Magellan’s revenge


In March we’ll be two years away from the 500th anniversary of Ferdinand Magellan’s visit to the Mariana Islands. There will surely be some hoopla when that milestone arrives. If you’re looking to hold a theme party you can’t miss.

While you’re adjusting your social calendar, some astronomers, thanks again to Magellan, are doing some adjusting of their own. They reckon that a galaxy named after Magellan is on a collision course with our galaxy, the Milky Way. We’re due to get belly-punched in 2.4 billion years, give or take about a billion either way.

So, eventually, our intrepid Portuguese navigator will get the last laugh.

The Milky Way galaxy has a number of smaller galaxies that hang out in the neighborhood. Two such galaxies are called the Large Magellanic Cloud and the Small Magellanic Cloud. These are so named because Magellan mentioned them in his notes when he saw them. They are very prominent features of the southern hemisphere’s sky. What looked like fuzzy “clouds” in the night sky were actually galaxies, but the “cloud” name stuck.

The LMC and the SMC are something of a cozy pair and, from what I think I know (no guarantees here) they’re gravitationally associated with each other.

It’s possible that the LMC and SMC are not of the same origins as the Milky Way but are, instead, travelers from somewhere distant. Whoa. That’s spooky.

Anyway, I’ll finally get to the point here. The Monthly Notices of the Royal Astronomical Society, February, 2019, issue contains an article: “The aftermath of the Great Collision between our Galaxy and the Large Magellanic Cloud.”

The LMC is, right now, actually heading away from the Milky Way, but this is expected to change in a billion years when the LMC will boomerang and then home-in on our mother galaxy.

The article predicts that the smash-up will suck so much material into the Milky Way that the supermassive black hole at our galaxy’s center will increase in mass by a factor of eight.

As things stand now, the Milky Way is apparently a bit underweight in its belly. But when it gobbles up the LMC’s mass the Milky Way will be have a more typical profile.

With that idea in mind, the article notes: “At the end of this exceptional event, the MW (Milky Way) will become a true benchmark for spiral galaxies, at least temporarily.”

You did note that “temporarily,” right? I sure did. I did because of something that freaks me out.

Before I get to that freak out, though, let me mention the “spiral galaxies” reference that came before the “temporary” reference. The “spiral” refers to the beautiful spiral shape (like a pinwheel) of the Milky Way galaxy. This shape must be scientifically inferred. It can’t be directly observed, at least in total, any more than you can directly observe the appearance of your house when you’re sitting within it. But the Milky Way inference is pretty reliable, and telescopes can see the structure of similarly-shaped galaxies.

A spiral galaxy shape is breathtaking, every bit as striking as Saipan’s coral lagoon. If you get a sense of pleasure living amidst the natural beauty of Saipan, then you can relate to the fact that many astronomy enthusiasts actually have the same sense of wonder about the appearance of our home galaxy.

Hey, so far, so good, right? Well, yeah, but now we have to look at this “temporary” reference.

The LMC (which is about 163,000 light-years distant) isn’t the only galaxy destined to smack into the Milky Way. There’s another one in the works. It’s called Andromeda galaxy.

Andromeda is far more distant (2.4 million light-years) than the LMC. Andromeda is also far bigger. It is, in fact, more massive than the Milky Way itself. Like the Milky Way it has a very nice spiral structure. Well, temporarily, that is. That’s because in about 4 billion or 5 billion years, long after the Milky Way has digested the LMC’s punch, Andromeda and the Milky Way are going to smoosh together. The resulting galaxy is expected to become a big blob, known more formally as an “elliptical” galaxy. The well-defined arms of our spiral shape will be merely a faded memory. Ditto for Andromeda.

If you want to take it personally, I guess that notion is a little bit depressing. But that’s not what freaks me out. No, what freaks me out is that when I look at Andromeda though binoculars or a telescope, where it’s this hugely impressive presence, I recall that it’s coming straight for us at a speed of 250,000 miles per hour. Sure, I know that it’s so distant that it’s no threat to any human (humans, and probably all life on Earth, will be long gone when the collision happens), but, well, in galaxies, as in artillery, incoming is incoming. Yikes!

So, in galactic terms, the long term isn’t looking so great. It’s probably better to focus on things nearer to home and closer on the calendar. So let’s ink that Magellan party for 2021, OK? We’ll toast each other. We’ll toast ol’ Ferdinand. And then we’ll toast our beloved Milky Way, which is destined to become a big-bellied cosmic blob.

Ed Stephens Jr. | Special to the Saipan Tribune
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