APOD: Open Cluster NGC 290: A Stellar Box... (2014 Jun 08)

[APOD Robot]

Open Cluster NGC 290: A Stellar Jewel Box

Explanation: Jewels don't shine this bright -- only stars do. Like gems in a jewel box, though, the stars of open cluster NGC 290 glitter in a beautiful display of brightness and color. The photogenic cluster, pictured above, was captured recently by the orbiting Hubble Space Telescope. Open clusters of stars are younger, contain few stars, and contain a much higher fraction of blue stars than do globular clusters of stars. NGC 290 lies about 200,000 light-years distant in a neighboring galaxy called the Small Cloud of Magellan (SMC). The open cluster contains hundreds of stars and spans about 65 light years across. NGC 290 and other open clusters are good laboratories for studying how stars of different masses evolve, since all the open cluster's stars were born at about the same time.

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[Ann]

APOD Robot wrote:
Open clusters of stars are younger, contain few stars, and contain a much higher fraction of blue stars than do globular clusters of stars.

Although today's APOD is a fine picture, portraying an interesting open cluster, I wouldn't describe it as a cluster that appears to contain few stars which, of which a high fraction are blue. On the contrary, the stellar field appears to be extremely rich, and the cluster contains a surprisingly high fraction of yellow stars.

But there is an explanation:

http://cseligman.com/text/stars/starclusters.htm wrote:
About two hundred thousand light-years distant, in the Small Magellanic Cloud, are the open clusters NGC 290 (above) and NGC 265 (below). Each cluster spans about 65 light years, and contains hundreds or thousands of brilliant young stars. Most of the stars in these images are not cluster members, but lie in front of (in our own galaxy, or the Small Magellanic Cloud) or behind (in the Small Magellanic Cloud) the clusters.

Ann

[geckzilla]

Maybe try it without the extreme processing. You have to look at it considerably darker to even detect any color at all from the fainter stars. I found zooming also helped. Did not remove any charge bleeds or cosmic rays...

[Ann]

Thanks for the pictures, Geck! Very interesting. The cluster is much more obvious now, when the background is darker and the stars are not so very bright.

I still find it interesting that the cluster has three evolved red stars and "only" four bright blue stars. Clearly NGC 290 is not a prime example of a cluster that is dominated by blue stars.

As for the fact that it is hard to discern any color in the fainter stars, I think that is to be expected. The brightest of the faint stars may well be late B-type and early A-type stars, and your processing shows them to be actually blue, although the color is faint. But we are almost certainly also seeing F-type stars and possibly even G-type stars here, and they are probably quite colorless in a picture like this one.

I'm trying to guess how old a cluster like this one might be. The fact that the brightest blue stars are brighter than the brightest red stars is interesting. Very few clusters are like that. A cluster that contains many red giants is NGC 884, but that cluster is a lot richer than NGC 290. That probably also means that NGC 884 contains more massive stars than NGC 290. As for the age of NGC 884, it is estimated to be 12.8 million years according to Wikipedia. Another open cluster, M41, is also rich in red giants, but the brightest red giants here are brighter than the brightest blue stars in the cluster. Therefore M41 contains no blue supergiants or no truly massive main sequence stars. M41 is estimated to be between between 190 and 240 million years old according to Wikipedia.

Ann

[Ann]

Click to view full size image

Source: http://blogs.discovermagazine.com/badas ... 5Q269Rhlzs

A reasonable explanation for the faintness of the red stars in NGC 290 might be that they are K-type stars whose light output peaks in the red or even in the red-orange part of the spectrum, but no red filter has been used to photograph them. Instead, the filter used for this image were F439W (B), F555W (V) and F814W (I).

As you can see from the picture, a star whose surface temperature is 4,500K has a light curve which peaks in the red-orange part of the spectrum. This peak of the light curve falls well within the bandwidth of a normal broad red filter. In fact, the green filter would also detect this color. A 4,500K star photographed with "normal" RGB filter would look yellow and comparatively bright.

An M-type star is so cool that its light curve peaks in the infrared part of the spectrum. An M-type star might look bright and orange when photographed through BVI filters. But a K star is disadvantaged by having the red filter switched for an infrared one.

If the red giants of NGC 290 are relatively modest and smallish K-type giants instead of swollen, cool M-type ones, that might explain their relative faintness seen in today's APOD and in your very fine processed images, Geck.

Ann

[Boomer12k]

Aaahhhhh....JEWELS....GEMS.....I'M GONNA BE RRRIIIIIICHH!!!!!!!!! And there mine....mine, I tell you....ALL MINE!!!! AAAAH AHA AHAHA A AHAHA A!!!!!

Oh....er....um....well....you see....yeah...I got carried away again.....sorry....my bad....Really nice pic from Hubble....

Heh, heh.....

They look so close. Yet are so far way...such an assortment.

:---[===] *

[JimWWhite]

It is thought that a globular cluster is the remnant of a smaller galaxy captured by the Milky Way. So are open and closed clusters like these the results of a super-massive nova and the new stars were born in the stellar nursery and emerged when the smoke cleared?

[BDanielMayfield]

It is thought that a globular cluster is the remnant of a smaller galaxy captured by the Milky Way. So are open and closed clusters like these the results of a super-massive nova and the new stars were born in the stellar nursery and emerged when the smoke cleared?

Some globular clusters are likely to have once been parts of other smaller captured galaxies, but most were probably formed here very long ago. Open clusters form continually as long as there is enough cool dust and gas to collapse into new stars. I've never heard of a "closed" cluster.

[ta152h0]

there has to be a " giant something " doing this

[Ann]

Indeed, clusters are not closed, but they can be gravitationally bound. That is why globular clusters have not dispersed after billions of years. On the other hand, some globular clusters probably have dispersed, so that we can't detect them any more. Those clusters were not rich enough for their mutual gravitational attraction to prevent dispersion. Here is a picture of rich globular cluster M53 and sparse globular cluster NGC 5053. These clusters are made of stars with the same "ancient" chemical composition, and they were probably born at the same time, 10-12 billion years ago. But NGC 5053 likely contained less mass than M53 right from the beginning, and it is likely that NGC 5053 has been "shedding stars" at a higher rate than M53 ever since it was born.

The crucial difference between globular and open clusters is their chemical composition. Open clusters were born from "metal-enriched" gas, which gives them different characteristics than the stars in the globular clusters. They were also born at a time when there was less free gas available, making it very hard (or impossible) for open clusters to be as rich in stars as the rich globulars, such as M53. However, some open clusters are indeed rich and massive and can stay intact as a cluster for billions of years. Here you can see two open clusters, M35 and NGC 2158. On the left is bluish cluster M35. It is relatively rich for an open cluster, but nowhere near as rich as more distant, yellowish cluster NGC 2158. M35 is going to disperse long before NGC 2158 "loses its integrity as a cluster".

Ann

[Chris Peterson]

Indeed, clusters are not closed, but they can be gravitationally bound.

I think all clusters are gravitationally bound. It's just a question of strength. Globulars are tightly bound, so they evaporate slowly. Open clusters are very loosely bound, so they only survive a few tens of millions of years before all their members are perturbed away.

That is why globular clusters have not dispersed after billions of years.

Or not fully dispersed. Globular clusters are all evaporating. All are shrinking in mass. It's just a very slow process.

[neufer]

... globular clusters have not dispersed after billions of years.

Or not fully dispersed. Globular clusters are all evaporating. All are shrinking in mass. It's just a very slow process.

Not as slow as I would have thought:

<<The results of N-body simulations have shown that the stars can follow unusual paths through the cluster, often forming loops and often falling more directly toward the core than would a single star orbiting a central mass. In addition, due to interactions with other stars that result in an increase in velocity, some of the stars gain sufficient energy to escape the cluster. Over long periods of time this will result in a dissipation of the cluster, a process termed evaporation. The typical time scale for the evaporation of a globular cluster is 10¹⁰ years.>>

[DavidLeodis]

In the explanation to the fascinating picture it states the picture was "captured recently by the orbiting Hubble Space Telescope". In the Fast Facts brought up through the "pictured above" link it states the exposure date was "November 8, 2004". I would not call an image taken almost 10 years ago as "captured recently"! As the same image and explanation have been used at least 3 times I think the explanation to the APOD of June 8 2014 should have been reworded to perhaps "captured in 2004 by the orbiting Hubble Space Telescope".

[Chris Peterson]

In the explanation to the fascinating picture it states the picture was "captured recently by the orbiting Hubble Space Telescope". In the Fast Facts brought up through the "pictured above" link it states the exposure date was "November 8, 2004". I would not call an image taken almost 10 years ago as "captured recently"!

Galileo might have a different opinion on that!

Seriously, Sunday APODs are generally repeats, so they're more likely to show dated captions.

[Chris Peterson]

Not as slow as I would have thought:

Yes, it's come up before in discussions around here that the lifetime of globulars is on the same order as the age of the Universe.

[DavidLeodis]

In the explanation to the fascinating picture it states the picture was "captured recently by the orbiting Hubble Space Telescope". In the Fast Facts brought up through the "pictured above" link it states the exposure date was "November 8, 2004". I would not call an image taken almost 10 years ago as "captured recently"!

Galileo might have a different opinion on that!

Seriously, Sunday APODs are generally repeats, so they're more likely to show dated captions.

Your "Galileo might have a different opinion on that!" made me Chris.

[DavidLeodis]

In the explanation to the fascinating picture it states the picture was "captured recently by the orbiting Hubble Space Telescope". In the Fast Facts brought up through the "pictured above" link it states the exposure date was "November 8, 2004". I would not call an image taken almost 10 years ago as "captured recently"! As the same image and explanation have been used at least 3 times I think the explanation to the APOD of June 8 2014 should have been reworded to perhaps "captured in 2004 by the orbiting Hubble Space Telescope".

I've just noticed in the Fast Facts that the NGC 290 image exposure was on October 30 2004. I had erroneously given the date for NGC 265 that was also in the Hubble NewsCenter release. Apologies for giving the wrong date.

[rstevenson]

there has to be a " giant something " doing this

There is. We like to call it "gravity".

Rob