APOD: The 37 Cluster (2024 May 14)

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APOD: The 37 Cluster (2024 May 14)

Post by APOD Robot » Tue May 14, 2024 4:06 am

Image The 37 Cluster

Explanation: For the mostly harmless denizens of planet Earth, the brighter stars of open cluster NGC 2169 seem to form a cosmic 37. Did you expect 42? From our perspective, the improbable numerical asterism appears solely by chance. It lies at an estimated distance of 3,300 light-years toward the constellation Orion. As far as galactic or open star clusters go, NGC 2169 is a small one, spanning about 7 light-years. Formed at the same time from the same cloud of dust and gas, the stars of NGC 2169 are only about 11 million years old. Such clusters are expected to disperse over time as they encounter other stars, interstellar clouds, and experience gravitational tides while hitchhiking through the galaxy. Over four billion years ago, our own Sun was likely formed in a similar open cluster of stars.

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Re: APOD: The 37 Cluster (2024 May 14)

Post by Ann » Tue May 14, 2024 5:19 am

If you have trouble seeing the 37...


...here it is! :D

APOD 14 May 2024.png

Ann


P.S. Oh, and if you're looking for 42 in the sky, this might be the best that astronomy can do for you.

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Re: APOD: The 37 Cluster (2024 May 14)

Post by workgazing » Tue May 14, 2024 7:55 am

now i see it :D

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Re: APOD: The 37 Cluster (2024 May 14)

Post by Christian G. » Tue May 14, 2024 11:37 am

Sparkling image!
NGC2169LRGBQHY183HR_c1024.jpg
And here's another stellar "3" in the same orientation! (off the tip of Canis Major's nose)
3.png
(from Stellarium)
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Re: APOD: The 37 Cluster (2024 May 14)

Post by Roy » Tue May 14, 2024 12:13 pm

Nowhere in the information supplied do they mention the classification or number of the stars in the cluster. Yet the age of the cluster is estimated to be only 11,668,000 years. Curiously short - and no leftover nebular material.

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Re: APOD: The 37 Cluster (2024 May 14)

Post by Chris Peterson » Tue May 14, 2024 1:25 pm

Roy wrote: Tue May 14, 2024 12:13 pm Nowhere in the information supplied do they mention the classification or number of the stars in the cluster. Yet the age of the cluster is estimated to be only 11,668,000 years. Curiously short - and no leftover nebular material.
About 30 stars. The cluster does lie inside a region of faint nebulosity, with wider, deeper images showing both dark nebulas and H II regions. At an age of 11 million years (not sure where your curiously precise number came from) we would expect an open cluster to have blown away most of its progenitor dust and gas. The stellar classifications vary; no reason the stars in an open cluster would have the same classification.
Chris

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Re: APOD: The 37 Cluster (2024 May 14)

Post by zendae » Tue May 14, 2024 1:55 pm

The write-up mentioned that our Sun may have been part of a cluster at one time.
Do we know where our sun was born? Was that theoretical cluster here, or did the Sun migrate to here from 'parts unknown'? Do astronomers have any theories of as to where our cluster was?

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Re: APOD: The 37 Cluster (2024 May 14)

Post by Chris Peterson » Tue May 14, 2024 1:59 pm

zendae wrote: Tue May 14, 2024 1:55 pm The write-up mentioned that our Sun may have been part of a cluster at one time.
Do we know where our sun was born? Was that theoretical cluster here, or did the Sun migrate to here from 'parts unknown'? Do astronomers have any theories of as to where our cluster was?
The cluster that the Sun formed in is long since scattered. Open clusters only last for a few tens (or at most hundreds) of millions of years. That said, I believe a few stars have been identified that possibly formed at the same time, and have been traveling nearby along with us.

Over nearly 5 billion years the entire galaxy has scrambled itself, so asking where our origin cluster was has little meaning. There's no reference system to use.
Chris

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Re: APOD: The 37 Cluster (2024 May 14)

Post by Roy » Tue May 14, 2024 3:05 pm

Chris Peterson wrote: Tue May 14, 2024 1:25 pm
Roy wrote: Tue May 14, 2024 12:13 pm Nowhere in the information supplied do they mention the classification or number of the stars in the cluster. Yet the age of the cluster is estimated to be only 11,668,000 years. Curiously short - and no leftover nebular material.
About 30 stars. The cluster does lie inside a region of faint nebulosity, with wider, deeper images showing both dark nebulas and H II regions. At an age of 11 million years (not sure where your curiously precise number came from) we would expect an open cluster to have blown away most of its progenitor dust and gas. The stellar classifications vary; no reason the stars in an open cluster would have the same classification.

The age is given in the WEBDA page for the cluster. It is linked in the introduction. Eleven million years is an eyeblink. So could A, F, G, K, M stars have all formed in that period? According to current theories of star formation? And then blown away most of the nebular afterbirth? It doesn't add up to me - as an explanation it is the broadest of brushes.

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Re: APOD: The 37 Cluster (2024 May 14)

Post by Chris Peterson » Tue May 14, 2024 3:13 pm

Roy wrote: Tue May 14, 2024 3:05 pm
Chris Peterson wrote: Tue May 14, 2024 1:25 pm
Roy wrote: Tue May 14, 2024 12:13 pm Nowhere in the information supplied do they mention the classification or number of the stars in the cluster. Yet the age of the cluster is estimated to be only 11,668,000 years. Curiously short - and no leftover nebular material.
About 30 stars. The cluster does lie inside a region of faint nebulosity, with wider, deeper images showing both dark nebulas and H II regions. At an age of 11 million years (not sure where your curiously precise number came from) we would expect an open cluster to have blown away most of its progenitor dust and gas. The stellar classifications vary; no reason the stars in an open cluster would have the same classification.

The age is given in the WEBDA page for the cluster. It is linked in the introduction. Eleven million years is an eyeblink. So could A, F, G, K, M stars have all formed in that period? According to current theories of star formation? And then blown away most of the nebular afterbirth? It doesn't add up to me - as an explanation it is the broadest of brushes.
The distance is given to four places in logarithmic notation. Your number makes little sense. The appropriate metric is "about 11 million years old". The stellar classification is determined by mass, not age. Stars of all these classifications form in about a million years. One or more original stars may even have already experienced a supernova, which is a common mechanism by which gas and dust are cleared from a region of new star formation.
Chris

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Re: APOD: The 37 Cluster (2024 May 14)

Post by florid_snow » Tue May 14, 2024 3:21 pm

Imagine if it started ticking down: "Astronomers report giant 37 in the sky is now a 36 - wait - this just in, it's 35!" Haha, feels like something that could've been in Clarke's "Nine Billion Names of God"

Roy

Re: APOD: The 37 Cluster (2024 May 14)

Post by Roy » Tue May 14, 2024 6:09 pm

Log Age

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Re: APOD: The 37 Cluster (2024 May 14)

Post by Chris Peterson » Tue May 14, 2024 6:10 pm

Roy wrote: Tue May 14, 2024 6:09 pmLog Age
What about it?
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Re: APOD: The 37 Cluster (2024 May 14)

Post by Roy » Tue May 14, 2024 6:29 pm

LOG Age = 7.067 means 10^^7.067, which on my Casio shows 11,668,096.

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Re: APOD: The 37 Cluster (2024 May 14)

Post by Chris Peterson » Tue May 14, 2024 6:33 pm

Roy wrote: Tue May 14, 2024 6:29 pm LOG Age = 7.067 means 10^^7.067, which on my Casio shows 11,668,096.
No, it means "about 11 million years". Or maybe, "about 11.5 million years". All but the first few digits are insignificant, and when you write them out it results in a misleading number, that might fool somebody into believing we actually know the age to that kind of precision. Which we don't. In fact, when you look at the literature, you'll see age estimates ranging from 7 million years to 15 million years. This number has a large uncertainty (which ideally would be provided with the number).
Chris

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Re: APOD: The 37 Cluster (2024 May 14)

Post by johnnydeep » Tue May 14, 2024 6:33 pm

Chris Peterson wrote: Tue May 14, 2024 6:10 pm
Roy wrote: Tue May 14, 2024 6:09 pmLog Age
What about it?
The link to the "webda" page mentioned (https://webda.physics.muni.cz/cgi-bin/o ... me=ngc2169) shows a "Log age" of 7.067 and 10 the power of that is about 11,668,096.17 😊

EDIT: oops: Roy beat me to it!
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Re: APOD: The 37 Cluster (2024 May 14)

Post by Chris Peterson » Tue May 14, 2024 6:34 pm

johnnydeep wrote: Tue May 14, 2024 6:33 pm
Chris Peterson wrote: Tue May 14, 2024 6:10 pm
Roy wrote: Tue May 14, 2024 6:09 pmLog Age
What about it?
The link to the "webda" page mentioned (https://webda.physics.muni.cz/cgi-bin/o ... me=ngc2169) shows a "Log age" of 7.067 and 10 the power of that is about 11,668,096.17 😊
That's because you have a cheap calculator. Mine has more digits, so I know the age of this cluster to within a few milliseconds!
Chris

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Re: APOD: The 37 Cluster (2024 May 14)

Post by johnnydeep » Tue May 14, 2024 6:36 pm

Chris Peterson wrote: Tue May 14, 2024 6:34 pm
johnnydeep wrote: Tue May 14, 2024 6:33 pm
Chris Peterson wrote: Tue May 14, 2024 6:10 pm

What about it?
The link to the "webda" page mentioned (https://webda.physics.muni.cz/cgi-bin/o ... me=ngc2169) shows a "Log age" of 7.067 and 10 the power of that is about 11,668,096.17 😊
That's because you have a cheap calculator. Mine has more digits, so I know the age of this cluster to within a few milliseconds!
I actually rounded it down. The Windows Calc app gives me 11,668,096.170609625164708884885897 !
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Re: APOD: The 37 Cluster (2024 May 14)

Post by Chris Peterson » Tue May 14, 2024 6:41 pm

johnnydeep wrote: Tue May 14, 2024 6:36 pm
Chris Peterson wrote: Tue May 14, 2024 6:34 pm
johnnydeep wrote: Tue May 14, 2024 6:33 pm

The link to the "webda" page mentioned (https://webda.physics.muni.cz/cgi-bin/o ... me=ngc2169) shows a "Log age" of 7.067 and 10 the power of that is about 11,668,096.17 😊
That's because you have a cheap calculator. Mine has more digits, so I know the age of this cluster to within a few milliseconds!
I actually rounded it down. The Windows Calc app gives me 11,668,096.170609625164708884885897 !
Cool. So we know the age of the cluster to within a few attoseconds!
Chris

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Re: APOD: The 37 Cluster (2024 May 14)

Post by johnnydeep » Tue May 14, 2024 6:52 pm

Chris Peterson wrote: Tue May 14, 2024 6:41 pm
johnnydeep wrote: Tue May 14, 2024 6:36 pm
Chris Peterson wrote: Tue May 14, 2024 6:34 pm

That's because you have a cheap calculator. Mine has more digits, so I know the age of this cluster to within a few milliseconds!
I actually rounded it down. The Windows Calc app gives me 11,668,096.170609625164708884885897 !
Cool. So we know the age of the cluster to within a few attoseconds!
I love those negative powers of 10 prefixes, from -3 to -24:
- milli, micro, nano, pico, femto, atto, zepto, yocto

To go along with the corresponding positive powers of 10 prefixes from +3 to +24:
- kilo, mega, giga, tera, peta, exa, zetta, yotta

For more, plus some example real-world comparison measurements at https://chem.libretexts.org/Bookshelves ... a_to_yocto
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Re: APOD: The 37 Cluster (2024 May 14)

Post by Ann » Tue May 14, 2024 7:48 pm

Roy wrote: Tue May 14, 2024 12:13 pm Nowhere in the information supplied do they mention the classification or number of the stars in the cluster. Yet the age of the cluster is estimated to be only 11,668,000 years. Curiously short - and no leftover nebular material.

There is a clue here that tells us that this cluster really is young, and that is the nature of its brightest star, HD 41943. This is a binary star of spectral classes B0 and B2. B0 is the hottest and most massive of the B-type stars, just below the O stars. So how bright are stars of spectral type B0 typically, if we talk about the main sequence B0 type stars (the B0V stars)? My impression - and mind you, that's my impression - is that stars of spectral class B0V are often some 800-1000 times brighter than the Sun in visible (yellow-green) light.

Now, stars get more and more luminous as they age, mostly because a larger and larger part of the entire star is involved in the process of fusion as the star ages. If a star of spectral class B is fainter than we typically expect such stars to be, and particularly if they sit inside a nebula, then we have a very good reason to believe that this star is indeed young.

Consider the ionizing star of the Cocoon Nebula, BD+46 3474, a star of spectral class B1V or B0.5V.


According to the paper, The Cocoon Nebula and its ionizing star: do stellar and nebular
abundances agree?
by J. García-Rojas et al., the estimated distance to the Cocoon Nebula and BD+46 3474 is some 800 parsecs. Coupled with the apparent V luminosity of BD+46 3474 of 9.6, that gives us an estimated absolute V magnitude of some 70 solar luminosities. Now, that is too faint, because the star is heavily reddened, but the dust reddening of yellow-green light is not nearly as bad as the dust reddening of blue light and UV light. Let's assume that BD+46 3474 has lost two magnitudes of its V light by dust reddening. Then its true V luminosity would be some 450 solar luminosities in V light. My personal gut feeling guess is that BD+46 3474 is not any brighter than that, and it could well be fainter.

So how old is BD+46 3474? According to Constellation Guide, BD+46 3474 is believed to be only 100,000 years.

Now let's return to the 37 cluster. How far away is its brightest star, binary HD 41943? Unfortunately, Gaia has not measured this star's parallax, but if we use the Gaia parallax of 1.0563 milliarcseconds for another of the 37 cluster's bright blue stars, HD 252214, convert this parallax into a distance of some 946 parsecs, and combine the distance with the apparent brightness of HD 41943, we get an absolute V luminosity for HD 41943 of about a thousand solar luminosities. That sounds reasonable. This star (or stars) is not significantly reddened, so we don't have to worry about compensating for reddening.

Still, HD 41943 is a binary star, and its companion is spectral class B2V. The magnitude of a thousand solar luminosities for HD 41943 is the combined luminosity of both of the components. That means that both components must be main sequence objects, because otherwise they would be definitely brighter, and they may just possibly be a little bit on the faint side for their spectral class. Conclusion: They are young!

But how young? Let's compare HD 41943 with one of my own favorite B0V stars, upsilon Orionis.

Upsilon Orionis Stanislav Volskiy Judy Schmidt.png
Upsilon Orionis and its Orion friends. Image credit: Stanislav Volskiy.
Annotation: Judy Schmidt

Actually, upsilon Orionis is classified as O9.7V, so it is just a little hotter and more massive than HD 41943. All other things being equal, we always expect more massive stars to give off more energy (and thus being more luminous) than less massive stars. According to the Gaia parallax of upsilon Orionis and its apparent V brightness of 4.63, its absolute V brightness is some 1,800 solar luminosities.

And then how old is upsilon Orionis? According to Wikipedia, it is 4.5 million years old. That makes it young for a star of "almost spectral class B0V but actually spectral class O9.7V", but not extremely young.

HD 41943, or at least the 37 cluster, is estimated to be some 11 million years old. Why not? That sounds reasonable to me.

But why are there red stars in the 37 cluster, if the cluster is so young? I guess it is possible that the red stars of the 37 cluster were formed a little earlier than the blue stars of the same cluster, so that they have also aged sooner. Another possibility is that HD 41943 is a blue straggler, so that it has "stolen gas" from a companion and thus rejuvenated itself, shining brighter and bluer than it would otherwise have done. Perhaps HD 41943 would have been a red star itself by now if it hadn't managed to swallow some gaseous youth potion. Who knows?

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Re: APOD: The 37 Cluster (2024 May 14)

Post by Ann » Tue May 14, 2024 7:50 pm

Chris Peterson wrote: Tue May 14, 2024 6:41 pm
johnnydeep wrote: Tue May 14, 2024 6:36 pm
Chris Peterson wrote: Tue May 14, 2024 6:34 pm

That's because you have a cheap calculator. Mine has more digits, so I know the age of this cluster to within a few milliseconds!
I actually rounded it down. The Windows Calc app gives me 11,668,096.170609625164708884885897 !
Cool. So we know the age of the cluster to within a few attoseconds!

Where is the "rolling on the floor laughing my a.. off" emoji?

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Re: APOD: The 37 Cluster (2024 May 14)

Post by johnnydeep » Tue May 14, 2024 9:04 pm

Ann wrote: Tue May 14, 2024 7:50 pm
Chris Peterson wrote: Tue May 14, 2024 6:41 pm
johnnydeep wrote: Tue May 14, 2024 6:36 pm

I actually rounded it down. The Windows Calc app gives me 11,668,096.170609625164708884885897 !
Cool. So we know the age of the cluster to within a few attoseconds!
Where is the "rolling on the floor laughing my a.. off" emoji?

Ann
Here you go: 🤣🤣🤣, or perhaps this animated gif:

Image
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Re: APOD: The 37 Cluster (2024 May 14)

Post by zendae » Wed May 15, 2024 12:14 am

Chris Peterson wrote: Tue May 14, 2024 1:59 pm

The cluster that the Sun formed in is long since scattered. Open clusters only last for a few tens (or at most hundreds) of millions of years. That said, I believe a few stars have been identified that possibly formed at the same time, and have been traveling nearby along with us.

Over nearly 5 billion years the entire galaxy has scrambled itself, so asking where our origin cluster was has little meaning. There's no reference system to use.
OK thanks Chris. Nice that there are a few possible brother-of-Sol stars.

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Re: APOD: The 37 Cluster (2024 May 14)

Post by FLPhotoCatcher » Wed May 15, 2024 7:45 am

I'm surprised no one posted this video about the number 37.

There's even more info in the comments, surprisingly.
Click to play embedded YouTube video.