formation has stopped near the center of NGC 4314 too, so that all of the galaxy is uniform, "straight" and monocolored.

So my guess is that NGC 4762 was a "normal" spiral galaxy that for some reason ran out of gas and dust. No new stars are being born in this galaxy, but the old stars, which are gathered in a thin disk, shine on.

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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by BDanielMayfield » Tue Nov 12, 2019 11:40 am

shaileshs wrote:
Tue Nov 12, 2019 6:41 am
There's a mention of another (thinner) galaxy - https://apod.nasa.gov/apod/ap141105.html It's not only thin but more interestingly it lacks dust (dust lanes/patches) which we are used to see+imagine in most galaxies. I wonder, what's the reason for lack of dust lanes/patches in such galaxies ? Is it normal or rare/unusual (based on info about known galaxies) ? Thanks in advance for all comments and answers.
This is a thought provoking question shaileshs. Dark dust is the leftover cold ashes from generations of stars that have expelled metals (elements other than the gases H and He) back into interstellar space. The stars of ALL galaxies are producing metals, but if such material doesn't cool off or is swept away before it can accumulate no dark dust clouds will form. The example you included is a galaxy in the Virgo Cluster, so I'd guess that its movement through the cluster has stripped it of its dust forming material.

Also, by far the most metals will be produced by very massive stars. Such massive stars are blue (because they are hotter) and they burn out fast. Many galaxies are said to be "red and dead" because they no longer have any young massive stars left. They are composed of old low mass red stars that produce very little dust forming material.

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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by orin stepanek » Tue Nov 12, 2019 1:02 pm

Did you ever notice that pinwheels seem to be the order of the universe? From the atom to solar systems (stellar systems) to Galaxies? :shock:
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by Chris Peterson » Tue Nov 12, 2019 1:08 pm

orin stepanek wrote:
Tue Nov 12, 2019 1:02 pm
Did you ever notice that pinwheels seem to be the order of the universe? From the atom to solar systems (stellar systems) to Galaxies? :shock:
An atom bears absolutely no resemblance to a pinwheel.
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by orin stepanek » Tue Nov 12, 2019 2:03 pm

I guess it depends on your perspective!
Helium atom image from search engine!
th.jpg
To me it looks like a pinwheel! & the electrons do orbit
around the neutron & proton! JMHO!
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by Chris Peterson » Tue Nov 12, 2019 2:36 pm

orin stepanek wrote:
Tue Nov 12, 2019 2:03 pm
I guess it depends on your perspective!
Helium atom image from search engine!th.jpg

To me it looks like a pinwheel! & the electrons do orbit
around the neutron & proton! JMHO!
No, electrons do not orbit around the nucleus. They exist in orbitals, which are lobe shaped regions which define probability zones.
Chris

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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by neufer » Tue Nov 12, 2019 2:45 pm

Chris Peterson wrote:
Tue Nov 12, 2019 1:08 pm
orin stepanek wrote:
Tue Nov 12, 2019 1:02 pm

Did you ever notice that pinwheels seem to be the order of the universe?
From the atom to solar systems (stellar systems) to Galaxies? :shock:
An atom bears absolutely no resemblance to a pinwheel.
https://en.wikipedia.org/wiki/Erwin_Schr%C3%B6dinger#Creation_of_wave_mechanics wrote:
<<An Armenian immigrant toy manufacturer, Tegran M. Samour (shortened from Samourkashian), invented the modern version of the pinwheel, originally titled "wind wheel," in 1919 in Boston, Massachusetts. Samour owned a toy store in Stoneham, Massachusetts, and sold the wind wheel along with two other toys which he invented.>>
......................................................................
<<In January 1926, Erwin Schrödinger published in Annalen der Physik the paper "Quantisierung als Eigenwertproblem" (Quantization as an Eigenvalue Problem) on wave mechanics and presented what is now known as the Schrödinger equation. In this paper, he gave a "derivation" of the wave equation for time-independent systems and showed that it gave the correct energy eigenvalues for a hydrogen-like atom. Schrödinger was not entirely comfortable with the implications of quantum theory. He wrote about the probability interpretation of quantum mechanics, saying: "I don't like it, and I'm sorry I ever had anything to do with it.">>
https://en.wikipedia.org/wiki/Logarithmic_spiral wrote:
<<Spira mirabilis, Latin for "miraculous spiral", is another name for the logarithmic spiral. Although this curve had already been named by other mathematicians, the specific name ("miraculous" or "marvelous" spiral) was given to this curve by Jacob Bernoulli, because he was fascinated by one of its unique mathematical properties: the size of the spiral increases but its shape is unaltered with each successive curve, a property known as self-similarity. Possibly as a result of this unique property, the spira mirabilis has evolved in nature, appearing in certain growing forms such as nautilus shells and sunflower heads. Jacob Bernoulli wanted such a spiral engraved on his headstone along with the phrase "Eadem mutata resurgo" ("Although changed, I shall arise the same."), but, by error, an Archimedean spiral was placed there instead.

In several natural phenomena one may find curves that are close to being logarithmic spirals. Here follow some examples and reasons:
  • The approach of a hawk to its prey in classical pursuit, assuming the prey travels in a straight line. Their sharpest view is at an angle to their direction of flight; this angle is the same as the spiral's pitch.

    The approach of an insect to a light source. They are used to having the light source at a constant angle to their flight path. Usually the sun (or moon for nocturnal species) is the only light source and flying that way will result in a practically straight line.

    Many biological structures including the shells of mollusks. In these cases, the reason may be construction from expanding similar shapes, as is the case for polygonal figures.

    The arms of spiral galaxies. Our own galaxy, the Milky Way, has several spiral arms, each of which is roughly a logarithmic spiral with a growth rate parameter b = 0.213, resulting in a pitch of arctan ⁡ b ≈ 12º.[The golden spiral is a logarithmic spiral that grows outward by a factor of the golden ratio for every 90 degrees of rotation (i.e., a growth rate parameter b = 0.3063489, resulting in a pitch of arctan ⁡ b ≈ 17.03239º). It can be approximated by a "Fibonacci spiral", made of a sequence of quarter circles with radii proportional to Fibonacci numbers.]

    The bands of tropical cyclones, such as hurricanes.

    The nerves of the cornea (this is, corneal nerves of the subepithelial layer terminate near superficial epithelial layer of the cornea in a logarithmic spiral pattern).

    Logarithmic spiral beaches can form as the result of wave refraction and diffraction by the coast. Half Moon Bay (California) is an example of such a type of beach.
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by orin stepanek » Tue Nov 12, 2019 3:31 pm

Thanks Art & Chris! Guess I'm not too old to learn a thing or more! Hope I didn't confuse anyone! OBTW Is this how confusing the atom is? https://www.youtube.com/watch?v=EOHYT5q5lhQ
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by neufer » Tue Nov 12, 2019 4:12 pm

Chris Peterson wrote:
Tue Nov 12, 2019 2:36 pm
orin stepanek wrote:
Tue Nov 12, 2019 2:03 pm

I guess it depends on your perspective!
Helium atom image from search engine!th.jpg

To me it looks like a pinwheel! & the electrons do orbit
around the neutron & proton! JMHO!
No, electrons do not orbit around the nucleus.
They exist in orbitals, which are lobe shaped regions which define probability zones.
In any event, those symmetrically lobed orbitals that remind
Orin of a pinwheel represent electrons with zero angular rotation.
  • Maybe a pinwheel f-block electron(...maybe).
https://en.wikipedia.org/wiki/Block_(periodic_table)#f-block wrote:
<<A block of the periodic table is a set of chemical elements having their differentiating electrons predominately in the same type of atomic orbital. Each block is named after its characteristic orbital: s-block; p-block; d-block; and f-block. The block names (s, p, d and f) are derived from the spectroscopic notation for the value of an electron's azimuthal quantum number: sharp (0), principal (1), diffuse (2), or fundamental (3). Succeeding notations proceed in alphabetical order, as g, h, etc.

Click to play embedded YouTube video.
The f-block appears as a footnote in a standard 18-column table but is located at the center-left of a 32-column full width table. While these elements are generally not considered part of any group some authors consider them to be part of group 3. They are sometimes called inner transition metals because they provide a transition between the s-block and d-block in the 6th and 7th row (period), in the same way that the d-block transition metals provide a transitional bridge between the s-block and p-block in the 4th and 5th rows.

The f-block elements come in two series, in periods 6 and 7. All are metals. The f-orbital electrons are largely inactive in determining the chemistry of the period 6 f-block elements. Their chemical properties are mostly determined by a single d and two s-orbital electrons. Consequently, there is less chemical variability within this series of elements. Among the early period 7 f-block elements, the energies of the 5f, 7s and 6d shells are quite similar; consequently these elements tend to show as much chemical variability as their transition metals analogues. The later f-block elements behave more like their period 6 counterparts.

The f-block elements are unified by mostly having one or more electrons in an inner f-orbital. Of the f-orbitals, five have six lobes each, and the sixth looks like a dumbbell with a donut with two rings. They can contain up to seven pairs of electrons hence the block occupies fourteen columns in the periodic table. They are not assigned group numbers, since vertical periodic trends cannot be discerned in a "group" of two elements.

The two 14-member rows of the f-block elements are sometimes confused with the lanthanides and the actinides, which are names for sets of elements based on chemical properties more so than electron configurations. The lanthanides are the 15 elements running from La to Lu; the actinides are the 15 elements running from Ac to Lr.>>
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by BDanielMayfield » Tue Nov 12, 2019 4:22 pm

Did anyone else notice something unusual about today's APOD subject? It looks like it has a double dust disk, with a lighter, less dusty strip in the middle. Resembles a double meat hamburger. :chomp:

I wonder what could have caused this doubly thick disk?

Bruce
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by DL MARTIN » Tue Nov 12, 2019 4:34 pm

Since we don't know about dark energy and dark matter, why don't we use the term 'dark time' to describe the difference between source and cognition?

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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by orin stepanek » Tue Nov 12, 2019 4:58 pm

BDanielMayfield wrote:
Tue Nov 12, 2019 4:22 pm
Did anyone else notice something unusual about today's APOD subject? It looks like it has a double dust disk, with a lighter, less dusty strip in the middle. Resembles a double meat hamburger. :chomp:

I wonder what could have caused this doubly thick disk?

Bruce
Ya! I noticed it! I also thought they came together at the right edge! Kinda like a high spiral arm and a low spiral arm! Bet you'd get some interesting views if you lived in certain places in that galaxy! :mrgreen:
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by neufer » Tue Nov 12, 2019 5:30 pm

orin stepanek wrote:
Tue Nov 12, 2019 4:58 pm
BDanielMayfield wrote:
Tue Nov 12, 2019 4:22 pm

Did anyone else notice something unusual about today's APOD subject? It looks like it has a double dust disk, with a lighter, less dusty strip in the middle. Resembles a double meat hamburger. :chomp:

I wonder what could have caused this doubly thick disk?
Ya! I noticed it! I also thought they came together at the right edge! Kinda like a high spiral arm and a low spiral arm! Bet you'd get some interesting views if you lived in certain places in that galaxy! :mrgreen:
https://www.spacetelescope.org/images/potw1940a/ wrote:
<<NGC 3717 is not captured perfectly edge-on in the image; the nearer part of the galaxy is tilted ever so slightly down, and the far side tilted up. This angle affords a view across the disc and the central bulge (of which only one side is visible).
https://en.wikipedia.org/wiki/ESO_510-G13 wrote:
:arrow: <<NASA's Hubble Space Telescope has captured an image of an unusual edge-on galaxy, ESO 510-G13, revealing remarkable details of its warped dusty disk and showing how colliding galaxies spawn the formation of new generations of stars. The dust and spiral arms of normal spiral galaxies, like our own Milky Way, appear flat when viewed edge-on. This image shows a galaxy that, by contrast, has an unusual twisted disk structure, first seen in ground-based photographs obtained at the European Southern Observatory (ESO) in Chile. ESO 510-G13 lies in the southern constellation Hydra, roughly 150 million light-years from Earth. Details of the structure of ESO 510-G13 are visible because the interstellar dust clouds that trace its disk are silhouetted from behind by light from the galaxy's bright, smooth central bulge. The strong warping of the disk indicates that ESO 510-G13 has recently undergone a collision with a nearby galaxy and is in the process of swallowing it. Gravitational forces distort the structures of the galaxies as their stars, gas, and dust merge together in a process that takes millions of years. Eventually the disturbances will die out, and ESO 510-G13 will become a normal-appearing single galaxy. In the outer regions of ESO 510-G13, especially on the right-hand side of the image, we see that the twisted disk contains not only dark dust, but also bright clouds of blue stars. This shows that hot, young stars are being formed in the disk. Astronomers believe that the formation of new stars may be triggered by collisions between galaxies, as their interstellar clouds smash together and are compressed. Hubble's Wide Field Planetary Camera 2 (WFPC2) was used to observe ESO 510-G13 in April 2001. Pictures obtained through blue, green, and red filters were combined to make this color-composite image, which emphasizes the contrast between the dusty spiral arms, the bright bulge, and the blue star-forming regions.>>
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by BDanielMayfield » Tue Nov 12, 2019 5:53 pm

Ann wrote:An interesting aspect of the dust lane is that it appears to be "double", as if it consisted of two dark relatively thin dust lanes with a broad, lighter swathe in between. Note the peanut shaped bulge of NGC 3717, suggesting that this is a barred galaxy.
Sorry that I had overlooked this part of your above comment Ann.
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by orin stepanek » Tue Nov 12, 2019 8:45 pm

neufer wrote:
Tue Nov 12, 2019 5:30 pm
orin stepanek wrote:
Tue Nov 12, 2019 4:58 pm
BDanielMayfield wrote:
Tue Nov 12, 2019 4:22 pm

Did anyone else notice something unusual about today's APOD subject? It looks like it has a double dust disk, with a lighter, less dusty strip in the middle. Resembles a double meat hamburger. :chomp:

I wonder what could have caused this doubly thick disk?
Ya! I noticed it! I also thought they came together at the right edge! Kinda like a high spiral arm and a low spiral arm! Bet you'd get some interesting views if you lived in certain places in that galaxy! :mrgreen:
https://www.spacetelescope.org/images/potw1940a/ wrote:
<<NGC 3717 is not captured perfectly edge-on in the image; the nearer part of the galaxy is tilted ever so slightly down, and the far side tilted up. This angle affords a view across the disc and the central bulge (of which only one side is visible).
https://en.wikipedia.org/wiki/ESO_510-G13 wrote:
:arrow: <<NASA's Hubble Space Telescope has captured an image of an unusual edge-on galaxy, ESO 510-G13, revealing remarkable details of its warped dusty disk and showing how colliding galaxies spawn the formation of new generations of stars. The dust and spiral arms of normal spiral galaxies, like our own Milky Way, appear flat when viewed edge-on. This image shows a galaxy that, by contrast, has an unusual twisted disk structure, first seen in ground-based photographs obtained at the European Southern Observatory (ESO) in Chile. ESO 510-G13 lies in the southern constellation Hydra, roughly 150 million light-years from Earth. Details of the structure of ESO 510-G13 are visible because the interstellar dust clouds that trace its disk are silhouetted from behind by light from the galaxy's bright, smooth central bulge. The strong warping of the disk indicates that ESO 510-G13 has recently undergone a collision with a nearby galaxy and is in the process of swallowing it. Gravitational forces distort the structures of the galaxies as their stars, gas, and dust merge together in a process that takes millions of years. Eventually the disturbances will die out, and ESO 510-G13 will become a normal-appearing single galaxy. In the outer regions of ESO 510-G13, especially on the right-hand side of the image, we see that the twisted disk contains not only dark dust, but also bright clouds of blue stars. This shows that hot, young stars are being formed in the disk. Astronomers believe that the formation of new stars may be triggered by collisions between galaxies, as their interstellar clouds smash together and are compressed. Hubble's Wide Field Planetary Camera 2 (WFPC2) was used to observe ESO 510-G13 in April 2001. Pictures obtained through blue, green, and red filters were combined to make this color-composite image, which emphasizes the contrast between the dusty spiral arms, the bright bulge, and the blue star-forming regions.>>
Nice; that's a clearer view!
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by TheOtherBruce » Tue Nov 12, 2019 11:32 pm

Something I've always wondered in large-scale galaxy images like this; are the groups of blue specks we see individual hot blue stars, or complete compact clusters of hot blue stars? There was an APOD some time back featuring a massive multi-megapixel image of the Andromeda galaxy, and I was never sure there either. This is a lot further away, though, so I find it hard to imagine that we can image single stars at such a distance.
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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by shaileshs » Wed Nov 13, 2019 4:10 am

TheOtherBruce wrote:
Tue Nov 12, 2019 11:32 pm
Something I've always wondered in large-scale galaxy images like this; are the groups of blue specks we see individual hot blue stars, or complete compact clusters of hot blue stars? There was an APOD some time back featuring a massive multi-megapixel image of the Andromeda galaxy, and I was never sure there either. This is a lot further away, though, so I find it hard to imagine that we can image single stars at such a distance.
I personally don't think there's a way to see/identify individual star in such galaxies at such long distances (60 million light years) unless the stars are soooooooooooo powerful (almost close to Supernova). Most blue regions seem to be "star clusters" (forming new stars). Some explanation and example given here - https://www.nasa.gov/multimedia/imagega ... _1513.html

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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by sillyworm 2 » Wed Nov 13, 2019 1:04 pm

So much dust from so many dying stars.Wrapping my mind around this.Is this a steady accumalitive process or could there have been more stars dying earlier when the galaxy was just forming?

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Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by Ann » Wed Nov 13, 2019 3:18 pm

sillyworm 2 wrote:
Wed Nov 13, 2019 1:04 pm
So much dust from so many dying stars.Wrapping my mind around this.Is this a steady accumalitive process or could there have been more stars dying earlier when the galaxy was just forming?
Well, astronomers talk about "cosmic noon, when star formation peaked in the Universe. This happened when the Universe was around 3.5 billion years old, or about 10 billion years ago.
Joanna Bridge of Astrobites wrote:

The last two decades of galaxy research have made it very clear that star formation in galaxies peaked at a redshift of z ~ 2, which occurred about 3.5 billion years after the Big Bang. In the approximately 10 billions years since then, the number of stars forming per year, or star formation rate, has been universally decreasing. This peak in star forming activity at z ~ 2 is often referred to as “cosmic noon.”
Star formation in the early Universe.
(Image: © NASA/ESA/ESO/Wolfram Freudling et al. (STECF))
What this means is that most galaxies, including NGC 3717 and the Milky Way, have most certainly formed most of their stars in the distant past. Of course, star formation didn't stop 3.5 billion years ago - not by any means! But for the Universe as a whole, the rate of star formation has declined during the last ten billion years. And for galaxies with overall red colors and little obvious star formation, we can be sure that they formed almost all their stars in the past.

As for gas and dust, that is an interesting question. The amount of gas has most certainly steadily decreased in the Universe. That is because star formation robs the Universe of "free gas", as gas gets locked up inside stars. Massive stars give back most of their gas to the Universe as they explode as supernovas. Even stars a little more massive than the Sun, and stars no more massive than the Sun, give back a lot of gas to the Universe as they swell into red giants and then "slough off" much of their gaseous outer atmospheres, which are briefly lit up as shimmering planetary nebulas.

But most of the gas is locked up inside little red dwarfs, which are as common as dirt in the cosmos, and which jealousy guard their supply of gas without letting the Universe recycle it. To the best of our knowledge, not a single M-type red dwarf has ever "died a natural death" since the Universe was born in the Big Bang. A few may have fallen into black holes, others may have merged with other stars and become massive enough to actually evolve into red giants. But left on their own, the red dwarfs may live as long as the Universe.

So, as more stars form, less and less of the gas that was created in the Big Bang is available for star formation. Dust, by contrast, accumulates in the Universe, as various "metals" (elements more massive than hydrogen and helium) are formed inside stars, in supernova explosions and in processes going on inside M-type red giants.

Galaxy cluster Abell 2218. NASA, ESA, and Johan Richard (Caltech, USA).
Acknowledgement: Davide de Martin & James Long
So why is it that some galaxies appear to lack dust?

Take a look at galaxy cluster Abell 2218. You can see, if you look carefully, that while some of the galaxies do show clear signs of dust, many of the galaxies appear to be dust free. Yet we know that they must once have contained dust, because dust is a by-product of star formation and also of star death.

So where did the dust go?

The way I understand it, the dust is still there, but it is widely scattered and not gathered into clumps or dust lanes like they are in almost all spiral galaxies. The way I understand it, hot and violent processes related to black holes, particularly supermassive black holes, prevent the dust (and gas) from "settling down" and cooling, which is necessary for star formation. For myself, I picture the gas and dust in elliptical and lenticular galaxies as being constantly battered by a relentless hot wind.

Ann
Color Commentator

sillyworm 2

Re: APOD: NGC 3717: A Nearly Sideways Spiral... (2019 Nov 12)

Post by sillyworm 2 » Wed Nov 13, 2019 8:34 pm

Thank you Ann!!!!!!

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neufer
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Red giants & dwarfs

Post by neufer » Thu Nov 14, 2019 1:29 am

Ann wrote:
Wed Nov 13, 2019 3:18 pm
.
...most of the gas is locked up inside little red dwarfs, which are as common as dirt in the cosmos, and which jealousy guard their supply of gas without letting the Universe recycle it. To the best of our knowledge, not a single M-type red dwarf has ever "died a natural death" since the Universe was born in the Big Bang. A few may have fallen into black holes, others may have merged with other stars and become massive enough to actually evolve into red giants. But left on their own, the red dwarfs may live as long as the Universe.
https://en.wikipedia.org/wiki/Cosmic_dust#Dust_grain_formation wrote:
Click to play embedded YouTube video.
<<The large grains in interstellar space are probably complex, with refractory cores that condensed within stellar outflows topped by layers acquired during incursions into cold dense interstellar clouds. That cyclic process of growth and destruction outside of the clouds has been modeled to demonstrate that the cores live much longer than the average lifetime of dust mass. Those cores mostly start with silicate particles condensing in the atmospheres of cool, oxygen-rich red-giants and carbon grains condensing in the atmospheres of cool carbon stars. Red giants have evolved or altered off the main sequence and have entered the giant phase of their evolution and are the major source of refractory dust grain cores in galaxies. Those refractory cores are also called stardust, which is a scientific term for the small fraction of cosmic dust that condensed thermally within stellar gases as they were ejected from the stars. Several percent of refractory grain cores have condensed within expanding interiors of supernovae, a type of cosmic decompression chamber. Meteoriticists who study refractory stardust (extracted from meteorites) often call it presolar grains but that within meteorites is only a small fraction of all presolar dust. Stardust condenses within the stars via considerably different condensation chemistry than that of the bulk of cosmic dust, which accretes cold onto preexisting dust in dark molecular clouds of the galaxy. Those molecular clouds are very cold, typically less than 50K, so that ices of many kinds may accrete onto grains, in cases only to be destroyed or split apart by radiation and sublimation into a gas component. Finally, as the Solar System formed many interstellar dust grains were further modified by coalescence and chemical reactions in the planetary accretion disk. The history of the various types of grains in the early Solar System is complicated and only partially understood.>>
Art Neuendorffer

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Ann
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Re: Red giants & dwarfs

Post by Ann » Thu Nov 14, 2019 1:53 am

neufer wrote:
Thu Nov 14, 2019 1:29 am
Ann wrote:
Wed Nov 13, 2019 3:18 pm
.
...most of the gas is locked up inside little red dwarfs, which are as common as dirt in the cosmos, and which jealousy guard their supply of gas without letting the Universe recycle it. To the best of our knowledge, not a single M-type red dwarf has ever "died a natural death" since the Universe was born in the Big Bang. A few may have fallen into black holes, others may have merged with other stars and become massive enough to actually evolve into red giants. But left on their own, the red dwarfs may live as long as the Universe.
https://en.wikipedia.org/wiki/Cosmic_dust#Dust_grain_formation wrote:
Click to play embedded YouTube video.
<<The large grains in interstellar space are probably complex, with refractory cores that condensed within stellar outflows topped by layers acquired during incursions into cold dense interstellar clouds. That cyclic process of growth and destruction outside of the clouds has been modeled to demonstrate that the cores live much longer than the average lifetime of dust mass. Those cores mostly start with silicate particles condensing in the atmospheres of cool, oxygen-rich red-giants and carbon grains condensing in the atmospheres of cool carbon stars. Red giants have evolved or altered off the main sequence and have entered the giant phase of their evolution and are the major source of refractory dust grain cores in galaxies. Those refractory cores are also called stardust, which is a scientific term for the small fraction of cosmic dust that condensed thermally within stellar gases as they were ejected from the stars. Several percent of refractory grain cores have condensed within expanding interiors of supernovae, a type of cosmic decompression chamber. Meteoriticists who study refractory stardust (extracted from meteorites) often call it presolar grains but that within meteorites is only a small fraction of all presolar dust. Stardust condenses within the stars via considerably different condensation chemistry than that of the bulk of cosmic dust, which accretes cold onto preexisting dust in dark molecular clouds of the galaxy. Those molecular clouds are very cold, typically less than 50K, so that ices of many kinds may accrete onto grains, in cases only to be destroyed or split apart by radiation and sublimation into a gas component. Finally, as the Solar System formed many interstellar dust grains were further modified by coalescence and chemical reactions in the planetary accretion disk. The history of the various types of grains in the early Solar System is complicated and only partially understood.>>
Interesting info on the red giants, Art. But why is your text a reply to what I said about red dwarfs?

Ann
Color Commentator