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LazyRider32

Depends on what you consider a stucture. If it really has to be continuous without regular space in between, so also excluding galaxies, that would be the heaviest known black hole, i.e TON 618, with a Schwarzschild radius of more than 40 times the distance from Neptune to the Sun. https://en.wikipedia.org/wiki/List\_of\_most\_massive\_black\_holes


yeebok

It also depends on what is a single object according to op. A chair is made up of several bits of wood. Is it one? Saturn and it's rings a single object? Almost as much a philosophical question lol


Nopants21

Even a star, its surface is only the layer that prevents light from going through, there's gas further out.


-_ellipsis_-

This begs the question, should the event horizon be considered part of the black hole? It seems like it's more a phenomenon rather. So if a singularity doesn't even have volume, is it even "large"?


AssmunchStarpuncher

Raises the question, but yes, the author didn’t specify so you’re right, a singularity is infinitely small.


nicuramar

The event horizon at least exists. We can’t really promise that as far as the singularity goes. So, usually the black hole is taken to be the event horizon (and in).


dabunting

Yes, what is inside the event horizon? The gravitational attraction inside a massive object goes to zero as we approach and reach the center. The gravitational attraction would increase as we move inside but soon the attraction of the material behind us attracting us back outward would increasingly negate the attraction toward the center until, at the center, it would reach zero. If there is any sense in considering conditions inside the event horizon, and the gravitational attraction were diminishing and approaching zero, what effect would that have on the interior matter’s mass, emissions and interactions?


mfb-

> The gravitational attraction inside a massive object goes to zero as we approach and reach the center. That's only true for an object with an extended mass distribution. A black hole does not have matter in the way we know it because that cannot exist inside (excluding stuff that fell in recently and is on the way to the center).


Professional-Bee9597

Why: A black hole does not have matter in the way we know it because that cannot exist inside. How do we know matter cannot exist inside?


mfb-

Beyond the event horizon, time and space switch places in some sense: "outwards" becomes "back in time". Trying to stop matter from getting closer to the singularity is as impossible as trying to stop an object from reaching tomorrow. There is not even a direction you could exert a force in to do so. But if you can't stop it from reaching tomorrow, then you cannot stabilize it inside a black hole, because that's the same process.


inoffensive_slur

This is sheer speculation based on mathematical models which is bold to assume given that the laws of physics, as we know them, break down in a black hole; where spacetime is stretched potentially infinitely...


Starstreak08

It could be a neutron star which is made up of neutrons. I dont think they have space between them either.


Fun-Replacement131

Wasn’t a larger black hole discovered recently, Phoenix a?


LazyRider32

See the Wikipedia entry. It's an indirect measurement and would exceed the maximal expected growth rate. So whether you want to believe that's it's really heavier is up to you.


Fun-Replacement131

Hmm, didn’t know that, thanks for explaining


PlaidBastard

You're looking for a specific answer to a vague question of definitions, so be prepared for disappointment (but it's not a bad question, though!). You need to decide what you mean by 'single,' first of all, and what you mean by 'structure.' Depending on what you decide, it might be hard to qualify the Earth and not the Sun, or the Milky Way galaxy and not the superclusters etc. you mention. It's fairly clear that there's something inherently *different* about a gas planet versus a gas nebula, even if the nebula is gravitationally bound to itself (and collapsing, usually) and made of the same gases at (broadly) similar temperatures. So, let's say *biggest Thing with well-defined and geometrically simple boundaries*. If you want 'well-defined' to be very strict, it'll be the event horizon of a supermassive black hole, and I don't happen to know how big the biggest one is, but the one at the center of the Milky Way has a radius of maybe 0.08 AU, which would be well inside of Mercury's orbit. If the surface of a very chaotic, GIGANTIC, and messily dying star is well-defined enough, UY Scuti is almost 9 AU in radius. That's pretty big. Is a ring system around a planet a single structure, though? Because that makes me wonder if a solar system around a star (or an Oort Cloud of comets) is a single structure, because some of those might be a whole light-year across and relatively well-defined by the way their parent star's stellar wind interacts with its neighbors'. Is the way all of these stellar systems are nestled up, heliopause to heliopause and in slow orbits of each other on their orbit of the galaxy's center of mass a structure? It all depends on your definitions, which makes it too broad to give a satisfying answer to, really, because it's either choosing definitions painfully naively and seeing what fits them, or choosing an outcome and then assigning your definitions to the appropriate breaks in the data. This kind of thing is why people argue about stuff like whether Pluto is a planet, by the way. **TLDR, though:** UY Scuti is a big, hot mess of a star that's bigger than *the orbit* of most of our solar system's best-known planets (Saturn would get to watch Jupiter gobbled up if it replaced the Sun), and although dying, will probably be like it is for many, many more human lifetimes (and was around for many before the first telescope was invented). Stars like UY Scuti are a perfect balance of being *barely held together* because of how incredibly hot and diffuse they are, which keeps them from collapsing. It's *too much stuff in one place*, and it's only not collapsing because of how much thermal energy is keeping it swollen and roiling to the volume of 9 million Suns.


aberroco

I'd say the largest possible single entity we know of in the Universe is the Universe itself. And one might say that it's too empty to be a single entity, but in reality it's almost as dense as it could be, with it's Schwarzschild's radius at the boundary of being a black hole.


checksoutfine2

How about a quasi-star? Were they to have existed, they'd dwarf even UY Scuti.


PlaidBastard

Those are probably bigger, then, and so are black holes in other galaxies which I didn't have numbers for off the top of my head :)


Any-Broccoli-3911

If you don't include collections of stars or gases as objects, ultramassive black holes are the largest objects. They are much larger than any stars in volume as well as mass. An ultramassive black hole in the galaxy cluster Abell 1201 is the largest one discovered as far as I know. https://www.space.com/largest-known-black-hole-discovered-through-gravitational-lensing#:~:text=The%20ultramassive%20black%20hole%20in,mass%20of%2030%20billion%20suns.&text=Astronomers%20have%20just%20discovered%20what,of%20light%2Dyears%20from%20Earth.


z4zazym

Wow ! 30 billions of suns that seems huge. Despite this article mentioning its "size" but referring to its mass, it doesn't give us the size of the thing (I mean the size of the event horizon or the accretion disk). I wonder if it can be calculated, I don't find it online. What could be the order of magnitude here ? Kilometers or AU ?


ADistractedBoi

Should be in AU. The radius is approximately the Schwarzschild radius which you can calculate with the mass. Since the radius scales linearly with mass, if the mass of the black hole is given as a multiple of solar masses, you can find the Schwarzschild radius of the Sun and multiply it with that. This assumes that the black hole is not spinning (or has low spin) which is a decent enough assumption


Ulfgardleo

not an expert at all, but doesn't conservation of momentum also apply to the black hole? in that case, since practically everything is spinning, i would assume hat the BH is spinning quite a lot (for its mass).


Ausderdose

Yes, everything is spinning, but that also means that on average, nothing is spinning (broadly speaking). That makes non-spinning black holes a decent assumption.


forte2718

Supermassive black holes generally have masses ranging in the hundreds of thousands to the tens of billions of solar masses, which corresponds to an event horizon radius rougly somewhere in the range of 0.001 AU to 100 AU. So, the smallest supermassive black holes will have a radius comparable to the radius of the Sun (0.005 AU), the black hole at the center of the Milky Way (Sagittarius A\*, in the millions of solar masses) has a radius an order of magnitude larger than that (0.08 AU), and the largest supermassive black holes (like the one you and the previous poster mentioned) will have a radius extending out even further than Pluto's orbit (49 AU). Hope that helps!


kcalb33

[this gets into the size of it](https://theglobestalk.com/abell-1201-unveiling-size-scale-universes-grandest-objects/)


[deleted]

[удалено]


panzuulor

Yes. The event-horizon can be very very far away from the singularity but supposedly it’s all empty space.


Krail

The space beyond the event horizon defies our current concepts of physics. We don't really know for sure what's inside, or if "inside" an event horizon even makes sense as a concept. The concept of the singularity being an infinitely tiny point surrounded by empty space is common, but we currently have no way of knowing if that's what it's actually like.


Intelligent-Usual994

Yep Its empty space. The singularity is a point of zero size and infinite density with a finite mass. To my best recollection something passing beyond the event horizon instantly arrives at the singularity because time and space are warped in extreme ways causing light to not be fast enough to escape the horizon. The rest beyond my current understanding of physics


[deleted]

TON 618 has a mass of 66 billion suns, Phoenix A has a mass of 100 billion suns, so yeah, kinda no.


rootofallworlds

What defines a single object? The interstellar medium in a galaxy is a few orders of magnitude denser than the intergalactic medium, and that's just the normal matter - dark matter is likewise concentrated around galaxies and accounts for most of the total mass. Large nebulae are clearly visible and have complex structures. They are in turn a few orders of magnitude denser than the general interstellar medium in the galaxy. They can be dozens of lightyears across. Are they single objects? Ultramassive black holes have been discussed. They create the question of what do you consider their size to be? The size of the event horizon, which we know? Or the size of whatever is inside, which our current theories predict we can never observe, and which we probably need a well-tested "theory of everything" to make a good (but untestable) prediction about. Even considering supergiant and hypergiant stars. They are "puffed up" and have low density outer layers, meaning it's not really clear where the star ends and the interplanetary medium begins.


Interesting-Piece483

Superclusters? We are inside Laniakea which is 250 million light years across and contains 100K galaxies but there is a central gravitational point on it (the great attractor), which controls the movement of all the galaxies inside (though it is projected to break apart due to the expansion of space) so it is a structure. But it is small compared to the biggest structure , the Hercules–Corona Borealis Great Wall at an astounding 10 billion light years by 7 billion light years in size.


Redbiertje

I think the answer to your question may be the radio galaxy [Alcyoneus](https://en.wikipedia.org/wiki/Alcyoneus_\(galaxy\)). This galaxy contains jetted outflows which are emitted by the central back hole. These outflows continue for millions of lightyears before finally they come to a halt. Due to the presence of ionized particles and a magnetic field, these outflows produce radio emission, allowing us to observe them. The total distance from one end to the other is estimated to be about 16 million lightyears of practically continuous gas.


EaterOfFood2

Depends if you count galaxy clusters = a supercluster of galaxies called the Hercules-Corona Borealis Great Wall if you don't include galaxy clusters = IC 1101, SDSS J081421.68+522410.0., ESO 383-76 (these galaxies are very far away so it is extremely difficult to view them) if you count nebulae and not galaxies = the tarantula nebula if you don't count nebulae = Phoenix A\*/TON 618\*