Starship Asterisk*

Sharpless 308: Star Bubble

Explanation: 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.

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I think Dean Martin saw this one! http://www.metrolyrics.com/im-forever-b ... artin.html

Roughly calculating the expansion speed of the bubble gases is about one light year for each 2000-2500 years. Is this a constant?

A lovely image of a magnificent bubble, one of the best WR nebulae in the sky! I really like the knots of Ha, which show up as purple in the southern part. This image was taken under the dark skies of Namibia and they certainly make a difference in revealing faint emission. Lots of WR nebulae discovered in the past 20-30 years have still yet to be imaged in detail.

NCTom wrote:Roughly calculating the expansion speed of the bubble gases is about one light year for each 2000-2500 years. Is this a constant?

60 ly / 70,000 y = 8.6e-4 ly/y or 1166 y/ly. That's 255 km/s, which is pretty typical.

That's the average speed, of course. In reality, this kind of expansion slows with time as the gas creates shock fronts and interacts with itself and with the interstellar medium. So this bubble was initially expanding faster than 255 km/s, and is now expanding much slower than that.

We were looking at this image and were wondering about the actual shape that we are seeing. The first impression is something generally spherical in nature with some lumps and bump here and there. Another impression is one of a donut type of structure, seen from an oblique angle. We also thought that is could be an hour-glass shape seen from a similar angle. Is there any definitive evidence as to exactly what we are looking at? Or is more study required?

Dad is watching wrote:We were looking at this image and were wondering about the actual shape that we are seeing. The first impression is something generally spherical in nature with some lumps and bump here and there. Another impression is one of a donut type of structure, seen from an oblique angle. We also thought that is could be an hour-glass shape seen from a similar angle. Is there any definitive evidence as to exactly what we are looking at? Or is more study required?

I think this actually is a bubble, i.e. a spherical shell. The nebulas that are created by supernovas or by ordinary low-mass stars at the end of their lives come in a variety of shapes, and it can be difficult to convert what we see from our point of view into the true shape. But this nebula is simply material being blown outward by a bright star that hasn't exploded, so the spherical shape makes sense.

Wow, divide this by twelve
and any two spots that far apart is the distance between the Sun and Proxima Kentauiri. Ah, time for an ice cold one and stare at this thing for a while

ta152h0 wrote:Wow, divide this by twelve
and any two spots that far apart is the distance between the Sun and Proxima Kentauiri. Ah, time for an ice cold one and stare at this thing for a while

That is only slightly less than half the distance our TV broadcasts have traveled

maybe broadcasting how intelligent political discourse is is not intelligent. Don't tell the UFO guys that a " gut science " politician is in charge of the NASA budget should make the laugh.

We recently listened to another great lecture from Professor Carolyn Crawford at Gresham on nebulas, so it is exciting to see this image.