The biggest star in the universe is Stephenson 2-18 or UY Scuti. Depending on which deep space astronomer you ask and what data they’ve collected and analyzed, you’ll find differing answers. However, UY Scuti is generally called the largest known star. So which one actually holds the title? The controversy over which star is the most massive comes from the difficulty in determining precise size because of stars’ evolving natures. And the measurement results themselves also depend on the manner in which scientists collected them.
UY Scuti is called the biggest star in the universe based on the results of extensive studies. Astronomers use spectroscopy, modeling, and interferometry to study the star’s size. And the measurements suggest a larger radius than Stephenson 2-18.
Scientists continue studying both giant stars. And as new observation techniques and improved modeling come along, the size estimates could revise.
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UY Scuti’s Discovery
German astronomers at the Boon Observatory discovered UY Scuti in 1860. They continued watching it for 740 days to determine that the red hypergiant had a pulsating variable magnitude. The pulsating variable magnitude was found to correlate to the star expanding and contracting. (Pretty cool!)
It was initially designated BD-12°5055, but after determining the star is variable, it received its name UY Scuti, the 38th variable star within the constellation Scutum. Variable stars whose brightness changes receive their names according to international standards.
The Biggest Star in the Universe
Find UY Scuti in the Scutum constellation. It’s a red supergiant star about 9,500 light-years from planet Earth. This massive star’s diameter is estimated to be around 1,700 times that of the Sun. So that means approximately five billion of our Suns could fit within its volume. When you realize that about a million Earths could fit inside the Sun, it helps to visualize the size.
Physical size and mass are different when it comes to stars. So UY Scuti is between seven and ten times the Sun’s mass, even though its radius is so much more significant. Yet, despite its immense size, UY Scuti is also relatively cool, with a surface temperature of approximately 6,089 ℉ (3,365℃.) Compare that with the Sun’s blistering surface (or photosphere) temperature of around 10,000℉ (5,500℃.)
UY Scuti’s Radius
Let’s think about the radius for a minute. At 1,700 times the Sun’s radius, if UY Scuti held our Sun’s position in the sky, its outer surface would extend past Jupiter’s orbit. That means Mercury, Venus, Earth, Mars, and Jupiter get swallowed up by UY Scuti’s mass.
In addition, the giant star is almost eight astronomical units across. Astronomical units are the distance of the Earth to the Sun, and the standard scientists use to measure celestial distances. Considering that one AU is approximately 93 million miles and eight AUs are about 744 million miles, you can start to grasp the immensity of UY Scuti.
One more way to consider UY Scuti’s enormous size is that if a spacecraft could fly around the giant star at the speed of light, it would take about seven hours. But the same hypothetical trip around the Sun would only take 14.5 seconds.
The Top Five Most Giant Stars in the Universe
UY Scuti and Stephenson 2-18 are two of the biggest stars in the universe. But astronomers continually make new discoveries while re-evaluating older ones. In addition, the James Webb Space Telescope continuously provides further information.
For example, researchers see evidence of supermassive stars that could be 10,000 times the Sun’s mass. These “celestial monsters” could dwarf every large star in the universe once scientists prove their existence.
So here’s a list of the current five most prominent stars after UY Scuti.
- Stephenson 2-18
- WOH G64
- HV 888 (WOH S140)
Find this red supergiant or hypergiant star in the constellation Scutum. Red hypergiants range from 200 to 2,200 times larger than the Sun. And Stephenson 2-18 has a radius of approximately 2,200 times the Sun, considerably larger than UY Scuti.
However, even though UY Scuti is named the largest, it does have blurry edges whose size varies over time. Thus the challenge of determining which of the two is indeed the biggest star in the universe.
Stephenson 2-18 belongs to the open cluster, Stephenson 2. And it can fit about 13 quadrillion Earths inside its perimeter. Now that’s what we’d call a giant star!
This Magellanic Cloud star is another red supergiant with a radius between 1,800 to 2,400 times the Sun’s. So, again, those sizes potentially make WOH G64 larger than UY Scuti. However, UY Scuti’s multiple observations make its size more provable, guaranteeing its current “biggest star in the universe” status.
WOH G64’s strong stellar wind creates a thick dust cloud around it. The cosmic dust is about a light-year in diameter. So between the star’s size and its surrounding materials, if WOH G64 replaced our Sun’s position at the Solar System’s center, it would obliterate the inner planets and engulf Jupiter’s orbit.
Another red supergiant, RSGC1-F02, resides in the open cluster RSGC1, also in the Scutum constellation. Scientists used the Stefan-Boltmann law to calculate this massive star’s radius at 1,500 to 1,549 times the Sun. In addition, its volume is about 3.5 billion times larger than the Sun’s.
HV 888 (WOH S140)
Another of the most prominent stars hails from the Large Magellanic Cloud in the Dorado constellation. HV88 is a red supergiant with a radius of 1,400 to 2,000 times the Sun’s radius. It also has 300,000 to 500,000 times the Sun’s luminosity, making it one of its type’s most luminous.
If HV 888 were at the center of the Solar System, this beast’s photosphere not only engulfs Jupiter’s orbit but possibly even Saturn’s.
The next in our list of the five biggest stars in the universe is RSGC1-F01. It is another red supergiant in the Scutum Constellation and part of the RSGC1 open star cluster. It has a radius between 1,435 and 1,551 times the Sun’s.
How Big Is the Sun Compared to Other Biggest Stars?
The illustration below shows the sizes of planets compared to the Sun. And then, the Sun’s comparison to other stars in image three. And you can see that even though UY Scuti is not depicted, it would completely dominate a small star the size of our Sun.
The Role of Massive Stars in Stellar Evolution
Massive stars play a crucial role in stellar evolution, influencing the formation and development of entire galaxies. First, their intense gravitational pull leads to the accumulation of gas and dust, initiating the process of star formation in stellar nurseries.
Next, their high luminosity and strong stellar winds shape the surrounding environment, triggering other stars’ formation and affecting the interstellar medium’s composition.
In addition, massive stars undergo dramatic transformations in their short lifetimes. For example, they go through nuclear fusion much faster, producing heavier elements in their cores, eventually leading to supernova explosions. The explosions release enormous amounts of energy and eject stellar material enriched with heavy elements back into space, becoming the building blocks for new star and planetary systems.
Lastly, the remnants of massive stars, such as neutron stars or black holes, continue influencing their surroundings through strong gravitational interactions, forming binary systems and potentially impacting neighboring stars’ evolution.
So you can see that overall, the existence and evolution of massive stars have a profound impact on the cosmic landscape, shaping the chemical composition, structure, and dynamics of galaxies throughout the universe.