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Okay, Dr. S. What's on our agenda today? I want to talk today about Messier 14 or NGC 4602, which is a globular cluster. This is a fairly ordinary globular cluster, containing about 100,000 stars and located about 30,000 light-years away; it's a pretty good target for those who want to see it in the night sky on their own. If you have binoculars, it should be very easy to find, it is in the constellation Ophiuchus. So, Ophiuchus is the same 13th constellation of the zodiac that ancient astrologers ignored because they didn't want 13 constellations, because 13 is an unlucky number. This means that most people who consider themselves Scorpios are actually Ophiuchus. Although, of course, that doesn't matter. What I want to talk about
today in connection with Messier 14 is how a globular cluster can be destroyed. This comes from understanding how they form, where they originate, how they evolve and change, and how they die or collapse, after which the stars from these clusters disperse across the Milky Way. So, globular clusters are quite old. This is what we call a simple stellar population, because all the stars, we believe, formed at the same time from one large cloud of gas. And they were, so to speak, provoked to do this. This is not exactly normal star formation for a galaxy, which usually happens a little differently. This happened because the gas was subjected to a shock wave, possibly caused to compress by a nearby supernova explosion, or something else, causing this
huge, dense cloud of gas to collapse and form hundreds of thousands of stars, instead of the slower process of forming a few stars. So when we look at globular clusters, we want to understand: when did they form? What is their age? And perhaps what we call a timeline of destruction, which sounds pretty apocalyptic. So, after they have formed, several things can happen. In a globular cluster, there are interactions between stars, that is, essentially, stars passing each other, right? If you imagine that these globular clusters are very, very dense, the stars in them will inevitably collide with each other at some point. So, it could happen that You know, when you use the Moon or Mars to gravitationally maneuver a satellite-
the same thing can happen with two stars. Let's say you have a massive star and a much less massive one, so the smaller one can get an acceleration from the larger one. They seem to be exchanging energy. In a globular cluster, over time, large stars sink to the center, while small ones are either thrown to the periphery or, as a result of this maneuver, are simply thrown out of the cluster. Another thing that can happen is tidal interactions. This is when gravity on one side of the cluster is stronger than on the other. This happens, for example, when encountering another cluster or the center of the Milky Way, if it comes too close to places with a large number of stars. If gravity
on one side becomes stronger, these globular clusters can stretch into stellar streams. This is another way of redistributing the stars around. It is these two processes, in our opinion, that can destroy globular clusters. Of course, the question arises: how quickly does this process happen? This depends on the size of the cluster, the number of stars in it, its density, and the path it takes through the galaxy. This can be simulated, but it is the so-called N-body problem. N is the number of objects you are trying to simulate in the computer at the same time. The complexity increases proportionally to N squared. So a globular cluster of 100,000 stars is billion times more difficult to model than the Earth-Sun system. As of 2010, we already had enough
computing power to do this. But the article I have today is dated 1997. It was technically impossible at the time, but researchers found a way. They made some simplifying assumptions: they divided the globular cluster into a grid. They considered each grid point individually, even though it might contain, say, a couple hundred stars. Just to It turns out that you are taking the average. This is the only article I found that mentions Messier 14. It has a great title. Come on, show me. It is called " Destruction of a globular cluster system Great name. Yeah, it's kind of a "da-da-da-da-da" name, right? So they calculated the timescale of the destruction for many different globular clusters, including Messier 14.
So Messier 14 is on that list. That's NGC 6402, down there. And they calculated the time scale of the destruction- 30 billion years. Quite a long time, as we can see. You know, the universe is only 14 billion years old, but in this paper we examined all 119 globular clusters and got a distribution of the rates at which they could be destroyed. I don't like this graph because of the scale. Because it was built in what 's called "Hubble time," which is essentially the age of the universe, you know? This is approximately Hubble time. But they took it to be 10 billion years to get a nice round number. So instead of billions of
years, there are units of 10 billion. So, one is 10 billion, and ten is 100 billion. 0.1 is actually a billion. So it's very confusing when you look at it. But if you find where on the 30 billion scale Messier 14 is, it turns out that it's actually in the middle. So, as I said at the beginning, this is a pretty normal average cluster, right? But this means that half of the clusters in the Milky Way have a decay time less than the current age of the Universe. Although it is obvious that they still exist. So, they are clearly still alive. Therefore, we can assume that they did not arise at the very beginning.
Especially those that have a time scale of destruction of hundreds of millions of years. So, when we think about it, we have to consider: if this distribution that they found is a general statistical law for any globular cluster in the Milky Way, then we can take a sample and say, " It's either going to be destroyed in hundreds of millions of years or in 100 billion years," right? There will be such a spread. So, half of the globular clusters that formed have already disappeared. But there are objects like Messier 14, in which the time scale of destruction is about 30 billion years. So if we think about the next 14 billion years of the evolution of the universe, about half of the globular clusters that are already in the Milky Way will be destroyed
over the next 14 billion years of the history of the universe, probably. This is quite interesting, but at the same time it makes you think, "Oh, poor globular clusters." They simply can't last long enough, and we might end up with a galaxy that looks very different than it does today, with far fewer globular clusters, which are very useful tools for determining distances and ages. I think in 30 billion years we'll probably invent some new tools. We would hope so, wouldn't we? By then, we will probably also merge with Andromeda. So Andromeda will also bring its own population of globular clusters. And a lot of what I
talked about earlier about tidal interactions, where they stretch into streams, is what would most likely happen during a merger of two galaxies. So it's very interesting to think that maybe this merger process with Andromeda could actually speed up that process as well. What is considered cluster destruction? Should it be like. at what point do you say the cluster is destroyed? Yes, when stars are no longer gravitationally bound to each other. All the stars? Actually, I don't know. Is there a point where you say, "Oh, now it's just six stars flying together in the universe." Are you going to stop calling it a cluster? But
globular clusters are defined as extremely dense areas of sky that have, you know, hundreds of thousands of stars. So I think maybe when you start to get closer to the definition of a loose cluster, we've already talked about loose clusters on this channel, right? They are much less dense. Perhaps then we can say that the globular cluster was destroyed. It was a bit mysterious. When you think about how we record the positions of objects in the sky, Messier had a very difficult task. There is no grid marking in the sky for him to navigate by.
