APOD: Sharpless 308: Star Bubble (2016 Dec 20)

[APOD Robot]

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.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

[Saeed Khan]

Quote: "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."

All of them? All Wolf-Rayet stars in the Universe?

[Ann]

Quote: "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."

All of them? All Wolf-Rayet stars in the Universe?

Wolf-Rayet stars are indeed thought to be in a brief, pre-supernova phase of massive star evolution. In other words, all Wolf-Rayet stars are thought to be doomed to explode as supernovas.

So, can we be sure that this is true? That all of them are going to explode? I don't think we can. We haven't witnessed enough supernova progenitors or enough Wolf-Rayet stars to be sure that there are no WR stars that don't explode. Maybe, for all we know, a few of them may turn into massive white dwarfs instead.

I'd also say that it is definitely not true that all WR stars have over 20 times the mass of the Sun. Wolf-Rayet stars lose mass at a prodigious rate, and some of them may well lose enough of their mass to retain less than 20 solar masses.

Ann

[neufer]

Click to play embedded YouTube video.

There’s a star on the horizon,
and it’s burning like a flame,

It’s lighting up this mighty wind,
that’s blowin’ everywhere,

[rstevenson]

Click to play embedded YouTube video.

[dlw]

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.

Would that imply that the irregularities in the bubble such as the hedgehog nose in the upper left indicate something about the distribution of slower moving material in that area?

[Ann]

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.

Would that imply that the irregularities in the bubble such as the hedgehog nose in the upper left indicate something about the distribution of slower moving material in that area?

hedgehog-pictures-20.jpg

The way I understand it, scientists believe that supernovas typically explode asymmetrically (although there might be some that don't).

You must also bear in mind that the environment around the star is different in different directions. In some directions there may be more matter, slowing the expansion that way, but in other directions space might be more than usually empty, allowing the debris to flow freely that way.

Click to play embedded YouTube video.

Ann

[neufer]

[size=150]ο² & ο[sup]1[/sup] CMa mark the centre of the[/size] Great Dog's body on Bayer's 1603 Uranometria.

---

<<Omicron2 Canis Majoris (ο² CMa, ο² Canis Majoris) is one of the brighter members of the constellation Canis Major. The distance to this star is roughly 2,800 light years (800 parsecs), with a 34% margin of error. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.

Omicron2 Canis Majoris is one of the most luminous stars known, as it radiates about 220,000 times as much luminosity as the Sun from its outer envelope at a temperature of 15,500 K. At this heat, the star is glowing with the blue-white hue of a B-type star. This star is classified as an Alpha Cygni-type variable star that undergoes periodic non-radial pulsations, which cause its brightness to cycle from magnitude +2.93 to +3.08 over a 24.44 day interval. It is losing mass from its stellar wind at the rate of around 2 × 10⁻⁹ times the mass of the Sun per year.

This is a massive supergiant star with a stellar classification of B3 Ia, indicating that, at the age of around 7 million years, it has exhausted the supply of hydrogen at its core and is now undergoing nuclear fusion of helium to generate energy. It has about 21 times the mass of the Sun and 65 times the Sun's radius. In all likelihood, it will end its life as a Type II supernova.

While this star lies in the field of view of the open cluster named Collinder 121, it is unlikely to be a member. In fact, its optical neighbor, the orange supergiant ο¹ Canis Majoris has a much higher likelihood of 23.1% based upon its proper motion being a closer match to the motion of the cluster.>>

<<Omicron1 Canis Majoris (ο¹ CMa, ο¹ Canis Majoris) is a variable star in the constellation of Canis Major. Though only separated by 2 degrees from the blue supergiant ο² Canis Majoris, the two appear to be unrelated. The star itself is ae K-type orange supergiant of spectral type K2.5 Iab and is an irregular variable star, varying between apparent magnitudes 3.78 and 3.99. A cool star, its surface temperature is around 3,900 K. Around 8 times as massive as the Sun with around 280 times its diameter, it shines with 16,000 times its luminosity. Thought to be around 18 million years old, ο¹ Canis Majoris is undergoing nuclear fusion of helium in its core to generate energy and will one day explode as a type II supernova.>>

[b][color=#0000FF][size=120]ο[sup]1[/sup] CMa appears to be interacting with the nebula around EZ CMa[/size] [size=85]This image was created using the POSS-II/UKSTU data of the Digitized Sky Survey[/size][/color][/b]

---

<<EZ Canis Majoris (EZ CMa) is a Wolf-Rayet star in the constellation of Canis Major. It is one of the ten brightest Wolf-Rayet stars. EZ CMa has an apparent visual magnitude which varies between 6.71 and 6.95 over a period of 3.766 days, along with changes in the spectrum. It has been proposed that it could be a binary star, with a neutron star as companion that would complete an orbit around the Wolf-Rayet with that period, being it the cause of those variations. The General Catalogue of Variable Stars lists it as a possible cataclysmic variable on this basis. However it seems more likely that companion does not exist and spectral variations are caused by activity on the star's surface.

The spectral type of WN4 indicates an extremely hot star, and this leads to a very high luminosity, mostly emitted as ultraviolet radiation. The spectrum shows a star entirely devoid of hydrogen at the surface. EZ CMa is surrounded by a faint bubble nebula, a small HII region blown by stellar winds up to 1,700 km/s and ionised by the intense UV radiation. This is catalogued as Sharpless 308 or just S308. It is likely to be a member of the very scattered open cluster Collinder 121, found around the orange supergiant ο¹ CMa.>>

[Boomer12k]

Reminded me of a Dolphin's head...

Really nice...

Just got rid of our snow and freezing weather, now WET...
:---[===] *

[neufer]

Reminded me of a Dolphin's head... Really nice...

This APOD was posted for a good porpoise.

[Ann]

<<Omicron1 Canis Majoris (ο¹ CMa, ο¹ Canis Majoris) is a variable star in the constellation of Canis Major. Though only separated by 2 degrees from the blue supergiant ο² Canis Majoris, the two appear to be unrelated. The star itself is ae K-type orange supergiant of spectral type K2.5 Iab and is an irregular variable star, varying between apparent magnitudes 3.78 and 3.99. A cool star, its surface temperature is around 3,900 K. Around 8 times as massive as the Sun with around 280 times its diameter, it shines with 16,000 times its luminosity. Thought to be around 18 million years old, ο¹ Canis Majoris is undergoing nuclear fusion of helium in its core to generate energy and will one day explode as a type II supernova.

Well, probably. Since its mass is about 8 solar masses today, when it has evolved into a red supergiant and undoubtedly lost a lot of mass through its stellar wind already, it must have started out with more than 8 solar masses, and its core has evolved accordingly. (It is, after all, the state of the core that determines if a massive star will go supernova.)

But stars with the initial mass of 8 solar masses may not go supernova. Not even 10 solar masses necessarily seal the supernova fate for a star.

Nancy Atkinson wrote:

White dwarfs are strange stars, but researchers recently discovered two of the strangest yet. However, these two oddballs are a missing link of sorts, between massive stars that end their lives as supernovae and small to medium sized stars that become white dwarfs. Somehow, these two once-massive stars avoided the core collapse of a supernova, and are the only two white dwarfs known to have oxygen-rich atmospheres. These so-called massive white dwarfs have been predicted, but never before observed.
...
Theoretical models predicted that if stars around 7 – 10 times the mass of our own Sun don’t end their lives as supernovae, the other option is that they will consume all of their hydrogen, helium and carbon, and end their lives as white dwarfs with very oxygen-rich cores.

Ann

[neufer]

[b][color=#0000FF][size=120]ο[sup]1[/sup] CMa appears to be interacting with the nebula around EZ CMa[/size] [size=85]This image was created using the POSS-II/UKSTU data of the Digitized Sky Survey[/size][/color][/b]

---

<<Omicron1 Canis Majoris (ο¹ CMa, ο¹ Canis Majoris) is a variable star in the constellation of Canis Major. Though only separated by 2 degrees from the blue supergiant ο² Canis Majoris, the two appear to be unrelated. The star itself is ae K-type orange supergiant of spectral type K2.5 Iab and is an irregular variable star, varying between apparent magnitudes 3.78 and 3.99. A cool star, its surface temperature is around 3,900 K. Around 8 times as massive as the Sun with around 280 times its diameter, it shines with 16,000 times its luminosity. Thought to be around 18 million years old, ο¹ Canis Majoris is undergoing nuclear fusion of helium in its core to generate energy and will one day explode as a type II supernova.

Well, probably. Since its mass is about 8 solar masses today, when it has evolved into a red supergiant and undoubtedly lost a lot of mass through its stellar wind already, it must have started out with more than 8 solar masses, and its core has evolved accordingly. (It is, after all, the state of the core that determines if a massive star will go supernova.) But stars with the initial mass of 8 solar masses may not go supernova. Not even 10 solar masses necessarily seal the supernova fate for a star.

The question here, however, is whether ο¹ CMa is primarily responsible (in a balloon animal sort of way) for blowing out the hedgehog/dolphin nose of a formally shapeless Sharpless 2-308.

[Ann]

Ah. I see your (dolphin) point.

Well, I think stars often lose mass asymmetrically, so why not? Fine round bubble around Antares anyone?

Ann

[starsurfer]

Ah. I see your (dolphin) point.

Well, I think stars often lose mass asymmetrically, so why not? Fine round bubble around Antares anyone?

Ann

I think in some areas, asymmetries arise due to the bubble expanding into an inhomogeneous interstellar medium?

[Ann]

Ah. I see your (dolphin) point.

Well, I think stars often lose mass asymmetrically, so why not? Fine round bubble around Antares anyone?

Ann

I think in some areas, asymmetries arise due to the bubble expanding into an inhomogeneous interstellar medium?

Yes, I'm sure that is a common cause of asymmetry.

But check out his youtube video of the simulation of a Supernova Type Ia. It sure looks kind of asymmetrical, at least it appears to start off asymmetrically.

Click to play embedded YouTube video.

Ann

[Cruncher]

*eeek* *eeek*