The Largest Known Things In The Universe, Ranked By Size

Space. It's really, really big. How big is it? Well, according to astronomers, the observable universe is around 92 billion light-years in diameter, but that's all we can see (hence the word "observable"). For all we know, the universe as we see it is but a tiny speck of an even larger reality, which honestly wouldn't be out of the question given the massive size of "objects" we have already discovered.

Many people have trouble comprehending the true scale of things. Imagine you took a road trip across the contiguous United States. That's over 2,900 miles. Now try picturing taking a similar journey across Jupiter's iconic Great Red Spot. It might look small, but that's only because the planet is so huge; the crimson storm is over 10,000 miles wide. And sizes only increase exponentially after you leave the interplanetary neighborhood we call the solar system.

Here are the largest objects and phenomena we've observed in the universe so far. For the sake of variety, we've divided it into four categories: planets, stars, galaxies, and structures (phenomena that don't fit into the previous categories). Furthermore, each item was selected using the metric of length. Since new discoveries are being made every day, entries in this article could easily become obsolete at a moment's notice.

Jupiter is the largest planet in our solar system. Heck, Jupiter is so big that scientists have postulated it could have become its own star. But it's still tiny compared to other gas giants.

The planet Kepler-435 b is a gas giant that was discovered in 2015. This planet circles the star Kepler-435, hence its uncreative name. Astronomers estimate Kepler-435 b has a radius of about 86,448 miles, give or take 7,819 miles. This would give the planet roughly double the radius of Jupiter. However, despite being significantly larger than Jupiter, Kepler-435 b is estimated to have around 85% as much mass – 1.6 * 1027 kg, give or take 2.75 *1026 kg.

Kepler-435 b's strangest feature is its distance from its star. Despite its size, the planet is only 0.0948 Astronomical Units (AU) from Kepler-435. For the sake of comparison, the Earth is one AU (around 93 million miles) from the Sun, whereas Mercury, the closest planet in our solar system, is barely 0.4 AU away. Not only does Kepler-435 b skirt with disaster every time it completes an orbit given this close proximity, but the planet also encircles its star every 8.6 days. Or at least it did over 4,600 years ago, as the planet is over 4,600 light-years away. That's the problem with examining exosolar planets; we can only see them as they were, never as they are.

Given the layout of our solar system, it is easy to assume a planet's structure is determined by its distance from a star. Planets within a certain distance are dense, rocky orbs, whereas anything past this distance is a gaseous giant. This isn't always true.

The planet HAT-P-67 b shares a lot in common with Kepler-435 b. Like that gas giant, HAT-P-67 b is a gaseous planetoid whose size doesn't match its mass, except HAT-P-67 b is even more of a featherweight. According to the latest estimates, HAT-P-67 b has a radius of 92,963.74 miles, give or take 1,086 miles, which makes it 2.14 times the radius of Jupiter. However, HAT-P-67 b's mass is only 8.55 * 1026 kg, give or take 2.85 * 1026kg, making it the second-least dense planet known to man. Marshmallows have a higher density than HAT-P-67 b.

Another trait HAT-P-67 b shares in common with Kepler-435 b is its orbit size. HAT-P-67 b sits a measly 0.06505 AU from HAT-P-67, which means its years only last a scant 4.8 days. This makes HAT-P-67 b and Kepler-435 b some of the few "Hot Jupiters" in the universe: gas giants that are situated in impossibly tight orbits around their stars. Currently, only seven Hot Jupiters have been recorded, the latest of which, TOI-5205 b, was discovered in 2023.

As previously stated, had Jupiter formed differently, it could have undergone a reaction that turned it into its own star. The same is likely true for many exosolar gas giants, some of which are so massive — and far away — that astronomers aren't sure they are even planets.

The gas giant ROXs 42 Bb is currently the largest known planet in existence. Possibly. This gas giant has an estimated radius of 91,226.1 miles, give or take 15,204.35 miles, which could potentially give it 2.5 times the radius of Jupiter. Even if this estimate is wrong, ROXs 42 Bb still takes the crown for the most massive planet known to man. Astronomers believe ROXs 42 Bb weighs a chart-topping 2.47 * 1028 kg, give or take 9.5 * 1027 kg.

Given ROXs 42 Bb's titanic mass, astronomers aren't fully convinced ROXs 42 Bb is a "super-Jupiter" as it were. One popular theory states ROXs 42 Bb is actually a "brown dwarf," a demi-star that can't sustain nuclear fusion but can produce some light and heat due to the fusion of other elements. ROXs 42 Bb has a composition and emissions similar to those of other brown dwarfs, but the evidence is far from conclusive. Plus, as far as brown dwarfs go, ROXs 42 Bb would be tiny, so its classification is up in the air.

As surprising as it sounds, our solar system is a relative rarity. Not because it has life, but because it has only one star. According to NASA, the majority of known solar systems have more than one star. Some even have as many as three, but the number of stars in a system doesn't necessarily impact the sizes of said stars.

WOH G64 is a noteworthy star for several reasons. It was the first extrasolar sun astronomers photographed "close up," but more importantly, the star is absolutely gargantuan. In 2018, astronomers estimated WOH G64 had a radius of about 346 million miles and a mass of about 5.57 *1031 kg — about 800 times the Sun's radius and 28 times its mass. However, there is a good chance that information is already outdated, and not just because the star is 160,000 light-years away.

When astronomers discovered WOH G64, the star was a red supergiant and possibly the largest extrasolar body known at the time. Back then, astronomers estimated that the star had a radius of 649 million miles, around 1,500 times that of the Sun. That would mean WOH G64 has lost around half of its size and mass in a relatively short amount of time. WOH G64 might have lost its potential crown thanks to its new classification as a yellow hypergiant, but it could provide astronomers a treasure trove of information on the death spiral of stars.

Even after stars and their surrounding planets form, they aren't done changing. Planets can undergo alterations that turn them into vastly different bodies. Stars, meanwhile, continue to burn unchanged for untold eons until they transform in a fit of autocannibalistic chemistry.

UY Scuti is currently one of the largest stars known to man, although its classification changes from time to time because it is "pulsating" and "variable." Depending on who you ask and when, UY Scuti could be a red supergiant or a red hypergiant. At its biggest, UY Scuti was estimated to have a radius that stretched almost 736 million miles (around 1,700 times that of the Sun), but more recent observations place its radius closer to 393.3 million miles (around 909 times that of the Sun). Understandably, it's difficult to get a read on UY Scuti's mass.

As UY Scuti's size is mercurial, the star's brightness changes frequently, which has forced astronomers to amend UY Scuti's location relative to Earth. When the star was initially discovered, astronomers guessed that it was 9,500 light-years away. However, according to more recent data, astronomers have placed the star closer to 5,900 light-years, give or take a few hundred. Given the star's variable nature, we might never know the star's true distance from Earth; it's not like we can use a tape measure or anything.

As stars start to die, they swell up like balloons and lose their outermost shells. Sometimes when a star finally gives out, it can explode into a supernova or collapse in on itself and form a black hole. Of course, these fates are only reserved for the biggest, most record-shatteringly massive stars.

As of writing, VY Canis Majoris is the largest star in the sky, unless UY Scuti swells back into the lead. Astronomers recently estimated that VY Canis Majoris' radius sits around 614.42 million miles, give or take an extra 52 million miles. That's around 1,420 times the radius of the Sun. Astronomers also believe the star has a mass in the ballpark of 3.38 *1031 kg, approximately 17 times that of the Sun. To put this in perspective, if we replaced our sun with VY Canis Majoris, the star would stretch well past Jupiter's orbit.

Due to its size, VY Canis Majoris is the brightest source of infrared radiation ever detected by the Hubble Space Telescope. However, since these traits are the product of advanced age, it's only a matter of time before the star loses its size. Data show that VY Canis Majoris has been subject to "mass-loss events" that are unusual when compared to similar events of other red supergiants. While many astronomers expect VY Canis Majoris to go out in a massive supernova blaze, these unusual mass-loss events could result in VY Canis Majoris turning into a black hole.

Galaxies come in several shapes. The Milky Way is a spiral galaxy, as its arms spiral out from the center like water going down a drain. Elliptical galaxies, meanwhile, are flat and round or oval-like. And then there are lenticular galaxies, whose shapes don't fit snugly into either category.

The galaxy IC 1101 is considered one of the biggest lenticular galaxies ever discovered. According to recent data, the galaxy's diameter sits around 125.62 kiloparsecs, or just over 409.72 thousand light-years. Moreover, this size makes IC 1101 more luminous than most other galaxies visible from Earth (with the aid of telescopes).

While IC 1101's size, brightness, and shape are all noteworthy characteristics, the galaxy's true claim to fame is its center. IC 1101's core is considered the largest ever discovered, around 4.2 kiloparsecs (13.7 thousand light-years). This size can be attributed to the fact that the core is mostly depleted, as well as the cause of said depletion: a supermassive black hole. This isn't that surprising since the Milky Way core also consists of a star cluster and a supermassive black hole of its own. While IC 1101 is tiny compared to the largest galaxies, it has a bigger heart.

When you look up at the night sky with the naked eye, you can only see stars within our galaxy. If you want to see stars outside of the Milky Way, you need to use powerful tools such as the Hubble Space Telescope. This telescope has snapped countless images of galaxies and galaxy clusters, but regardless of the tool you use, larger galaxies are generally brighter.

A2261-BCG is one of the largest elliptical galaxies in the Abell 2261 galaxy cluster, as well as one of the largest galaxies ever discovered. The galaxy is slightly ovaloid, as one diameter stretches over 544 thousand light-years, while another is a slightly shorter 533 thousand light-years. A2261-BCG's core, meanwhile, is only 10,000 light-years across. This might sound small (comparatively speaking), but A2261-BCG's core actually set records at the time of discovery.

Unlike most galactic cores, the heart of A2261-BCG looks more akin to puffy fog than a concentrated point of light. This naturally raised the question of what made the core so unusual. Astronomers proposed two promising theories: Either merging black holes stirred up the star cluster in the center, or the black holes were catapulted out of the core and left it without a gravitational anchor. In 2021, a team of scientists uncovered data that pointed to the latter theory.

Contrary to popular belief, black holes come in a variety of sizes, including supermassive black holes with masses estimated to be billions of times that of the Sun. Despite the name's implications, supermassive black holes are actually somewhat common, but only the biggest galaxies can safely contain the biggest black holes.

Currently, ESO 383-76 is the largest elliptical galaxy and the largest galaxy ever discovered. Recent data places the galaxy's diameter over 540 kiloparsecs, or 1.7 to 1.8 million light-years. As with other galaxies, this prodigious size grants ESO 383-76 intense luminosity, and we don't just mean in the visible spectrum. According to astronomers, ESO 383-76 is the sixth-brightest source of x-ray radiation in the night sky, which in turn makes its galaxy cluster, Abell 3571, the sixth-brightest galaxy cluster in terms of x-rays.

As with most galaxies, ESO 383-76 literally revolves around a supermassive black hole, and like the galaxy itself, this gravitational anchor tips the scales. ESO 383-76's central black hole is one of, if not the most massive examples ever discovered, but nobody can agree as to the scope of its enormity. Some estimates go as low as 3.98 * 1039 kg (2 billion times the Sun's mass) to as high as 5.57 * 1040 kg (28 billion times the Sun's mass).

Arguably the biggest hurdle to proper interstellar travel is space itself. The majority of space is just this empty void absent of matter. While most regions of space are pockmarked with solar systems, one area terrifies astronomers due to its sheer nothingness.

The CMB Cold Spot is one of the more perplexing and fascinating "structures" in the known universe. Cosmic microwave background (CMB) is believed to be an afterglow of microwave radiation created by the Big Bang. CMB is uniformly present throughout most of the observable universe, but some small sections (relatively speaking) don't have any CMB. And then there's the CMB Cold Spot, a huge area in space completely devoid of any background radiation. One of the more popular explanations for the CMB Cold Spot's presence is the Eridanus Supervoid.

The Eridanus Supervoid is a semi-hypothetical, unusually large area in space around 2 billion light-years away from Earth believed to stretch 1.8 billion light-years. As its name suggests, the Supervoid is far more empty than the surrounding space — not completely empty, but enough for a general lack of gravity to negatively impact the light particles that make up CMB. While the Eridanus Supervoid doesn't fully explain the CMB Cold Spot, it is crucial to mapping and understanding CMB as well as other forms of matter, including hypothetical dark matter.

When you think of a "structure" in space, your mind probably jumps to something physical. Turns out giant structures don't need a physical form to be tangible.

As previously stated, when stars die, they either explode into supernovas or collapse into black holes. While all supernovas release catastrophic amounts of energy, the biggest supernovas produce gamma-ray bursts (GRBs). Each burst unleashes a quintillion times more light than the Sun, and these bursts are thought to be the second-most powerful explosions in existence; the Big Bang, of course, was the most powerful. In 2022, astronomers recorded the largest GRB ever, but even that was nothing compared to the Giant GRB Ring.

The Giant GRB Ring isn't a structure in the physical sense but more of a statistical anomaly given form via data. As its name suggests, the Giant GRB Ring is a ring of nine GRBs that lies around 9 billion light-years away from Earth with a total diameter of 5.6 billion light-years. This size is noteworthy in and of itself, but the Giant GRB's significance goes even deeper. According to astronomers, this structure could only have formed if the nine stars that produced the giant ring were part of another intergalactic structure and were located roughly the same distance from Earth. Given current cosmological models, that should be impossible, yet the Giant GRB Ring exists. Either the topography of the universe is more interconnected than we thought, or the Ring GRB Ring is the long-delayed aftermath of a local galaxy-on-galaxy collision.

Many galaxies clump together into collections known as galaxy clusters. These gravitational wells can hold hundreds or even thousands of galaxies. One particularly large galaxy cluster is so big that it warps space-time, but the biggest is so prodigiously large that astronomers aren't even sure it exists. Kind of.

The Hercules-Corona Borealis Great Wall is something known as a "galaxy filament," a supercluster made out of smaller galaxy clusters strung together. Current estimates place this galactic gigastructure at about 10 billion light-years wide and one billion light-years thick. For the sake of comparison, the observable universe is around 92 billion light-years in diameter. While astronomers discovered the Great Wall in 2014 (or 2015, according to some sources), they didn't know its true size until a GRB shed some light on the structure's scale. But not everyone is convinced.

Some astronomers believe the Hercules-Corona Borealis Great Wall is too big to exist. That's not to say they're conspiracy nuts who think stars are actually tiny stage lights or anything; they just don't believe we have enough information on the Great Wall to draw conclusions. Since much of what we know about the structure is the result of a GRB and not constant observation, data are spotty at best. For all we know, what we think are galaxies within the Hercules-Corona Borealis Great Wall are just misinterpreted data points.

We decided to divide the article's entries into different categories for the sake of variety. Otherwise, the list would have been full of nothing but structures that spanned light-years. And to ensure each category got equal time in the spotlight, we went with three entries per category.

For simplicity and consistency, we used the literal definition of "largest" and prioritized entries with the most prodigious sizes. While technically all measurements of extrasolar bodies and structures are guesses, estimating size is easier than mass, especially for super-sized galaxies and galaxy clusters made out of countless stars and planets. The largest of the large of each category was selected for the article and ordered from "smallest" to biggest. However, some potential entries were ruled out because the data around their existence weren't convincing beyond a reasonable doubt. For example, the planet GQ Lupi b is theorized to be the largest planet ever discovered, even bigger than ROXs 42 Bb. However, GQ Lupi b is a nascent planet of sorts, so the models usually used to determine a planet's size and mass are unreliable in this scenario. This left ROXs 42 Bb as the largest planet we were comfortable including in this article.