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SYFY WIRE Bad Astronomy

Astrophoto: Dusty Star Birth and Future Spectacular Death in the Swan

By Phil Plait

Judy Schmidt is a wonder.

She’s an amateur astronomer who loves to play with astronomical images from big observatories, and when she does, the results are, well, wondrous.


That is an area of the sky in Cygnus, the constellation of the Swan (also called the Northern Cross), and shows a region called Cyg X, and I hadn’t heard of it before seeing that glorious image. Cya X is a dense molecular cloud very roughly 3,000 to 4,000 light-years away. Molecular clouds are vast complexes of cold gas and dust that can form stars. A more famous example is the Orion Molecular Cloud, in which sits the magnificent Orion Nebula.

Orion is well-known because massive stars recently formed near the edge of it facing Earth, and they ate their way through the wall of the cloud. Bursting forth, the thinner gas from the erupted blister reveals the luminous stars therein.

But Cyg X is more subtle. Stars are forming, but they haven’t blown through the thicker dust, so the cloud is dark to our eyes. But not to the eyes of WISE and Spitzer, space telescopes that took the images Schmidt used to make this picture. Knots and tendrils of dust, warmed by stars deeply embedded within, litter the view. The details in the cloud are lovely (and she created a whopping 10,000 x 7,600 pixel version that’ll keep your eyes busy for a long time).

Schmidt notes one peculiarity: the bright red ring to the left and below center. That is the star G79.29+0.46, what astronomers call a Luminous Blue Variable. These are a class of rare, very massive stars. The amount of energy a star generates depends on its mass, and these stars are so huge that they are ridiculously luminous; so energetic that they can barely hold themselves together under the onslaught of photons. They are on the edge of literally tearing themselves apart.

That makes them unstable, and prone to outbursts. The most famous example is Eta Carinae, a star roughly 8,000 light-years away that is nevertheless visible to the naked eye. In the 1800s it underwent a vast paroxysm, erupting with so much energy it was just this side of a supernova, and blowing out two expansing lobes of gas with as much mass as our entire Sun.

G79.29+0.46 is actually much closer than Eta Car, less than 4,000 light-years distant, but apparently its luminosity is dimmed by all the dust. Still, two eruptions in its past are apparent; they formed the two rings you can see in Schmidt’s image. These occurred something like 10,000 and 30,000 years or so ago, each launching shells of gas expanding rapidly away from the star. They swept up material in the cloud, compressing it, and forming soap bubble-like shells that look like rings from our perspective.

Someday—probably not more than a million years from now, perhaps much less—G79.29+0.46 will run out of fuel in its core and explode. I wonder how bright the resulting supernova will be? From that distance a typical supernova would be many times brighter than Venus in our sky, visible even in daytime! But in this case the dust will dim the event, but I’m not sure by how much. It may not even be visible to the naked eye at all.

Happily (assuming it happens soon) we have telescopes far better than our eyes to pierce the veil of dust, and we’ll be able to see the explosion very well. It may be the closest supernova we’ve had for millennia. I hope those astronomers in the future appreciate what they witness, and enjoy studying one of the most amazing events the Universe has to offer. Until then, and for now, we’ll just have to look upon Schmidt’s images of that region of the sky and gape in awe.

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