wolf rayet

Beware of the Big, Bad Wolf

Visible within the center of the Crescent nebula is what’s classified as a Wolf-Rayet star. This star is a staggering 250,000 times brighter than the Sun, 15 times more massive, and 3.3 times larger. Its surface temperature is nearly 70,000° C/ 125,000° F. At just 4.7 million years old, it is already toward the end of it’s life and is shedding its outer envelope, ejecting the equivalent of the Sun’s mass every 10,000 years. Within a few hundred thousand years, it is expected to explode as a supernova.  

(Image Credit: Michael Miller, Jimmy Walker)

10

The Hottest Stars In The Universe Are All Missing One Key Ingredient

“In astronomy, there’s a simple formula for stars: add more mass, and your star becomes brighter, bluer, and hotter. This pattern hold from stars just a few percent the mass of the Sun to over 200 times as massive. But there’s a limit to the temperature these stars achieve, even the most massive ones. If you want to go hotter, you need something extra: to lose your hydrogen.”

The most massive stars in the Universe are true behemoths, rising to hundreds of times the mass of our Sun and burning at temperatures upwards of 30,000 K at their surface. But there are stars out there that are even hotter, despite only being 10% or less as massive: Wolf-Rayet stars. The key to their cosmic success? Blowing off their outer layers of hydrogen. By only leaving the dense, massive core of already-fused elements, Wolf-Rayet stars burn helium, carbon, oxygen or even heavier elements at their centers, while the journey to the surface “only” cools the star down to ~200,000 K by time the edge of the photosphere is reached. Elements like carbon, nitrogen, and oxygen may be ionized up to four times when their spectra are viewed.

Come learn the secret – and get the spectacular images and descriptions – of the hottest stars in the Universe for today’s Mostly Mute Monday!

Blown by fast winds from a hot, massive star, this cosmic bubble is huge. Cataloged as Sharpless 2-308 it lies some 5,200 light-years away toward the constellation of the Big Dog (Canis Major) and covers slightly more of the sky than a full moon. That corresponds to a diameter of 60 light-years at its estimated distance. The massive star that created the bubble, a Wolf-Rayet star, is the bright one near the center of the nebula. Wolf-Rayet stars have over 20 times the mass of the Sun and are thought to be in a brief, pre-supernova phase of massive star evolution. Fast winds from this Wolf-Rayet star create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of evolution. The windblown nebula has an age of about 70,000 years. Relatively faint emission captured in the expansive image is dominated by the glow of ionized oxygen atoms mapped to a blue hue.

Credit: Anis Abdul (Via NASA APOD)

Time And Space

In this stunning picture of the giant galactic nebula NGC 3603, the crisp resolution of NASA’s Hubble Space Telescope captures various stages of the life cycle of stars in one single view.

To the upper right of center is the evolved blue supergiant called Sher 25. The star has a unique circumstellar ring of glowing gas that is a galactic twin to the famous ring around the supernova 1987A. The grayish-bluish color of the ring and the bipolar outflows (blobs to the upper right and lower left of the star) indicates the presence of processed (chemically enriched) material.

Near the center of the view is a so-called starburst cluster dominated by young, hot Wolf-Rayet stars and early O-type stars. A torrent of ionizing radiation and fast stellar winds from these massive stars has blown a large cavity around the cluster.

The most spectacular evidence for the interaction of ionizing radiation with cold molecular-hydrogen cloud material are the giant gaseous pillars to the right and lower left of the cluster. These pillars are sculptured by the same physical processes as the famous pillars Hubble photographed in the M16 Eagle Nebula.

Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation.

To the lower left of the cluster are two compact, tadpole-shaped emission nebulae. Similar structures were found by Hubble in Orion, and have been interpreted as gas and dust evaporation from possibly protoplanetary disks (proplyds). The “proplyds” in NGC 3603 are 5 to 10 times larger in size and correspondingly also more massive.

This single view nicely illustrates the entire stellar life cycle of stars, starting with the Bok globules and giant gaseous pillars, followed by circumstellar disks, and progressing to evolved massive stars in the young starburst cluster. The blue supergiant with its ring and bipolar outflow marks the end of the life cycle.

The color difference between the supergiant’s bipolar outflow and the diffuse interstellar medium in the giant nebula dramatically visualizes the enrichment in heavy elements due to synthesis of heavier elements within stars.

This true-color picture was taken on March 5, 1999 with the Wide Field Planetary Camera 2.

This picture is being presented at the 194th Meeting of the American Astronomical Society in Chicago.

Object Names: NGC 3603, Sher 25

Image Type: Astronomical

Credit: Wolfgang Brandner (JPL/IPAC), Eva K. Grebel (Univ. Washington), You-Hua Chu (Univ. Illinois Urbana-Champaign), and NASA

Time And Space

Hubble’s cosmic bubbles

This entrancing image shows a few of the tenuous threads that comprise Sh2-308, a faint and wispy shell of gas located 5,200 light-years away in the constellation of Canis Major (The Great Dog).

Sh2-308 is a large bubble-like structure wrapped around an extremely large, bright type of star known as a Wolf-Rayet Star – this particular star is called EZ Canis Majoris. These type of stars are among the brightest and most massive stars in the Universe, tens of times more massive than our own sun, and they represent the extremes of stellar evolution. Thick winds continually poured off the progenitors of such stars, flooding their surroundings and draining the outer layers of the Wolf-Rayet stars. The fast wind of a Wolf-Rayet star therefore sweeps up the surrounding material to form bubbles of gas.

EZ Canis Majoris is responsible for creating the bubble of Sh2-308 – the star threw off its outer layers to create the strands visible here. The intense and ongoing radiation from the star pushes the bubble out farther and farther, blowing it bigger and bigger. Currently the edges of Sh2-308 are some 60 light-years apart!

Beautiful as these cosmic bubbles are, they are fleeting. The same stars that form them will also cause their death, eclipsing and subsuming them in violent supernova explosions.

This entrancing image shows a few of the tenuous threads that comprise Sh2-308, a faint and wispy shell of gas located 5,200 light-years away in the constellation of Canis Major (The Great Dog). Credit ESA/Hubble & NASA

NGC 6888, also known as the Crescent Nebula, is a cosmic bubble about 25 light-years across, blown by winds from its central, bright, massive star. This sharp telescopic portrait uses narrow band image data that isolates light from hydrogen and oxygen atoms in the wind-blown nebula. The oxygen atoms produce the blue-green hue that seems to enshroud the detailed folds and filaments. Visible within the nebula, NGC 6888’s central star is classified as a Wolf-Rayet star (WR 136). The star is shedding its outer envelope in a strong stellar wind, ejecting the equivalent of the Sun’s mass every 10,000 years. The nebula’s complex structures are likely the result of this strong wind interacting with material ejected in an earlier phase. Burning fuel at a prodigious rate and near the end of its stellar life this star should ultimately go out with a bang in a spectacular supernova explosion. Found in the nebula rich constellation Cygnus, NGC 6888 is about 5,000 light-years away.

Object Names: NGC 6888, The Crescent Nebula

Image Type: Astronomical

Credit: Michael Miller, Jimmy Walker

Time And Space

(NASA)  Sharpless 308: Star Bubble
Image Credit & Copyright: Kfir Simon

Blown by fast winds from a hot, massive star, this cosmic bubble is huge. Cataloged as Sharpless 2-308 it lies some 5,200 light-years away toward the constellation of the Big Dog (Canis Major) and covers slightly more of the sky than a Full Moon. That corresponds to a diameter of 60 light-years at its estimated distance. The massive star that created the bubble, a Wolf-Rayet star, is the bright one near the center of the nebula. Wolf-Rayet stars have over 20 times the mass of the Sun and are thought to be in a brief, pre-supernova phase of massive star evolution. Fast winds from this Wolf-Rayet star create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of evolution. The windblown nebula has an age of about 70,000 years. Relatively faint emission captured in the expansive image is dominated by the glow of ionized oxygen atoms mapped to a blue hue.

Seeing a supernovae within hours of the explosion

For the first time ever, scientists have gathered direct evidence of a rare Wolf-Rayet star being linked to a specific type of stellar explosion known as a Type IIb supernova. Peter Nugent of the Lawrence Berkeley National Laboratory says they caught this star – a whopping 360 million light years away – just a few hours after it exploded.

Hear more about this discovery →