APOD: The Heart Shaped Antennae Galaxies (2024 Feb 07)

APOD Robot · Post by **APOD Robot** » Wed Feb 07, 2024 1:30 pm

The Heart Shaped Antennae Galaxies

Explanation: Are these two galaxies really attracted to each other? Yes, gravitationally, and the result appears as an enormous iconic heart -- at least for now. Pictured is the pair of galaxies cataloged as NGC 4038 and NGC 4039,known as the Antennae Galaxies. Because they are only 60 million light years away, close by intergalactic standards, the pair is one of the best studied interacting galaxies on the night sky. Their strong attraction began about a billion years ago when they passed unusually close to each other. As the two galaxies interact, their stars rarely collide, but new stars are formed when their interstellar gases crash together. Some new stars have already formed, for example, in the long antennae seen extending out from the sides of the dancing duo. By the time the galaxy merger is complete, likely over a billion years from now, billions of new stars may have formed.

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aildoux · Post by **aildoux** » Wed Feb 07, 2024 2:38 pm

Great post as usual. Still, APOD should have kept this one for Valentine's Day coming up soon.

Christian G. · Post by **Christian G.** » Wed Feb 07, 2024 2:47 pm

From their initial attraction to their complete merger into one, these two will have taken two billion years! Galaxies sure don't rush into things.

Chris Peterson · Post by **Chris Peterson** » Wed Feb 07, 2024 2:59 pm

Christian G. wrote: ↑Wed Feb 07, 2024 2:47 pm From their initial attraction to their complete merger into one, these two will have taken two billion years! Galaxies sure don't rush into things.

These two galaxies have always been gravitationally bound, in orbit around each other. Nothing has really changed since their formation. Their orbits around each other are approximately described by ordinary Keplerian dynamics. (Approximate because they are extended, non-rigid bodies and as their shapes change because of gravitational interaction, the centers of mass change as well.)

The only thing that can substantially change the orbits of a pair of bodies is interaction with a third. I don't know if there is any evidence that another galaxy passed near them a few billion years ago or not.

Christian G. · Post by **Christian G.** » Wed Feb 07, 2024 3:35 pm

Chris Peterson wrote: ↑Wed Feb 07, 2024 2:59 pm
Christian G. wrote: ↑Wed Feb 07, 2024 2:47 pm From their initial attraction to their complete merger into one, these two will have taken two billion years! Galaxies sure don't rush into things.
These two galaxies have always been gravitationally bound, in orbit around each other. Nothing has really changed since their formation. Their orbits around each other are approximately described by ordinary Keplerian dynamics. (Approximate because they are extended, non-rigid bodies and as their shapes change because of gravitational interaction, the centers of mass change as well.)

The only thing that can substantially change the orbits of a pair of bodies is interaction with a third. I don't know if there is any evidence that another galaxy passed near them a few billion years ago or not.

Thanks for these clarifications. That sounds even better then, these two were destined to one another since the day they were born!

Chris Peterson · Post by **Chris Peterson** » Wed Feb 07, 2024 3:46 pm

Christian G. wrote: ↑Wed Feb 07, 2024 3:35 pm
Chris Peterson wrote: ↑Wed Feb 07, 2024 2:59 pm
Christian G. wrote: ↑Wed Feb 07, 2024 2:47 pm From their initial attraction to their complete merger into one, these two will have taken two billion years! Galaxies sure don't rush into things.
These two galaxies have always been gravitationally bound, in orbit around each other. Nothing has really changed since their formation. Their orbits around each other are approximately described by ordinary Keplerian dynamics. (Approximate because they are extended, non-rigid bodies and as their shapes change because of gravitational interaction, the centers of mass change as well.)

The only thing that can substantially change the orbits of a pair of bodies is interaction with a third. I don't know if there is any evidence that another galaxy passed near them a few billion years ago or not.
Thanks for these clarifications. That sounds even better then, these two were destined to one another since the day they were born!

I should also add that the orbits of a pair of galaxies can slowly drift over time because tidal interactions can transfer angular momentum between them in complex ways.

Ann · Post by **Ann** » Wed Feb 07, 2024 5:27 pm

In the same way that M51, the Whirlpool galaxy, was the first "cosmic cloud" to be found to be spiral-shaped, and the Andromeda galaxy was the first "cosmic cloud" to be discovered to be an independent galaxy, and NGC 5128 (Centaurus A) was the first galaxy to be thought to perhaps be exploding, so the Antennae galaxies were the iconic first truly strange maybe merging and maybe something else "shrimp-tail" galaxy!

: M51 was the first galaxy to be found to be spiral-shaped. But Lord Rosse, who made the discovery, didn't know that M51 was an independent galaxy.

: The Andromeda galaxy was the first 'cosmic cloud' to be found to be an independent galaxy, when Edwin Hubble found a variable star in it (hence the triumphant note 'Var!').

NGC 5128, drawing by Anne Wölk after old black and white
Carnegie photographs. There was speculation at the time that maybe
NGC 5128 was exploding.

: So this is a Two Micron All Sky Survey photo of the Antennae galaxies from, apparently, 1999, but the first black and white pictures of these two galaxies may have looked a bit like this.

The Antennae galaxies are of course a fantastic pair of galaxies. First compared to a cosmic shrimp, they were later named after their long antenna-like tails:

: The tails of the Antennae galaxies. The picture at left is by Rolf Wahl Olsen, and the picture at right is by David Malin, the Anglo Australian Observatory and UK Schmidt plates.

: The long tail from one of the Antennae galaxies, NGC 4038, ends in clusters of young stars. There is a group of red background galaxies behind the end of the tail of NGC 4038.

A beautiful Hubble picture of the Antennae galaxies is probably the best picture of this iconic galaxy pair. But cosmic "cosmetologist" Stuart Rankin does not want to be outdone by Hubble in the galactic beauty department!

: The Antennae galaxies by Hubble. You can see two yellow 'blobs' which are the cores of the two galaxies, NGC 4038 and NGC 4039. There are many bright blue star clusters and many large pink nebulas. A huge brown dust cloud is located between the two galaxies, and a torrent of star formation is taking place inside this dust cloud. Credit: ESA/Hubble.

Not to be outdone by Hubble in the beauty department, Stuart Rankin
has portrayed the Antennae galaxies like only he can do.

Ann

Ann · Post by **Ann** » Wed Feb 07, 2024 6:12 pm

Chris Peterson wrote: ↑Wed Feb 07, 2024 2:59 pm
Christian G. wrote: ↑Wed Feb 07, 2024 2:47 pm From their initial attraction to their complete merger into one, these two will have taken two billion years! Galaxies sure don't rush into things.
These two galaxies have always been gravitationally bound, in orbit around each other. Nothing has really changed since their formation. Their orbits around each other are approximately described by ordinary Keplerian dynamics. (Approximate because they are extended, non-rigid bodies and as their shapes change because of gravitational interaction, the centers of mass change as well.)

The only thing that can substantially change the orbits of a pair of bodies is interaction with a third. I don't know if there is any evidence that another galaxy passed near them a few billion years ago or not.

Surely it must be possible for galaxies that were not initially bound together to drift closer to one another and indeed become bound? The way I understand it, the Magellanic Clouds have only relatively recently been captured by the Milky Way. That is why they are so vigorously starforming. Most satellite galaxies are not like that, and instead they are either "red and dead" or at least very low in star formation. See, for example, Andromeda's two major satellites M32 and NGC 205.

If the Magellanic Clouds have only recently been captured by the Milky Way, isn't it possible that NGC 4038 and NGC 4039 have relatively recently become bound?

Ann

Chris Peterson · Post by **Chris Peterson** » Wed Feb 07, 2024 6:24 pm

Ann wrote: ↑Wed Feb 07, 2024 6:12 pm
Chris Peterson wrote: ↑Wed Feb 07, 2024 2:59 pm
Christian G. wrote: ↑Wed Feb 07, 2024 2:47 pm From their initial attraction to their complete merger into one, these two will have taken two billion years! Galaxies sure don't rush into things.
These two galaxies have always been gravitationally bound, in orbit around each other. Nothing has really changed since their formation. Their orbits around each other are approximately described by ordinary Keplerian dynamics. (Approximate because they are extended, non-rigid bodies and as their shapes change because of gravitational interaction, the centers of mass change as well.)

The only thing that can substantially change the orbits of a pair of bodies is interaction with a third. I don't know if there is any evidence that another galaxy passed near them a few billion years ago or not.

Surely it must be possible for galaxies that were not initially bound together to drift closer to one another and indeed become bound? The way I understand it, the Magellanic Clouds have only relatively recently been captured by the Milky Way. That is why they are so vigorously starforming. Most satellite galaxies are not like that, and instead they are either "red and dead" or at least very low in star formation. See, for example, Andromeda's two major satellites M32 and NGC 205.

If the Magellanic Clouds have only recently been captured by the Milky Way, isn't it possible that NGC 4038 and NGC 4039 have relatively recently become bound?

Ann

Two bodies that are not gravitationally bound in a closed orbit cannot become bound by drifting closer together. One body can only capture another if there is at least one additional body involved. The Magellanic Clouds (did you know they're looking at changing their names?) could be captured in a couple of different ways. The most likely is simply because they and the Milky Way are not a two-body system, but rather, part of a complex multiple body system called the Local Group. Another mechanism would be by some form of collision (since these are extended, non-rigid entities) where momentum was transferred between different parts of each. But I'd bet on the first.

There's a classic first-year physics two-body problem. Two masses are separated by some distance and stationary with respect to each other. What happens? Gravity results in an attractive force causing the two to get closer, and they approach each other faster and faster, with the fastest speed being when they would collide. We don't allow a collision, and they now continue past each other, slowing down and coming to zero relative speed when they're the same distance apart they started. Then this repeats. Forever. This is a gravitationally bound system, of course, no matter how far apart the two bodies are at the start.

johnnydeep · Post by **johnnydeep** » Wed Feb 07, 2024 7:06 pm

Chris Peterson wrote: ↑Wed Feb 07, 2024 6:24 pm
Ann wrote: ↑Wed Feb 07, 2024 6:12 pm
Chris Peterson wrote: ↑Wed Feb 07, 2024 2:59 pm

These two galaxies have always been gravitationally bound, in orbit around each other. Nothing has really changed since their formation. Their orbits around each other are approximately described by ordinary Keplerian dynamics. (Approximate because they are extended, non-rigid bodies and as their shapes change because of gravitational interaction, the centers of mass change as well.)

The only thing that can substantially change the orbits of a pair of bodies is interaction with a third. I don't know if there is any evidence that another galaxy passed near them a few billion years ago or not.

Surely it must be possible for galaxies that were not initially bound together to drift closer to one another and indeed become bound? The way I understand it, the Magellanic Clouds have only relatively recently been captured by the Milky Way. That is why they are so vigorously starforming. Most satellite galaxies are not like that, and instead they are either "red and dead" or at least very low in star formation. See, for example, Andromeda's two major satellites M32 and NGC 205.

If the Magellanic Clouds have only recently been captured by the Milky Way, isn't it possible that NGC 4038 and NGC 4039 have relatively recently become bound?

Ann
Two bodies that are not gravitationally bound in a closed orbit cannot become bound by drifting closer together. One body can only capture another if there is at least one additional body involved. The Magellanic Clouds (did you know they're looking at changing their names?) could be captured in a couple of different ways. The most likely is simply because they and the Milky Way are not a two-body system, but rather, part of a complex multiple body system called the Local Group. Another mechanism would be by some form of collision (since these are extended, non-rigid entities) where momentum was transferred between different parts of each. But I'd bet on the first.

There's a classic first-year physics two-body problem. Two masses are separated by some distance and stationary with respect to each other. What happens? Gravity results in an attractive force causing the two to get closer, and they approach each other faster and faster, with the fastest speed being when they would collide. We don't allow a collision, and they now continue past each other, slowing down and coming to zero relative speed when they're the same distance apart they started. Then this repeats. Forever. This is a gravitationally bound system, of course, no matter how far apart the two bodies are at the start.

Are galaxy clusters at all like clusters of stars that all form together from the same source "cloud" of gas an dust?

Chris Peterson · Post by **Chris Peterson** » Wed Feb 07, 2024 7:09 pm

johnnydeep wrote: ↑Wed Feb 07, 2024 7:06 pm
Chris Peterson wrote: ↑Wed Feb 07, 2024 6:24 pm
Ann wrote: ↑Wed Feb 07, 2024 6:12 pm

Surely it must be possible for galaxies that were not initially bound together to drift closer to one another and indeed become bound? The way I understand it, the Magellanic Clouds have only relatively recently been captured by the Milky Way. That is why they are so vigorously starforming. Most satellite galaxies are not like that, and instead they are either "red and dead" or at least very low in star formation. See, for example, Andromeda's two major satellites M32 and NGC 205.

If the Magellanic Clouds have only recently been captured by the Milky Way, isn't it possible that NGC 4038 and NGC 4039 have relatively recently become bound?

Ann
Two bodies that are not gravitationally bound in a closed orbit cannot become bound by drifting closer together. One body can only capture another if there is at least one additional body involved. The Magellanic Clouds (did you know they're looking at changing their names?) could be captured in a couple of different ways. The most likely is simply because they and the Milky Way are not a two-body system, but rather, part of a complex multiple body system called the Local Group. Another mechanism would be by some form of collision (since these are extended, non-rigid entities) where momentum was transferred between different parts of each. But I'd bet on the first.

There's a classic first-year physics two-body problem. Two masses are separated by some distance and stationary with respect to each other. What happens? Gravity results in an attractive force causing the two to get closer, and they approach each other faster and faster, with the fastest speed being when they would collide. We don't allow a collision, and they now continue past each other, slowing down and coming to zero relative speed when they're the same distance apart they started. Then this repeats. Forever. This is a gravitationally bound system, of course, no matter how far apart the two bodies are at the start.
Are galaxy clusters at all like clusters of stars that all form together from the same source "cloud" of gas an dust?

There are still so many questions about how galaxies form at all! But yeah... it seems likely that galaxy clusters form when their members form. That is, they aren't the product of distantly formed galaxies coming together later.

johnnydeep · Post by **johnnydeep** » Wed Feb 07, 2024 7:11 pm

Nit: at the "billion years from now" link that is a poor depiction of what the Sun and Earth will look like 5 Gy from now. If the Earth ever really does get that close, the Sun's edge will look very very straight! Heck, it would look very straight even now with the Earth that close!

Timeline of the far future
Image of what Earth may look like 5-7 billion years from now, when the Sun swells and becomes a Red Giant. It is a modified version of the File:Red Giant Earth.jpg image uploaded by Fsgregs. The main difference is that the Sun has been brightened and given an orange hue.

Click to view full size image

johnnydeep · Post by **johnnydeep** » Wed Feb 07, 2024 7:13 pm

Chris Peterson wrote: ↑Wed Feb 07, 2024 7:09 pm
johnnydeep wrote: ↑Wed Feb 07, 2024 7:06 pm
Chris Peterson wrote: ↑Wed Feb 07, 2024 6:24 pm

Two bodies that are not gravitationally bound in a closed orbit cannot become bound by drifting closer together. One body can only capture another if there is at least one additional body involved. The Magellanic Clouds (did you know they're looking at changing their names?) could be captured in a couple of different ways. The most likely is simply because they and the Milky Way are not a two-body system, but rather, part of a complex multiple body system called the Local Group. Another mechanism would be by some form of collision (since these are extended, non-rigid entities) where momentum was transferred between different parts of each. But I'd bet on the first.

There's a classic first-year physics two-body problem. Two masses are separated by some distance and stationary with respect to each other. What happens? Gravity results in an attractive force causing the two to get closer, and they approach each other faster and faster, with the fastest speed being when they would collide. We don't allow a collision, and they now continue past each other, slowing down and coming to zero relative speed when they're the same distance apart they started. Then this repeats. Forever. This is a gravitationally bound system, of course, no matter how far apart the two bodies are at the start.
Are galaxy clusters at all like clusters of stars that all form together from the same source "cloud" of gas an dust?
There are still so many questions about how galaxies form at all! But yeah... it seems likely that galaxy clusters form when their members form. That is, they aren't the product of distantly formed galaxies coming together later.

Makes sense.

Avalon · Post by **Avalon** » Thu Feb 08, 2024 3:09 am

Is there any evidence whatsoever of stars actually colliding in a galactic interaction? I've read so many times how stars HARDLY EVER would collide during such an event, which infers that it is possible. Would it even be observable?

Ann · Post by **Ann** » Thu Feb 08, 2024 5:49 am

Avalon wrote: ↑Thu Feb 08, 2024 3:09 am Is there any evidence whatsoever of stars actually colliding in a galactic interaction? I've read so many times how stars HARDLY EVER would collide during such an event, which infers that it is possible. Would it even be observable?

A stellar collision - make that a stellar merger - is thought to have created the extreme swelling and cooling of a previously run-of-the-mill B-type star. B-type stars themselves belong to a small minority of all Milky Way stars, but, after asking Google how many stars there are in the Milky Way and how many of all stars are spectral class B, I was told that there should be 120 million B-type stars in our galaxy! So the progenitor of this star, V838 Monocerotis, went from being one of a hundred million to being a unique star in the Milky Way - at least it was unique at the time when the merger happened!

: V838 Monocerotis. Credit: NASA/ESA Hubble Space Telescope

Wikipedia wrote:

V838 Monocerotis (Nova Monocerotis 2002) is a spectroscopic binary star system in the constellation Monoceros about 19,000 light years (6 kpc) from the Sun. The previously unremarked star was observed in early 2002 experiencing a major outburst, and was one of the largest known stars for a short period following the outburst. Originally believed to be a typical nova eruption, it was then identified as the first of a new class of eruptive variables known as luminous red novae. The reason for the outburst is still uncertain, but is thought to have been a merger of two stars within a triple system.

Click here to see a cool animation of the evolution of V838 Monocerotis.

But the V838 Mon eruption is not believed to have happened because an unrelated star just entered the V838 Mon system and collided with one of the stars. Instead, as Wikipedia said, it is believed to have happened in a system of three stars that were already in orbit around one another.

Ann

Chris Peterson · Post by **Chris Peterson** » Thu Feb 08, 2024 2:09 pm

Avalon wrote: ↑Thu Feb 08, 2024 3:09 am Is there any evidence whatsoever of stars actually colliding in a galactic interaction? I've read so many times how stars HARDLY EVER would collide during such an event, which infers that it is possible. Would it even be observable?

Or to be less technical than Ann, it's a really, really, really big Universe, so if something is possible, and you can think of it, it can probably happen.

Sam · Post by **Sam** » Fri Feb 09, 2024 12:43 am

aildoux wrote: ↑Wed Feb 07, 2024 2:38 pm Great post as usual. Still, APOD should have kept this one for Valentine's Day coming up soon.

Yes but it was also a great reminder to get things in motion for the 14th!
Maybe Hallmark's Big Romance industry has gotten the APOD editors...

MelvzLuster · Post by **MelvzLuster** » Wed Feb 21, 2024 2:14 pm

Happy Galactic Heart Month in the entire Universe! <3 O:) * (Y)

Starship Asterisk*

APOD: The Heart Shaped Antennae Galaxies (2024 Feb 07)

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