What’s the most massive star in the universe?

The UniverseFridays

March 20, 2026

5 min read

Add Us On GoogleAdd SciAm

What’s the most massive star in the universe?

Just how big can a star become? The answer depends on when in cosmic history you’re asking the question

By Phil Plait edited by Lee Billings

This artist’s concept shows the relative sizes of various stars, from the smallest “red dwarfs” at about a tenth of a solar mass, through low-mass “yellow dwarfs” such as our sun, to massive “blue dwarf” stars weighing eight times more than our sun, and finally the most massive and luminous star known—a 291-solar-mass star named R136a1.

ESO/M. Kornmesser

Stay connected to The Universe: Get email alerts for this weekly column by Phil Plait

Enter your email

I agree my information will be processed in accordance with the Scientific American and Springer Nature Limited Privacy Policy. We leverage third party services to both verify and deliver email. By providing your email address, you also consent to having the email address shared with third parties for those purposes.

Sign Up

It’s “common knowledge”—and the scare quotes should be a warning—that the sun is an average star.

But it’s not, and in fact it’s not even close: The sun is in the top 90th percentile of stars by mass. That’s because well more than half of the universe’s stars are tiny, cool red dwarfs, dim bulbs with half to less than 10 percent of the sun’s mass. The lower limit is around 7 to 8 percent of the sun’s mass; any less than that, and there isn’t enough pressure in the core to sustain nuclear fusion, which is the prime characteristic of what makes a star a star.

But what about the other end? There are stars far beefier than our own. Is there an upper limit to how massive a star can be?

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

Yes, there is, and we do see some stars edging close to it. If they get too close, however, they produce so much energy that they tear themselves apart. One reason this “too close” region isn’t itself the hard limit on stellar mass is because its value has changed over time!

Before we dive into the fun science of all this, let’s remember the reasons why mass is what’s important here rather than size or weight. Size is a problem because stars lack well-defined surfaces, and this problem gets worse the larger a star gets—the biggest ones are so bloated that they just fade away with distance from their respective centers like clouds of fog. Weight won’t work because it’s just a second-order measure of mass—or rather how strong the gravitational force is on an object with mass. You have the same mass on Earth as you do on the moon, though you weigh differently because the moon’s gravity is weaker.

Mass is critical because it dictates the delicate equilibrium that defines a star, a balance between the inward pull of gravity and the outward push of light emanating from the star’s core. Gravity is a direct result of mass, but the amount of energy generated in a star’s core comes from mass as well. The more massive the star is, the more pressure there is in the star’s center and the hotter it gets.

A star’s radiance comes from nuclear fusion—specifically, squeezing hydrogen atoms together hard enough to create helium (though the actual process is a bit more complicated). This releases energy mostly in the form of gamma rays, which are absorbed by the surrounding material, heating it up. The rate of fusion depends on the star’s core temperature, which depends on, yup, its mass. The rate depends very strongly on the core temperature, in fact: in a star like the sun, the fusion rate scales as the fourth power of the temperature, so a small change in temperature hugely affects how rapidly the core generates energy.

Higher-mass stars use a different fusion process that is ridiculously dependent on temperature; the fusion rate can scale with temperature to about the 20th power! This coupling is so strong that doubling the temperature in a massive star’s core increases the energy generation rate by a factor of a million.

You might see now why stars can only get so big. If you pile on too much mass, the star’s gravity strengthens, the pressure in the core rises, the temperature increases, and then the fusion rate skyrockets. If too much energy is dumped into the star’s upper layers, they get so hot that they don’t just expand; they also blast away material, thus losing mass. This forms a negative feedback loop that limits how massive a star can be. Also, stars in this frenzied