Stephenson 2-18 – Largest Star Ever Discovered in the Universe

Stephenson 2-18 – Largest Star Ever, often referred to as RSGC2-18 and Stephenson 2 DFK 1, is a red supergiant or a red hypergiant star situated in the Scutum constellation and part of the Stephenson 2 supercluster. It is situated around 19,000 light years away from Earth.

It is located near the supermassive black hole Sagittarius A*. The star is enormous, with a massive diameter that is almost 2150 times larger than the Sun‘s. It is most likely one of the biggest stars in the universe.

Stephenson 2-18 stands out as a colossal red supergiant, currently holding the title of the largest known star in the entire universe. If Stephenson 2-18 were at the Sun’s position, its surface would extend well past the orbit of Mars, reaching a distance of approximately 8.0 billion kilometers.

What is the Size of Stephenson 2-18 (Largest Star ever)?

Stephenson 2-18 is the biggest star ever discovered, surpassing other stars like VY Canis Majoris and UY Scuti. Stephenson 2-18 is a red hypergiant star with the greatest size that has a mind-boggling radius of 1.5 billion kilometers (930 million miles), estimated to be 2,150 times larger than the Sun, making it a true cosmic giant.

Stephenson 2-18 is significantly larger as compared to the Sagittarius A*, clocking in at 243 times wider, Stephenson 2-18’s immense diameter dwarfs the event horizon of Sagittarius A*.

Stephenson 2-18 is larger than nearly the whole orbit of Saturn (1,940 – 2,169 solar radii). According to that calculation, the volume of this star is at least ten billion times more than that of the Sun. The Sun seems nearly as little as a grain of dust when compared to this star, which is roughly the size of an enormous basketball.

What is the Mass of Stephenson 2-18 (Largest Star ever)?

The mass of Stephenson 2-18 is unknown. At the moment, Stephenson 2-18 burns through an increasing amount of mass as it fuses helium into heavier elements like lithium and carbon. It’s possible that Stephenson 2-18 lost a significant portion of its mass from its huge size as a Red Supergiant star. Stephenson 2-18 will ultimately perish and return its mass to the galaxy when it burns elements in its core. Planets and stars will form as a result of this mass.

What is the Luminosity of Stephenson 2-18 (Largest Star ever)?

In addition to its size, Stephenson 2-18 is also one of the most luminous stars, at 440,000 units of solar luminosity, making it one of the brightest stars. Solar luminosity refers to the brightness of the Sun.

Stephenson 2-18’s luminosity (L) is approximately 2.87 x 10^47 L☉, which is roughly 2.87 x 10^47 times more luminous than our Sun (The Sun’s luminosity is approximately 3.828 x 10^26 Watts). Given that Red Supergiant stars are among the brightest and biggest stars in the universe,

Stephenson 2-18 has a high brightness. Stephenson 2-18 has an average temperature of 3,200 kelvin, however, this estimate is close to the red supergiant luminosity limit.

The immense luminosity of Stephenson 2-18 has significant implications for its surroundings. The star likely bathes its neighboring celestial bodies in intense radiation, potentially influencing the formation and evolution of planetary systems within its reach.

What is the Temperature of Stephenson 2-18 (Largest Star ever)?

The star’s classification as a red supergiant indicates a cooler surface temperature compared to hotter, blue stars. However, “cool” in this context is a relative term. Stephenson 2-18’s estimated surface temperature is around 3,200 Kelvin (approximately 5,430 degrees Fahrenheit), which is still incredibly hot by human standards.

What is Stephenson 2-18 (Largest Star ever)’s Distance from Earth?

Stephenson 2-18 is situated at a staggering 19,000 light-years from Earth and resides in the constellation Scutum within our Milky Way galaxy.

When and Who Discovered Stephenson 2-18 (Largest Star ever)?

The discovery of Stephenson 2-18 wasn’t a singular moment, but rather a gradual process. In 1990, astronomer Charles Bruce Stephenson identified a cluster of red supergiants in the constellation Scutum through a deep infrared survey.

Later studies using different techniques helped pinpoint Stephenson 2-18 within this cluster, solidifying its status as the largest known star in the Milky Way, and possibly the entire universe, based on current observations.

What is the Composition of the Stephenson 2-18 (Largest Star ever)?

Stephenson 2-18 isn’t just a colossal star, it’s a compositional mosaic. Like most stars, it began brimming with hydrogen and helium, but nuclear fusion has transformed its core, potentially cooking up heavier elements like carbon and oxygen.

Stellar winds fiercely blow these heavier elements outward, enriching the surrounding space for future star and planet formation. The star’s intense heat also cooks up dust particles, contributing to the dusty veil around it.

As Stephenson 2-18 nears its fiery demise, a potential supernova will scatter these forged elements far and wide, providing the raw materials for future generations of stars and planets, potentially even seeding them with the building blocks for life.

What is the Interior Structure of the Stephenson 2-18 (Largest Star ever)?

While directly observing the interior of a star like Stephenson 2-18 is impossible, astronomers theorize its structure based on models and observations of similar stars. The immense size suggests intense internal pressure, likely triggering nuclear fusion of heavier elements beyond hydrogen and helium in its core.

Layers of burning shells, with progressively lighter elements undergoing fusion, surround the core. However, unlike smaller stars, Stephenson 2-18 might be nearing the end of its fusion processes, potentially experiencing strong convection and mass loss due to its unstable nature.

What does the Atmosphere of the Stephenson 2-18 (Largest Star ever) consist of?

Unlike our Sun, Stephenson 2-18 doesn’t have a well-defined atmosphere in the traditional sense. Due to its immense size and scorching surface temperature, the star’s outer layers are likely a turbulent and constantly churning region of hot, ionized gas.

This gas, potentially enriched with heavier elements produced by fusion processes, bleeds into the surrounding interstellar medium due to powerful stellar winds. The presence of dust particles within these outer layers further complicates the picture, making direct observations of the star’s surface challenging.

Stephenson 2-18 (Largest Star ever) as compared to our Sun:

Stephenson 2-18 Vs. Sun

FeatureStephenson 2-18Sun
TypeRed Supergiant (potentially Red Hypergiant)Yellow Dwarf
Radius2,150 times Sun’s radius (estimated)695,700 kilometers (432,688 miles)
Diameter4,300 times Sun’s diameter (estimated)1,391,400 kilometers (864,940 miles)
VolumeApproximately 10 billion times Sun’s volume (estimated)1.308 x 10^28 cubic kilometers (9.94 x 10^27 cubic miles)
Mass10-50 times Sun’s mass (estimated)1.989 x 10^30 kilograms (4.38 x 10^30 pounds)
Surface Temperature3,200 Kelvin (approximately 5,430 degrees Fahrenheit)5,500 Kelvin (approximately 9,932 degrees Fahrenheit)
Luminosity437,000 times Sun’s luminosity (estimated)3.828 x 10^26 Watts
Distance from EarthApproximately 19,000 light-years1 Astronomical Unit (AU) (on average)
Stage in Life CycleNearing the end of its life, potentially a pre-supernova stageMiddle-aged star, stable hydrogen fusion in core

Stephenson 2-18 (Largest Star ever) as compared to UY Scuti (Second Largest ever):

Stephenson 2-18 Vs. UY Scuti

FeatureStephenson 2-18UY Scuti
Radius (Sun radii)2,1581,708
Diameter (Sun diameters)4,3163,416
Luminosity (Sun luminosity)440,000340,000
Size ComparisonLargest known starPreviously largest known star
Sun’s Orbit ComparisonOuter reaches would extend beyond Saturn’s orbitOuter reaches would extend beyond Saturn’s orbit

Stephenson 2-18 – Largest Star Ever as compared to TON 618 – Largest Black Hole ever:

Stephenson 2-18 Vs. TON 618

FeatureStephenson 2-18 (Largest Star ever)TON 618 (Largest Black Hole ever)
Type of ObjectRed Hypergiant StarSupermessive Black Hole
Size (Radius)Estimated 2,150 times the Sun’s radius (approx. 1.50 x 10^12 meters)Has no physical size, characterized by its event horizon
MassEstimated 10 to 50 times the Sun’s massMillions to billions of times the Sun’s mass
LuminosityEstimated 437,000 times more luminous than the Sun (in watts)Does not emit light itself
TemperatureEstimated 3,200 KelvinNot applicable (extremely hot accretion disk)
Distance from EarthApproximately 19,000 light-yearsApproximately 10.4 billion light-years
Life Cycle StageNearing the end of its life, potentially on the verge of a supernovaSingularity; considered to be a very long-lived object

What are the Challenges to study Stephenson 2-18?

Despite its immense size and luminosity, Stephenson 2-18 remains somewhat of an enigma. Located roughly 19,000 light-years away in the constellation Scutum, the star resides within a cluster of other red supergiants. This distance and the dusty environment present challenges for astronomers studying Stephenson 2-18 in detail.

Our current understanding of the star relies heavily on data collected through infrared telescopes. Visible light struggles to penetrate the dust clouds surrounding Stephenson 2-18, making it difficult to observe the star directly using optical telescopes.

However, advancements in technology are providing new avenues for studying this cosmic giant. Infrared telescopes with improved sensitivity are allowing astronomers to gather more detailed information about Stephenson 2-18’s properties and environment.

What is the Future of Stephenson 2-18?

Stephenson 2-18 is a star nearing the end of its life cycle. As red supergiants age, they become increasingly unstable, shedding mass through powerful stellar winds and potentially undergoing dramatic explosions known as supernovae.

The fate of Stephenson 2-18 remains uncertain. While its immense size suggests it will eventually explode as a hypernova, a more powerful type of supernova, the exact timeline for this event is unknown.

Studying Stephenson 2-18 can provide valuable insights into the final stages of massive star evolution. Observing the processes leading up to its potential supernova could shed light on the creation of heavy elements and the influence of these explosions on the surrounding interstellar medium.

Why Stephenson 2-18 Matters?

The discovery and study of Stephenson 2-18 hold immense importance for our understanding of the universe. Here’s a closer look at some key reasons why:

Redefining Stellar Limits: Stephenson 2-18’s colossal size pushes the boundaries of what we thought possible for stars. Existing models of star formation suggest a limit to a star’s size based on factors like radiation pressure and internal stability. The existence of Stephenson 2-18 challenges these models, prompting astronomers to refine their understanding of how stars like this behemoth form and evolve.

Unlocking Stellar Secrets: Studying Stephenson 2-18 offers a window into the final stages of massive stars. By observing its properties, astronomers can gain valuable insights into the processes leading up to a potential supernova. This knowledge can help us understand the creation of heavier elements in the universe, elements essential for life as we know it.

Shaping the Environment: The intense radiation and stellar winds emanating from Stephenson 2-18 likely have a profound impact on its surrounding environment. Studying this influence can shed light on how massive stars influence the formation and evolution of planetary systems within their reach.

It can also help us understand how these giants contribute to the overall structure and composition of interstellar space.

A Window into the Past and Future: Stephenson 2-18 is a reminder of the vastness and diversity of stars in the universe. By studying objects like this, we gain a deeper understanding of the star life cycle, from the formation of massive stars to their explosive deaths.

This knowledge helps us piece together the history of our galaxy and potentially predict the future of stars like our own Sun.

What is a Red Hypergiant Star?

Red Hypergiant stars are the largest stars known by volume, dwarfing even our Sun by a staggering margin. Red hypergiants boast immense size, with radii estimated to be tens to hundreds of times larger than the Sun. Based on a simple relationship between radius and mass, this would suggest incredibly high masses for these stars.

Red hypergiants are also incredibly luminous, outshining our Sun by thousands or even millions of times. Despite their cooler temperatures (ranging from 3,000 to 4,500 Kelvin compared to the scorching temperatures of blue stars), red hypergiants are simply enormous. This vast surface area allows them to radiate a tremendous amount of energy, making them luminous giants in the night sky.

The name “red hypergiant” itself is a clue to their nature. The “red” refers to their cooler surface temperature, which gives them a reddish hue when compared to the blazing blue light emitted by hotter stars. The “hypergiant” part signifies their status as the most extreme version of red supergiants.

As a massive star nears the end of its life, it runs out of fuel for stable nuclear fusion in its core. This lack of fuel triggers a series of dramatic changes. The star’s core collapses, while the outer layers expand outward at an alarming rate. This expansion is what leads to the red supergiant and eventually the hypergiant stage.

These cosmic giants only exist for a few million years before succumbing to a violent supernova explosion. This spectacular event marks the end of the star’s life and can leave behind a dense remnant like a neutron star or even a black hole.


In conclusion, Stephenson 2-18 stands as a testament to the awe-inspiring scale and power of the universe. Studying this colossal star pushes the boundaries of our knowledge, offering valuable insights into stellar evolution, the creation of elements, and the shaping of interstellar environments.

As technology advances and our observations become more refined, Stephenson 2-18 will continue to be a source of wonder and discovery, helping us unravel space mysteries.

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