Ethan Siegel , Contributor

This Wolf–Rayet star is known as WR 31a, located about 30 000 light-years away in the constellation of Carina. The outer nebula is expelled hydrogen and helium, while the central star burns at over 100,000 K.

In astronomy, there's a simple formula for stars: add more mass, and your star becomes brighter, bluer, and hotter.

The (modern) Morgan–Keenan spectral classification system, with the temperature range of each star class shown above it, in kelvin. The overwhelming majority (75%) of stars today are M-class stars, with only 1-in-800 being massive enough for a supernova. Yet as hot as O-stars get, they're not the hottest stars in the entire Universe.

This pattern hold from stars just a few percent the mass of the Sun to over 200 times as massive.

The giant star-forming region 30 doradus in the gas-rich Tarantula nebula. The most massive stars known to humanity can be found in the central cluster highlighted at right, with R136a1 coming in at ~260 solar masses.

But there's a limit to the temperature these stars achieve, even the most massive ones.

O-class stars are the hottest main-sequence stars, but by expelling their outer hydrogen layers, as this illustration shows, they can achieve even greater temperatures. The star illustrated here, WR 122, is the first Wolf-Rayet star to be found with a disk.

If you want to go hotter, you need something extra: to lose your hydrogen.

The Crescent Nebula in Cygnus is powered by the central massive star, WR 136, where the hydrogen expelled during the red giant phase is shocked into a visible bubble by the hot star at the center.

As the most massive stars evolve, they burn through their core's fuel, expanding into a red giant and fusing helium.

The anatomy of a very massive star throughout its life, culminating in a Type II Supernova when the core runs out of nuclear fuel. This is how fusion works if a star holds onto its outer, hydrogen envelope, but a small percentage of massive stars do not, becoming Wolf-Rayet stars.

Normally, this progresses into even heavier elements: carbon fusion, then oxygen, and so on.

The Wolf-Rayet star WR 124 and the nebula M1-67 which surrounds it both owe their origin to the same originally massive star that blew off its outer layers. The central star is now far hotter than what came before.

But in a special stellar class — Wolf-Rayet — the outer hydrogen layers get blown off, leaving only heavier elements behind.

The unusual hot massive young star WR 22 is silhouetted against a portion of the Carina nebula here, and exhibits signs of highly, multiply ionized heavy elements like carbon and nitrogen.

With strongly, multiply ionized atoms of carbon, nitrogen, and oxygen in their atmospheres, these stars are the hottest known.

The extremely high-excitation nebula shown here is powered by a binary star system: a Wolf-Rayet star orbiting an O-star. The stellar winds coming off of the central Wolf-Rayet member are between 10,000,000 and 1,000,000,000 times as powerful as our solar wind, and illuminated at a temperature of 120,000 degrees. The green supernova remnant off-center is unrelated.

Largely at only be 10-to-20 times the Sun's mass, they burn at up to 200,000 K, emitting hundreds of thousands of times the light of the Sun.



The nova of the star GK Persei, shown here in an X-ray (blue), radio (pink), and optical (yellow) composite, contains Wolf-Rayet elements in its spectrum, indicating that perhaps it had a Wolf-Rayet progenitor.

Only a few of them are visible to the naked eye, as most of this energetic radiation is ultraviolet, not visible.

The Wolf-Rayet star WR 102 is the hottest star known, at 210,000 K. In this infrared composite from WISE and Spitzer, it's barely visible, as almost all of its energy is in shorter-wavelength light. The blown-off, ionized hydrogen, however, stands out spectacularly.

Only ~1,000 Wolf-Rayet stars populate the entire Local Group.
Mostly Mute Monday tells the story of an astronomical objects, class, or phenomenon in images, visuals, and no more than 200 words.

Astrophysicist and author Ethan Siegel is the founder and primary writer of Starts With A Bang! Check out his first book, Beyond The Galaxy, and look for his second, Treknology, this October!

http://www.forbes.com/sites/startswithabang/2017/08/21/the-hottest-stars-in-the-universe-are-all-missing-one-key-ingredient/#7b6b3f3b19de

Awesome pics, moe

yea, it's kinda a picture story, less words with more visuals... i hope they do this more often

Cool

Outstanding post mightymoe!

http://medium.com/starts-with-a-bang
~ Ethan Siegel; Editor/Writer

hi, I had seen better pics of stars. url of msn find out it! Do you have any question ?

not at the moment, but i'll be sure and ask if i do...

Those are amazing photos moe, thanks!
The info is cool too, just difficult for my non-scientific mind to grasp.