Star Clusters

Messier 35

This is the "young" open star cluster Messier 35 in the constellation Gemini. This cluster is about 150 million years old and located about 2500 light-years away. Most of the stars you see here are more massive than the sun and burning at very hot temperatures, which makes them blue-white in color. The red stars in the cluster are nearing the ends of their lives and have swelled into red giant stars. At the upper right of the picture you can see the edge of the open cluster NGC 2158, an older and more distant star cluster. This image is made from three colors taken at the Kitt Peak Mayall Telescope with the Mosaic camera. The design of the camera explains the linear gaps you can see traversing the cluster if you look closely at the picture. The full moon would just barely fit in this image.


Messier
67

The star cluster Messier 67 is an old (about 4 billion years) open star cluster located in our galaxy. The image above is a composite of short exposures taken with the MMT "Megacam" camera. The camera is a 268 megapixel camera, and covers an area about the size of the full moon. This image is cropped to show the center of the cluster, and is roughly 15 arcminutes on a side. The reddish stars are red giants, stars reaching the ends of their lives and swelling from about the size of the sun into monsters that would engulf the Earth.


Messier 67

This image of Messier 67 is a close-up of the northern portion of the cluster taken with the Keck Telescope. The bright stars are about 250 times fainter than the faintest objects visible to the unaided eye (12th magnitude), while the faintest objects visible in the large version of this image are about a million times fainter than the faintest stars visible to the unaided eye (about 26th magnitude). When all of our images are stacked together, the faintest visible stars are about another factor of 10 fainter yet (28.5 magnitude). Besides stars in our own galaxy, this image also shows very faint galaxies extending most of the way across the universe, including a quasar at a redshift of 3.0, or about 11 billion light-years away. The streaks extending off of the bright stars are called "bleed trails" and are due to overexposure of those stars.


NGC 6397

This is a composite color image of the outer regions of the globular cluster NGC 6397 taken with the VLT. The total exposure time is 8 hours in the I band (near infrared) and 5.8 hours in the V band (green). The long trails from the brighter stars are due to saturation of the CCD camera. In other words, the stars are too bright!


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Galaxies

NGC 3656

This image of NGC 3656 (the name stands for "New General Catalog" entry #3656) reveals the galaxy to be fairly irregular in shape. The averaged light profile looks like an elliptical galaxy, but unlike an elliptical galaxy, we see dust lanes and a loop of light to the upper left. My guess would be that this elliptical has recently merged with another galaxy, and is in the process of swallowing another. The image was taken at the Keck Observatory using the LRIS imaging spectrometer.


NGC 3079

This is a composite color image of the nearby galaxy NGC 3079 in the constellation Ursa Major (the Big Bear), taken with the Mosaic camera on the Kitt Peak 4-meter telescope. Exposure time is just 30 seconds in B (blue), V (green), and I (near infrared). The purple color is a result of the combination of light from bright young stars (which are blue) and from stars behind thick clouds of dust (which appear red because of the dust).


Galaxy Cluster Behind M67

This image is another part of the M67 image above and shows a group of galaxies at a redshift of 0.37, or about 4 billion light-years away. (The star cluster Messier 67 is in our own Milky Way Galaxy, only about 2800 light-years away.) The orangish-white "faint fuzzies" are galaxies in the group; their orange color is due to the expansion of the Universe shifting the yellowish-white light of the stars toward the red part of the rainbow. We call this phenomenon "redshift". With one exception, anything that is not the same orangish hue is probably between us and the galaxy group, either stars in our own galaxy or other galaxies.

The whitish, fuzzy "star" just above center is the biggest member galaxy of the same group. The fact that this galaxy is not orange like the other group galaxies indicates that something is strange about this galaxy. Our best guess is that this galaxy has recently formed new stars (strange for an elliptical galaxy) and that it has a super-massive black hole at the center gobbling down lots of dust and gas.

Also visible in the upper right is what looks like a smoke ring around a star. This is probably a galaxy that, seen close-up, would look like either the Cartwheel Galaxy or Hoag's Object. I don't know how far away this galaxy is, but it is probably much closer than the galaxy group, maybe only(!) a billion light-years away.

The image above is about 6.7 arcminutes by 4.7 arcminutes across (an arcminute is 1/60th of a degree).


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