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What’s the hottest star?

What’s the hottest star?

Stars come in a wide range of temperatures and brightnesses. The hottest and brightest stars are classified as O-type stars, while the coolest stars are M-type red dwarfs. But what is the single hottest star known to astronomers? Let’s take a look at some of the contenders for this fiery title.

Contenders for the Hottest Star

Here are some of the stars that rank among the hottest we’ve discovered:

  • WR 102 – A Wolf-Rayet star with a surface temperature of 210,000 degrees Fahrenheit (120,000 Kelvin).
  • Eta Carinae – This volatile, unstable star may have temperatures exceeding 400,000 degrees F (220,000 K).
  • Rigel – A blue supergiant that’s over 44,000 times brighter than our sun and around 27,000 degrees F (15,000 K).
  • Naos – At 120,000 degrees F (66,000 K), this O-type star in the constellation Puppis beats our sun’s surface temperature by a factor of more than 200.

And the Winner Is…

Based on current data, most astronomers agree that the hottest known star is NGC 3603-A1. This blue hypergiant is located in the stellar nursery nebula NGC 3603, about 20,000 lightyears away in the Carina constellation.

NGC 3603-A1 has a searing surface temperature of 180,000 degrees Fahrenheit (100,000 Kelvin) – that’s more than 300 times hotter than the surface of our sun! At this extreme temperature, the star blazes with the brilliance of several million suns. But it’s also an unstable beast – NGC 3603-A1 is estimated to be only about 3-4 million years old, and it may already be poised to explode as a supernova in just hundreds of thousands of years.

What Makes NGC 3603-A1 So Hot?

What enables this star to reach such tremendous temperatures and luminosities? Here are some key facts:

  • Mass: Estimated at 110-165 solar masses – making it one of the most massive stars known.
  • Classification: WN6ha spectral type – a very hot and luminous Wolf-Rayet star.
  • Luminosity: 3.5-5.4 million times brighter than the sun.
  • Size: Roughly 90 times wider than our sun.

Like other massive stars, NGC 3603-A1 is able to achieve such extreme temperatures due to its huge mass and luminosity. Fusion reactions in its core release tremendous energy, causing it to heat up and generate a tremendous amount of outgoing radiation. This fierce output of energy also causes the star to shed its outer layers rapidly, creating a distinctive Wolf-Rayet appearance.

A Volatile Life Cycle

As an extremely massive star, NGC 3603-A1 burns through the hydrogen fuel in its core very quickly. This rapid depletion of fuel results in such massive stars having lifetimes of just a few million years, rather than the billions of years lower-mass stars like our sun can exist. After exhausting the hydrogen in its core, NGC 3603-A1 began fusing helium to generate energy, swelling up into a cool red supergiant phase before losing its outer layers and heating up again as a hotter blue Wolf-Rayet star.

This volatile life cycle makes NGC 3603-A1 prone to instability and dramatic changes. Astronomers think it may already be in a pre-supernova state and could explode as a powerful supernova or hypernova in the relatively near future. The remains would likely form a black hole.

Seeing the Hottest Star

At an estimated distance of 20,000 lightyears, NGC 3603-A1 is too far away to be seen in any detail even with powerful telescopes. But its home nebula of NGC 3603 is visible through larger backyard telescopes and reveals the blue tint and glow indicative of extremely hot, massive stars:

Observation Tips Details
Constellation Location Carina
Right Ascension 11 hours 15 minutes 7 seconds
Declination -61 degrees 15′ 30″
Apparent Magnitude +6.3
Suggested Aperture 6″ or larger recommended

With its extraordinary temperature and volatility, NGC 3603-A1 represents the extreme upper limit of stellar hotness and power. This searing blue beast well deserves the title of the hottest known star in the universe!


NGC 3603-A1, located 20,000 lightyears away in the Carina Nebula, is the hottest star currently known with an estimated surface temperature of 180,000 degrees Fahrenheit or 100,000 Kelvin. This massive, unstable Wolf-Rayet star is 3.5-5.4 million times brighter than our sun and lives fast and furiously, already entering its final evolutionary stages. Its extreme temperature is driven by its huge mass of over 100 solar masses, resulting in tremendous energy output that causes it to shed layers quickly. With its volatile life cycle, NGC 3603-A1 is expected to die in a massive supernova explosion in just hundreds of thousands of years. Observing the blue color and glow of its nebula NGC 3603 in a backyard telescope offers a glimpse at this hottest known inferno of the stars.