APOD: Arp 87: Merging Galaxies from Hubble (2023 Oct 24)

[APOD Robot]

Arp 87: Merging Galaxies from Hubble

Explanation: This dance is to the death. As these two large galaxies duel, a cosmic bridge of stars, gas, and dust currently stretches over 75,000 light-years and joins them. The bridge itself is strong evidence that these two immense star systems have passed close to each other and experienced violent tides induced by mutual gravity. As further evidence, the face-on spiral galaxy on the right, also known as NGC 3808A, exhibits many young blue star clusters produced in a burst of star formation. The twisted edge-on spiral on the left (NGC 3808B) seems to be wrapped in the material bridging the galaxies and surrounded by a curious polar ring. Together, the system is known as Arp 87. While such interactions are drawn out over billions of years, repeated close passages will ultimately create one merged galaxy. Although this scenario does look unusual, galactic mergers are thought to be common, with Arp 87 representing a stage in this inevitable process. The Arp 87 dancing pair are about 300 million light-years distant toward the constellation of the Lion (Leo). The prominent edge-on spiral galaxy at the far left appears to be a more distant background galaxy and not involved in the on-going merger.

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[Ann]

Arp 87: Merging Galaxies from Hubble. Image Credit: NASA, ESA, Hubble; Processing: Harshwardhan Pathak

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Wow, what a fascinating pair!

Since I'm a lover of all things blue, today's APOD obviously has me smiling. I checked Arp 87 with my software, and the two galaxies are indeed relatively blue, even though they are sufficiently far away that redshift reddening should affect them at least a little bit. Fascinatingly, it is the smaller, edge-on galaxy, NGC 3808B, that has the bluest colors, both according to my software and according to Simbad. And indeed, you can see that the long bar or edge-on disk of NGC 3808B is brilliantly white, probably from large numbers of very hot stars.

Which brings us to this...

How can you tell at a glance that the galaxy to the lower left of NGC 3808B is a background galaxy? You can tell because the the other galaxy is both smaller-looking and decidedly redder than NGC 3808B. It is redder because of redshift reddening, and it looks smaller because it is farther away. In reality, this galaxy is probably quite big. It has a large disk, and we can see dust lanes in the disk. This is a large, undisturbed galaxy.

Which brings me to this...

NGC 7733 /bottom) and NGC 7734 (top). Credit: ESA/Hubble & NASA, J. Dalcanton, Dark Energy Survey/DOE/FNAL/NOIRLab/NSF/AURA Acknowledgement: L. Shatz

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NGC 7733 and NGC 7734 form another fascinating interacting pair. But there is a third galaxy making an appearance here. This galaxy looks like a yellow-brown blob in the upper arm of galaxy NGC 3377.

But we can tell at a glance that "the blob" is a background object. How? Well, because it is small and reddish. But also because it seems to sit inside the upper arm of NGC 7733, but NGC 7733 is absolutely undisturbed by its presence. That would almost certainly not have been the case if this brown blob was a true dwarf galaxy tangled in one arm of NGC 7733. Just look at what dwarf galaxy NGC 1510 is doing to the arms of NGC 1512!

NGC 1512 and satellite galaxy NGC 1510. Credit: NASA/Caltech-JPL

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Of course, there is also NGC 6050, which is a pair of interacting galaxies with a most strange little dwarf galaxy that is positively entwined in an arm connecting the the two larger galaxies. Yes, but at least this arm seems to feel the presence of this "extra galaxy" - oh well...

Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and K. Noll (STScI)

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Anyway. What is most fascinating about today's APOD is how a stream of gas and stars from NGC 3808 seems to wrap itself around the disk of NGC 3808B to form a polar ring. Polar ring galaxies are so rare, but they are so fascinating!

NGC 4650A. Credit: The Hubble Heritage Team (AURA/STScI/NASA)

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NGC 4650A is an iconic polar ring galaxy. And just like NGC 3808B, NGC 4650A is located close to another, larger galaxy! The designation of this larger galaxy is - you guessed it - NGC 4650.

NGC 4650A and NGC 4650. Credit: Detlef (?)

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And indeed, NGC 4650 and NGC 4650A have the same recessional velocity. They are indeed close enough to be interacting. Although, as you can see, there is another galaxy that is even closer to NGC 4650. My amateur guess is that there are no current large scale streams of gas and stars between NGC 4650 and NGC 4650A, and that the polar ring of NGC 4650 could be a remnant of past interactions between NGC 4650 and 4650A, when the two galaxies were closer to one another.

So is it true, then, that polar ring galaxies are formed through interactions with another galaxy? Or else, perhaps the "polar ring galaxy to be" just "happened upon" a large detached gas cloud and interacted with it to form a polar ring?

Questions, questions. I can only offer speculation, unfortunately!

Ann

[JohnD]

Great series of pics, Ann! Now, I KNOW that every star in those galaxies is light years from the next, and I KNOW that a process such as this is over a very long period, but what would it be like to live in one of colliding galaxies? "Violent tides", "bursts of star formation" it's all very violent! Would life on a planet in those galaxies be more or less likely as a result?

Our galaxy will collide with Andromeda in about four billion years, should we start to think about it?
JOhn

[Chris Peterson]

Great series of pics, Ann! Now, I KNOW that every star in those galaxies is light years from the next, and I KNOW that a process such as this is over a very long period, but what would it be like to live in one of colliding galaxies? "Violent tides", "bursts of star formation" it's all very violent! Would life on a planet in those galaxies be more or less likely as a result?

Our galaxy will collide with Andromeda in about four billion years, should we start to think about it?
JOhn

The problem is that two stars passing within a light year or so of each other will alter the orbits of each other's planetary systems. And that's a problem for life. It's especially a problem for complex life, which requires at least hundreds of millions of years of stability to develop. Earth's orbit would only have to be perturbed by a few percent to pretty much end most life on the planet.

[Christian G.]

In a universe where everything is pushed apart until all freezes to death, mergers are not duels but rebirths! - Galaxies, unite!
Spectacular sight..

[Pastorian]

In a universe where everything is pushed apart until all freezes to death, mergers are not duels but rebirths! - Galaxies, unite!
Spectacular sight..

Reminds me of the G.K. Chesterton quotable: "Marriage is a duel to the death which no man of honour should decline."

[Maxedwell7]

Would any stars in the “bridge” be able to support planets with life? What would those stars revolve around if they are pulled out of their respective galaxies without the gravitational pull of their central black holes?

[Pastorian]

Another anthropomorphic possibility:
In other news today, NGC 3808A Corp. continued its hostile takeover bid of NGC 3808B, Inc., which sought an antitrust injunction to block the merger. The two are expected to battle it out in InterGalactic Court over the next 10K millenia.

[Chris Peterson]

Would any stars in the “bridge” be able to support planets with life? What would those stars revolve around if they are pulled out of their respective galaxies without the gravitational pull of their central black holes?

The gravitational force of the central black holes of galaxies is insignificant in terms of defining the orbits of the stars in those galaxies. And there's no reason a star needs to be in a galaxy at all for it to support a planetary system that could have life. Indeed, a rogue star, outside of a galaxy, would offer the most stable possible conditions for a planetary system.

[Ann]

Great series of pics, Ann! Now, I KNOW that every star in those galaxies is light years from the next, and I KNOW that a process such as this is over a very long period, but what would it be like to live in one of colliding galaxies? "Violent tides", "bursts of star formation" it's all very violent! Would life on a planet in those galaxies be more or less likely as a result?

Our galaxy will collide with Andromeda in about four billion years, should we start to think about it?
JOhn

The problem is that two stars passing within a light year or so of each other will alter the orbits of each other's planetary systems. And that's a problem for life. It's especially a problem for complex life, which requires at least hundreds of millions of years of stability to develop. Earth's orbit would only have to be perturbed by a few percent to pretty much end most life on the planet.

As Chris said, even a small change of the Earth's orbit could be catastrophic for most life on our planet. And a collision between Andromeda and the Milky Way will result in enormous tidal forces ripping through the entire Milky Way.

Click to play embedded YouTube video.

The prospects for life on Earth are not good, I think, during and after the merger between Andromeda and the Milky Way.

Ann

[JohnD]

Thank you, Ann and Chris!

So, what factor should be added to Drake's Equation, R* x FP x Ne x FL x FI x FC x L = Number of intelligent civs?
And does this answer Fermi's question, "Where is everybody?" ?

John

[orin stepanek]

As to whether Earths life status would be disrupted during a galactic
merger; I have a feeling that it wouldn't matter much to me!

[Ann]

Thank you, Ann and Chris!

So, what factor should be added to Drake's Equation, R* x FP x Ne x FL x FI x FC x L = Number of intelligent civs?
And does this answer Fermi's question, "Where is everybody?" ?

John

Yeah, having a planet with a good, stable orbit for billions of years, which is staying warm and wet for the same amount of time, is a good start for (complex) life.

Many little "miracles" have made complex life on Earth possible. I like this momentous "merger" - yeah, speaking about mergers - that joined bacteria and archea together and gave us powerhouse cells that could build large complex life forms, such as us. And this apparently happened just once in the history of the Earth. I do recommend the video!

Click to play embedded YouTube video.

If this mutation (or merger) hadn't happened, we would still all be Bacteria. Or Archaea.

We wouldn't be doing much computer science or spacefaring if we were all still just Bacteria (or Archaea).

Ann

[johnnydeep]

Great series of pics, Ann! Now, I KNOW that every star in those galaxies is light years from the next, and I KNOW that a process such as this is over a very long period, but what would it be like to live in one of colliding galaxies? "Violent tides", "bursts of star formation" it's all very violent! Would life on a planet in those galaxies be more or less likely as a result?

Our galaxy will collide with Andromeda in about four billion years, should we start to think about it?
JOhn

The problem is that two stars passing within a light year or so of each other will alter the orbits of each other's planetary systems. And that's a problem for life. It's especially a problem for complex life, which requires at least hundreds of millions of years of stability to develop. Earth's orbit would only have to be perturbed by a few percent to pretty much end most life on the planet.

It's only a problem for "life as we know it" on Earth's surface. A planet warmed by radioactive decay in its core could maintain stable liquid water in a subsurface ocean for billions of years, and support life that was entirely oblivious to any goings on above the planet's thick ice crust, regardless of whether it was even still orbiting its original parent star. Granted we have yet to discover any such life, but for all we know, subsurface ice crust liquid water ocean life is the predominant form of life in the universe.

[Chris Peterson]

Great series of pics, Ann! Now, I KNOW that every star in those galaxies is light years from the next, and I KNOW that a process such as this is over a very long period, but what would it be like to live in one of colliding galaxies? "Violent tides", "bursts of star formation" it's all very violent! Would life on a planet in those galaxies be more or less likely as a result?

Our galaxy will collide with Andromeda in about four billion years, should we start to think about it?
JOhn

The problem is that two stars passing within a light year or so of each other will alter the orbits of each other's planetary systems. And that's a problem for life. It's especially a problem for complex life, which requires at least hundreds of millions of years of stability to develop. Earth's orbit would only have to be perturbed by a few percent to pretty much end most life on the planet.

It's only a problem for "life as we know it" on Earth's surface. A planet warmed by radioactive decay in its core could maintain stable liquid water in a subsurface ocean for billions of years, and support life that was entirely oblivious to any goings on above the planet's thick ice crust, regardless of whether it was even still orbiting its original parent star. Granted we have yet to discover any such life, but for all we know, subsurface ice crust liquid water ocean life is the predominant form of life in the universe.

Yes... but I'm skeptical enough energy would be present in that model to allow for complex life within a complex ecosystem.

[RocketRon]

We wonder what our Milky Way and Andromeda galaxies look like from afar ?

Have we also been involved in such a dance, or is it yet to begin ?
And, at what stage does that star bridge begin to form.
In advance, or afterwards ??

[johnnydeep]

The problem is that two stars passing within a light year or so of each other will alter the orbits of each other's planetary systems. And that's a problem for life. It's especially a problem for complex life, which requires at least hundreds of millions of years of stability to develop. Earth's orbit would only have to be perturbed by a few percent to pretty much end most life on the planet.

It's only a problem for "life as we know it" on Earth's surface. A planet warmed by radioactive decay in its core could maintain stable liquid water in a subsurface ocean for billions of years, and support life that was entirely oblivious to any goings on above the planet's thick ice crust, regardless of whether it was even still orbiting its original parent star. Granted we have yet to discover any such life, but for all we know, subsurface ice crust liquid water ocean life is the predominant form of life in the universe.

Yes... but I'm skeptical enough energy would be present in that model to allow for complex life within a complex ecosystem.

Well, what about that environment would be fundamentally different from the extant ecosystems of thriving complex life that Earth has evolved in its deep oceans, where sunlight doesn't penetrate, and the water is calm and cold?

[Chris Peterson]

It's only a problem for "life as we know it" on Earth's surface. A planet warmed by radioactive decay in its core could maintain stable liquid water in a subsurface ocean for billions of years, and support life that was entirely oblivious to any goings on above the planet's thick ice crust, regardless of whether it was even still orbiting its original parent star. Granted we have yet to discover any such life, but for all we know, subsurface ice crust liquid water ocean life is the predominant form of life in the universe.

Yes... but I'm skeptical enough energy would be present in that model to allow for complex life within a complex ecosystem.

Well, what about that environment would be fundamentally different from the extant ecosystems of thriving complex life that Earth has evolved in its deep oceans, where sunlight doesn't penetrate, and the water is calm and cold?

I don't think complex life developed in the deep ocean. And all life in the oceans derives almost all its energy from photosynthesis, either directly or indirectly. Life in the deep ocean is fed by surface life that gets its energy from sunlight. The explosion of complex life on Earth occurred in very shallow seas.

[johnnydeep]

Yes... but I'm skeptical enough energy would be present in that model to allow for complex life within a complex ecosystem.

Well, what about that environment would be fundamentally different from the extant ecosystems of thriving complex life that Earth has evolved in its deep oceans, where sunlight doesn't penetrate, and the water is calm and cold?

I don't think complex life developed in the deep ocean. And all life in the oceans derives almost all its energy from photosynthesis, either directly or indirectly. Life in the deep ocean is fed by surface life that gets its energy from sunlight. The explosion of complex life on Earth occurred in very shallow seas.

I guess that's right, but perhaps with an active enough molten magma-water boundary, there would be enough energy available for a long enough period of time, to facilitate ever complex life, even without the benefit of photosynthesis (and maybe photosynthesis could still develop using infrared radiation rather than visible light?). I remain hopeful that the particular path life took on Earth is not the only way possible!