Starship Asterisk*

Chris Peterson wrote: ↑Wed Oct 09, 2024 1:46 pm

VictorBorun wrote: ↑Wed Oct 09, 2024 1:35 pm

Chris Peterson wrote: ↑Wed Oct 09, 2024 1:07 pm
I'm not understanding your concern. With galaxies the tidal forces distort structures because the structures are weakly bound and exist in a gradient force field. There is nothing "bilateral" about that.

it's a stretching and therefore the core sees the opposite parts pulled off at two opposite directions.
How come the LMS's one arm is distorted while the other arm is lost if all there is a tidal stretching?

All of the forces are in the same direction, though. But this is not a static situation. You have a small galaxy in an elliptical orbit around a large one, both are extended objects that are large in comparison with the distance between them, so the gravitational fields vary significantly across the bodies, and both bodies are rotating, as well. Why would you expect in such a dynamic environment, over hundreds of millions of years of rotation and displacement, that the consequences would be symmetrical on either body (especially as "losing and arm" doesn't mean losing much material, just disrupting a resonant structure)?

VictorBorun wrote: ↑Wed Oct 09, 2024 1:35 pm

Chris Peterson wrote: ↑Wed Oct 09, 2024 1:07 pm

VictorBorun wrote: ↑Wed Oct 09, 2024 10:15 am

what's not bilateral when the closest part of a small galaxy is pulled the hardest while the most distant part is pulled the weakest?
The tidal component of the gravity must be stretching that small galaxy but bilaterally, both ways from the core of the small galaxy.

an easy but hazy answer that comes to my mind is that the LMC's orbital movement is somehow at cross with the whirls of the Milky Way's outer space and a bumpy ride just ripped an arm off the LMC. It would be hard to disprove such an idea without a precise map of the whirls

[offtopic: And yes the tides on Earth are tiny because Earth's own gravity is so much stronger than the tidal component of Moon's pull… and the tidal component of Sun's pull for that matter]

I'm not understanding your concern. With galaxies the tidal forces distort structures because the structures are weakly bound and exist in a gradient force field. There is nothing "bilateral" about that.

it's a stretching and therefore the core sees the opposite parts pulled off at two opposite directions.
How come the LMS's one arm is distorted while the other arm is lost if all there is a tidal stretching?

Chris Peterson wrote: ↑Wed Oct 09, 2024 1:07 pm

VictorBorun wrote: ↑Wed Oct 09, 2024 10:15 am

Chris Peterson wrote: ↑Fri Oct 04, 2024 10:19 pm

Tidal forces are not bilateral! The effect of the Moon's gravity on the Earth is that the force is greater on the side facing the Moon than it is on the opposite side. So the net force across the Earth creates tension, which distorts both the planet and its oceans. That creates a deviation above the nominal sphere both towards the Moon and away from it, and when that's combined with the Earth's rotation, you get a pair of tides.

With a galaxy, all the stars are pulled towards the colliding (or nearby) galaxy, but those that are closest are pulled harder, and move faster towards it. There is no rotating rigid body involved.

what's not bilateral when the closest part of a small galaxy is pulled the hardest while the most distant part is pulled the weakest?
The tidal component of the gravity must be stretching that small galaxy but bilaterally, both ways from the core of the small galaxy.

an easy but hazy answer that comes to my mind is that the LMC's orbital movement is somehow at cross with the whirls of the Milky Way's outer space and a bumpy ride just ripped an arm off the LMC. It would be hard to disprove such an idea without a precise map of the whirls

[offtopic: And yes the tides on Earth are tiny because Earth's own gravity is so much stronger than the tidal component of Moon's pull… and the tidal component of Sun's pull for that matter]

I'm not understanding your concern. With galaxies the tidal forces distort structures because the structures are weakly bound and exist in a gradient force field. There is nothing "bilateral" about that.

VictorBorun wrote: ↑Wed Oct 09, 2024 10:15 am

Chris Peterson wrote: ↑Fri Oct 04, 2024 10:19 pm

VictorBorun wrote: ↑Fri Oct 04, 2024 10:05 pm I am confused when they picture the one-armed Large Magellanic Cloud Galaxy as a victim of the tidal forces from the Milky Way Galaxy or the Small Magellanic Cloud Galaxy.
Because you see the tidal forces are bilateral. For example our Earth has one high tide under the moon and another high tide 12 hours later.
Why should tidal forces pull the core from the centre of the LMC? Why should they cut off just one of its arms?

Tidal forces are not bilateral! The effect of the Moon's gravity on the Earth is that the force is greater on the side facing the Moon than it is on the opposite side. So the net force across the Earth creates tension, which distorts both the planet and its oceans. That creates a deviation above the nominal sphere both towards the Moon and away from it, and when that's combined with the Earth's rotation, you get a pair of tides.

With a galaxy, all the stars are pulled towards the colliding (or nearby) galaxy, but those that are closest are pulled harder, and move faster towards it. There is no rotating rigid body involved.

what's not bilateral when the closest part of a small galaxy is pulled the hardest while the most distant part is pulled the weakest?
The tidal component of the gravity must be stretching that small galaxy but bilaterally, both ways from the core of the small galaxy.

an easy but hazy answer that comes to my mind is that the LMC's orbital movement is somehow at cross with the whirls of the Milky Way's outer space and a bumpy ride just ripped an arm off the LMC. It would be hard to disprove such an idea without a precise map of the whirls

[offtopic: And yes the tides on Earth are tiny because Earth's own gravity is so much stronger than the tidal component of Moon's pull… and the tidal component of Sun's pull for that matter]

Chris Peterson wrote: ↑Fri Oct 04, 2024 10:19 pm

VictorBorun wrote: ↑Fri Oct 04, 2024 10:05 pm I am confused when they picture the one-armed Large Magellanic Cloud Galaxy as a victim of the tidal forces from the Milky Way Galaxy or the Small Magellanic Cloud Galaxy.
Because you see the tidal forces are bilateral. For example our Earth has one high tide under the moon and another high tide 12 hours later.
Why should tidal forces pull the core from the centre of the LMC? Why should they cut off just one of its arms?

Tidal forces are not bilateral! The effect of the Moon's gravity on the Earth is that the force is greater on the side facing the Moon than it is on the opposite side. So the net force across the Earth creates tension, which distorts both the planet and its oceans. That creates a deviation above the nominal sphere both towards the Moon and away from it, and when that's combined with the Earth's rotation, you get a pair of tides.

With a galaxy, all the stars are pulled towards the colliding (or nearby) galaxy, but those that are closest are pulled harder, and move faster towards it. There is no rotating rigid body involved.

VictorBorun wrote: ↑Fri Oct 04, 2024 10:05 pm I am confused when they picture the one-armed Large Magellanic Cloud Galaxy as a victim of the tidal forces from the Milky Way Galaxy or the Small Magellanic Cloud Galaxy.
Because you see the tidal forces are bilateral. For example our Earth has one high tide under the moon and another high tide 12 hours later.
Why should tidal forces pull the core from the centre of the LMC? Why should they cut off just one of its arms?

AVAO wrote: ↑Fri Oct 04, 2024 5:16 am

VictorBorun wrote: ↑Fri Oct 04, 2024 4:08 am

Ann wrote: ↑Thu Oct 03, 2024 5:02 am


Very good comparison, Jac! NGC 4449 has its own "Tarantula Nebula" that is "below" the galactic bar. We can see, too, that NGC 4449 is a true starburst galaxy where the level of star formation is extremely high all over the optically bright galaxy, more so than in the LMC. However, NGC 4449 is wrapped inside a huge halo of small faint red stars, and a tiny, tiny dwarf galaxy is feeding matter into it.

NGC 4449. Credit: Mark Hanson.

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NGC 4449 and its tiny, tiny dwarf galaxy companion. Credit: Cosmotography

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I think that the color of the halo around NGC 4449 is more correct in Mark Hanson's image than in the image by Cosmotography.

Ann

(well I never) thanks guys very interesting

"sucked out" — I am not sure what it means
picture a smallish or dwarf galaxy speed through the outer space of a large galaxy, partly going with the whirl, but partly moving through the media
The Core of that smallish or dwarf stranger galaxy is more dense in its stellar population and less dense in its interstellar gas and dust than the Disk.
So the the Core should be less slowed down by the headwind and shift from the centre of the Disk in the direction of the movement through the whirl of the outer space of this large galaxy…

Hmm. My wink at the end indicates that my statement was only partly serious, which doesn't change the fact that the impression is created that this is the case. Usually the arms are affected first (theoretically one could also assume that the SMC is a remnant of it) and the cores only react last in the immediate near field. I don't have a convincing answer to that myself.

"Galaxy cores on the run are an exciting scenario. The question of whether galaxy cores can be ripped out of dwarf galaxies is a fascinating.
When a small dwarf galaxy approaches a large galaxy, immense gravitational interactions occur.
These can lead to a variety of phenomena, including:
- Tidal forces: The stronger gravitational force of the larger galaxy can distort and pull the smaller dwarf galaxy apart. This can affect stars, gas and even the central core of the dwarf galaxy.
- Star formation triggers: The shock waves caused by the interaction can lead to increased star formation in the dwarf galaxy.
- Cannibalism: In extreme cases, the larger galaxy can completely devour the smaller galaxy.

Whether the galactic core of a dwarf galaxy is actually ripped out depends on several factors:
- Mass of the galaxies: The greater the mass difference between the two galaxies, the stronger the tidal forces.
- Proximity of passage: The closer the dwarf galaxy passes to the larger galaxy, the stronger the interactions are.
- Speed ​​of passage: A fast passage leads to stronger tidal forces than a slow one.
- Structure of galaxies: The internal structure of galaxies, especially the distribution of dark matter, plays a role.

What could be the cause of a galactic core being ripped out?
- Direct hit: If the central region of the dwarf galaxy is hit directly by the strong gravitational force of the larger galaxy, it could be thrown out of its original trajectory.
- Tidal forces: The tidal forces could stretch the core so much that it eventually breaks apart and parts of it are captured by the larger galaxy.

Although the LMC is a large dwarf galaxy, it is still significantly smaller than the Milky Way. The two galaxies are interacting and the LMC will likely be swallowed up by the Milky Way in the future. So it is possible that parts of the LMC's core are torn out to drift in direction of the Milky Way."

Verified by gemini.


... however, the scenario being discussed is based on the assumption that the Tarantula Nebula is or was the heart of the LMC. And this is probably where the correct answer to the question lies ...

VictorBorun wrote: ↑Fri Oct 04, 2024 4:08 am

Ann wrote: ↑Thu Oct 03, 2024 5:02 am

AVAO wrote: ↑Thu Oct 03, 2024 4:48 am
Well, I also like the comparison with NGC 4449, where you can clearly see that the center of the LMC is drifting out of the middle. I would assume that it is being "sucked out" by the Milky Way

Click to view full size image

Click to view full size image

Original data: NASA/ESA jac berne (flickr)

Very good comparison, Jac! NGC 4449 has its own "Tarantula Nebula" that is "below" the galactic bar. We can see, too, that NGC 4449 is a true starburst galaxy where the level of star formation is extremely high all over the optically bright galaxy, more so than in the LMC. However, NGC 4449 is wrapped inside a huge halo of small faint red stars, and a tiny, tiny dwarf galaxy is feeding matter into it.

NGC 4449. Credit: Mark Hanson.

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NGC 4449 and its tiny, tiny dwarf galaxy companion. Credit: Cosmotography

---

I think that the color of the halo around NGC 4449 is more correct in Mark Hanson's image than in the image by Cosmotography.

Ann

(well I never) thanks guys very interesting

"sucked out" — I am not sure what it means
picture a smallish or dwarf galaxy speed through the outer space of a large galaxy, partly going with the whirl, but partly moving through the media
The Core of that smallish or dwarf stranger galaxy is more dense in its stellar population and less dense in its interstellar gas and dust than the Disk.
So the the Core should be less slowed down by the headwind and shift from the centre of the Disk in the direction of the movement through the whirl of the outer space of this large galaxy…

VictorBorun wrote: ↑Fri Oct 04, 2024 4:08 am

Ann wrote: ↑Thu Oct 03, 2024 5:02 am

AVAO wrote: ↑Thu Oct 03, 2024 4:48 am
Well, I also like the comparison with NGC 4449, where you can clearly see that the center of the LMC is drifting out of the middle. I would assume that it is being "sucked out" by the Milky Way

Click to view full size image

Click to view full size image

Original data: NASA/ESA jac berne (flickr)

Very good comparison, Jac! NGC 4449 has its own "Tarantula Nebula" that is "below" the galactic bar. We can see, too, that NGC 4449 is a true starburst galaxy where the level of star formation is extremely high all over the optically bright galaxy, more so than in the LMC. However, NGC 4449 is wrapped inside a huge halo of small faint red stars, and a tiny, tiny dwarf galaxy is feeding matter into it.

NGC 4449. Credit: Mark Hanson.

---

NGC 4449 and its tiny, tiny dwarf galaxy companion. Credit: Cosmotography

---

I think that the color of the halo around NGC 4449 is more correct in Mark Hanson's image than in the image by Cosmotography.

Ann

(well I never) thanks guys very interesting

"sucked out" — I am not sure what it means
picture a smallish or dwarf galaxy speed through the outer space of a large galaxy, partly going with the whirl, but partly moving through the media
The Core of that smallish or dwarf stranger galaxy is more dense in its stellar population and less dense in its interstellar gas and dust than the Disk.
So the the Core should be less slowed down by the headwind and shift from the centre of the Disk in the direction of the movement through the whirl of the outer space of this large galaxy…

Ann wrote: ↑Thu Oct 03, 2024 5:02 am

AVAO wrote: ↑Thu Oct 03, 2024 4:48 am
Well, I also like the comparison with NGC 4449, where you can clearly see that the center of the LMC is drifting out of the middle. I would assume that it is being "sucked out" by the Milky Way

Click to view full size image

Click to view full size image

Original data: NASA/ESA jac berne (flickr)

Very good comparison, Jac! NGC 4449 has its own "Tarantula Nebula" that is "below" the galactic bar. We can see, too, that NGC 4449 is a true starburst galaxy where the level of star formation is extremely high all over the optically bright galaxy, more so than in the LMC. However, NGC 4449 is wrapped inside a huge halo of small faint red stars, and a tiny, tiny dwarf galaxy is feeding matter into it.

NGC 4449. Credit: Mark Hanson.

---

NGC 4449 and its tiny, tiny dwarf galaxy companion. Credit: Cosmotography

---

I think that the color of the halo around NGC 4449 is more correct in Mark Hanson's image than in the image by Cosmotography.

Ann

AVAO wrote: ↑Thu Oct 03, 2024 4:48 am
Well, I also like the comparison with NGC 4449, where you can clearly see that the center of the LMC is drifting out of the middle. I would assume that it is being "sucked out" by the Milky Way

Click to view full size image

Click to view full size image

Original data: NASA/ESA jac berne (flickr)

Ann wrote: ↑Thu Oct 03, 2024 4:32 am

VictorBorun wrote: ↑Wed Oct 02, 2024 9:19 pm

Christian G. wrote: ↑Wed Oct 02, 2024 12:14 pm if the LMC has a central bar but only one arm coming out of it, what happens at the other end of the bar? Do Magellanians believe this is where the world ends?

I wonder if Tarantula Nebula is what's left of the LMC's lost arm

You may be right, Victor, even though I think that the Tarantula Nebula has more to do with LMC's bar than with a lost arm. The Tarantula Nebula could be an unusually vigorous bar-end enhancement.

NGC 6217 annotated NASA ESA and the Hubble SM4 ERO Team.png

The largest and brightest nebula of NGC 6217 is located at one on of its bar.
Credit: NASA, ESA and the Hubble SM4 ERO Team

NGC 7292 annotaated ESA Hubble and NASA C Kilpatrick.png

The largest and brightest nebula of NGC 7292is located at one end of its bar.
Credit: ESA/Hubble and NASA; C. Kilpatrick

Bar-end enhancements are locations near the end (or ends) of a galaxy's bar, where star formation is particularly vigorous. That's why we also find very large and bright nebulas near the ends of bars.

Perhaps you are saying that the Tarantula nebula is not located exactly at the end of LMC's bar, but above (or below) the end of it. Yes, but that happens, too.

And Victor, very bright nebulas at the end of a galactic bar may indeed be a part of the beginning of a galactic arm. But if you look at the bright nebula at the end of the bar in NGC 6217, you can see that the arm that emerges from it is very short. Indeed, that arm is more like an arc!

Ann

VictorBorun wrote: ↑Wed Oct 02, 2024 9:19 pm

Christian G. wrote: ↑Wed Oct 02, 2024 12:14 pm if the LMC has a central bar but only one arm coming out of it, what happens at the other end of the bar? Do Magellanians believe this is where the world ends?

I wonder if Tarantula Nebula is what's left of the LMC's lost arm

Christian G. wrote: ↑Wed Oct 02, 2024 12:14 pm if the LMC has a central bar but only one arm coming out of it, what happens at the other end of the bar? Do Magellanians believe this is where the world ends?

Roy wrote: ↑Wed Oct 02, 2024 2:09 pm The time scales being spoken of are so large as to make predictions impossible. Two and one-half billion years ago micro organisms had begun learning how to live on carbon dioxide and exhale oxygen. Animalcules living on the oxygen scat were yet to come.

Christian G. wrote: ↑Wed Oct 02, 2024 12:14 pm
Delightful and informative commentary!
(and if the LMC has a central bar but only one arm coming out of it, what happens at the other end of the bar? Do Magellanians believe this is where the world ends?)

Ann wrote: ↑Wed Oct 02, 2024 6:39 am Talk about the Large Magellanic Cloud? Where to start? Well... that's a gorgeous APOD!

The Large Magellanic Cloud Galaxy. Image Credit & Copyright: Ireneusz Nowak; Text: Natalia Lewandowska (SUNY Oswego)

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APOD 2 October 2024 annotated.png

Okay. If my annotations are hard to read, I'm sure you can see the long bar of the Large Magellanic Cloud (the LMC). The large pink splotch to the upper right of the bar (in this picture) is the Tarantula Nebula, the the most active star-forming region in the Local Group according to Wikipedia. To the lower left of the Tarantula Nebula (in this picture) is the remnant of the closest supernova recorded by humans since the 17th century, SN 1987A.

The Tarantula Nebula and SN1987A. Credit: Science Photo Library. I believe that the real author was David Malin and the Anglo-Australian Telescope.

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Inside the bar, but near the lower left end of it, is young globular cluster NGC 1850.

NGC 1850. Credit: Judy Scmidt, using data form the Hubble telescope.

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NGC 1850 is near center, NGC 1854/1855 to the right of NGC 1850 and and NGC 1858 to the lower right. Credit: Erik Westermann.

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Wikipedia wrote:

NGC 1850 is a double cluster and a super star cluster in the Dorado constellation, located in the northwest part[3] of the bar of the Large Magellanic Cloud, at a distance of 168 kly (51.5 kpc) from the Sun. It was discovered by Scottish astronomer James Dunlop in 1826.

This is an unusual cluster system because the main distribution of stars is like a globular cluster, but unlike the globular clusters of the Milky Way it is composed of young stars. The only similar object in the Milky Way is Westerlund 1. The main cluster has the appearance of a globular cluster with an age of 50±10 Myr. The second is a more loosely distributed sub-cluster with an age of 4.3±0.9 Myr, located at an angular separation of 30″ to the west of the main cluster.

I don't have much to say about the large blue ring in the LMC, except that I want you to pay attention to it. I guess that something enormously energetic must have taken place inside it.

Little-known N11, which so often gets overlooked when the LMC is photographed, is actually the second largest nebula complex in the LMC!

The LMC without N11. Credit: Pablo Carlos Budassi

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The LMC including N11. Credit: DOCdb and possibly Dieter Willasch.

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Closeup of N11. Credit: Legacy Surveys / D.Lang (Perimeter Institute) & Meli thev

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Wikipedia wrote:

N11 (also known as LMC N11, LHA 120-N 11) is the brightest emission nebula in the north-west part of the Large Magellanic Cloud in the Dorado constellation. The N11 complex is the second largest H II region of that galaxy, the largest being the Tarantula Nebula. It covers an area approximately 6 arc minutes across. It has an elliptical shape and consists of a large bubble, generally clear interstellar area, surrounded by nine large nebulae. It was named by Karl Henize in 1956.

Okay, so how important is the LMC as a galaxy? Well, which is the fourth largest galaxy in the Local Group?

The six largest galaxies in the Local Group. Credit: SkyFlubbler

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Ta-daaah! It's the Large Magellanic Cloud!

While smallish, the LMC is not a dwarf galaxy. Its mass, according to Laura L. Watkins et al., is circa 17% of the mass of the Milky Way. That is not negligible. Oh, and Wikipedia claims that the mass of the LMC is "roughly one-hundredth the mass of the Milky Way", but you shouldn't take that seriously. Wikipedia is quoting an Encyclopedia Britannica source from 2009. The Laura Watkins source is from January 2024.


But did you know that the Large Magellanic Cloud will be our doom?

Space.com wrote:

You may be aware that the huge and beautiful spiral galaxy Andromeda will plow into the Milky Way about 5 billion years from now, livening up the night skies of any Earth creatures who are still around to look up. But one of our smaller galactic neighbors, the Large Magellanic Cloud (LMC), will actually hit the Milky Way about 2.5 billion years before the epic Andromeda event, according to a new study.

"The destruction of the Large Magellanic Cloud, as it is devoured by the Milky Way, will wreak havoc with our galaxy, waking up the black hole that lives at its center and turning our galaxy into an active galactic nucleus or quasar," lead author Marius Cautun, a postdoctoral fellow at the Institute for Computational Cosmology at Durham University in England, said in a statement.

Oh no!!! Imagine being hit on the head by a galaxy weighing 17% of the mass of the Milky Way! I think the asteroid that killed the dinosaurs is dwarfed by this!

The LMC is coming! Boooh!!! Credit: NASA/JPL-Caltech/STScI

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Mark Garlick/Science Photo Library/Getty Images

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All things considered, I think the LMC ramming our galaxy will cause more damage than that asteroid that hit us 65 million years ago. Do you think we could find shelter on Alpha Centauri?

Ann

Wikipedia wrote:

NGC 1850 is a double cluster and a super star cluster in the Dorado constellation, located in the northwest part[3] of the bar of the Large Magellanic Cloud, at a distance of 168 kly (51.5 kpc) from the Sun. It was discovered by Scottish astronomer James Dunlop in 1826.

This is an unusual cluster system because the main distribution of stars is like a globular cluster, but unlike the globular clusters of the Milky Way it is composed of young stars. The only similar object in the Milky Way is Westerlund 1. The main cluster has the appearance of a globular cluster with an age of 50±10 Myr. The second is a more loosely distributed sub-cluster with an age of 4.3±0.9 Myr, located at an angular separation of 30″ to the west of the main cluster.

Wikipedia wrote:

N11 (also known as LMC N11, LHA 120-N 11) is the brightest emission nebula in the north-west part of the Large Magellanic Cloud in the Dorado constellation. The N11 complex is the second largest H II region of that galaxy, the largest being the Tarantula Nebula. It covers an area approximately 6 arc minutes across. It has an elliptical shape and consists of a large bubble, generally clear interstellar area, surrounded by nine large nebulae. It was named by Karl Henize in 1956.

Space.com wrote:

You may be aware that the huge and beautiful spiral galaxy Andromeda will plow into the Milky Way about 5 billion years from now, livening up the night skies of any Earth creatures who are still around to look up. But one of our smaller galactic neighbors, the Large Magellanic Cloud (LMC), will actually hit the Milky Way about 2.5 billion years before the epic Andromeda event, according to a new study.

"The destruction of the Large Magellanic Cloud, as it is devoured by the Milky Way, will wreak havoc with our galaxy, waking up the black hole that lives at its center and turning our galaxy into an active galactic nucleus or quasar," lead author Marius Cautun, a postdoctoral fellow at the Institute for Computational Cosmology at Durham University in England, said in a statement.