APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

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APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by APOD Robot » Wed Nov 17, 2021 5:06 am

Image NGC 3314: When Galaxies Overlap

Explanation: Why doesn't the nearby galaxy create a gravitational lensing effect on the background galaxy? It does, but since both galaxies are so nearby, the angular shift is much smaller than the angular sizes of the galaxies themselves. The featured Hubble image of NGC 3314 shows two large spiral galaxies which happen to line up exactly. The foreground spiral NGC 3314a appears nearly face-on with its pinwheel shape defined by young bright star clusters. Against the glow of the background galaxy NGC 3314b, though, dark swirling lanes of interstellar dust can also be seen tracing the nearer spiral's structure. Both galaxies appear on the edge of the Hydra Cluster of Galaxies, a cluster that is about 200 million light years away. Gravitational lens distortions are much easier to see when the lensing galaxy is smaller and further away. Then, the background galaxy may even be distorted into a ring around the nearer. Fast gravitational lens flashes due to stars in the foreground galaxy momentarily magnifying the light from stars in the background galaxy might one day be visible in future observing campaigns with high-resolution telescopes.

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by Ann » Wed Nov 17, 2021 5:57 am

APOD November 17 2021 NGC 3314 Ostling.png

Wow, these two overlapping non-interacting galaxies are certainly one of my absolutely favorite galactic pairs!

As you can see, one of the galaxies (and I'm not sure if it is A or B) is the foreground one and therefore much smaller than the background galaxy which is well in the background.

Note that we can see the dust lanes of the foreground galaxy extremely well as it is being backlit by the background galaxy, but we can't see the young blue stars very well against the massive and luminous disk of the background galaxy. The young blue stars are very visible against the blackness of space, but here we can't see the dust lanes.

Note that the foreground galaxy does have two relatively short, rather well-formed and not very star-forming arms. But then it also has what looks like the magnificent trail of a bridal gown of long delicate arms fanning out "below and to one side", but not to the other.

NGC 3314 A and B belong to the Hydra Cluster of galaxies. I guess that at least the foreground member of NGC 3314 is moving through the intergalactic medium of the Hydra Cluster in such a way that it is being stripped of at least some of its gas, although NGC 3314A (or B?) is not a typical member of a "jellyfish galaxy" which is being "bled dry" through terrific ram pressure:


Of course, the long violet tails hanging from galaxy ESO 137-001 can be seen only in X-rays, not even in invisible ultraviolet. Perhaps an X-ray examination of NGC 3314 would turn up something interesting?

Ann
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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by VictorBorun » Wed Nov 17, 2021 7:59 am

The foreground galaxy is not in fact face on to us; I think we can uncompress the compessed disk like this:
NGC 3314-When Galaxies Overlap..png
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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by VictorBorun » Wed Nov 17, 2021 8:38 am

in 2005 APOD the core was more visible:
https://apod.nasa.gov/apod/ap050507.html

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by Ann » Wed Nov 17, 2021 9:50 am

VictorBorun wrote:
Wed Nov 17, 2021 8:38 am
in 2005 APOD the core was more visible:
https://apod.nasa.gov/apod/ap050507.html
That APOD almost certainly provides a "truer" portrait of the luminosity distribution across the face of the foreground galaxy. After all, we always expect the central part of a galaxy to be the brightest. And if it isn't, the picture of it has either been "manipulated" to bring ut faint outer features, or else we are dealing with a very unusual galaxy indeed!

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by orin stepanek » Wed Nov 17, 2021 12:46 pm

NGC3314_HubbleOstling_960.jpg
I was wondering if the two are or will be interacting; they seem
so close! :roll:
18w9o6xdiip21.jpg
Cats are waiting!
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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by Fred the Cat » Wed Nov 17, 2021 3:24 pm

I was curious about the physical size of these two objects in relation to their distances. :?:
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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by neufer » Wed Nov 17, 2021 3:35 pm

https://en.wikipedia.org/wiki/NGC_3314 wrote:
<<NGC 3314 is a pair of overlapping spiral galaxies between 117 (NGC 3314a) and 140 million (NGC 3314b) light-years away in the constellation Hydra. This unique alignment gives astronomers the opportunity to measure the properties of interstellar dust in the face-on foreground galaxy (NGC 3314a). The dust appears dark against the background galaxy (NGC 3314b). In a March 2000 observation of the galaxies, a prominent green star-like object was seen in one of the arms. Astronomers theorized that it could have been a supernova, but the unique filtering properties of the foreground galaxy made it difficult to decide definitively.>>
Albert Einstein predicted that:
  • 1) rays of light from the same direction that skirt the edges of the Sun
    would converge to a focal point approximately 542 AU from the Sun.

    2) rays of light from the same direction that pass by the Sun at 1 AU
    would converge to a focal point approximately 396 light years from the Sun.

    3) rays of light from the same direction that pass by the Sun at 220 AU
    would converge to a focal point approximately 19.22 Mlys from the Sun.
Hence: rays of light from a point 140 Mly away (NGC 3314b) that pass by a solar mass object 117 Mly away (NGC 3314a) at a radial distance of 220 AU would converge onto us :!: {Note: Focal length rule: [1/19.22] = [1/(140-117) + 1/117]}

So was that prominent green star actually due to a ~440 AU wide stellar mass gravitational lens :?:
Art Neuendorffer

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by gquainta » Wed Nov 17, 2021 4:04 pm

Looks like a UFO :D

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by Fred the Cat » Wed Nov 17, 2021 4:13 pm

neufer wrote:
Wed Nov 17, 2021 3:35 pm
https://en.wikipedia.org/wiki/NGC_3314 wrote:
<<NGC 3314 is a pair of overlapping spiral galaxies between 117 (NGC 3314a) and 140 million (NGC 3314b) light-years away in the constellation Hydra. This unique alignment gives astronomers the opportunity to measure the properties of interstellar dust in the face-on foreground galaxy (NGC 3314a). The dust appears dark against the background galaxy (NGC 3314b). In a March 2000 observation of the galaxies, a prominent green star-like object was seen in one of the arms. Astronomers theorized that it could have been a supernova, but the unique filtering properties of the foreground galaxy made it difficult to decide definitively.>>
Albert Einstein predicted that:
  • 1) rays of light from the same direction that skirt the edges of the Sun
    would converge to a focal point approximately 542 AU from the Sun.

    2) rays of light from the same direction that pass by the Sun at 1 AU
    would converge to a focal point approximately 396 light years from the Sun.

    3) rays of light from the same direction that pass by the Sun at 220 AU
    would converge to a focal point approximately 19.22 Mlys from the Sun.
Hence: rays of light from a point 140 Mly away (NGC 3314b) that pass by a solar mass object 117 Mly away (NGC 3314a) at a radial distance of 220 AU would converge onto us :!: {Note: Focal length rule: [1/19.22] = [1/(140-117) + 1/117]}

So was that prominent green star actually due to a ~440 AU wide stellar mass gravitational lens :?:
It's not easy bein' green! :wink:
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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by johnnydeep » Wed Nov 17, 2021 8:36 pm

orin stepanek wrote:
Wed Nov 17, 2021 12:46 pm
NGC3314_HubbleOstling_960.jpg
I was wondering if the two are or will be interacting; they seem
so close! :roll:
18w9o6xdiip21.jpg
Cats are waiting!
The foreground and background galaxies are not that close. Wikipedia says they are 23 Mly apart, at 117 Mly for 3314a and 140 Mly for 3314b.
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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by Mostly empty » Wed Nov 17, 2021 10:35 pm

This is where you realize that these big galaxy things are mostly vacuum (like atoms!) and transparent. Which you knew, right, but it's not like you can wave your hand behind one.

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by Cousin Ricky » Wed Nov 17, 2021 10:47 pm

This image really shows just how diaphanous galaxies are.

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by VictorBorun » Thu Nov 18, 2021 5:53 am

Suppose there are two spiral stellar arms separated by the dusty arms and that the pair is symmetric relative to their common appex.
We can use a spline to fit visible parts of one stellar arm that shine against the cosmic black and to fit between visible parts of dusty arms that look brown against the background disc galaxy.
Then we can clone that spline and rotate by 180° to see if the clone fits well.
We can switch between fitting the master spline to one arm and to the other arm by rotating both the master spline and the clone spline by 180°.
Here is my try:
NGC 3314-2.png
NGC 3314-3.png
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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by VictorBorun » Thu Nov 18, 2021 6:07 am

neufer wrote:
Wed Nov 17, 2021 3:35 pm
https://en.wikipedia.org/wiki/NGC_3314 wrote:
<<NGC 3314 is a pair of overlapping spiral galaxies between 117 (NGC 3314a) and 140 million (NGC 3314b) light-years away in the constellation Hydra. This unique alignment gives astronomers the opportunity to measure the properties of interstellar dust in the face-on foreground galaxy (NGC 3314a). The dust appears dark against the background galaxy (NGC 3314b). In a March 2000 observation of the galaxies, a prominent green star-like object was seen in one of the arms. Astronomers theorized that it could have been a supernova, but the unique filtering properties of the foreground galaxy made it difficult to decide definitively.>>
rays of light from a point 140 Mly away (NGC 3314b) that pass by a solar mass object 117 Mly away (NGC 3314a) at a radial distance of 220 AU would converge onto us :!: {Note: Focal length rule: [1/19.22] = [1/(140-117) + 1/117]}

So was that prominent green star actually due to a ~440 AU wide stellar mass gravitational lens :?: [/b]
A SN event takes a day to brighten up and a year to fade.
A gravi-lensing event where a foreground star has a light day zone of focusing and a relative velocity of с/365 would take a year to brighten up and then a year to fade, and the brightness against time would be symmetric bell-shape curve, would not it?

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by orin stepanek » Thu Nov 18, 2021 1:23 pm

johnnydeep wrote:
Wed Nov 17, 2021 8:36 pm
orin stepanek wrote:
Wed Nov 17, 2021 12:46 pm
NGC3314_HubbleOstling_960.jpg
I was wondering if the two are or will be interacting; they seem
so close! :roll:
18w9o6xdiip21.jpg
Cats are waiting!
The foreground and background galaxies are not that close. Wikipedia says they are 23 Mly apart, at 117 Mly for 3314a and 140 Mly for 3314b.
I missed that; thank you!
Orin

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by neufer » Thu Nov 18, 2021 2:11 pm

Mostly empty wrote:
Wed Nov 17, 2021 10:35 pm

This is where you realize that these big galaxy things are mostly vacuum (like atoms!) and transparent.
Which you knew, right, but it's not like you can wave your hand behind one.
The diameter of a nucleus is ~1/100,000 that of an atom.

The diameter of the Sun is ~1/10,00,000 that of the Oort Cloud.


If galaxies weren't mostly vacuum then they would be as bright as the surface of a star (in it's dust free zones).
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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by neufer » Thu Nov 18, 2021 2:33 pm

VictorBorun wrote:
Thu Nov 18, 2021 6:07 am
neufer wrote:
Wed Nov 17, 2021 3:35 pm
https://en.wikipedia.org/wiki/NGC_3314 wrote:
<<NGC 3314 is a pair of overlapping spiral galaxies between 117 (NGC 3314a) and 140 million (NGC 3314b) light-years away in the constellation Hydra. This unique alignment gives astronomers the opportunity to measure the properties of interstellar dust in the face-on foreground galaxy (NGC 3314a). The dust appears dark against the background galaxy (NGC 3314b). In a March 2000 observation of the galaxies, a prominent green star-like object was seen in one of the arms. Astronomers theorized that it could have been a supernova, but the unique filtering properties of the foreground galaxy made it difficult to decide definitively.>>
rays of light from a point 140 Mly away (NGC 3314b) that pass by a solar mass object 117 Mly away (NGC 3314a) at a radial distance of 220 AU would converge onto us :!: {Note: Focal length rule: [1/19.22] = [1/(140-117) + 1/117]}

So was that prominent green star actually due to a ~440 AU wide stellar mass gravitational lens :?: [/b]
A SN event takes a day to brighten up and a year to fade.

A gravi-lensing event where a foreground star has a light day zone of focusing and a relative velocity of с/365 would take a year to brighten up and then a year to fade, and the brightness against time would be symmetric bell-shape curve, would not it?
The "zone of focusing" in this case would have to be much less than ~440 AU wide.

Relative velocities might be on the order of с/1000 (= ~1.2 AU/week).
https://en.wikipedia.org/wiki/Gravitational_microlensing wrote:
<<Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit much light (stars) or large objects that block background light (clouds of gas and dust). These objects make up only a minor portion of the mass of a galaxy. Microlensing allows the study of objects that emit little or no light.

A typical microlensing event like OGLE-2005-BLG-006 one has a very simple shape, and only one physical parameter can be extracted: the time scale, which is related to the lens mass, distance, and velocity. There are several effects, however, that contribute to the shape of more atypical lensing events:
  • Lens mass distribution. If the lens mass is not concentrated in a single point, the light curve can be dramatically different, particularly with caustic-crossing events, which may exhibit strong spikes in the light curve. In microlensing, this can be seen when the lens is a binary star or a planetary system.

    Finite source size. In extremely bright or quickly-changing microlensing events, like caustic-crossing events, the source star cannot be treated as an infinitesimally small point of light: the size of the star's disk and even limb darkening can modify extreme features.

    Parallax. For events lasting for months, the motion of the Earth around the Sun can cause the alignment to change slightly, affecting the light curve.
Most focus is currently on the more unusual microlensing events, especially those that might lead to the discovery of extrasolar planets. Another way to get more information from microlensing events involves measuring the astrometric shifts in the source position during the course of the event and even resolving the separate images with interferometry. The first successful resolution of microlensing images was achieved with the GRAVITY instrument on the Very Large Telescope Interferometer

In practice, because the alignment needed is so precise and difficult to predict, microlensing is very rare. Events, therefore, are generally found with surveys, which photometrically monitor tens of millions of potential source stars, every few days for several years. Dense background fields suitable for such surveys are nearby galaxies, such as the Magellanic Clouds and the Andromeda galaxy, and the Milky Way bulge. In each case, the lens population studied comprises the objects between Earth and the source field: for the bulge, the lens population is the Milky Way disk stars, and for external galaxies, the lens population is the Milky Way halo, as well as objects in the other galaxy itself. The density, mass, and location of the objects in these lens populations determines the frequency of microlensing along that line of sight, which is characterized by a value known as the optical depth due to microlensing. (This is not to be confused with the more common meaning of optical depth, although it shares some properties.) The optical depth is, roughly speaking, the average fraction of source stars undergoing microlensing at a given time, or equivalently the probability that a given source star is undergoing lensing at a given time. The MACHO project found the optical depth toward the LMC to be 1.2×10−7, and the optical depth toward the bulge to be 2.43×10−6 or about 1 in 400,000.

Complicating the search is the fact that for every star undergoing microlensing, there are thousands of stars changing in brightness for other reasons (about 2% of the stars in a typical source field are naturally variable stars) and other transient events (such as novae and supernovae), and these must be weeded out to find true microlensing events. After a microlensing event in progress has been identified, the monitoring program that detects it often alerts the community to its discovery, so that other specialized programs may follow the event more intensively, hoping to find interesting deviations from the typical light curve. This is because these deviations – particularly ones due to exoplanets – require hourly monitoring to be identified, which the survey programs are unable to provide while still searching for new events. The question of how to prioritize events in progress for detailed followup with limited observing resources is very important for microlensing researchers today.>>
Art Neuendorffer

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by VictorBorun » Thu Nov 18, 2021 2:58 pm

neufer wrote:
Thu Nov 18, 2021 2:33 pm
Wow thanks for enlighting me! I was taking for granted that observed lensing events were few, the lenses were some rogue planets and the durations were some 20 minutes.

Now I see that a star and a binary star as a lense can last for a month and, in theory, play tricks in time

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Re: APOD: NGC 3314: When Galaxies Overlap (2021 Nov 17)

Post by Ann » Thu Nov 18, 2021 4:55 pm

VictorBorun wrote:
Thu Nov 18, 2021 5:53 am
Suppose there are two spiral stellar arms separated by the dusty arms and that the pair is symmetric relative to their common appex.
We can use a spline to fit visible parts of one stellar arm that shine against the cosmic black and to fit between visible parts of dusty arms that look brown against the background disc galaxy.
Then we can clone that spline and rotate by 180° to see if the clone fits well.
We can switch between fitting the master spline to one arm and to the other arm by rotating both the master spline and the clone spline by 180°.
Here is my try:
It works quite well, Victor. I think that NGC 3314A (the foreground galaxy) looks like a quite regular spiral (except it has a long "train" of a large number of star forming arms trailing off to one side), and your annotation underscores the regular morphology of it.

Ann
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