APOD: NGC 4676: When Mice Collide (2021 Oct 04)

[APOD Robot]

NGC 4676: When Mice Collide

Explanation: These two mighty galaxies are pulling each other apart. Known as the "Mice" because they have such long tails, each spiral galaxy has likely already passed through the other. The long tails are created by the relative difference between gravitational pulls on the near and far parts of each galaxy. Because the distances are so large, the cosmic interaction takes place in slow motion -- over hundreds of millions of years. NGC 4676 lies about 300 million light-years away toward the constellation of Bernice's Hair (Coma Berenices) and are likely members of the Coma Cluster of Galaxies. The featured picture was taken with the Hubble Space Telescope's Advanced Camera for Surveys in 2002. These galactic mice will probably collide again and again over the next billion years so that, instead of continuing to pull each other apart, they coalesce to form a single galaxy.

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[Ann]

1) Disk of NGC 4676 A. Note that we can't see the nucleus, because it is hidden behind a foreground tidal dust tail, which ends in a region of star formation.

2) Disk of NGC 4676 B. This is clearly a barred spiral. We can see the nucleus and dust lanes related to the bar.

3) A bright blue tidal tail, possibly being fed by the region of star formation at the end of the dust tail passing in front of the nucleus of NGC 4676 A. It may also be fed by other blue tidal features of NGC 4676 B.

4) A very bright and broad tidal feature of NGC 4676 B, strongly dominated by young blue stars.

5) A tidal feature of dust and stars linking NGC 4676 A and NGC 4676 B. This tidal feature may originate in either or both of the galaxies.

It is inevitable that we want to compare The Mice, NGC 4676 A+B with the Antennae galaxies, NGC 4038/NGC 4039. I searched for images with muted colors, as that should make the comparison easier.

NGC 4676 and B. Image: SDSS/Donald Pelletier.

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NGC 4638.The Carnegie-Irvine Galaxy Survey.

Note that in the Mice galaxies, the bluest features are the tails or tidal features. In the Antennae galaxies, the tails are also bluish, but the brightest blue features are the brilliant young star clusters in NGC 4038, which are the products of a starburst.

The are no prominent star clusters in the Mice galaxies, and the blue color of their tails and tidal features is probably due to the presence of millions and millions of relatively modest A- and late B-type stars like Sirius, Vega and Regulus. In NGC 4038, by contrast, we are talking about stars like the brightest, hottest stars in Orion and in the brilliant Large Magellanic Cloud.

Ann

[JohnD]

If there was a Big Bang, and the Universe has continued to expand ever since, why are any colliding?

That they do implies that someone is drunk in charge of a Galaxy!
JOhn

[orin stepanek]

I kinda wonder how many stars and planets get kicked out of
the galaxy and wonder alone in the universe during one of
these happenings!
Is the photo kind of out of focus; or is it meant to be kind of soft?

Kitty love; notice the heart shaped by the tails?

The faith of the Milky-way and Andromeda; but don't worry; we won't
mind at all!

[Ann]

If there was a Big Bang, and the Universe has continued to expand ever since, why are any colliding?

That they do implies that someone is drunk in charge of a Galaxy!
JOhn

Galaxies collide because some galaxies are located quite close to one another. Consider the Milky Way and Andromeda. The distance between (the luminous disks of) our two galaxies is about 2 million light-years. (The halos of our two galaxies may already be touching.)

The Milky Way and Andromeda are gravitationally locked to one another. The "common gravity well" that we are located in can't be affected by the expansion of the Universe. That's why our two galaxies are going to collide in the future.

Ann

[JohnD]

That's NOW, Ann. What drew them together, when they started off on diverging trajectories, as in 'expanding'?
I call it careless driving, and someone should be prosecuted!

[neufer]

Rat king from Dellfeld, Germany, in the Musée zoologique de la ville de Strasbourg, France. Found in 1895.

---

<<A rat king is a collection of rats whose tails are intertwined and bound together by one of several possible mechanisms, such as entangling material like hair or sticky substances like sap or gum or getting tied together. Historically, this alleged phenomenon is particularly associated with Germany. There are several specimens preserved in museums but very few instances of rat kings have been observed in modern times.

In folklore, rat kings are associated with various superstitions and were often seen as a bad omen, particularly associated with plagues. Hoffmann's The Nutcracker and the Mouse King features a "Mouse King" (Mausekönig) with seven heads, seemingly inspired by the multiple-bodied rat king. The character is typically depicted as multi-headed in productions of the Tchaikovsky ballet The Nutcracker, based on the novella. The film The Nutcracker and the Four Realms, based on the short story, similarly features a "Mouse King", a rat-king like creature formed from a teeming mass of small mice. The Mouse King is also portrayed as a three-headed rat in Moscow Ballet's production of The Great Russian Nutcracker.>>

[Chris Peterson]

That's NOW, Ann. What drew them together, when they started off on diverging trajectories, as in 'expanding'?
I call it careless driving, and someone should be prosecuted!

They didn't start out diverging. They formed from material in regions that weren't expanding because of local gravity wells.

[Eclectic Man]

Rat king from Dellfeld, Germany, in the Musée zoologique de la ville de Strasbourg, France. Found in 1895.

---

<<A rat king is a collection of rats whose tails are intertwined and bound together by one of several possible mechanisms, such as entangling material like hair or sticky substances like sap or gum or getting tied together. Historically, this alleged phenomenon is particularly associated with Germany. There are several specimens preserved in museums but very few instances of rat kings have been observed in modern times.

In folklore, rat kings are associated with various superstitions and were often seen as a bad omen, particularly associated with plagues. Hoffmann's The Nutcracker and the Mouse King features a "Mouse King" (Mausekönig) with seven heads, seemingly inspired by the multiple-bodied rat king. The character is typically depicted as multi-headed in productions of the Tchaikovsky ballet The Nutcracker, based on the novella. The film The Nutcracker and the Four Realms, based on the short story, similarly features a "Mouse King", a rat-king like creature formed from a teeming mass of small mice. The Mouse King is also portrayed as a three-headed rat in Moscow Ballet's production of The Great Russian Nutcracker.>>

At the end of his book 'The Amazing Maurice and his educated rodents', the late Terry Pratchett discusses his research on rats and rat kings:

"I think I have read, in the past few months, more about rats than is good for me. Most of the true stuff - or, at least, the stuff that people say is true - is so unbelievable that I didn't include it in case readers thought I'd made it up.
...
Rat kings really exist. How they came into existence a mystery; in this book Malicia mentions a couple of the theories. I am indebted to Dr Jack Cohen for a more modern and and depressing one, which is that down the ages some cruel and inventive people have had altogether too much time on their hands."

Although squirrel kings also exist, so it could be a natural phenomenon: https://en.wikipedia.org/wiki/Squirrel_king

[johnnydeep]

Is the photo kind of out of focus; or is it meant to be kind of soft?
…

Yes, I’d say it does look “soft” and slightly out of focus. I take it Hubble’s optics are fine and this is simply the best it can do with something over 100 times farther away than Andromeda!

[neufer]

Is the photo kind of out of focus; or is it meant to be kind of soft?

Yes, I’d say it does look “soft” and slightly out of focus. I take it Hubble’s optics are fine and this is simply the best it can do with something over 100 times farther away than Andromeda!

It “looks soft” because it's all puffy/swollen from the collision.

(Observe how sharp the background galaxies appear.)

[Fred the Cat]

I've thought sharp focus and depth-of-field might be a way to measure distance. Did Hubble use this type of process to image one if its most famous views?

[Chris Peterson]

I've thought sharp focus and depth-of-field might be a way to measure distance. Did Hubble use this type of process to image one if its most famous views? :?

Optically, everything Hubble images is at infinity. Everything is in focus or nothing is.

[orin stepanek]

I've thought sharp focus and depth-of-field might be a way to measure distance. Did Hubble use this type of process to image one if its most famous views?

Optically, everything Hubble images is at infinity. Everything is in focus or nothing is.

Thanks everyone; I'm OK with the picture; soft is fine as it is supposed to look that way!

[johnnydeep]

Is the photo kind of out of focus; or is it meant to be kind of soft?

Yes, I’d say it does look “soft” and slightly out of focus. I take it Hubble’s optics are fine and this is simply the best it can do with something over 100 times farther away than Andromeda!

It “looks soft” because it's all puffy/swollen from the collision.

(Observe how sharp the background galaxies appear.)

I did indeed observe them before I posted and concluded that the background galaxies didn't look particularly sharp to me either. Are those in the pic below sharp? Maybe, and the largest in this view would be about 10 times farther away (assuming it is about the same absolute size).

A Mouse and some Background Galaxies - Sharp?

On the other hand, ARP 273 is another pair of interacting galaxies, also about 300 mly away, and I suppose it looks similarly "soft"...or does it?:

The upper galaxy is labelled UGC 1810 by itself, but together with its collisional partners is known as Arp 273. The overall shape of the UGC 1810 -- in particular its blue outer ring -- is likely a result of wild and violent gravitational interactions. The blue color of the outer ring at the top is caused by massive stars that are blue hot and have formed only in the past few million years. The inner part of the upper galaxy -- itself an older spiral galaxy -- appears redder and threaded with cool filamentary dust.

---

So, to what do we attribute the "puffy and swollen" appearance? More gas and less clumping due to being stirred up by tidal forces?

[neufer]

So, to what do we attribute the "puffy and swollen" appearance?
More gas and less clumping due to being stirred up by tidal forces?

It works for me.

To what do we attribute the "sharp & crisp" appearance of most galactic balls of stars & gas?

[Ann]

Yes, I’d say it does look “soft” and slightly out of focus. I take it Hubble’s optics are fine and this is simply the best it can do with something over 100 times farther away than Andromeda!

It “looks soft” because it's all puffy/swollen from the collision.

(Observe how sharp the background galaxies appear.)

I did indeed observe them before I posted and concluded that the background galaxies didn't look particularly sharp to me either. Are those in the pic below sharp? Maybe, and the largest in this view would be about 10 times farther away (assuming it is about the same absolute size).

Click to view full size image

On the other hand, ARP 273 is another pair of interacting galaxies, also about 300 mly away, and I suppose it looks similarly "soft"...or does it?:

The upper galaxy is labelled UGC 1810 by itself, but together with its collisional partners is known as Arp 273. The overall shape of the UGC 1810 -- in particular its blue outer ring -- is likely a result of wild and violent gravitational interactions. The blue color of the outer ring at the top is caused by massive stars that are blue hot and have formed only in the past few million years. The inner part of the upper galaxy -- itself an older spiral galaxy -- appears redder and threaded with cool filamentary dust.

---

So, to what do we attribute the "puffy and swollen" appearance? More gas and less clumping due to being stirred up by tidal forces?

There are at least two reasons for the different degrees of "softness" in the Mice galaxies versus UGC 1810.

UGC 1810 is a pair of galaxies where the arms, particularly in the upper, larger galaxy, are particularly well defined. They are undoubtedly a log brighter than the underlying disk. In the Mice galaxies, by contrast, there aren't really any arms. These galaxies are basically all disks with tidal tails attached. Neither the disks nor the tails are extremely well defined.

Second, consider the filters used for the two images. For the Mice galaxies image, the filter used were 475 nm, 606 nm and 814 nm. Of these, both the 606 nm and the 814 nm filters are good at detecting the small red stars that undoubtedly form soft "halos" or at least "puffed-up outer disks" around the main disks.

For the UGC 1810 image, the filters were 390 nm, 475 nm and 600 nm. Both the 390 nm and the 475 nm filters are very good at detecting the the bright hot stars in the arms. The 600 nm will do an okay, but in no way an outstanding job, at detecting an outer halo of old red stars around these galaxies.

So in short: The filters used for UGC are well designed for pickiing out the bright well-formed arms dominated by hot bright stars in these galaxies. The filters used for the Mice galaxies are well designed for picking out the "fog" of old cool stars that are undoubtedly surrounding the disks of these galaxies.

To see what I mean, take a look at this Hubble picture of NGC 4214:

NGC 4214. Image: NASA, ESA and the Hubble Heritage Team. Acknowledgement: R O'ConnelL

As you can see, NGC 4214 contains some brilliantly bright sites of star formation, which have given birth to a number of extremely luminous supermassive blue stars. But NGC 4214 also contains a "fog" of millions and millions of small red stars.

It is the same kind of small red stars that make the disks of the Mice galaxies look diffuse.

However... I think it is also true that astrophotographers apply "sharpening" to their images, whatever that is and however that is done.

So I guess it is possible that those who created the picture of UGC 1810 applied more sharpening to their image than those who created the picture of the Mice galaxies.

Ann

[farlightteam]

Así será el futuro de la galaxia nuestra y andrómeda