Starship Asterisk*

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.

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.

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!

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.

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

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.

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?

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

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.

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?

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.

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?

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.