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Posted: **Sun Nov 18, 2012 5:06 am**

NGC 6357s Cathedral to Massive Stars

Explanation: How massive can a normal star be? Estimates made from distance, brightness and standard solar models had given one star in the open cluster Pismis 24 over 200 times the mass of our Sun, nearly making it the record holder. This star is the brightest object located just above the gas front in the above image. Close inspection of images taken with the Hubble Space Telescope, however, have shown that Pismis 24-1 derives its brilliant luminosity not from a single star but from three at least. Component stars would still remain near 100 solar masses, making them among the more massive stars currently on record. Toward the bottom of the image, stars are still forming in the associated emission nebula NGC 6357. Appearing perhaps like a Gothic cathedral, energetic stars near the center appear to be breaking out and illuminating a spectacular cocoon.

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Posted: **Sun Nov 18, 2012 6:36 am**

Hi, I am the person credited for this image. Could you please correct my name? It is "Jesús Maíz Apellániz" or "J. Maíz Apellániz", not "J. M. Apellániz". "Maíz" is not my middle name but part of my family name. You can check my web page at http://jmaiz.iaa.es and learn more about Spanish-style names at http://en.wikipedia.org/wiki/Spanish_names .

Posted: **Sun Nov 18, 2012 7:08 am**

Jesús, I emailed Robert about your name. I'm sure he'll fix it as soon as he realizes the error is there.

Posted: **Sun Nov 18, 2012 7:08 am**

I'm always very interested in high-mass stars, so of course I find this APOD hugely interesting. It is a joy to see, once more, Hubble ability to sharply resolve fascinating objects. NGC 6357 is far away and also considerably dimmed by intervening dust. Astrophotographer David Malin once demonstrated that NGC 6457 lacks the magenta hue that we associate with emission nebulae like the Lagoon Nebula. Instead, the blue-green light of hydrogen beta emission has been scattered away by dust, making NGC 6357 glow deep-red.

As always, though, I'm confused by the color of this picture. How can the star in the "cave" at bottom be so very much bluer than the stars of the cluster, even though the star in the "cave" can be assumed to be even more reddened than the others. The bright stars of the clusters "above the cave" are not blue at all, but white, and the brightest ones are the most non-blue. Well, this is actually possible. In NGC 869, one of the two Double Clusters, the brightest stars have evolved off the main sequence and are less blue than many of the fainter stars. Yet the difference is slight. In the Hubble image, the difference in color between the non-blue brightest stars and the intensely blue bluest stars is huge.

So what about the filters that were used to produce this image? Well, an image taken through a green filter at 550 nm was mapped as blue. Another image taken through a similar but sligthly bluer green filter at 547 nm was mapped as green. Ha and SII filters at 656 and 658 nm were mapped as red, as well as an infrared filter at 850 nm. I don't understand how these filters could produce the differences in star colors that we see in this picture, unless the brightest stars are actually red giants.

Maybe the star in the "cave" is the bluest of the lot. But I'm not convinced.

Ann

Posted: **Sun Nov 18, 2012 10:49 am**

Is this a composite image?
I wonder because the diffraction spikes of some (two) stars at the bottom of the image have a different orientation than the rest ...

Thanks

Posted: **Sun Nov 18, 2012 10:50 am**

Thanks, geckzilla.

Anne, I can answer your question. This image was built by the OPO people at STScI combining my ACS data at the top with archival WFPC2 data at the bottom. So, what you are seeing are different filters sets tuned out to look continuous in the nebulosity (there is not actually much of it in the ACS data). I suspect that sacrifices continuity in the stellar colors.

Indeed, this object is heavily reddened, with ~6 magnitudes of foreground optical extinction. If you were to look at it in real colors the stars will appear to be very red, even though they are intrinsically blush-white. You can read about the scientific results we got out of the data at (http://adsabs.harvard.edu/abs/2007ApJ...660.1480M , follow the arXiv link if you do not have access to ApJ).

Posted: **Sun Nov 18, 2012 2:32 pm**

What is the distance between the 2 stars that were thought to be one?

Posted: **Sun Nov 18, 2012 2:37 pm**

geckzilla wrote:
jmaiz wrote:
Hi, I am the person credited for this image. Could you please correct my name? It is "Jesús Maíz Apellániz" or "J. Maíz Apellániz", not "J. M. Apellániz". "Maíz" is not my middle name but part of my family name. You can check my web page at http://jmaiz.iaa.es and learn more about Spanish-style names at http://en.wikipedia.org/wiki/Spanish_names .
Jesús, I emailed Robert about your name. I'm sure he'll fix it as soon as he realizes the error is there.

It also needs fixing for the Nov 21, 2010 APOD.

And: http://apod.nasa.gov/apod/ap081026.html
& http://apod.nasa.gov/apod/ap061219.html

Posted: **Sun Nov 18, 2012 2:48 pm**

We can actually see in this picture that the brightest star above the cloud is indeed a double. By looking at the diffraction pattern on the left, we see that there are 2 parallel lines, which gives a rough indication of the position angle and separation (likely one star above the other in this picture orientation). Is this correct?

Posted: **Sun Nov 18, 2012 2:55 pm**

If you look at the picture of the day ,And the cloud of the massive stars you will spot and evil image,
with face and shoulders,eyes and mouth ,blowing a smoke ball from his mouth.
My brother Jerry pointed this out to me, like everyone else ,i only saw the cloud.
By. Robert L. Grisham/The Hammer And Nail /11/18/12

Posted: **Sun Nov 18, 2012 3:36 pm**

So, what are the steps in a star forming? Clearly there has to be enough matter to form the star, and most of it has to be hydrogen. Secondly, the kinetic energies have to be such that enough of the mass is able to coalesce gravitationally. So far, so good. If it's about the amount of mass as the sun, we get, well, the sun. But what happens when the amount is far more than the theoretical upper limit? Obviously a collapse will occur, but does it simply reach so high a temperature that the whole thing just flies apart and doesn't make a star for more than a moment--in essence, a hydrogen bomb instead of a sustained fusion reactor?

Clearly, I don't know a lot about astrophysics, which is why I'm asking.

Posted: **Sun Nov 18, 2012 4:07 pm**

jsintegral wrote:
What is the distance between the 2 stars that were thought to be one?

The resolved Pismis 24-1SW has an apparent separation of ~900 AU (=360 mas at ~8150 light-years away).

The unresolved spectroscopic binary Pismis 24-1NE has a separation of ~ 0.135 AU (period of 2.36088 days/reduced mass ~ 60 M⊙)

http://en.wikipedia.org/wiki/Pismis_24-1 wrote:
<<Pismis 24-1 (also known as HDE 319718) is part of the open cluster Pismis 24 within the nebula NGC 6357 about 8150 light-years away. Pismis 24-1 is the largest and more brilliant of the visible stars of this cluster, and is one of the most massive and luminous stars known. Pismis 24-1 is composed of at least three objects, the resolved Pismis 24-1SW and the unresolved spectroscopic binary Pismis 24-1NE.>>

http://iopscience.iop.org/0004-637X/660/2/1480/fulltext/70939.text.html wrote:
Pismis 24-1: The Stellar Upper Mass Limit Preserved1
J. Maíz Apellániz, Nolan R. Walborn, N. I. Morrell, V. S. Niemela, E. P. Nelan
The Astrophysical Journal, 660:1480-1485, 2007 May 10
© 2007. The American Astronomical Society.

<<In this paper we use HST and ground-based data to investigate the brightest members of the cluster Pismis 24, one of which (Pismis 24-1) was previously inferred to have a mass greater than 200 M⊙, in apparent disagreement with that limit. We determine that Pismis 24-1 is composed of at least three objects, the resolved Pismis 24-1SW and the unresolved spectroscopic binary Pismis 24-1NE. The evolutionary zero-age masses of Pismis 24-1SW, the unresolved system Pismis 24-1NE, and the nearby star Pismis 24-17 are all ≈100 M⊙, very large but under the stellar upper mass limit.

Phil Massey and collaborators (2006, private communication) have detected optical variability in the unresolved Pismis 24-1NE+SW photometry with a peak-to-peak amplitude of 0.07 mag and a period of 2.36088 days. This variability, together with the observed radial velocity variations, is a clear sign that Pismis 24-1 is at least a triple system.

We have presented HST and ground-based data that clearly resolve Pismis 24-1 into two objects separated by 363.86 mas and that indicate the existence of at least a third unresolved component in Pismis 24-1NE. We have also derived zero-age evolutionary masses for the three most massive objects at the core of Pismis 24-1, with values of 92–97 M⊙, one of them corresponding to the unresolved system Pismis 24-1NE. These values are very large, making the cores of Pismis 24-1 and Trumpler 14 (Nelan et al. 2004) the two locations within 3 kpc of the Sun with the highest density of very massive stars. However, these masses are not above what it is currently thought to be the stellar upper mass limit.>>

http://asterisk.apod.com/viewtopic.php? ... 88#p137226

Posted: **Sun Nov 18, 2012 4:12 pm**

nrivard wrote:
We can actually see in this picture that the brightest star above the cloud is indeed a double. By looking at the diffraction pattern on the left, we see that there are 2 parallel lines, which gives a rough indication of the position angle and separation (likely one star above the other in this picture orientation). Is this correct?

Seems about right to me.

Posted: **Sun Nov 18, 2012 5:16 pm**

It also looks like a big alien APE monster pulling up, opening the "Cave"....holding with his right hand, and pulling up with his left....

OR...it also looks like he is holding down a PELICAN'S HEAD...The Pelican has wings on his back, and his Beak forms the top of the cave...

In the lower left corner is a BIRD pecking at OUR lower left of the cave...
On the bottom right...in the cave...is a small baby Vulture....

Ok....I have obviously been at this TOOOO LONG.....

Great Pic....Thanks.

:---[===] *

Posted: **Sun Nov 18, 2012 5:42 pm**

as background, i think the current guesstimate of maximum stellar mass is about 150 solar masses.

Posted: **Sun Nov 18, 2012 8:21 pm**

The blue star embedded in the cloud near the bottom of the picture (north) is Pismis 24-13. It is an O6.5 main sequence star, slightly cooler than the three brightest stars in the photo, but still around 40,000K. The brightest star is the barely resolved double (actually at least triple) Pismis 24-1 O3.5If*/O4III. To its right is Pismis 24-17 O3.5III, now considered to be the most luminous individual star in the cluster but slightly more heavily obscured. Close by is Pismis 24-16 O7.5V. At the top is Pismis 24-2 O5.5III(f). This is only the core of the Pismis 24 cluster.

This Wikipedia image shows more or less the whole cluster, rotated about 45 degrees relative to the APOD image:
http://en.wikipedia.org/wiki/File:Pismis_24.jpg

You can see the two brightest stars at the centre, with the bulk of the cluster above and to the right not visible in the APOD closeup. On the left is a foreground star (not so reddened) and at bottom right is an intriguing Wolf-Rayet star every bit as massive and luminous as the Pismis 24 monsters. It isn't clear whether this evolved WC7 star is part of Pismis 24, but it is part of the larger star forming region and may be a runaway from an obscured cluster nearby.

Posted: **Sun Nov 18, 2012 8:32 pm**

Since we're on the subject Pismis clusters - I'm old enough to have met Paris Pişmiş when she was still frequently at meetings. She was born in Turkey and emigrated to Mexico, where she played an important role in building up their astronomical infrastructure (especially at the Universidad Autonoma Nacional), and she maintained a refreshing willingness to consider way-out hypotheses in areas where our collection of facts lagged behind. She pronounced her last name in a way I would render as "Pishmish". http://en.wikipedia.org/wiki/Paris_Pismis is the Wikipedia bio article.

Posted: **Sun Nov 18, 2012 8:40 pm**

Here is the image used for the bottom half of this construct:
http://apod.nasa.gov/apod/ap101121.html

Posted: **Sun Nov 18, 2012 11:56 pm**

This is a great APOD. Again.

Posted: **Mon Nov 19, 2012 2:00 am**

Wow, it's like another place's big entrance in the lower half of the picture. My monitor allows me only to see the smaller version when I want to see it full, and it is still stunning

Posted: **Mon Nov 19, 2012 5:04 am**

Hello again:

We see here the most wonderful astronomy imaginable. I always wonder though, where the mass that formed that cloud came from originally. If it was an object that exploded, it must have been a kind of big bang on its own. Such an event, if near enough to the earth could possibly cause one of those mass extinctions through geologic time without an impact crater. Are there theories or is there evidence along these lines?

JW Albany OR

Posted: **Mon Nov 19, 2012 3:57 pm**

lakeside wrote:I always wonder though, where the mass that formed that cloud came from originally. If it was an object that exploded, it must have been a kind of big bang on its own.

It came from the debris of many exploded stars, by different mechanisms, some more violent, some less.

Such an event, if near enough to the earth could possibly cause one of those mass extinctions through geologic time without an impact crater. Are there theories or is there evidence along these lines?

A nearby supernova could certainly produce a mass extinction. It has been suggested that the Ordovician extinction event 450 million years ago might have been caused by a supernova, although there isn't good supporting evidence, and relatively few scientists think it likely.

Posted: **Tue Nov 20, 2012 8:34 am**

neufer wrote:
geckzilla wrote:
jmaiz wrote:
Hi, I am the person credited for this image. Could you please correct my name? It is "Jesús Maíz Apellániz" or "J. Maíz Apellániz", not "J. M. Apellániz". "Maíz" is not my middle name but part of my family name. You can check my web page at http://jmaiz.iaa.es and learn more about Spanish-style names at http://en.wikipedia.org/wiki/Spanish_names .
Jesús, I emailed Robert about your name. I'm sure he'll fix it as soon as he realizes the error is there.
It also needs fixing for the Nov 21, 2010 APOD.

And: http://apod.nasa.gov/apod/ap081026.html
& http://apod.nasa.gov/apod/ap061219.html

I think that these are all the same image. Isn't it?
Cheers

Starship Asterisk*

APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

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Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Cathedral to Maízive Stars

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

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Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

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Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: APOD: NGC 6357s Cathedral to Massive Stars (2012 Nov 18)

Re: Cathedral to Maízive Stars