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 the relatively near future, this star will explode in a supernova, enriching the surrounding interstellar medium with new, heavy elements.
ESA/Hubble & NASA; Acknowledgement: Judy Schmidt
Surprise! The biggest, most massive stars aren’t always the hottest.
Although its neighbor, Messier 42, gets all the attention, Messier 43 lies just across a dust lane … [+] and continues the great nebula, illuminated largely by a single star that shines hundreds of thousands of times brighter than our own Sun. Located between 1000 and 1500 light-years away, this is part of the same molecular cloud complex as the main Orion Nebula.
Yuri Beletsky (Carnegie Las Campanas Obs.), Igor Chilingarian (Harvard-Smithsonian CfA)
To first become a star, your core must cross a critical temperature threshold: ~4,000,000 K.
Deep inside the Sun’s core, where temperatures rise above ~4 million K, nuclear fusion occurs … [+] between subatomic particles. This produces photons, particles and antiparticles, and neutrinos, the last of which carries a little more than 1% of the Sun’s total energy output away.
James Josephides, CAS Swinburne University of Technology
Such temperatures are required to initiate core fusion of hydrogen into helium.
The most straightforward and lowest-energy version of the proton-proton chain, which produces … [+] helium-4 from initial hydrogen fuel. Note that only the fusion of deuterium and a proton produces helium from hydrogen; all other reactions either produce hydrogen or make helium from other isotopes of helium.
Sarang / Wikimedia Commons
However, the surrounding layers diffuse heat, capping photosphere temperatures at ~50,000 K.
This cutaway showcases the various regions of the surface and interior of the Sun, including the … [+] core, which is where nuclear fusion occurs. With a radius of approximately 432,000 miles (~700,000 km), neutrinos take less than three seconds to exit the Sun from the time they are produced.
WIKIMEDIA COMMONS USER KELVINSONG
Higher temperatures require additional evolutionary steps.
The triple-alpha process, which occurs in stars, is how we produce elements carbon and heavier in … [+] the Universe, but it requires a third He-4 nucleus to interact with Be-8 before the latter decays. Otherwise, Be-8 goes back to two He-4 nuclei. If the Beryllium-8 is formed in an excited state, it can emit a high-energy gamma-ray before decaying back into two helium-4 nuclei as well.
E. Siegel / Beyond The Galaxy
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Your star’s core contracts and heats up upon exhausting its hydrogen.
The Sun, when it becomes a red giant, will become similar in side to Arcturus. Antares is more of a … [+] supergiant star, and is much larger than our Sun (or any Sun-like stars) will ever become. Even though red giants put out far more energy than our Sun, they are cooler and radiate at a lower temperature.
English Wikipedia author Sakurambo
Helium fusion then begins, injecting even more energy.
As the Sun becomes a true red giant, the Earth itself may be swallowed or engulfed, but will … [+] definitely be roasted as never before. The Sun’s outer layers will swell to more than 100 times their present diameter, but the exact details of its evolution, and how those changes will affect the orbits of the planets, still have large uncertainties in them.
However, “red giant” stars are quite cool, expanding to lower their surface temperatures.
The evolution of a solar-mass star on the Hertzsprung-Russell (color-magnitude) diagram from its … [+] pre-main-sequence phase to the end of fusion. Every star of every mass will follow a different curve, but the Sun is only a star once it begins hydrogen burning, and ceases to be a star once helium burning is completed.
Wikimedia Commons user Szczureq
Most red giants blow their outer layers away, revealing a heated, contracted core.
Normally, a planetary nebula will appear similar to the Cat’s Eye Nebula, shown here. A central core … [+] of expanding gas is lit up brightly by the central white dwarf, while the diffuse outer regions continue to expand, illuminated far more faintly. This is in contrast to the more unusual Stingray Nebula, which appears to be contracting.
Nordic Optical Telescope and Romano Corradi / Wikimedia Commons / CC BY-SA 3.0
With white dwarf surfaces reaching ~150,000 K, they surpass even blue supergiants.
The largest group of newborn stars in our Local Group of galaxies, cluster R136, contains the most … [+] massive stars we’ve ever discovered: over 250 times the mass of our Sun for the largest. The brightest of the stars found here are more than 8,000,000 times as luminous as our Sun. And yet, these stars only achieve temperatures of up to ~50,000 K, with white dwarfs, Wolf-Rayet stars, and neutron stars all getting hotter.
NASA, ESA, and F. Paresce, INAF-IASF, Bologna, R. O’Connell, University of Virginia, Charlottesville, and the Wide Field Camera 3 Science Oversight Committee
The highest stellar temperatures, however, are achieved by Wolf-Rayet stars.
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, as Wolf-Rayet stars typically have temperatures between 100,000 and 200,000 K, with some stars cresting even higher.
ESA/Hubble & NASA; Acknowledgement: Judy Schmidt (geckzilla.com)
Destined for cataclysmic supernovae, Wolf-Rayet stars are fusing the heaviest elements.
Imaged in the same colors that Hubble’s narrowband photography would reveal, this image shows NGC … [+] 6888: the Crescent Nebula. Also known as Caldwell 27 and Sharpless 105, this is an emission nebula in the Cygnus constellation, formed by a fast stellar wind from a single Wolf-Rayet star.
© J-P Metsavainio
They’re highly evolved, luminous, and surrounded by ejecta.
The extremely high-excitation nebula shown here is powered by an extremely rare 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.) Systems like this are estimated, at most, to represent 0.00003% of the stars in the Universe.
The hottest one measures ~210,000 K; the hottest known star.
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.
Judy Schmidt, based on data from WISE and Spitzer/MIPS1 and IRAC4
The remnant cores of supernovae can form neutron stars: the hottest objects of all.
At the center of this Chandra image, a pulsar — only twelve miles in diameter — is responsible for … [+] this X-ray nebula that spans 150 light years. This pulsar is spinning around almost 7 times a second and has a magnetic field at its surface estimated to be 15 trillion times stronger than the Earth’s magnetic field. This combination of rapid rotation and ultra-strong magnetic field drives an energetic wind of electrons and ions, ultimately creating the elaborate nebula seen by Chandra.
NASA/CXC/SAO/P.Slane, et al.
With initial interior temperatures cresting ~1 trillion K, they radiate heat quickly.
The remnant of supernova 1987a, located in the Large Magellanic Cloud some 165,000 light years away. … [+] It was the closest observed supernova to Earth in more than three centuries, and has the hottest known object, at its surface, currently known in the Milky Way. It’s surface temperature now is estimated at around ~600,000 K.
Noel Carboni & the ESA/ESO/NASA Photoshop FITS Liberator
After mere years, their surfaces cool to ~600,000 K.
A combination of X-ray, optical, and infrared data reveal the central pulsar at the core of the Crab … [+] Nebula, including the winds and outflows that the pulsars care in the surrounding matter. The central bright purplish-white spot is, indeed, the Crab pulsar, which itself spins at about 30 times per second.
X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech
Despite all we’ve discovered, neutron stars remain the hottest and densest individual objects known.
The two best-fit models of the map of the neutron star J0030+0451, constructed by the two … [+] independent teams who used the NICER data, show that either two or three ‘hot spots’ can be fitted to the data, but that the legacy idea of a simple, bipolar field cannot accommodate what NICER has seen. Neutron stars, just ~12 km across, are not only the densest objects in the Universe, but the hottest at their surface, as well.
Zaven Arzoumanian & Keith C. Gendreau (NASA Goddard Space Flight Center)
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.