APOD: The Necklace Nebula (2010 Nov 03)

[APOD Robot]

The Necklace Nebula

Explanation: The small constellation Sagitta sports this large piece of cosmic jewelry, dubbed the Necklace Nebula. The newly discovered example of a ring-shaped planetary nebula is about 15,000 light-years distant. Its bright ring with pearls of glowing gas is half a light-year across. Planetary nebulae are created by sun-like stars in a final phase of stellar evolution. But the Necklace Nebula's central star, near the center of a ring strongly tilted to our line of sight, has also been shown to be binary, a close system of two stars with an orbital period of just over a day. Astronomers estimating the apparent age of the ring to be around 5,000 years, also find more distant gas clouds perpendicular to the ring plane, seen here at the upper left and lower right. Those clouds were likely ejected about 5,000 years before the clouds forming the necklace. This false color image combines emission from ionized hydrogen in blue, oxygen in green, and nitrogen in red.

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[R.D.Wilbur]

A question re the Necklace Nebula.
The ten or so bright spots making the “necklace”. Their appearance seems to indicate they are a part of the system as opposed to background objects. I wondered if they were the remnants of planetary objects about the central star(s). The fact that they appear to all be about the same distance from the center would cast doubt on this notion. If they are debris of the expanding star, why discrete objects as opposed to a homogeneous shell? Are they in a plane or scattered through a sphere? How difficult would it be to get spectra of individual objects? To someone who is involved in the field, these may seem silly questions, But they do occur to those of us in the general public. Please excuse my one off intrusion. I am an avid APOD follower, bur hesitate to expose too much of my ignorance by jumping into the discussion group. This one I just could not let pass.

[harry]

G'day

What we are seeing is the front on image of an hour glass formation.

Reagardless this paper may put some light to the discussion.

The Necklace: equatorial and polar outflows from the binary central star of the new planetary nebula IPHASXJ194359.5+170901
Authors: R.L.M. Corradi, L. Sabin, B. Miszalski, P. Rodríguez-Gil, M. Santander-García, D. Jones, J. Drew, A. Mampaso, M. Barlow, M.M. Rubio-Díez, J. Casares, K. Viironen, D.J. Frew, C. Giammanco, R. Greimel, S. Sale
(Submitted on 6 Sep 2010)
Abstract: IPHASXJ194359.5+170901 is a new high-excitation planetary nebula with remarkable characteristics. It consists of a knotty ring expanding at a speed of 28 km/s, and a fast collimated outflow in the form of faint lobes and caps along the direction perpendicular to the ring. The expansion speed of the polar caps is 100 km/s, and their kinematical age is twice as large as the age of the ring. Time-resolved photometry of the central star of IPHASXJ194359.5+170901 reveals a sinusoidal modulation with a period of 1.16 days. This is interpreted as evidence for binarity of the central star, the brightness variations being related to the orbital motion of an irradiated companion. This is supported by the spectrum of the central star in the visible range, which appears to be dominated by emission from the irradiated zone, consisting of a warm (6000-7000 K) continuum, narrow C III, C IV, and N III emission lines, and broader lines from a flat H I Balmer sequence in emission. IPHASXJ194359.5+170901 helps to clarify the role of (close) binaries in the formation and shaping of planetary nebulae. The output of the common-envelope evolution of the system is a strongly flattened circumstellar mass deposition, a feature that seems to be distinctive of this kind of binary system. Also, IPHASXJ194359.5+170901 is among the first post-CE PNe for which the existence of a high-velocity polar outflow has been demonstrated. Its kinematical age might indicate that the polar outflow is formed before the common-envelope phase. This points to mass transfer onto the secondary as the origin, but alternative explanations are also considered.

http://arxiv.org/abs/1009.1043

[neufer]

This is the same structural event as surrounds Supernova 1987a. Just compare them.

The survey has already discovered a large number of previously unknown planetary nebulae, such as the Necklace Nebula in this image.

---

<<The INT Photometric H-Alpha Survey (IPHAS) is an astronomical survey of the northern plane of our Galaxy, the Milky Way, as visible from the Isaac Newton Telescope (INT) in the Canary Islands, Spain. The survey uses two broad-band filters and a narrow H-alpha filter to obtain deep images of nebulae in our Galaxy and for identifying rare types of stars.

Observations for the survey began in 2003 and are almost complete. The survey will soon be complemented by a sister survey of the southern Galactic plane. Once these two surveys are completed the data is expected to provide a significant leap in our knowledge of the extreme phases of stellar evolution.

The goals of the survey include:

• * Identification of rare objects that are often characterized by strong emission in H-Alpha compared to that in broad-band filters. This includes massive OB stars, supergiants, interacting binary stars and supernova progenitors.
  
  * Mapping Galactic extinction and nebulosity.
  
  * Identifying compact and extended planetary nebulae and symbiotic stars.
  
  * Cataloging of vast numbers of stars in our Galaxy.

Because of the selection for young stars and nebulae, the survey will also increase the number of known OB associations, and other clusters.>>

Circumstellar rings around SN 1987A, with the ejecta from the supernova explosion at the center of the inner ring.

---

The expanding supernova remnant around Supernova 1987A and its interaction with its surroundings, seen in X-ray and visible light.

---

A time sequence of Hubble Space Telescope images, taken in the 9 years from 1994 to 2003, showing the collision of the expanding supernova remnant with a ring of dense material ejected by the progenitor star 20,000 years before the supernova.

<<The three bright rings around SN 1987A are material from the stellar wind of the progenitor. These rings were ionized by the ultraviolet flash from the supernova explosion, and consequently began emitting in various emission lines. These rings did not "turn on" until several months after the supernova, and the turn-on process can be very accurately studied through spectroscopy. The rings are large enough for their angular size to be measured accurately: the inner ring is 0.808 arcseconds in radius. Using the distance light must have traveled to light up the inner ring as the base of a right angle triangle, and the angular size as seen from the Earth for the local angle, one can use basic trigonometry to calculate the distance to SN1987A, which is about 168,000 light-years.

During its excursions into the red supergiant region of the HR-diagram, it threw off large amounts of material. 10 million years after it formed, its central temperature had reached 3.5 billion degrees and iron was being created. The core collapsed in less than a second and the infalling material rebounded causing a shock wave to pass through the star. This reached the surface a few hours later, traveling at the local speed of sound in the star, still being heated by the massive release of neutrinos and we observed the outburst on Earth some 160,000 years later. The material from the explosion is catching up with the material expelled during its red giant phase and heating it, so we observe ring structures around the star.>>

[orin stepanek]

I think today's APOD looks more like a bracelet than a necklace. Either way it is pretty neat. Here's an interesting planetary nebula that I never knew about. It is the lemon slice nebula. It is pretty cool also. I found it in the links.

Click to view full size image

[zbvhs]

So, is the Necklace a supernova remnant? Would that be the consensus? If not, what is the preferred mechanism for its formation?

[neufer]

So, is the Necklace a supernova remnant? Would that be the consensus?
If not, what is the preferred mechanism for its formation?

They certainly seem to be related.

I'm guessing:

• The 1987a is a planetary nebula supergiant remnant lit up by a supernova.
  
  The Necklace Nebula is a planetary nebula red giant remnant lit up by a white dwarf.

[RisinOrion]

Maybe I'm missing something....How can an object that is only ~5,000 years old be 15,000 light years away? Does this actually mean 5,000 years old as viewed currently (thus making it ~20,000 years total)?

[Chris Peterson]

Maybe I'm missing something....How can an object that is only ~5,000 years old be 15,000 light years away? Does this actually mean 5,000 years old as viewed currently (thus making it ~20,000 years total)?

It is customary to ignore the light travel time, because it rarely makes any difference how old something "really" is. We are seeing an object that appears to be 5000 years old. The fact that it "really" happened 20,000 years ago (in one particular frame of reference) isn't important.

[dougettinger]

So, is the Necklace a supernova remnant? Would that be the consensus?
If not, what is the preferred mechanism for its formation?

They certainly seem to be related.

I'm guessing:

• The 1987a is a planetary nebula supergiant remnant lit up by a supernova.
  
  The Necklace Nebula is a planetary nebula red giant remnant lit up by a white dwarf.

I am really, really confused. What did explode? And what is left at the center of the explosion that has two parts, one orbiting every day? How do we know that this remnant is a red giant remnant and not a supernova remnant ? Do astronomers know of other such red giant remnants with knots of material in a ring ? What hypothesis is used to predict these knots after the demise of a red giant ? Just whisper if it happens to be electromagnetic phenomena.

Art, from you guessing (you are allowed to guess and not quote sometimes) am I to presume that a white dwarf was stealing mass from a aging binary neighbor and the neighbor evolved into the red giant phase leaving the white dwarf unaffected ? I have lotsa of questions because I am confused about the explanation of the Necklace Nebula and your guessing.

Doug Ettinger
Pittsburgh, PA

[Chris Peterson]

So, is the Necklace a supernova remnant? Would that be the consensus? If not, what is the preferred mechanism for its formation?

Planetary nebulas are not produced by supernovas. I would presume this formed like any PN, from the ejected shells of gas produced by the central star near the end of its evolution. There is no suggestion that this is a supernova remnant, and if it were, it would not be so compact after 5000 years.

[Chris Peterson]

I am really, really confused. What did explode? And what is left at the center of the explosion that has two parts, one orbiting every day?

Nothing exploded. There was a binary system, and one of the stars reached the point in its evolution that it ejected its outer shell, which is the mechanism for planetary nebula formation. What is now at the center is what was always there- the two original stars.

How do we know that this remnant is a red giant remnant and not a supernova remnant ?

A supernova wouldn't leave its central star intact, still in a fusing stage of its evolution. Also, a supernova would produce a supernova remnant, which can superficially resemble a planetary nebula, but which has much higher outflow velocities. A supernova remnant would be much more dispersed after 5000 years.

What hypothesis is used to predict these knots after the demise of a red giant ? Just whisper if it happens to be electromagnetic phenomena.

There is nothing to suggest electromagnetic phenomena are involved. If I understand the paper Harry referenced, the knots are the product of rotation and punctuated episodes of material ejection.

[neufer]

I'm guessing:

• The 1987a is a planetary nebula supergiant remnant lit up by a supernova.
  
  The Necklace Nebula is a planetary nebula red giant remnant lit up by a white dwarf.

I am really, really confused. What did explode? And what is left at the center of the explosion that has two parts, one orbiting every day? How do we know that this remnant is a red giant remnant and not a supernova remnant ? Do astronomers know of other such red giant remnants with knots of material in a ring ? What hypothesis is used to predict these knots after the demise of a red giant ? Just whisper if it happens to be electromagnetic phenomena.

Art, from you guessing (you are allowed to guess and not quote sometimes) am I to presume that a white dwarf was stealing mass from a aging binary neighbor and the neighbor evolved into the red giant phase leaving the white dwarf unaffected ? I have lotsa of questions because I am confused about the explanation of the Necklace Nebula and your guessing.

Eruptions of dying giant/supergiant stars often tend to be equatorial & quasi-polar:
http://antwrp.gsfc.nasa.gov/apod/ap080617.html

Under certain rare circumstances such "last gasp" eruptions may even result
in three rather neat quasi-symmetric rings (as in the case of SN 1987a).

If the dying star then ends up as a supernova (as Sanduleak -69° 202a did)
that will irradiate these (normally dark) cast off rings temporarily.

If the dying star ends up as a white dwarf then it will irradiate
the three rings as a bright planetary nebula as in the case of today's APOD.

The formation of Planetary nebulae:
http://upload.wikimedia.org/wikipedia/c ... ebulae.OGG

[dougettinger]

Chris, thanks for that quick reply. Can the knots in the ring for SN 1987A be attributed to the same mechanisms ? Or are these knots due to the more electromagnetic nature of superheated supernova plasma ?

You stated that the star attributed to the red giant structure is still fusing. I thought that after the red giant phase, the source star would become a white dwarf itself(?) Are there two white dwarfs orbiting each other? I cannot remember the current theory about red giants; do the materials in the red giant disperse into space or collapse and return to the source star besides making the observed ring of knots ? A ring of knots after the red giant phase is entirely new to me.

Doug Ettinger
Pittsburgh, PA



Doug Ettinger
Pittsburgh, PA

[drollere]

the photo discussion forum would be a great place to post the celestial coordinates and visual magnitude of the object, so that amateur astronomers can place it in relation to the galactic background and the range of objects they are able to see. i infer from its "recently discovered status" that this object is small and quite faint, if not completely invisible, in light wavelengths.

(and no, infrared is not light. light is exclusively the electromagnetic radiation that produces a visual response in the human eye, conventionally bounded at 700 to 840 nm. If infrared is light, then so too are microwaves and x rays.)

[owlice]

In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.

[dougettinger]

Chris, thanks for that quick reply. Can the knots in the ring for SN 1987A be attributed to the same mechanisms ? Or are these knots due to the more electromagnetic nature of superheated supernova plasma ?

You stated that the star attributed to the red giant structure is still fusing. I thought that after the red giant phase, the source star would become a white dwarf itself(?) Are there two white dwarfs orbiting each other? I cannot remember the current theory about red giants; do the materials in the red giant disperse into space or collapse and return to the source star besides making the observed ring of knots ? A ring of knots after the red giant phase is entirely new to me.

Doug Ettinger
Pittsburgh, PA

I will answer my last question since I reread Wiki's planetary nebula supplied by Art. The red giant, a rather short phase, finally disperses into space to become a planetary nebula. I never had the complete realization that planetary nebula have so many configurations that include features of a supernova remnants and newly forming stars.

I am still a little puzzled how one tells the difference between a supernova remnant and a planetary nebula that have occurred thousands of years ago. Am I correct in saying that supernovae Type II have neutron stars (although it cannot be found for SN1987A) and planetary nebulae have white dwarfs.

Doug Ettinger

[neufer]

Am I correct in saying that supernovae Type II have neutron stars (although it cannot be found for SN1987A) and planetary nebulae have white dwarfs.

Supernovae Type II below about 20 solar masses are supposed to end up having neutron stars;
although some (e.g., SN1987A ?) might end up having quark stars instead.

<<In a typical Type II supernova the newly formed neutron core has an initial temperature of about 100 billion kelvin. A further release of neutrinos carries away much of the thermal energy, allowing a stable neutron star to form (the neutrons would "boil away" if this cooling did not occur). These 'thermal' neutrinos form as neutrino-antineutrino pairs of all flavors, and total several times the number of electron-capture neutrinos.

When the progenitor star is below about 20 solar masses (depending on the strength of the explosion and the amount of material that falls back), the degenerate remnant of a core collapse is a neutron star. Above this mass the remnant collapses to form a black hole. (This type of collapse is one of many candidate explanations for gamma ray bursts, possibly producing a large burst of gamma rays through a hypernova explosion.) The theoretical limiting mass for this type of core collapse scenario was estimated around 40–50 solar masses.

Above 50 solar masses stars were believed to collapse directly into a black hole without forming a supernova explosion, although uncertainties in models of supernova collapse make accurate calculation of these limits difficult. Above about 140 solar masses stars may become pair-instability supernovae that do not leave behind a black hole remnant.>>

<<A quark-nova is a hypothetical type of supernova that could occur if a neutron star spontaneously collapsed to become a quark star. The concept of quark-novae was suggested by Dr. Rachid Ouyed (University of Calgary, Canada) and Drs. Dey and Dey (Calcutta University, India).

When a neutron star spins down, it could convert to a quark star through a process known as quark deconfinement. The resultant star would have quark matter in its interior. The process would release immense amounts of energy, perhaps explaining the most energetic explosions in the universe; rough calculations have estimated that as much as 1047 joules of energy could be released from the phase transition inside a neutron star. Quark-novae may be one cause of gamma ray bursts. According to Jaikumar et al., they may also be involved in producing heavy elements such as platinum through r-process nucleosynthesis.

Rapidly spinning neutron stars with masses between 1.5 and 1.8 solar masses are theoretically the best candidates for conversion due to spin down of the star within a Hubble time. This amounts to a small fraction of the projected neutron star population. A conservative estimate based on this indicates that up to two quark-novae may occur in the observable universe each day.

Theoretically quark stars would be radio-quiet, so radio-quiet neutron stars may be quark stars. Direct evidence for quark-novae is scant; however recent observations of supernovae SN2006gy, SN2005gj and SN2005ap may point to their existence.>>

<<White dwarfs are thought to be the final evolutionary state of all stars whose mass is not high enough to supernova—over 97% of the stars in our galaxy. After the hydrogen-fusing lifetime of a main-sequence star of low or medium mass ends, it will expand to a red giant which fuses helium to carbon and oxygen in its core by the triple-alpha process. If a red giant has insufficient mass to generate the core temperatures required to fuse carbon, an inert mass of carbon and oxygen will build up at its center. After shedding its outer layers to form a planetary nebula, it will leave behind this core, which forms the remnant white dwarf. Usually, therefore, white dwarfs are composed of carbon and oxygen. It is also possible that core temperatures suffice to fuse carbon but not neon, in which case an oxygen-neon–magnesium white dwarf may be formed. Also, some helium white dwarfs appear to have been formed by mass loss in binary systems.>>

[Chris Peterson]

I am still a little puzzled how one tells the difference between a supernova remnant and a planetary nebula that have occurred thousands of years ago.

Well, the easiest way is probably just to look at the velocity of the ejected material. Planetary nebulas have expansion rates on the order of a few tens of km/s. Supernova remnants have expansion rates on the order of 1000 km/s. The velocity of the expansion is a primary measurement, made by looking at the Doppler shift of specific emission lines at different parts of the structures.

[workgazer]

Loved this discussion, Hope i am not to late, i saw this image and could not help but think of the ring galaxy image from an apod about a month ago.
I understand that one is at star level and the other at galactic level but the structure looks so close to one another, is it possible that the ring galaxy under went the same process as star in this image? a galactic planetary nebula?
thanks

[Chris Peterson]

Loved this discussion, Hope i am not to late, i saw this image and could not help but think of the ring galaxy image from an apod about a month ago.
I understand that one is at star level and the other at galactic level but the structure looks so close to one another, is it possible that the ring galaxy under went the same process as star in this image? a galactic planetary nebula?
thanks

No, the processes are completely different. In the case of the planetary nebula, you are seeing regions of hot gas that was ejected at different times by a star. In the case of the galaxy, you are seeing star forming regions caused by shocked regions associated with the galactic rotation.

[owlice]

Five to ten percent of the stars visible to us are visual binary stars. Careful spectroscopic studies of nearby solar-type stars show that about two thirds of them have stellar companions. We estimate that roughly half of all stars in the sky are indeed members of binaries.

(Emphasis mine.)

Given the number of all stars in the sky, there must be a whoooooooooole lotta binary stars out there.

[dougettinger]

I am still a little puzzled how one tells the difference between a supernova remnant and a planetary nebula that have occurred thousands of years ago.

Well, the easiest way is probably just to look at the velocity of the ejected material. Planetary nebulas have expansion rates on the order of a few tens of km/s. Supernova remnants have expansion rates on the order of 1000 km/s. The velocity of the expansion is a primary measurement, made by looking at the Doppler shift of specific emission lines at different parts of the structures.

Thanks, Chris, for this succinct answer. I was expecting such an answer. I did not know whether a survey already revealed the average expansion rate of planetary nebulas.

What possible mechanism causes polar jets in the case of the Necklace Nebula or a dying star ? These jets, according to the article, occurred 5000 years prior to the nebula cloud being created.

What are the possible candidate types for the two stars orbiting in less than two days ? Would not the lesser mass body be eaten by the larger mass ? Could a neutron star feed on a white dwarf ?

Doug Ettinger
Pittsburgh, PA

[harry]

G'day

Supernova is where a star explodes completely and a Nova is where the solar envelope is ejected to some degree.

Doug asked the questiion

What possible mechanism causes polar jets in the case of the Necklace Nebula or a dying star ? These jets, according to the article, occurred 5000 years prior to the nebula cloud being created.

What are the possible candidate types for the two stars orbiting in less than two days ? Would not the lesser mass body be eaten by the larger mass ? Could a neutron star feed on a white dwarf ?

The power for such jets lies in the dynamic properties of Nuclear phase transitions within compact Nuclear matter and their ability to form spontaneous dipolar jets with enough stability to form jets that may go for light years.

Rings are not limited to stars, as the following link shows.

http://arxiv.org/abs/1006.4717
NGC 4262: a Virgo galaxy with an extended ultraviolet ring

Authors: Bettoni, D. (1), Buson, L. M. (1), Galletta, G. (2) ((1)INAF, Osservatorio Astronomico di Padova, (2) Dipartimento di Astronomia Universita' di Padova)
(Submitted on 24 Jun 2010)

Abstract: The Galaxy Ultraviolet Explorer (GALEX) satellite has recently shown the presence of an extended, outer ring studded with UV-bright knots surrounding the lenticular galaxy NGC 4262. Such a structure---not detected in the optical---is coupled with a ring of atomic (HI) gas. We want to show that both star-forming and HI rings surrounding this SB0 galaxy share the same radial distance from the galaxy center and spatial orientation. We want also to model the kinematics of the ring(s) and of the galaxy body. We make use of archive FUV and NUV GALEX data plus HI observations from the literature. We confirm that the UV-bright and atomic gas rings of NGC 4262 have the same extent and projected spatial orientation. Their kinematics is not coupled with that of the galaxy stars. It is possible that NGC 4262 has undergone a major gas stripping event in the past which gave origin to the present "necklace" of UV-bright knots.

[harry]

G'day Doug

This link may add some understaning to your questiion.

http://arxiv.org/abs/1009.4912
A Reconnecting Current Sheet Imaged in A Solar Flare

Authors: Rui Liu, Jeongwoo Lee, Tongjiang Wang, Guillermo Stenborg, Chang Liu, Haimin Wang
(Submitted on 24 Sep 2010)

Abstract: Magnetic reconnection changes the magnetic field topology and powers explosive events in astrophysical, space and laboratory plasmas. For flares and coronal mass ejections (CMEs) in the solar atmosphere, the standard model predicts the presence of a reconnecting current sheet, which has been the subject of considerable theoretical and numerical modeling over the last fifty years, yet direct, unambiguous observational verification has been absent. In this Letter we show a bright sheet structure of global length (>0.25 Rsun) and macroscopic width ((5 - 10)x10^3 km) distinctly above the cusp-shaped flaring loop, imaged during the flare rising phase in EUV. The sheet formed due to the stretch of a transequatorial loop system, and was accompanied by various reconnection signatures that have been dispersed in the literature. This unique event provides a comprehensive view of the reconnection geometry and dynamics in the solar corona.