APOD: The Nebulous Realm of WR 134 (2024 May 31)

[APOD Robot]

The Nebulous Realm of WR 134

Explanation: Made with narrowband filters, this cosmic snapshot covers a field of view over twice as wide as the full Moon within the boundaries of the constellation Cygnus. It highlights the bright edge of a ring-like nebula traced by the glow of ionized hydrogen and oxygen gas. Embedded in the region's expanse of interstellar clouds, the complex, glowing arcs are sections of shells of material swept up by the wind from Wolf-Rayet star WR 134, brightest star near the center of the frame. Distance estimates put WR 134 about 6,000 light-years away, making the frame over 100 light-years across. Shedding their outer envelopes in powerful stellar winds, massive Wolf-Rayet stars have burned through their nuclear fuel at a prodigious rate and end this final phase of massive star evolution in a spectacular supernova explosion. The stellar winds and final supernova enrich the interstellar material with heavy elements to be incorporated in future generations of stars.

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[Ann]

I find it a little irritating that this APOD is so large that I have to post it here as an attachment!

The Nebulous Realm of WR 134. Image Credit & Copyright: Xin Long

What I really like about this image is that it doesn't just show us that bright and slightly tousled nebula at upper left, but we can also see the fainter, underlying, almost perfectly symmetrical nebulosity surrounding the star in a drafting-compass perfect circle!

Yet the rim of that circle isn't smooth, but divided into hundreds(?) of little nebular "fingers" all pointing at the central star. In fact, the rim of WR 124 is similar to the nebular rim of the Helix Nebula:

A part of the Helix Nebula in infrared light. Note all the little 'fingers' all pointing at the central star. Credit: M. Matsuura (UCL / NAOJ) & N.J. Wright (CfA)

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The most famous bubble nebula in the Milky Way is of course the Bubble Nebula. But the inner rim of the Bubble Nebula shows no signs of nebular fingers pointing at the central star.

The Bubble Nebula, also known as NGC 7635, is an emission nebula located 8,000 light-years away. NASA, ESA, Hubble Heritage Team

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We may note that, just as in WR 134, the Bubble Nebula is brightest at upper left. But, in contrast to WR 134, the hot star of the Bubble Nebula is not located at the center of its own nebula, but displaced far to the upper left.

What gives? The fact that both WR 134 and the Bubble Nebula are brighter in one spot is just due to the fact that the interstellar medium is thicker in that direction, and the outward-pushing nebula is "crashing harder" into the interstellar medium where the nebula is brighter. The "crash" leads to a stronger ionization and a brighter OIII emission.


But how do we explain the "fingers" of the nebular rim of WR 134, and the lack of such fingers in the Bubble Nebula?

The answer is probably the fact that WR 134 is indeed a Wolf-Rayet star. As such, it blows a tremendous wind, and it has bared deeper, hotter layers of itself, driving its temperature (in the case of WR 134) to 63,000 K. The central star of the Bubble Nebula, by contrast, is an O-type star of spectral class O6.5 and a temperature of 37,000 K, and while it is blowing a strong wind indeed, that wind is nothing compared with the wind of a Wolf-Rayet star.

Wolf-Rayet star WR 124 and nebula M1–67. Credit: NASA, ESA, CSA, STScI, Webb ERO Production Team

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You can see at top of nebula M1-67 surrounding WR 124 that the rim seems to show many little "fingers" pointing at the central star. Also note that the star is very centrally placed inside its own nebula. In the same way, a hot and windy young white dwarf can shape its nebular rim into the same kind of fingers as we see in WR 134.


My guess is that the Bubble Nebula is the product of a single major outburst of the central star. The star itself is not hot enough or windy enough to break up the outer nebular rim into little fingers. And since the nebular bubble is not being replenished, it is buffeted by outside forces into a shape where the central star is very much off-center.

By contrast, a Wolf-Rayet nebula is primarily shaped by the tremendous heat and wind of its own central star, so the star remains centrally placed in its own nebula, and the outer nebular rim is broken up into hundreds of little fingers.

Of course, in the case of WR 134, we see both the effects of outside buffeting (the bright "tousled hair" part of the nebula) and the effects of inside regulation (the perfectly circular rim of the nebula).

Ann

[JimB]

a Wolf-Rayet nebula is primarily shaped by the tremendous heat and wind of its own central star
Ann

I have trouble getting my head wrapped round the way that things work on these scales.

If the nebula has something like a 40 light year radius, does that mean that the glow from the nebula has actually been created by radiation that left the star 40 years previously? Or does the nebula glow because it is composed of hot plasma from the star?

[Christian G.]

Wolf-Rayet stars are so tumultuous and fiery, even when they look this adorable!

[Chris Peterson]

I find it a little irritating that this APOD is so large that I have to post it here as an attachment!

For reasons unclear the images are posted as PNG files. That's a totally inappropriate format in this case. If you want to use them in your response, you can simply open them in your favorite image viewer and resave them as JPEGs (most viewers let you do this) and then they'll be much smaller files, and visually the same.

[Christian G.]

If you compare a Wolf-Rayet with an LBV of the exact same mass (leaving aside ejectae), which one would be most luminous? Would it be the WR by virtue of the burning core being more exposed so to speak, or could it be either one depending on various other factors?

[Chris Peterson]

a Wolf-Rayet nebula is primarily shaped by the tremendous heat and wind of its own central star
Ann

I have trouble getting my head wrapped round the way that things work on these scales.

If the nebula has something like a 40 light year radius, does that mean that the glow from the nebula has actually been created by radiation that left the star 40 years previously? Or does the nebula glow because it is composed of hot plasma from the star?

The nebula consists of atoms that are ionized by radiation from the star. Most of the gas is already ionized, and a typical atom remains in that state for decades before it recombines with a free electron and releases a photon that we see. Very quickly (probably less than a second) that atom gets hit by another energetic photon from the star and is reionized. Most emission nebulas are highly ionized plasmas, with only a very small percentage of neutral atoms.

[Rauf]

It is estimated that about 50% of Wolf-Rayet stars occur in binary systems. Proposed companions are another Wolf-Rayet star, or a compact companion such as a black hole or neutron star. There is some evidence for both of these scenarios, but conclusive observations have yet to be obtained. The only confirmed companions to Wolf-Rayet stars have so far been other massive stars.

But why they occur in binary systems? And why their companion is most likely a compact object?

[Ann]

a Wolf-Rayet nebula is primarily shaped by the tremendous heat and wind of its own central star
Ann

I have trouble getting my head wrapped round the way that things work on these scales.

If the nebula has something like a 40 light year radius, does that mean that the glow from the nebula has actually been created by radiation that left the star 40 years previously? Or does the nebula glow because it is composed of hot plasma from the star?

The Wolf-Rayet phase of a very massive star's life begins when it starts blowing an incredibly strong wind that blows off its outer layers. I don't know how long this stage lasts, but I am sure, nevertheless, that it lasts more than 40 years. So yes, WR 134 is eminently capable of ionizing the gas that it has blown off of itself.

Ann

[Chris Peterson]

It is estimated that about 50% of Wolf-Rayet stars occur in binary systems. Proposed companions are another Wolf-Rayet star, or a compact companion such as a black hole or neutron star. There is some evidence for both of these scenarios, but conclusive observations have yet to be obtained. The only confirmed companions to Wolf-Rayet stars have so far been other massive stars.

But why they occur in binary systems? And why their companion is most likely a compact object?

Given that something like 85% of high mass stars are part of binary systems, maybe the question to ask is why only 50% of WR stars are binaries?

[Rauf]

It is estimated that about 50% of Wolf-Rayet stars occur in binary systems. Proposed companions are another Wolf-Rayet star, or a compact companion such as a black hole or neutron star. There is some evidence for both of these scenarios, but conclusive observations have yet to be obtained. The only confirmed companions to Wolf-Rayet stars have so far been other massive stars.

But why they occur in binary systems? And why their companion is most likely a compact object?

Given that something like 85% of high mass stars are part of binary systems, maybe the question to ask is why only 50% of WR stars are binaries?

OK, so I ask: Why 85% of high mass stars are part of binary systems?

[Chris Peterson]

But why they occur in binary systems? And why their companion is most likely a compact object?

Given that something like 85% of high mass stars are part of binary systems, maybe the question to ask is why only 50% of WR stars are binaries?

OK, so I ask: Why 85% of high mass stars are part of binary systems?

I think it's just the nature of how stars form from collapsing nebulas. The product of fluid dynamics- viscosity and turbulence.

[Ann]

But why they occur in binary systems? And why their companion is most likely a compact object?

Given that something like 85% of high mass stars are part of binary systems, maybe the question to ask is why only 50% of WR stars are binaries?

OK, so I ask: Why 85% of high mass stars are part of binary systems?

Probably because high-mass stars typically form in clusters, and the very high-mass stars bend spacetime so strongly that other stars of that cluster will fall down into the "gravity well" of the largest star. Sometimes this probably leads to stellar mergers, but much more often the smaller star will simply start orbiting the larger star.

Ann

[Chris Peterson]

Given that something like 85% of high mass stars are part of binary systems, maybe the question to ask is why only 50% of WR stars are binaries?

OK, so I ask: Why 85% of high mass stars are part of binary systems?

Probably because high-mass stars typically form in clusters, and the very high-mass stars bend spacetime so strongly that other stars of that cluster will fall down into the "gravity well" of the largest star. Sometimes this probably leads to stellar mergers, but much more often the smaller star will simply start orbiting the larger star.

Ann

Keep in mind, however, that one star cannot capture another into a closed orbit. That requires at least three bodies to interact (which may well happen in a cluster).

[Cousin Ricky]

It looks like the mouth of a sandworm (Villeneuve version).

[johnnydeep]

Is the source of the gas in prominent blue arc at the upper left the W-R star? Or is that just gas that happened to be in the vicinity?

[Chris Peterson]

Is the source of the gas in prominent blue arc at the upper left the WR star? Or is that just gas that happened to be in the vicinity?

It's complicated. W-R stars blow off a lot of material which often generates a local nebula, similar in some ways to a planetary nebula. But they can certainly exist within existing nebulas. I think we're seeing both of those here.

[johnnydeep]

Is the source of the gas in prominent blue arc at the upper left the W-R star? Or is that just gas that happened to be in the vicinity?

It's complicated. W-R stars blow off a lot of material which often generates a local nebula, similar in some ways to a planetary nebula. But they can certainly exist within existing nebulas. I think we're seeing both of those here.

The "fingery" blue ring is clearly from the W-R star, but are you saying that the blue gas arc is likely at least partly gas from the W-R or, that only the ring material is and the arc is just nearby gas? (Though there may be nothing definitive here to prove it one way of the other.)

[Chris Peterson]

Is the source of the gas in prominent blue arc at the upper left the W-R star? Or is that just gas that happened to be in the vicinity?

It's complicated. W-R stars blow off a lot of material which often generates a local nebula, similar in some ways to a planetary nebula. But they can certainly exist within existing nebulas. I think we're seeing both of those here.

The "fingery" blue ring is clearly from the W-R star, but are you saying that the blue gas arc is likely at least partly gas from the W-R or, that only the ring material is and the arc is just nearby gas? (Though there may be nothing definitive here to prove it one way of the other.)

Since it's not really concentric with the star I'm inclined to guess it's a shock front created when material from the stellar wind hits the surrounding medium. But that really is just a hunch.

[Ann]

But why they occur in binary systems? And why their companion is most likely a compact object?

Given that something like 85% of high mass stars are part of binary systems, maybe the question to ask is why only 50% of WR stars are binaries?

OK, so I ask: Why 85% of high mass stars are part of binary systems?

One answer probably has to do with the formation process of high-mass stars.

A binary star is in the process of forming as the disk around 'the first star' has fragmented. Credit: NRAO.

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Spaceref.com wrote:

Astronomers know that about half of all Sun-like stars are members of double or multiple-star systems, but have debated over how such systems are formed.

“The only way to resolve the debate is to observe very young stellar systems and catch them in the act of formation,” said John Tobin, of the National Radio Astronomy Observatory (NRAO). “That’s what we’ve done with the stars we observed, and we got valuable new clues from them,” he added.

Their new clues support the idea that double-star systems form when a disk of gas and dust whirling around one young star fragments, forming another new star in orbit with the first. Young stars that still are gathering matter from their surroundings form such disks, along with jet-like outflows rapidly propelling material in narrow beams perpendicular to the disk.

Massive stars form from particularly large disks. It seems likely, at least to me, that large disks are more prone than smaller ones to fragmenting, thus creating massive stars that are born as binaries.

Ann

[Ann]

I have to show you this new JWST picture of the Ring Nebula:

A NIRCam (near infrared) image of the Ring Nebula. Note the tremendous numbers of 'fingers', or cometary knots, along both the inner and the outer rim of the nebula. Credit: NASA/ESA/JWST

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Central stars of planetary nebulas are in some ways similar to Wolf-Rayet stars. A crucial difference is that white dwarf of a planetary nebula formed from a much smaller star, so that it is a lot less powerful. The white dwarf of the Ring nebula has a mass of 0.61–0.62 M_☉ and a luminosity of 200 L_☉ according to Wikipedia, versus 18 M_☉ and some 400,000 L_☉ for WR 134.

Yes, but the central star of the Ring Nebula is twice as hot as WR 134, 125,000±5,000 K, versus some 63,000 K for WR 134. My own guess is that the wind of the central star of the Ring Nebula also blows much faster, perhaps twice as fast, as the wind of WR 134.

Ann

[Ann]

Can't help myself, I've got to show you planetary nebula Abell 78:

Abell 78. Note the underlying faint and symmetrical nebula and the irregular new shell and the bright 'spikes' all pointing at the central star. ESA/Hubble & NASA, M. Guerrero. Acknowledgement: Judy Schmidt

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ESA/Hubble wrote:

After exhausting the nuclear fuel in their cores, stars with a mass of around 0.8 to 8 times the mass of our Sun collapse to form dense and hot white dwarf stars. As this process occurs, the dying star will throw off its outer layers of material, forming an elaborate cloud of gas and dust known as a planetary nebula. This phenomenon is not uncommon, and planetary nebulae are a popular focus for astrophotographers because of their often beautiful and complex shapes. However, a few like Abell 78 are the result of a so-called “born again” star.

Although the core of the star has stopped burning hydrogen and helium, a thermonuclear runaway at its surface ejects material at high speeds. This ejecta shocks and sweeps up the material of the old nebula, producing the filaments and irregular shell around the central star seen in this Picture of the Week, which features data from Hubble’s Wide Field Camera 3 and PANSTARSS.

Ann

[Rauf]

Given that something like 85% of high mass stars are part of binary systems, maybe the question to ask is why only 50% of WR stars are binaries?

OK, so I ask: Why 85% of high mass stars are part of binary systems?

One answer probably has to do with the formation process of high-mass stars.

A binary star is in the process of forming as the disk around 'the first star' has fragmented. Credit: NRAO.

---

Spaceref.com wrote:

Thanks Ann. I have hard time understanding what are the possible causes for a stellar disk to fragment. Gravity a nearby star, or blackhole maybe? Or maybe the original star's radiation and wind?
Astronomers know that about half of all Sun-like stars are members of double or multiple-star systems, but have debated over how such systems are formed.

“The only way to resolve the debate is to observe very young stellar systems and catch them in the act of formation,” said John Tobin, of the National Radio Astronomy Observatory (NRAO). “That’s what we’ve done with the stars we observed, and we got valuable new clues from them,” he added.

Their new clues support the idea that double-star systems form when a disk of gas and dust whirling around one young star fragments, forming another new star in orbit with the first. Young stars that still are gathering matter from their surroundings form such disks, along with jet-like outflows rapidly propelling material in narrow beams perpendicular to the disk.

Massive stars form from particularly large disks. It seems likely, at least to me, that large disks are more prone than smaller ones to fragmenting, thus creating massive stars that are born as binaries.

Ann

Thanks Ann. But what causes this fragmentations? Gravity from a nearby star, or a black hole? Or maybe radiation and wind from the original star?

[Christian G.]

OK, so I ask: Why 85% of high mass stars are part of binary systems?

One answer probably has to do with the formation process of high-mass stars.

A binary star is in the process of forming as the disk around 'the first star' has fragmented. Credit: NRAO.

---

Spaceref.com wrote:

Thanks Ann. I have hard time understanding what are the possible causes for a stellar disk to fragment. Gravity a nearby star, or blackhole maybe? Or maybe the original star's radiation and wind?
Astronomers know that about half of all Sun-like stars are members of double or multiple-star systems, but have debated over how such systems are formed.

“The only way to resolve the debate is to observe very young stellar systems and catch them in the act of formation,” said John Tobin, of the National Radio Astronomy Observatory (NRAO). “That’s what we’ve done with the stars we observed, and we got valuable new clues from them,” he added.

Their new clues support the idea that double-star systems form when a disk of gas and dust whirling around one young star fragments, forming another new star in orbit with the first. Young stars that still are gathering matter from their surroundings form such disks, along with jet-like outflows rapidly propelling material in narrow beams perpendicular to the disk.

Massive stars form from particularly large disks. It seems likely, at least to me, that large disks are more prone than smaller ones to fragmenting, thus creating massive stars that are born as binaries.

Ann

Thanks Ann. But what causes this fragmentations? Gravity from a nearby star, or a black hole? Or maybe radiation and wind from the original star?

One thing I've read is that as the dust and gas cloud increasingly falls onto the protostar, it speeds up the latter's rotation to the point where it could tear itself apart. This rotational acceleration can be slowed down either by jets as in HH objects, or it can be slowed down if the cloud, which is itself rotating to begin with, fragments into two star-forming clouds, in which case part of the rotational energy is converted to orbital energy. (provided I got that correctly!)

[johnnydeep]

It's complicated. W-R stars blow off a lot of material which often generates a local nebula, similar in some ways to a planetary nebula. But they can certainly exist within existing nebulas. I think we're seeing both of those here.

The "fingery" blue ring is clearly from the W-R star, but are you saying that the blue gas arc is likely at least partly gas from the W-R or, that only the ring material is and the arc is just nearby gas? (Though there may be nothing definitive here to prove it one way of the other.)

Since it's not really concentric with the star I'm inclined to guess it's a shock front created when material from the stellar wind hits the surrounding medium. But that really is just a hunch.