ESO: Young, Hot and Blue (NGC 2547)

[bystander]

Young, Hot and Blue
European Southern Observatory | 2013 Mar 27

Young stars in the open star cluster NGC 2547 - Credit: ESO

Wide-field view of the open star cluster NGC 2547
Credit: ESO/DSS 2. Acknowledgement: Davide De Martin

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Stars in the cluster NGC 2547

This pretty sprinkling of bright blue stars is the cluster NGC 2547, a group of recently formed stars in the southern constellation of Vela (The Sails). This image was taken using the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile.

The Universe is an old neighbourhood — roughly 13.8 billion years old. Our galaxy, the Milky Way, is also ancient — some of its stars are more than 13 billion years old (eso0425). Nevertheless, there is still a lot of action: new objects form and others are destroyed. In this image, you can see some of the newcomers, the young stars forming the cluster NGC 2547.

But, how young are these cosmic youngsters really? Although their exact ages remain uncertain, astronomers estimate that NGC 2547’s stars range from 20 to 35 million years old. That doesn't sound all that young, after all. However, our Sun is 4600 million years old and has not yet reached middle age. That means that if you imagine that the Sun as a 40 year-old person, the bright stars in the picture are three-month-old babies.

Most stars do not form in isolation, but in rich clusters with sizes ranging from several tens to several thousands of stars. While NGC 2547 contains many hot stars that glow bright blue, a telltale sign of their youth, you can also find one or two yellow or red stars which have already evolved to become red giants. Open star clusters like this usually only have comparatively short lives, of the order of several hundred million years, before they disintegrate as their component stars drift apart.

Clusters are key objects for astronomers studying how stars evolve through their lives. The members of a cluster were all born from the same material at about the same time, making it easier to determine the effects of other stellar properties.

The star cluster NGC 2547 lies in the southern constellation of Vela (The Sail), about 1500 light-years from Earth, and is bright enough to be easily seen using binoculars. It was discovered in 1751 by the French astronomer Nicolas-Louis de Lacaille during an astronomical expedition to the Cape of Good Hope in South Africa, using a tiny telescope of less than two centimetres aperture.

Between the bright stars in this picture you can see plenty of other objects, especially when zooming in. Many are fainter or more distant stars in the Milky Way, but some, appearing as fuzzy extended objects, are galaxies, located millions of light-years beyond the stars in the field of view.

NGC 2547 Zoomable Image
Wide Field Zoomable Image

[Beyond]

Young hot and blue... Ann is going to be eyeing you

[Ann]

Young hot and blue... Ann is going to be eyeing you

Yeah, they sure are hotties!!! Ten points!

Ann

[starsurfer]

I really don't see the point of using a huge observatory to take a very narrow image of a large cluster. I wish ESO would image more obscure objects that are more suitable for a professional observatory, there's many interesting southern protoplanetary nebulae that have never been imaged in addition to other exotic things such as bowshocks. A great amateur image of NGC 2547 by José Joaquín Pérez: http://www.astro-austral.cl/imagenes/st ... 7/info.htm

[bystander]

I really don't see the point of using a huge observatory to take a very narrow image of a large cluster.

Obviously, some team of astrophysicists was conducting a study that included the stars in this cluster. Pretty pictures are rarely, if ever, the objective of professional observatories, they are just a bonus from the image data collected.

[Ann]

Thank you for that image of NGC 2547 by José Joaquín Pérez, starsurfer. His image is lovely indeed.

Anyway, I need to object a bit to this part of the ESO caption:

While NGC 2547 contains many hot stars that glow bright blue, a telltale sign of their youth, you can also find one or two yellow or red stars which have already evolved to become red giants.

I agree that the red stars that can be seen in the image are probably all red giants, but it is not clear that any of the red stars in the image are members of NGC 2547. Note that the red stars that are very close to the cluster center are relatively faint. This suggests that they have not evolved from any of the young bright blue stars in the cluster, since this kind of evolution should not make the stars fainter. Besides, the brightest blue stars should use up their core hydrogen first and turn into quite bright red giants, so any member of NGC 2547 that had turned into a red giant should be at least as bright as the brightest blue stars of the cluster.

Other red stars in the image are relatively bright, but they are also rather far away from the obvious center of NGC 2547, which again suggests that they are not members.

Since it isn't clear that any of the red stars in the image are members of the young cluster NGC 2547, we can't really say that the red stars have already evolved to become red giants. These red stars may all be considerably older than the members of NGC 2547.

Ann