The European Southern Observatory has just announced they have discovered a previously unknown globular cluster orbiting the Milky Way.
Globular clusters are roughly globe-shaped (duh) collections of stars, usually containing a few hundred thousand to a few million stars. They orbit the centers of galaxies like bees buzzing around a hive, spending most of the time well outside their galaxies. We know of about 150 such clusters orbiting the Milky Way. Our Galaxy is a flattened disk, so globular clusters are usually easy to spot when they are well outside that plane. But sometimes, during their orbit, the pass right through that plane, and we see them against a crowded background of stars. Worse, the dust in the Galaxy obscures the clusters, making them very difficult to find.
This one, named FSR 1735, had been seen in previous surveys but it was unsure if it was a globular cluster or not. The image above, from the New Technology Telescope in Chile, appears to have removed that doubt. The cluster, containing something like 100,000 stars, is a bit difficult to see in the image, but it’s the clot of stars in the center, somewhat denser than the distribution of background stars.
The cluster is fairly rich, but has remained hidden because it’s located only about 10,000 light years from the center of the Milky Way, where the Galaxy is fairly thick with stars. To bring up that analogy again, it’s a bit like trying to find a fly in a swarm of bees suspended in thick fog — or in this case, dust. Infrared light can pass through the dust, so searches for new globular clusters are made in the IR: this image is in the near-infrared, with wavelengths just outside the range of the human eye. The colors in the image are therefore not real, but represent different wavelengths of IR light.
The cluster is about 30,000 light years away, and is only about 7 light years across. Imagine, 100,000 stars packed into a sphere that tiny! For comparison, the nearest known star system to the Sun, Alpha Centauri, is 4.3 light years away. What would the sky look like from a planet orbiting a star in such a cluster? It would be filled with stars, most yellowish,orange, or red, with hundreds of them blazing away brighter than Venus appears in our night sky.
The Universe is a beautiful place, and a surprising one. I’m always amazed at what delights are so close, yet lurk just beneath — or for this case, just outside — our notice.
March 13th, 2007 at 10:22 am
Aren’t globular clusters deficient in elements beyond helium, so there’s debate about how well planets may form inside? I know that the world’s largest radio dish at the Arecibo Observatory broadcast a signal in the direction of a globular cluster.
March 13th, 2007 at 10:41 am
Sigh. Now I’m getting hooked on astronomy too. yay!
You said it orbits the milky way… how long does it take to make one full revolution? Must be a hell of a long time?
March 13th, 2007 at 11:01 am
Wow, thanks for that link, Phil. Some fascinating stuff there.
I was aware that globular clusters were relatively old, and mostly Population II stars. I had no idea their projected “lifespan” as stellar groups was correspondingly great… amazing.
March 13th, 2007 at 11:21 am
In fact, there are 2 problems with having a planet in a cluster like this. The first is the lack of metals, as Tim G pointed out. However, even if you could make a jovian-type planet without much metal (I have my doubts, but some folks think it’s possible) then there is the problem of all of those neighbors. In such a dense cluster, it becomes likely that another star will pass within a few AU of the any possible planet’s star, scattering the planets right out of the system. The same process means that binaries are quite rare in globular cluster systems.
Does anyone have an estimate now of how many more clusters are likely to be lurking on the other side of the galactic center near the plane of the galaxy? We should be able to make a pretty good statistical argument just based on how much of the sky is hard to see in that direction (and allowing for the increased consentration of clusters around the bulge). Or are IR studies like this one simply making it too hard for any of those clusters to hide now?
DK
March 13th, 2007 at 3:03 pm
Currently, we know of only one planet in a globular cluster, orbiting a close pulsar-white dwarf binary. The millisecond pulsar is designated PSR B1620-26, and the system is the only triple system known in a globular cluster.
March 14th, 2007 at 7:20 am
Ah, globular clusters. So round. So firm. So fully packed,,,
Oh, wait, I was thinking of a tobacco commercial,,,
,,,never mind,,,
100,000 stars packed into a sphere 7 Lt. Years in diameter? What a SciFi story that would enable. Just think, Fire Fly could reach any star in the cluster in a single human life time, even at sub-light velocities. So many stories,,,
I wonder, what is the closest dense cluster to our old solar system? Just for the sake of possible ScfFi stories?
GAry 7
March 14th, 2007 at 7:40 am
It’s called “Nightfall”, and it was written by Isaac Asimov. (I haven’t read the novel, but the short story is a classic, even if the gravitational physics wouldn’t really work out.)
I’d link to it, but who knows if these comments will accept links? I’ll just paraphrase Jayne: Sure would be nice if we had some PREVIEW, dont’cha think?
March 15th, 2007 at 12:17 am
AS I’VE POSTED BEFORE- Westerlund I beats this hands down. Half a million stars in an even smaller volume. And dem stars is NEW, too! Lots of blue giants ready to go boom. No old bag of bones like this wheezing corpse. They have Godzilla vs. Rodan, Freddy vs. Jason, and Alien vs. Predator. So let’s go, bring it on….!
March 15th, 2007 at 9:02 pm
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