APOD: M7: Open Star Cluster in Scorpius (2014 Jan 07)

[Chris Peterson]

I am still happy with " visible are literally millions of stars". I would also be content with the addition "many thousands of which are resolved".

I have no complaint with the wording of the caption. But neither have I any complaint with a mildly pedantic comment about that wording that serves to illustrate some important ideas.

[Nitpicker]

I have no complaint with the wording of the caption. But neither have I any complaint with a mildly pedantic comment about that wording that serves to illustrate some important ideas.

Yes, muehlner's comment (and yours) certainly helped me to resolve my understanding of the matter.

[Anthony Barreiro]

This is a breathtakingly beautiful image. In addition to the bright young stars of M7 and the the distant glow of millions of stars (plus or minus an order of magnitude) I'm also captivated by the sinuous, clumpy dark dust lanes. I wonder what's going on in there?

[MarkBour]

Beautiful image. I liked starsurfer's characterization: "... glittering sapphires on the golden galactic beach".

As usual, here's a post full of questions ...

I assume the blue-ish stars are the cluster, and are at about 1000 light-years away, as the caption described. But around the core of the cluster, one sees other blue stars, smaller and spreading far and wide. Also, there are a few large yellow-hued stars in the image, and then again, some smaller, and it seems that for the yellows at least, the field of view holds a vast number of them.
Q1: Are the large yellow stars as close as the large blue stars?
Q2: Are the large yellow stars part of this cluster?
Q3: I'm assuming most of these small yellow dots are stars in the further part,
perhaps a spiral arm of the Milky Way, and I am guessing they are some
10-20 times as far away as the M7 cluster. Is that correct?
Q4: I wonder about them. As dense as they appear, are they actually separated on average by
greater distances than the stars in the M7 cluster?

And finally, suppose an instrument like the Kepler space telescope were pointed at this region. Would it be able to watch these stars for light variations, to hunt for planets, or is there just too much light coming from this area for it to work? I had heard that Kepler had been pointed at a relatively dark area, with fewer stars in view.

[Ann]

Beautiful image. I liked starsurfer's characterization: "... glittering sapphires on the golden galactic beach".

As usual, here's a post full of questions ...

I assume the blue-ish stars are the cluster, and are at about 1000 light-years away, as the caption described. But around the core of the cluster, one sees other blue stars, smaller and spreading far and wide. Also, there are a few large yellow-hued stars in the image, and then again, some smaller, and it seems that for the yellows at least, the field of view holds a vast number of them.
Q1: Are the large yellow stars as close as the large blue stars?
Q2: Are the large yellow stars part of this cluster?
Q3: I'm assuming most of these small yellow dots are stars in the further part,
perhaps a spiral arm of the Milky Way, and I am guessing they are some
10-20 times as far away as the M7 cluster. Is that correct?
Q4: I wonder about them. As dense as they appear, are they actually separated on average by
greater distances than the stars in the M7 cluster?

And finally, suppose an instrument like the Kepler space telescope were pointed at this region. Would it be able to watch these stars for light variations, to hunt for planets, or is there just too much light coming from this area for it to work? I had heard that Kepler had been pointed at a relatively dark area, with fewer stars in view.

Yes, the three largest yellow stars are as close as the large blue stars, and they are members of the same cluster. They have the same parallax as the large blue stars, which shows that they are as far away as the blue stars, and they have the same proper motion as the large blue stars, which means that they move in the same direction across the sky as the large blue stars.

The small yellow dots are parts of the bulge of the Milky Way. They may indeed be 10-20 times as far away as cluster M7. Not all the stars that we see in the bulge are at the same distance from us either. The stars that appear to form a dense wall of stars are actually superimposed on one another at various distances from us.

The stars in the bulge of the Milky Way are relatively close together. Take a look at this image of the Milky Way. The bulge is the brightest-looking part of it. Why is it so bright? Because the stars in it are very bright themselves? No, most of the stars in the bulge are quite faint. The bulge is bright because it contains such a large number of stars, and the average distance between them is smaller than the distance between stars in the disk.

However, stars in a cluster are also closer to one another than the average stars in the disk. However, cluster M7 is larger than it immediately appears to be, and the stars in the outskirts of the cluster are not as close together as the stars nearer the cluster center. When it comes to the average separation between the stars in the bulge (which varies with the distance from the galactic core, remember) and the average separation between the stars in M7, I'm afraid I can't help you.

Ann

[BDanielMayfield]

And finally, suppose an instrument like the Kepler space telescope were pointed at this region. Would it be able to watch these stars for light variations, to hunt for planets, or is there just too much light coming from this area for it to work? I had heard that Kepler had been pointed at a relatively dark area, with fewer stars in view.

Mark, since no one else has addressed your last paragraph I’ll take a stab at it. I don’t see why a Kepler-like space telescope couldn’t be pointed at a region like this one closer to the core of our galaxy. Continually staring long enough (by a robot satellite, of course) at a star packed area like this would very likely reveal tens of thousands of exoplanets by the transit method, and maybe dozens of rogue planets also via gravitational microlensing. I hope something like what you supposed is in the works, although I haven’t heard of such a plan yet.

Kepler wasn’t pointed at as rich a star field as today’s apod, but it wasn’t exactly pointed at a dark area either. There were about 156,000 targeted stars in its data set! It was designed to look for earth-like planets in earth-like orbits around sun-like stars back in the day when the presence of planets around stars couldn’t be taken for granted like it is now. If you go to the Kepler mission’s main webpage at http://kepler.nasa.gov the center illustration shows the Kepler Field of View that shows where it was pointed at in Cygnus. This location was chosen for it’s similarity to our Sun’s location in the Milky Way.

I hope that helped Mark. If anyone knows why what he supposed couldn’t be done I’d like to know too, and if it can be done, is anything like this in the works? And if not, why not, because it seems like a very attractive idea.

Bruce

[Tom Ferry]

I wonder what its like there in that cluster? Our closest neighbor is the Alpha Centauri system and that is just a bright binary system in the Big Dipper. But there you have 1000 stars all within 25 light years of each other? and many of them are raging Blue Giants?
I imagine that would set new records in light polution

[Nitpicker]

I wonder what its like there in that cluster? Our closest neighbor is the Alpha Centauri system and that is just a bright binary system in the Big Dipper. But there you have 1000 stars all within 25 light years of each other? and many of them are raging Blue Giants?
I imagine that would set new records in light polution

Perhaps all true, except that the Alpha Centauri system (which is most likely to be a trinary system including Proxima Cen [or Alpha Cen C]) is in the southern constellation Centaurus, whilst the Big Dipper is in the northern constellation Ursa Major. Those blue stars, they might be giants, I don't really know, but I like their albums.

[Tom Ferry]

ah oupseedoo ...Centauri ...Centaurus..go figure ! =)

and I think that the nomiker "Proxima" would indicate that Proxima Cen would actually be the one that orbits closest to us?

[Nitpicker]

and I think that the nomiker "Proxima" would indicate that Proxima Cen would actually be the one that orbits closest to us?

At least for the next ~25,000 years:

Click to view full size image

I think Alpha Cen A and B orbit each other and are known as binary system Alpha Cen AB. Alpha Cen C (Proxima) is understood to orbit Alpha Cen AB.

[Ann]

ah oupseedoo ...Centauri ...Centaurus..go figure ! =)

and I think that the nomiker "Proxima" would indicate that Proxima Cen would actually be the one that orbits closest to us?

Yes, Proxima is the one that is closest to us. Proxima orbits Alpha Centauri A and B in such a wide orbit that it takes at least 750,000 years for this little star to make one full "round" around Alpha Centauri A and B! It is in fact possible that Proxima Centauri isn't even orbiting Alpha Centauri A and B at all, but is just passing them by. Currently, Proxima Centauri is 6,000 astronomical units closer to us than Alpha Centauri A and B. An astronomical unit is the distance between the Earth and the Sun.

Alpha and Beta Centauri, and Prxoima at the arrow.
Photo: ESO.

Proxima Centauri is an itty bitty little star. And it is not only small, but it is cool, too, which makes it terribly faint. Alpha Centauri A is a bit brighter than the Sun, and Alpha Centauri B is a bit fainter than the Sun, but Proxima is so faint that it would take 600 of these little runts to produce as much energy as the Sun does by itself. And if you are looking for visible light, Proxima just manages to put out one part in 18,000 as much light as the Sun is emitting!

Ann