APOD: A Double Star Cluster in Perseus (2020 Nov 18)

[APOD Robot]

A Double Star Cluster in Perseus

Explanation: Most star clusters are singularly impressive. Open clusters NGC 869 and NGC 884, however, could be considered doubly impressive. Also known as "h and chi Persei", this unusual double cluster, shown above, is bright enough to be seen from a dark location without even binoculars. Although their discovery surely predates recorded history, the Greek astronomer Hipparchus notably cataloged the double cluster. The clusters are over 7,000 light years distant toward the constellation of Perseus, but are separated by only hundreds of light years. In addition to being physically close together, the clusters' ages based on their individual stars are similar - evidence that both clusters were likely a product of the same star-forming region.

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[Ann]

Observation: South appears to be up in today's APOD, because when north is up, NGC 869 (the one without red giants) is to the right of NGC 884 (the one with the red giants.

Minor nit: The caption told us that that NGC 869 and NGC 884 are of similar age, but it didn't tell us how old they are thought to be. Clue: There are no O stars left in them, which die very young, and there are five prominent red giants in one of them which take some time to evolve. On the other hand, there are some really brilliant supergiant stars in them, which don't live long. According to Wikipedia, the two clusters are believed to be around 12.8 million years old.

It's interesting to compare the Double Cluster of Perseus with the Pleiades. How can we tell that the Pleiades is older than the Double Cluster? Why, because there are no supergiant stars left in the Pleiades. The Pleiades is such a rich cluster that it must have contained at least one or two really brilliant stars in the cluster's earliest youth, but these stars are gone now.

Of course, when it comes to humans, particularly males, a young adult man is supposed to be much more powerful than pre-adolescent boys. Not so in the realm of massive stars.

Finally, can you tell what the picture at left is showing us? Yes, you can read the name of what you're seeing at the top of the picture, but don't... okay, this is the Double Cluster in infrared light. The red giants look extremely bright in infrared light, but the blue stars look puny indeed.

Ann

[neufer]

<<The Double Cluster (also known as Caldwell 14) consists of the open clusters NGC 869 and NGC 884 (often designated h Persei and χ Persei, respectively). NGC 869 has a mass of 3,700 solar masses and NGC 884 weighs in at 2,800 solar masses; however, later research has shown 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. Based on their individual stars, the clusters are relatively young, both 12.8 million years old. In comparison, the Pleiades have an estimated age ranging from 75 million years to 150 million years. There are more than 300 blue-white super-giant stars in each of the clusters. The clusters are also blueshifted, with NGC 869 approaching Earth at a speed of 39 km/s and NGC 884 approaching at a similar speed of 38 km/s. Their hottest main sequence stars are of spectral type B0. NGC 884 includes five prominent red supergiant stars, all variable and all around 8th magnitude: RS Persei, AD Persei, FZ Persei, V403 Persei, and V439 Persei.>>

[E Fish]

I feel like most people's comments on the images we get are so intelligent and/or clever and I'm like, "Oooh, pretty!" I was very pleased with myself that I recognized the Double Cluster before I scrolled down to the caption, though.

[BDanielMayfield]

One night decades ago I came across the Double Cluster by accident while randomly scanning the sky with a pair of new binoculars. It was quite impressive!

[orin stepanek]

Double Cluster is nice; maybe connected by the smaller stars in-between!??
Are the golden stars part of the cluster? They must be a lot older!

Ann; aren't identical twins supposed to look alike? Or did something change
during their growing?

[johnnydeep]

A Double Star Cluster in Perseus

Explanation: Most star clusters are singularly impressive. Open clusters NGC 869 and NGC 884, however, could be considered doubly impressive. Also known as "h and chi Persei", this unusual double cluster, shown above, is bright enough to be seen from a dark location without even binoculars. Although their discovery surely predates recorded history, the Greek astronomer Hipparchus notably cataloged the double cluster. The clusters are over 7,000 light years distant toward the constellation of Perseus, but are separated by only hundreds of light years. In addition to being physically close together, the clusters' ages based on their individual stars are similar - evidence that both clusters were likely a product

So, the "double cluster" link to Wikipedia - https://en.wikipedia.org/wiki/Double_Cluster - acts like this is the only double cluster known to exist. Is that true? Google searches for "double star cluster" also seem to imply that there is only one. Do we really not know of any others? And for that matter, considering the proliferation of double, triple, and higher multiple star systems, I would think there should be lots of double and even triple clusters out there.

[Ann]

DoubleCluster_Polanski_960.jpg


Double Cluster is nice; maybe connected by the smaller stars in-between!??
Are the golden stars part of the cluster? They must be a lot older!

Ann; aren't identical twins supposed to look alike? Or did something change
during their growing?

No, the golden stars are almost certainly the same age as the bright blue stars. For some reason, the golden stars turned into red giants sooner than the bright still-blue ones. The most likely reason has to do with mass, because more massive stars will use up their core hydrogen sooner and turn into red giants sooner.

In any case, there are very many young clusters which are nevertheless old enough that at least one of the members has turned into a red giant. Take a look at these examples:

Star cluster Messier 6. Photo: CELESTIAL IMAGE CO. / SCIENCE PHOTO LIBRARY.

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Star cluster Messier 7. Photo: azzkicker7283.

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There are many more examples of mainly blue clusters where one or a few of the stars have turned into red giants, for example M11, M35, M37, M38, M41, M52, M67 and many others.

As for the twin boys, Orin, maybe they have learnt to smile differently! They have slightly different hairstyles, too, and different glasses!

Ann

[Ann]

A Double Star Cluster in Perseus

Explanation: Most star clusters are singularly impressive. Open clusters NGC 869 and NGC 884, however, could be considered doubly impressive. Also known as "h and chi Persei", this unusual double cluster, shown above, is bright enough to be seen from a dark location without even binoculars. Although their discovery surely predates recorded history, the Greek astronomer Hipparchus notably cataloged the double cluster. The clusters are over 7,000 light years distant toward the constellation of Perseus, but are separated by only hundreds of light years. In addition to being physically close together, the clusters' ages based on their individual stars are similar - evidence that both clusters were likely a product

So, the "double cluster" link to Wikipedia - https://en.wikipedia.org/wiki/Double_Cluster - acts like this is the only double cluster known to exist. Is that true? Google searches for "double star cluster" also seem to imply that there is only one. Do we really not know of any others? And for that matter, considering the proliferation of double, triple, and higher multiple star systems, I would think there should be lots of double and even triple clusters out there.

The Tarantula Nebula with large open cluster NGC 2070, at the center of which is compact massive cluster R136. An older, less massive cluster, Hodge 301, is at upper right. Photo: ESO.

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The Double Cluster of Perseus. The two clusters are both massive and very much alike. Photo: Greg Polanski.

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We see a lot of triggered star formation in regions fertile for star birth, but what is unusual (and to my knowledge, unique) about the Double Cluster is that they seem to be the same age and more or less the same size, as if they were born at the same time, and both contained more or less the same mass and the same number of stars. I don't think we see that anywhere else in the Local Group, or at least not in the Milky Way and its satellites.

Take a look at the picture at left. The compact core of star cluster NGC 2070, R136, is (or so I believe) the most massive young cluster known in the local group. But there is another cluster moderately nearby, Hodge 301, which, however, is not a "twin" of R136.

Wikipedia wrote:

Hodge 301, along with the cluster R136, is one of two major star clusters situated in the Tarantula Nebula, a region which has seen intense bursts of star formation over the last few tens of millions of years. R136 is situated in the central regions of the nebula, while Hodge 301 is located about 150 light years away, to the north west as seen from Earth. Hodge 301 was formed early on in the current wave of star formation, with an age estimated at 20-25 million years old, some ten times older than R136.[2]

Ann

[neufer]

Are the golden stars part of the cluster? They must be a lot older!

Ann; aren't identical twins supposed to look alike?
Or did something change during their growing?

No, the golden stars are almost certainly the same age as the bright blue stars. For some reason, the golden stars turned into red giants sooner than the bright still-blue ones. The most likely reason has to do with mass, because more massive stars will use up their core hydrogen sooner and turn into red giants sooner.

[Chris Peterson]

Ann; aren't identical twins supposed to look alike? :?: Or did something change
during their growing?

At birth, identical twins will look nearly identical... although even then you may detect slight differences. But our bodies are the product of both nature and nurture. It isn't at all uncommon for the appearances of identical twins to deviate from each other as they grow older.

[BDanielMayfield]

A Double Star Cluster in Perseus

Explanation: Most star clusters are singularly impressive. Open clusters NGC 869 and NGC 884, however, could be considered doubly impressive. Also known as "h and chi Persei", this unusual double cluster, shown above, is bright enough to be seen from a dark location without even binoculars. Although their discovery surely predates recorded history, the Greek astronomer Hipparchus notably cataloged the double cluster. The clusters are over 7,000 light years distant toward the constellation of Perseus, but are separated by only hundreds of light years. In addition to being physically close together, the clusters' ages based on their individual stars are similar - evidence that both clusters were likely a product

So, the "double cluster" link to Wikipedia - https://en.wikipedia.org/wiki/Double_Cluster - acts like this is the only double cluster known to exist. Is that true? Google searches for "double star cluster" also seem to imply that there is only one. Do we really not know of any others? And for that matter, considering the proliferation of double, triple, and higher multiple star systems, I would think there should be lots of double and even triple clusters out there.

Based on your search Johnny this probably is the only example of such a pairing in our limited field of view. Other pairs of clusters could certainly exist in parts of the MW that are blocked from our vantage.

But these are open star clusters, which means that the individual stars are unbound, and so are dispersing over time. Open star clusters are therefore transitory phenomena. And if the stars are unbound gravitationally, I’d guess that these two clusters aren’t bound together either.

Bruce

[johnnydeep]

Thank you Ann and Bruce. So the conclusion I take from this is that this double (open) cluster in Perseus really is unique, in that the two separate clusters are about the same size and age, and are physically close to each other (not just optically).

[Ann]

So, the "double cluster" link to Wikipedia - https://en.wikipedia.org/wiki/Double_Cluster - acts like this is the only double cluster known to exist. Is that true? Google searches for "double star cluster" also seem to imply that there is only one. Do we really not know of any others? And for that matter, considering the proliferation of double, triple, and higher multiple star systems, I would think there should be lots of double and even triple clusters out there.

Based on your search Johnny this probably is the only example of such a pairing in our limited field of view. Other pairs of clusters could certainly exist in parts of the MW that are blocked from our vantage.

But these are open star clusters, which means that the individual stars are unbound, and so are dispersing over time. Open star clusters are therefore transitory phenomena. And if the stars are unbound gravitationally, I’d guess that these two clusters aren’t bound together either.

Bruce

Diffuse globular cluster NGC 5053 (left) and rich globular cluster M53 (right). Photo: Bart Delsaert.

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Interesting observation about the dispersal of open clusters, Bruce. I actually think that h and chi Persei stand a better chance than most open clusters to stay moderately intact for a long time. These clusters are massive as open clusters go, and they are located in the Perseus arm, at a fairly safe distance from the sound and the fury of the inner parts of the Milky Way.

Anyway, I was reminded of a fascinating "double cluster" among globulars, M53 and NGC 5053. Even their designations sound vaguely fraternal. These two globulars are situated quite close to one another in the sky, and there is a bridge of material between them, so there is some interaction going on between them.

Both globulars are extremely metal-poor, especially NGC 5053.

Wikipedia wrote about NGC 5053:

This is a metal-poor cluster, meaning the stars have a low abundance of elements other than hydrogen and helium—what astronomers term metallicity. As recently as 1995, it was considered the most metal-poor globular cluster in the Milky Way.The chemical abundances of the stars in NGC 5053 are more similar to those in the dwarf galaxy Sagittarius Dwarf Spheroidal Galaxy than to the Milky Way halo. Along with the kinematics of the globular cluster, this suggests that NGC 5053 may have been stripped from the dwarf galaxy.

Wikipedia wrote about M53:

This is considered a metal-poor cluster and at one time was thought to be the most metal-poor cluster in the Milky Way.

So both these clusters are metal-poor, but their metallicity is clearly not the same, so I find it unlikely that they were born out of the same nebula. And I find it very hard to believe that these two clusters have orbited the center of the Milky Way in tandem for as long as they have existed. Because these are a pair of Methuselahs, some 12.67 billion years for M53 and 12.3±0.7 billion years for NGC 5053, according to Wikipedia.

Just think: The two clusters of the Double Cluster of Perseus are believed to be 12.8 million years old. Well, M53 and NGC 5053 are about a thousand times older.

Ann

Old open cluster M67. Photo: Bob Franke.

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By the way, the oldest of the Messier open clusters, M67, is located in or near the Perseus arm of our galaxy, or so I believe. M67 is some ~4 billion years old and located pretty far away from the hustle and bustle of the center of the Galaxy. As are h and chi Persei.

[orin stepanek]

Ann; aren't identical twins supposed to look alike? Or did something change
during their growing?

At birth, identical twins will look nearly identical... although even then you may detect slight differences. But our bodies are the product of both nature and nurture. It isn't at all uncommon for the appearances of identical twins to deviate from each other as they grow older.

OK I agree; but those two boys aren't gonna fool anyone by exchanging places!

[Ann]

Ann; aren't identical twins supposed to look alike? Or did something change
during their growing?

At birth, identical twins will look nearly identical... although even then you may detect slight differences. But our bodies are the product of both nature and nurture. It isn't at all uncommon for the appearances of identical twins to deviate from each other as they grow older.

OK I agree; but those two boys aren't gonna fool anyone by exchanging places!

Picture-21.png
These are harder to tell apart; and yes there are some differences!

Pictures taken from Image resulys

Okay Orin, you may be right that those two 12-year-old boys aren't identical twins! I can't find the original picture now, because I took a screenshot and uploaded it to my computer in case the boys' Mom wasn't happy that I nicked the portrait of her sons and prevented me from using it here at Starship Asterisk*.


So yes, those boys may be fraternal twins. But really, doesn't that make them an even better metaphor for the Double Cluster? Because h and chi Persei aren't identical twins either. They are fraternal twins, that's for sure!

Ann