Globular clusters are one of those types of astronomical objects that make everyone happy: they are incredibly beautiful to observe, jaw-dropping even in small telescopes; and they are also tailor-made laboratories for studying stellar evolution, an environment where studying how stars age and interact is almost too easy.

But that last bit has run into a problem of late. A wrinkle has turned up that makes examining globulars a bit more complicated than previously thought.

Globular clusters (or just GCs) are roughly spherical collections of hundreds of thousands or millions of stars held together by their own gravity. They look a bit like beehives, and in fact the individual stars orbit the center on mostly randomly distributed paths, so a time-lapse movie (lasting millions of years) of a GC would strongly remind you of bees around a hive.

Early on, astronomers noticed that GCs appeared to lack massive stars, and in fact when examined closely it was seen that all stars above a cutoff mass were gone. This implied that a GC forms all at once from a cloud of gas, with all the stars switching on simultaneously, or near enough. A star’s lifetime is dependent on its mass, and more massive stars live shorter lives. Some high-mass stars explode after 10 million years, some after 100 million. A GC older than that will therefore not have those kinds of stars in it. They’ll all have died.

The Sun will turn into a red giant when it’s about 12 billion years old. So if you don’t see any Sun-like stars in a GC, you know it must be older than that age. By observing the kind of stars in a GC, we can get an idea of its age! In fact, this caused a problem some years ago: the oldest GCs looked to be older than the Universe itself! It turns out this was due to astronomers not knowing the age of the Universe very well, and as time went on we figured out that the Universe was older than first thought (it’s 13.73 billion years old now) and the paradox was resolved.

Anyway, over time, the stars inside a GC orbit around, and because they are so tightly packed together, encounters between two stars are common. They pass close enough to gravitationally affect each other, changing their orbits. In general, if two stars of different mass pass each other, the lower mass star will gain energy, boosting it to a larger orbit, and the higher mass star will lose energy, dropping it to the center of the cluster. Over time, you get "mass segregation", with the hefty stars all in the center and the lighter-weight ones relegated to the cluster’s suburbs.

Not only that, but the stars near the center can actually interact and become bound to each other, forming binary stars. That takes time, though, billions of years. First the stars have to fall to the center, and then they need time to interact. So another way to get the age of a GC is by looking at the binaries in the core. This is called the dynamical age of the GC — how long stars have been interacting with one another — as opposed to the actual ages of the stars in it.

Binaries in the core reveal themselves through X-rays. High mass stars explode and leave behind neutron stars or black holes. If one of these is orbiting a normal star, then it can siphon off gas from the star and gobble it down, which produces a lot of X-rays (see here for details). So detecting these binaries is not terribly hard: point your X-ray telescope at a GC and count up the sources of X-rays in the middle.

Astronomers did this recently using the Chandra X-Ray Observatory. And there’s the problem: in several GCs, they found too many X-ray binaries.

Chandra image of two GCs: NGC 6397 (left) and NGC 6121 (right); 6397 is old, but it has far more binaries than expected, making it look younger.

When the GC is young, you don’t expect to see too many binaries in the core. When it’s middle aged, you see quite a few as the stars in the center interact, and then when it’s old the number tapers off again (as the normal stars die off and the source of X-rays shuts off). What the astronomers found is that in some clusters that were presumed to be really old (due to the age determined by looking at the stars in them), there were still more binaries than expected, as if they were younger.

Why? Well, all this also depends on how dense the cores of the GCs are. A less dense core should have fewer encounters between stars, and therefore fewer binaries. But one older GC which was expected to only have a few binaries had quite a few more than predicted. In other words, the stars themselves in that GC are old, but the core appears to be somewhat more immature.

What this means is that age is not the only thing that drives the number of binaries in the core, and that they are not the simple laboratories that has always been assumed. Most likely, this doesn’t affect things too much; they can still be used to study how stars age and interact, but you have to be more careful when poking around in the details. As usual, the Universe is a wee bit more complex than we usually assume. But the beauty of it, too, is that this complexity can be revealed, and we can revise our ideas to accommodate it.

So obviously, you have to be careful when dating heavenly bodies. They might look older on the outside, but be younger and less mature on the inside.

If there’s a life lesson in there, you’re welcome to determine it your own self.

I’m going to be heading to Michigan in May to attend the premier of — get this — the Bad Astronomy planetarium show!

I’ve been working with folks from the New Detroit Science Center for some time now on this project. Well, to be more honest, they’ve been working really hard, and I’ve been heckling them. Last year I flew to Detroit to film some segments for it, and from what I have seen the show will be funny, informative, silly, and perhaps with a slight hint of fromage. I have not seen the final product, so it’ll be as big a surprise to me as it is to everyone there.

I’ll be at the NDSC all day on May 10th from 10 a.m. to 6 p.m., and giving a talk at 1:00. They’re charging a nominal fee for this, seeing as how I’ll be a huge star after the premier. Click here for the flyer. I’ll be happy to sign books, too; they’ll have copies of my first book there for purchase. The second book, Death from the Skies!, won’t be out until October but as usual I’ll be shilling it mercilessly and without remorse.

While I’m in Michigan I’ll be giving a talk at the nearby Cranbrook Institute of Science, a nice museum outside of Detroit. The talk is on May 9th from 7:30 to 9:30 p.m., and tickets are $10 ($8 for members). They require pre-registration, so they know how many rotten tomatoes to stock.

I graduated from the University of Michigan, so it’ll be nice to be back in the land of harsh vowels, Vernor’s soda pop, and holding up your hand to show people where you’re from. And if you don’t get that last one, well, you’re just not from Meeechigan.

It’s difficult to express just how fracking impressive the Large Hadron Collider is. You really have to be there to understand how overwhelming and ginormous it is. Still and all, maybe the video I took of the tour will help get the idea across (if you go to that YouTube page, there is a link right under the video that allows you to watch it in higher quality. I recommend doing that).

ATLAS and CMS are detectors, built to detect the shrapnel from the collisions of protons moving just a whisper slower than light itself. For the cast of characters and a description of this tour, take a look at my earlier post describing it. There are pictures there from the journey as well.

My live video live chat starts at 3:00 p.m. Mountain Time (21:00 UT) today (Sunday April 27). If you look below and see/hear me nattering away about black holes or UFOs, then you’re in. I urge you to go to the UStream page, though, so you can participate in the chat room. If you want to change your nickname there, type "/nick JoeRogan" (or whatever) in the text field.

See you there! Oh wait, no I won’t. But you’ll see me.

Reminder: I’m doing a live video chat today at 3:00 Mountain time.

Another day, another grainy, out-of-focus, weird UFO picture trumpeted by the media. Well, not so much the media as The Sun.

The headline screams, "Tourist snaps UFO in Croydon" and is accompanied by what one guesses is the best of the series of pix.

The object is reported as "speeding through the sky" and the photographer, Anastasiya Gavrilenko (which, I must say, is an awesome name), said,

It was quite large and moving really fast. It was size of a plane but did not look like one – it looked more like a big mushroom.

I’m not saying it was a mushroom — that’s as likely as it being an actual spaceship — but it’s resemblance to a hat being blown across the sky by the wind is perhaps more a clue of its origin.

…then again, we’re talking Croydon here. Maybe it’s the Fourth Doctor’s hat. Call Sarah Jane!

Tip o’ the tin foil beanie to Fark, as usual, and I note that they now have a Sarah Jane joke in the comments as well, but I was first.

The past few days have seen a large number of people commenting on this site who have been jerks, who have moaned and groaned over nothing, and who have been, really, just negative nellies about everything. I had to call one person out publicly due to a grossly inappropriate comment about me personally, as well. So here we go again: this is my commenting policy. If you don’t like it, don’t comment here on the blog.

The commenting policy is posted below. Learn it. Love it. Listen to it, or you’ll be wasting your time commenting here.

I didn’t want to do this, I really didn’t, but my hand is forced.

For some reason, this past week, I have had to edit a comment every day because someone has used "bad" words in it. I like this blog to remain, if not kid-friendly, then young-adult friendly. That means getting it into schools and such, and that means I have to be a nanny.

So here is my policy for commenting here. It is neither complete nor unchangeable. But this will do for now.

1) Be polite.

That’s it. That’s my rule.

That should be easy, right? Don’t go attacking other people, don’t swear, don’t be a jerk.

I reserve the right to edit out strong language and such. I will also delete comments that go over the line, or try to sell a product, or because I feel like it. OK, I won’t do that last part. The point is, this is my blog, and if you are being a jerk in some way I will take action. That may sound rather vague. Too bad. There is no line in the sand that says Here be good, there be jerk.

Look, when you comment on a blog, it’s like you’re in that person’s house. Be polite. Flush the toilet when you’re done, or, better yet, don’t foul the place up in the first place.

Simple, right?

Space, especially in near-Earth orbit, is not really a vacuum. The atmosphere is thin, sure, but it’s there. Any object orbiting the Earth only a few hundred klicks up is plowing through that ethereally thin stuff, which causes drag on it. This robs the object of energy, and the orbit lowers. That in turn drops it into thicker air, which increases the drag, which speeds up the process. Unless action is taken, a fiery fate awaits.

The International Space Station is in such an orbit. Every day it loses altitude due to drag, and left on its own would burn up in the Earth’s atmosphere in a matter of years. The European Space Agency, however, has built the Jules Verne Automated Transfer Vehicle, which is capable of boosting the orbit of ISS to safer heights. And that’s just what they did a few days ago, lifting the station’s orbit by 4.5 kilometers.

Universe Today has all the details. This is a cool story, and if you like it, Digg it! More people should read about space success stories.