APOD: The Antennae Galaxies in Collision (2020 Dec 03)

[APOD Robot]

The Antennae Galaxies in Collision

Explanation: Sixty million light-years away toward the southerly constellation Corvus, these two large galaxies are colliding. The cosmic train wreck captured in stunning detail in this Hubble Space Telescope snapshot takes hundreds of millions of years to play out. Cataloged as NGC 4038 and NGC 4039, the galaxies' individual stars don't often collide though. Their large clouds of molecular gas and dust do, triggering furious episodes of star formation near the center of the wreckage. New star clusters and interstellar matter are jumbled and flung far from the scene of the accident by gravitational forces. This Hubble close-up frame is about 50,000 light-years across at the estimated distance of the colliding galaxies. In wider-field views their suggestive visual appearance, with extended structures arcing for hundreds of thousands of light-years, gives the galaxy pair its popular name, The Antennae Galaxies.

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[Ann]

Today's APOD is an oldie but goodie! This galactic pair is a textbook example of what happens when two galaxies collide, and at least one of them is gas-rich.

'Dry merger' of the gas-poor galaxies IC 1178 and IC 1181. Photo: SDSS.

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Let's look at the four most standout features of galaxies NGC 4038 and NGC 4039. Look at the picture at left.

1) This is the nucleus of galaxy NGC 4038. You can tell the nucleus by its yellow color. The nucleus is also pretty bright and quite centrally located.

2) This is the nucleus of galaxy NGC 4039. Again the nucleus is yellow. Fascinatingly, the nucleus of NGC 4039 appears to be about as bright and about as big as the nucleus of NGC 4038. This suggests that the two galaxies are of similar mass.

3) This is the contorted arm of NGC 4038, which is chock full of hot young blue star clusters and huge pink emission nebulas. NGC 4038 is indeed a starburst galaxy.

4) This is the extremely dusty "bridge" between the two galaxies. An enormous amount of star formation is going on inside the dust. I have been unable to find out the far infrared magnitude of these galaxies, but my personal guess is that the enormous dust cloud inside them and between them makes them at least second cousins to an ultraluminous infrared galaxy.


So what happens when two gas-poor galaxies collide? Well... not much! Look at the picture at right. Two galaxies without gas have collided, and we get no star clusters, no emission nebulas and no dust clouds. Everything is uniformly yellow in most gas-poor galaxies. But long tidal tails of old yellow stars have been flung out from the two colliding galaxies IC 1178 and IC 1181.


When two galaxies have collided, what does the more "advanced" merger product look like?

Distorted spiral galaxy NGC 3310 that might be a merger product. Photo: NASA and The Hubble Heritage Team (STScI/AURA).

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Galaxy NGC 7252, a merger product. Credit: NASA & ESA, Acknowledgement: Judy Schmidt (Geckzilla).

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I'm not sure that NGC 3310 at left really is a merger product, but it looks like it to me. Strong winds seem to sweep through the galaxy, creating a whirlwind-like ring around the nucleus, tattered arms and windblown "streamers" of gas and dust. NGC 3310 is a gas-rich galaxy like NGC 4038, and furious star formation is taking place inside it.

What happens when the dust has settled? NGC 7252 provides one possible answer. This galaxy contains a small "inner spiral", only about 10,000 light-years across. Outside of this small spiral galaxy is a ring of dust with some adjoining tails, and outside this dust ring is a large amorphous disk seemingly consisting of several overlapping smooth shell-like structures with no star formation. We can see a tidal feature at right that clearly contains gas and forms new stars, but otherwise this galaxy appears to have "spent" most of its gas.

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Is this what "Milkomeda" will look like, the collision product of the Milky Way and the Andromeda galaxy? Time will tell! Good thing we don't have to be there and watch.

Ann

[Tszabeau]

Is the streak, just right of center, a nearby object streaking through the field of view or an edge-on galaxy, far far away?

[XgeoX]

Is the streak, just right of center, a nearby object streaking through the field of view or an edge-on galaxy, far far away?

Even in the 14 mb Hubble image it’s just a marbled blur.
It looks like a highly redshifted galaxy that is indeed very far away.

Eric

[Sa Ji Tario]

I agree with XgeoX

[orin stepanek]

The Antennae make beautiful pair dancing in Heaven's Ballroom!
In a few million years the wedding will be complete! I wonder what
the finished merger will look like!

[VictorBorun]

This I find strange: how come the bridge is dustier than either of the tidal arms?

And this is a question from driveline analogy: considering two colliding galaxies as a two rotating wheels coming to a point of clutch, does that friction accelerate the rotation, decelerate it, or both, or none of that?

[Ann]

This I find strange: how come the bridge is dustier than either of the tidal arms?

And this is a question from driveline analogy: considering two colliding galaxies as a two rotating wheels coming to a point of clutch, does that friction accelerate the rotation, decelerate it, or both, or none of that?

Click to play embedded YouTube video.

Maybe it helps to think of the two colliding galaxies as two colliding cars? The worst wreckage is going to happen at the point of contact. In the same way, the force of the collision between two galaxies is going to be felt the hardest near the point of impact. When cars collide they produce debris, but when gas-rich galaxies collide and their gas gets compressed and shifted around violently, they produce a lot of dust, particularly (I would guess) at their point of contact.

Dust is a natural by-product of star formation. Some starburst galaxies produce so much dust due to their star formation that they become extremely bright in infrared light, because dust hinders a lot of optical light to escape, but it lets through infrared light.

IRAS 14348-1447 is an ultraluminous infrared galaxy, located over a billion light-years away. Almost 95% of the energy emitted by IRAS 14348-1447 is in the far-infrared! ESA/Hubble.

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Wikipedia wrote:

Infrared galaxies appear to be single, gas-rich spirals whose infrared luminosity is created largely by the formation of stars within them.[1] These types of galaxies were discovered in 1983 with IRAS.[2] A LIRG's excess infrared luminosity may also come from the presence of an active galactic nucleus (AGN) residing at the center.[3][4]

These galaxies emit more energy in the infrared portion of the spectrum, not visible to the naked eye. The energy given off by LIRGs is comparable to that of a quasar (a type of AGN), which formerly was known as the most energetic object in the universe.[5]

LIRGs are brighter in the infrared than in the optical spectrum because the visible light is absorbed by the high amounts of gas and dust, and the dust re-emits thermal energy in the infrared spectrum.

Ann

To the mods: I can't seem to get the "float" function to work properly for my Wikipedia quote. Is it just me?

[neufer]

This I find strange: how come the bridge is dustier than either of the tidal arms?

And this is a question from driveline analogy: considering two colliding galaxies as a two rotating wheels coming to a point of clutch, does that friction accelerate the rotation, decelerate it, or both, or none of that?

Click to play embedded YouTube video.

IRAS 14348-1447 is an ultraluminous infrared galaxy, located over a billion light-years away. Almost 95% of the energy emitted by IRAS 14348-1447 is in the far-infrared! ESA/Hubble.

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Maybe it helps to think of the two colliding galaxies as two colliding cars? The worst wreckage is going to happen at the point of contact. In the same way, the force of the collision between two galaxies is going to be felt the hardest near the point of impact. When cars collide they produce debris, but when gas-rich galaxies collide and their gas gets compressed and shifted around violently, they produce a lot of dust, particularly (I would guess) at their point of contact.

Dust is a natural by-product of star formation. Some starburst galaxies produce so much dust due to their star formation that they become extremely bright in infrared light, because dust hinders a lot of optical light to escape, but it lets through infrared light.

Infrared galaxies appear to be single, gas-rich spirals whose infrared luminosity is created largely by the formation of stars within them. These types of galaxies were discovered in 1983 with IRAS. A LIRG's excess infrared luminosity may also come from the presence of an active galactic nucleus (AGN) residing at the center.

These galaxies emit more energy in the infrared portion of the spectrum, not visible to the naked eye. The energy given off by LIRGs is comparable to that of a quasar (a type of AGN), which formerly was known as the most energetic object in the universe.

LIRGs are brighter in the infrared than in the optical spectrum because the visible light is absorbed by the high amounts of gas and dust, and the dust re-emits thermal energy in the infrared spectrum.

Ann: To the mods: I can't seem to get the "float" function to work properly for my Wikipedia quote. Is it just me?

Click to play embedded YouTube video.

Keep it simple, Ann: stack your videos/images together and stick them all to one side with a single float command. Even if you produce your ideal format on your screen it can look like a real mess on other's screens (often with loads of black spaces).

[johnnydeep]

Ann wrote above:

Dust is a natural by-product of star formation. Some starburst galaxies produce so much dust due to their star formation that they become extremely bright in infrared light, because dust hinders a lot of optical light to escape, but it lets through infrared light

That seems strange to me. I figured it would be the reverse: that the dust that happens to be present gives rise to star formation, not the other way around. Why does star formation/creation increase the amount of dust present? ...Ok, I could see star death producing dust, but not birth. Or is it that when a star "ignites" it blows off some of its outer layers of gas along with any nearby dust that had been gravitationaly accumulating?

[Chris Peterson]

Ann wrote above:

Dust is a natural by-product of star formation. Some starburst galaxies produce so much dust due to their star formation that they become extremely bright in infrared light, because dust hinders a lot of optical light to escape, but it lets through infrared light

That seems strange to me. I figured it would be the reverse: that the dust that happens to be present gives rise to star formation, not the other way around. Why does star formation/creation increase the amount of dust present? ...Ok, I could see star death producing dust, but not birth. Or is it that when a star "ignites" it blows off some of its outer layers of gas along with any nearby dust that had been gravitationaly accumulating?

Agreed. Star formation does not create dust. Dust is produced inside of stars (or from material produced inside of stars) and is released late in the evolution of those stars. The energy released in star forming regions may redistribute dust, and that could be important for future star formation. New stars form from hydrogen clouds, and having a trace of dust (1-2% typically) seems to catalyze that formation in ways not entirely understood.

[VictorBorun]

The Dust comes from stars formation, OK. Ann and Chris, thanks for explaining.

But is a normal car crush analogy in any way?
Before the auto break system there were cars rotating after having tried to use breaks on a sleazy road. But even those unhappy cars could not rotate fast enough to rival with the velocity of a collision, could they?

[Ann]

The Dust comes from stars formation, OK. Ann and Chris, thanks for explaining.

But is a normal car crush analogy in any way?
Before the auto break system there were cars rotating after having tried to use breaks on a sleazy road. But even those unhappy cars could not rotate fast enough to rival with the velocity of a collision, could they?

A car crash is not a good analog for a collision between galaxies. Cars are solid bodies welded together by mechanical force, but galaxies are huge collections of "loose" objects held together by gravity.

When galaxies collide, it is mostly their molecular clouds that actually collide with each other, while stars get scattered by tidal forces. When colliding galaxies don't contain any molecular clouds, it is just the stellar orbits inside the galaxies that get strongly disturbed because of the entirely new tidal forces that the collision induces. Therefore we see tidal tails and tidal shells that result from collisions even in very gas-poor galaxies.

Ann

[Ann]

Ann wrote above:

Dust is a natural by-product of star formation. Some starburst galaxies produce so much dust due to their star formation that they become extremely bright in infrared light, because dust hinders a lot of optical light to escape, but it lets through infrared light

That seems strange to me. I figured it would be the reverse: that the dust that happens to be present gives rise to star formation, not the other way around. Why does star formation/creation increase the amount of dust present? ...Ok, I could see star death producing dust, but not birth. Or is it that when a star "ignites" it blows off some of its outer layers of gas along with any nearby dust that had been gravitationaly accumulating?

You are right, Johnny. It is not the star birth per se that creates dust, but a starburst will soon give rise to star death, which does create dust.

Astronomers recently found the most unobscured, dust-poor starburst galaxy they had ever seen, BOSS-EUVLG1.

BOSS-EUVLG1 is seen at a time when the Universe was just 2 billion years old,
about 20% of its current age. Image credit: DESI Legacy Imaging Surveys.

Wolf-Rayet star WR 124. ESA/Hubble.

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Natali Anderson of Sci News wrote:

A young starburst galaxy named BOSS-EUVLG1 is by far the most luminous, almost un-obscured star-forming galaxy known at any redshift.

Also known as SDSS J122040.72+084238.1, BOSS-EUVLG1 is located approximately 12 billion light-years away.

First classified as a quasar, the galaxy is extremely luminous in ultraviolet (UV) and Lyman-α light...

BOSS-EUVLG1 has a very high rate of star formation — about 1,000 solar masses per year, although the galaxy is 30 times smaller than our Milky Way Galaxy. For comparison, the Milky Way makes about one solar mass worth of stars per year.

“This rate of star formation is comparable only to the most luminous infrared galaxies known, but the absence of dust in BOSS-EUVLG1 allows its ultraviolet and visible emission to reach us with hardly any attenuation,” said co-author Dr. Ismael Pérez Fournon, an astronomer in the Instituto de Astrofisica de Canarias and the Universidad de La Laguna...

According to the team, BOSS-EUVLG1 is in the earliest stage of massive galaxy formation.

“The galaxy will evolve towards a dustier phase, similar to the infrared galaxies,” said co-author Camilo Jiménez-Ángel, a doctoral student in the Instituto de Astrofisica de Canarias and the Universidad de La Laguna.

As an almost dust-free starburst galaxy, BOSS-EUVLG1 is the only one known to astronomers so far. This suggests that, while star formation in itself doesn't create dust, massive star death (which will surely follow relatively soon after a major starburst) does indeed create a lot of dust.

Akio K. Inoue wrote:

Dust grains are formed in rapidly-cooling gas of stellar outflows (Draine and Salpeter, 1977; Yamamoto and Hasegawa, 1977). We call such grains ‘stardust’. Sources of the stardust are asymptotic giant branch (AGB) stars, supernovae (SNe), red supergiants, novae, Wolf-Rayet stars, and so on (e.g., Gehrz, 1989).

Really massive stars will relatively soon turn into Wolf-Rayet stars. A starburst at the point of impact of the collision between NGC 4038 and NGC 4039 may have produced a good number of them. In any case, a starburst is expected to create a lot of dust in in a relatively short time. Remember that many ultraluminous infrared galaxies (dusty starburst galaxies) are known, but BOSS-EUVLG1 is the only mostly dust-free starburst galaxy that astronomers know of.

Ann