APOD: Three Clusters in Puppis (2022 Feb 18)

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APOD: Three Clusters in Puppis (2022 Feb 18)

Post by APOD Robot » Fri Feb 18, 2022 5:05 am

Image Three Clusters in Puppis

Explanation: Galactic or open star clusters are young. The swarms of stars are born together near the plane of the Milky Way, but their numbers steadily dwindle as cluster members are ejected by galactic tides and gravitational interactions. Caught in this telescopic frame over three degrees across are three good examples of galactic star clusters, seen toward the southern sky's nautical constellation Puppis. Below and left, M46 is some 5,500 light-years in the distance. Right of center M47 is only 1,600 light-years away and NGC 2423 (top) is about 2500 light-years distant. Around 300 million years young M46 contains a few hundred stars in a region about 30 light-years across. Sharp eyes can spot a planetary nebula, NGC 2438, at about 11 o'clock against the M46 cluster stars. But that nebula's central star is billions of years old, and NGC 2438 is likely a foreground object only by chance along the line of sight to youthful M46. Even younger, aged around 80 million years, M47 is a smaller and looser star cluster spanning about 10 light-years. Star cluster NGC 2423 is pushing about 750 million years in age though. NGC 2423 is known to harbor an extrasolar planet, detected orbiting one of its red giant stars.

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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by Ann » Fri Feb 18, 2022 9:24 am

I would love to write a lot about today's APOD and the fascinating properties of clusters, but I have no time!

ThreeClustersPuppis1024[1].jpg
Three Clusters in Puppis.
Image Credit & Copyright: Dave Doctor

So I'll just say this: You can tell at a glance that M47 (80 million years old) is a young cluster, because its brightest stars are all blue, and the brightest stars stand out as being much brighter than the other cluster members. That is because these stars are massive, and massive stars shine bright and blue when they are young, but they burn out soon and fade and die. Okay, first they turn into bright red giants.

There are red giants in M47, but they are fainter than the brightest blue stars. I frankly can't explain that, unless the brightest blue stars are blue stragglers that have gained mass from a companion. But this seems unlikely based on the fact that there are at the very least four stars that stand out as bright and blue, and they can't all be blue stragglers. So to me it is the faint red giants that are mysterious.

As for M46, 300 years old, it is very rich in stars that are relatively similar in brightness. Many stars are obviously blue, but there are several red giants there too, which appear to be about equally bright as the blue stars. M46 therefore looks like a cluster where a number of intermediate-mass blue stars have begun to naturally transform into red giants.

In NGC 2423, the blue stars frankly aren't blue. NGC 2423 is about 750 million years old, and there are no B-type stars left in it, and probably not too many (or any) early A-type stars Sirius and Vega, either. Note, too, that even though NGC 2423 is closer to us than M46 its stars look fainter. That is because the stars in it are fainter, because more and more of a cluster's bright and massive stars will die as the cluster ages.

Note, too, that even though NGC 2423 obviously started out as a rich cluster, it looks as if it is beginning to disperse.

Ann
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Last edited by Ann on Fri Feb 18, 2022 7:28 pm, edited 1 time in total.
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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by heehaw » Fri Feb 18, 2022 10:42 am

Lovely!

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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by orin stepanek » Fri Feb 18, 2022 12:40 pm

ThreeClustersPuppis1024.jpg
Wow:What a Hodgepodge of stars!🤩
More staars than you can shake a stick at! :mrgreen:
Like grains of sand on a beach! :lol2:
It'd be pretty hard to count them!
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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by bystander » Fri Feb 18, 2022 3:11 pm

Ann wrote: Fri Feb 18, 2022 9:24 am...
In NGC 2438, the blue stars frankly aren't blue. NGC 2438 is about 750 million years old, and there are no B-type stars left in it, and probably not too many (or any) early A-type stars Sirius and Vega, either. Note, too, that even though NGC 2438 is closer to us than M46 its stars look fainter. That is because the stars in it are fainter, because more and more of a cluster's bright and massive stars will die as the cluster ages.

Note, too, that even though NGC 2438 obviously started out as a rich cluster, it looks as if it is beginning to disperse. ...

NGC 2438 is a planetary nebula in the foreground of M46. NGC 2423 is the third star cluster.
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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by Ann » Fri Feb 18, 2022 7:26 pm

bystander wrote: Fri Feb 18, 2022 3:11 pm
Ann wrote: Fri Feb 18, 2022 9:24 am...
In NGC 2438, the blue stars frankly aren't blue. NGC 2438 is about 750 million years old, and there are no B-type stars left in it, and probably not too many (or any) early A-type stars Sirius and Vega, either. Note, too, that even though NGC 2438 is closer to us than M46 its stars look fainter. That is because the stars in it are fainter, because more and more of a cluster's bright and massive stars will die as the cluster ages.

Note, too, that even though NGC 2438 obviously started out as a rich cluster, it looks as if it is beginning to disperse. ...

NGC 2438 is a planetary nebula in the foreground of M46. NGC 2423 is the third star cluster.
Thanks, bystander, and sorry for the mistake.
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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by Ann » Fri Feb 18, 2022 8:54 pm

Wait a minute!!!
APOD Robot wrote:

Sharp eyes can spot a planetary nebula, NGC 2438, at about 11 o'clock against the M46 cluster stars. But that nebula's central star is billions of years old, and NGC 2438 is likely a foreground object only by chance along the line of sight to youthful M46.
ESA/Hubble wrote:

Planetary nebulae only last for about 20 000 years, making them a very short-lived part of the stellar life cycle.
Therefore a planetary nebula can't be billions of years old! That's impossible! So, are astronomers saying that the ionizing star of this planetary nebula was billions of years old when it turned into a white dwarf? The central star of the planetary nebula was, like, a Sunlike star, or maybe possibly maybe a late F-type star, living for billions of years, until it finally became a white dwarf so that it could ionize a planetary nebula?

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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by johnnydeep » Fri Feb 18, 2022 10:00 pm

Ann wrote: Fri Feb 18, 2022 8:54 pm Wait a minute!!!
APOD Robot wrote:

Sharp eyes can spot a planetary nebula, NGC 2438, at about 11 o'clock against the M46 cluster stars. But that nebula's central star is billions of years old, and NGC 2438 is likely a foreground object only by chance along the line of sight to youthful M46.
ESA/Hubble wrote:

Planetary nebulae only last for about 20 000 years, making them a very short-lived part of the stellar life cycle.
Therefore a planetary nebula can't be billions of years old! That's impossible! So, are astronomers saying that the ionizing star of this planetary nebula was billions of years old when it turned into a white dwarf? The central star of the planetary nebula was, like, a Sunlike star, or maybe possibly maybe a late F-type star, living for billions of years, until it finally became a white dwarf so that it could ionize a planetary nebula?

Ann
WikiPedia quoth:
https://en.wikipedia.org/wiki/NGC_2438 wrote:The nebula consists of material ejected from the central star during the asymptotic giant branch stage, beginning some 8,500 years ago. The main nebula was formed at about half that age.[8] The central star of this planetary nebula is a 17.7-magnitude white dwarf,[3] with surface temperature of about 75,000 K (74,700 °C).[10] It is one of the hottest stars known.
And following that link:
https://en.wikipedia.org/wiki/Asymptotic_giant_branch wrote:The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) late in their lives.
Does that not explain it?
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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by Ann » Sat Feb 19, 2022 4:58 am

johnnydeep wrote: Fri Feb 18, 2022 10:00 pm
Ann wrote: Fri Feb 18, 2022 8:54 pm Wait a minute!!!
APOD Robot wrote:

Sharp eyes can spot a planetary nebula, NGC 2438, at about 11 o'clock against the M46 cluster stars. But that nebula's central star is billions of years old, and NGC 2438 is likely a foreground object only by chance along the line of sight to youthful M46.
ESA/Hubble wrote:

Planetary nebulae only last for about 20 000 years, making them a very short-lived part of the stellar life cycle.
Therefore a planetary nebula can't be billions of years old! That's impossible! So, are astronomers saying that the ionizing star of this planetary nebula was billions of years old when it turned into a white dwarf? The central star of the planetary nebula was, like, a Sunlike star, or maybe possibly maybe a late F-type star, living for billions of years, until it finally became a white dwarf so that it could ionize a planetary nebula?

Ann
WikiPedia quoth:
https://en.wikipedia.org/wiki/NGC_2438 wrote:The nebula consists of material ejected from the central star during the asymptotic giant branch stage, beginning some 8,500 years ago. The main nebula was formed at about half that age.[8] The central star of this planetary nebula is a 17.7-magnitude white dwarf,[3] with surface temperature of about 75,000 K (74,700 °C).[10] It is one of the hottest stars known.
And following that link:
https://en.wikipedia.org/wiki/Asymptotic_giant_branch wrote:The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) late in their lives.
Does that not explain it?
Yes, it explains that the star that created the planetary nebula started out as a low- to intermediate-mass stars (about 0.5 to 8 solar masses)! :D :wink: Thanks! ❤️

Honestly though, there is a huge, huge difference between a 0.5 and an 8 solar masses star. An 8 solar masses star is certainly massive enough to have evolved into a white dwarf even in a cluster as young as M47, whereas, by contrast, a 0.5 solar masses star is too light-weight to have exhausted its core hydrogen during the ~14 billion years that the Universe has so far existed.

Click to play embedded YouTube video.

In this video, astronomer Mike Merrifield describes the properties and progenitor star mass of a white dwarf belonging to M47, which is (as you know) the youngest of the clusters in this APOD.

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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by bystander » Sat Feb 19, 2022 5:48 am

The planetary nebula isn't in M47, nor even in M46 as it appears, but just inline with it somewhere between M46 and Earth. The age of M46 has nothing to do with the age of the progenitor star of the nebula.
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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by Ann » Sat Feb 19, 2022 8:08 am

I didn't have time yesterday, but I can't resist posting a few clusters and commenting on their ages!


Yeah, yeah, we all know about the Hyades and the Pleiades. Nevertheless, it is still interesting to see a good color photo like Alson Wong's, where you can really see that the stars of the Pleiades, some 100 million years old, are blue, whereas the stars of the Hyades, some 650 (or possibly 790) million years old, don't look blue in this picture. (Admittedly a number of them are much bluer than the Sun.) Also note that even though the Pleiades stars are more than twice as far away as the stars of the Hyades - some 440 light-years versus 153 light-years - the stars of the Pleiades look just as bright, or brighter, than the stars of the Hyades. You've got to remember that bright red giant Aldebaran isn't a member of the Hyades, but instead a foreground star. So not only are the stars of the Pleiades bluer, but they are intrinsically much brighter, too.

To me it is a bit of a mystery that there ar no red giants in the Pleiades. They are certainly old enough for at least one of their members to have turned into a red giant, and moreover, the Pleiades is a sufficiently rich cluster that we have reason to believe it started out with at least one or two members that were more massive than the present luminary of the Seven Sisters, Alcyone, whose mass according to Wikipedia is 5.9-6.1 M. If the Pleiades originally contained a star of 8 M, then that star should have evolved into a white dwarf by now, after first having gone through its red giant stage.

Perhaps that is what happened. Perhaps there once was an 8 M star in the Pleiades that turned into a bright red giant and then shrank into a tiny and faint white dwarf. I don't know if there are any confirmed white dwarfs in the Pleiades, but there are definitely white dwarfs in the Hyades.

All right. Let's look at Alson Wong's picture again. Can you see that there is a small, faint cluster to the upper left (northeast) of the Hyades? That is NGC 1657. How old is that cluster?


When you first look at this image, you may ask yourself, where's the cluster? But if you enlarge the picture you will see it in the center of the image. Roberto Mura's image is a good color picture, and if you compare the color of stars in the cluster with the yellow and reddish stars in the foreground, you can clearly see that the stars in NGC 1647 are not red or even yellow. You must bear in mind, too, that NGC 1647 is quite distant, some 1800 light-years, some 4 times more distant than the Pleiades and more than 10 times more distant than the Hyades. Therefore we should expect the stars of NGC 1647 to be reddened, and they are, but they still don't look yellow.

So we should conclude that this cluster is young, and it is, according to Wikipedia: It is some 150 million years, so it's a bit older than the Pleiades, but much younger than the Hyades. But there are indeed orange stars seen at the outskirts of NGC 1647 that may be members of the clusters, and if so, stellar evolution into red gianthood has started in NGC 1647.


Let's compare the Hyades and the Beehive Cluster, M44!

The Hyades Bijan Moravej alahkami.png
The Hyades. Photo: Bijan Moravej alahkami
M44 Jakub Korbel.png
M44. Photo: Jakub Korbel.

Can you see that these two clusters, the Hyades at left and the Beehive Cluster, M44, at right, are of similar ages? M44, the Beehive Cluster, is estimated to be 600–700 million years old, according to Wikipedia, similar to the Hyades. But M44 is a little more massive than the Hyades.

It is harder to "see" the Hyades than M44, because bright foreground star Aldebaran is so distracting, and there is quite some dust along our line of sight to the Hyades, and there is a really non-negligent population of background Milky Way stars there, too. M44 is much easier, because it is much more detached from the band of the Milky Way, and there is no dust in the vicinity and no bright foreground stars. But can you see that the proportion of bluish and orange bright stars is about the same in both M44 and the Hyades? Also the bluish and the orange stars are about equally bright - this is again easier to see in the picture of M44.

Jakub Korbel's picture of M44 is great. Do note the profusion of faintly reddish stars peppering the image. In my opinion, these are most likely faint and low-mass members of M44.


Let's look at another one!


Take a look at NGC 3293 in Carina and the Double Cluster of Perseus! Can you see, or guess, that these cluster are of smilar ages?

All the red nebulosity in the vicinity of NGC 3293, plus the cluster's compact size, high number of bright blue stars, plus one bright red member, strongly suggests that this is a cluster of really massive stars, and therefore it must be young. According to Wikipedia it is about 12 million years old, and its brightest, hottest members are blue supergiants of spectral class B0, which would be similar to the the bright blue stars in Orion's Belt. But there is also an M-type supergiant in the cluster, which would be similar to Betelgeuse.

The Double Cluster in Perseus looks different, particularly because there is no nebulosity in its vicinity. But the central parts of the member clusters are compact and bright, and there are a few bright red supergiants scattered among the blue stars, which have been reddened to a white color.

According to Wikipedia, the two clusters of the Double Cluster, NGC 869 and NGC 884, are both 14 million years old. Their hottest main sequence members are said to be of spectral class B0. In NGC 3293, the brightest star is a supergiant of spectral class B0. Since blue supergiant stars are always a little cooler than the main sequence stars they evolved from, this means that NGC 869 and NGC 884 are a little further along in their evolution than NGC 3293.

NGC 869 and NGC 884 are very massive:
Wikipedia wrote:

NGC 869 has a mass of 4,700 solar masses and NGC 884 weighs in at 3,700 solar masses; both clusters are surrounded with a very extensive halo of stars, with a total mass for the complex of at least 20,000 solar masses.
That's a lot! NGC 3293 is less massive: Wikipedia puts its mass at 1457 M. Perhaps the higher mass of the Double Cluster explains why all the gas in the vicinity has either been used up or "blown away".


The most remarkable cluster in the Local Group of galaxies is R136 in the Large Magellanic Cloud:


R136 is an incredible cluster. Not only are there hundreds of blue stars in it, but there are hundreds of O-type stars!

Wikipedia wrote:

R136 is thought to be less than 2 million years old. None of the member stars is significantly evolved and none is thought to have exploded as supernova. The brightest stars are WNh, O supergiants, and OIf/WN slash stars, all extremely massive fully convective stars. There are no red supergiants, blue hypergiants, or luminous blue variables within the cluster. A small number of class B stars have been detected in the outskirts of the cluster, but less massive and less luminous stars cannot be resolved from the dense cluster core at the large distance of the LMC.
Wowzers! :shock:
Wikipedia wrote:

The cluster contains many of the most massive and luminous stars known, including R136a1. Within the central 5 parsecs there are 32 of the hottest type O stars (O2.0–3.5), 40 other O stars, and 12 Wolf-Rayet stars, mostly of the extremely luminous WNh type. Within 150 parsecs there are a further 325 O stars and 19 Wolf-Rayet stars.
Wowzers! :shock:

We can indeed see that R136 is a massive, fantastic cluster. We can see from the Hubble image that it contains huge numbers of stars that are all blue, except one red star near the top of the "cavity"(?) to the left of R136 proper in the Hubble image. Otherwise, though, there is a myriad of blue stars, and at the center of the extended cluster is a very tight and compact core. No lightweight or old cluster can ever look like that!

Well, I could go on - I'd really love to discuss one of the greatest clusters in the Milky Way, NGC 3603, but hey - I'll just post a picture of it and leave it for you to google it, okay?


Ann
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Re: APOD: Three Clusters in Puppis (2022 Feb 18)

Post by XgeoX » Sat Feb 19, 2022 12:16 pm

The image is three degrees across which illustrates that the full moon at about one half degree would fit neatly in between all three clusters. This gives you a nice idea of the size of this beautiful triplet in the sky!

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