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Hey folks, a quick ask for y’all: I have an invitation to speak in the Los Angeles area on November 14, 2026. I enjoy giving public talks! I really would love to be able to give more while I’m in town there. If any of you have contacts at museums, community groups, schools, or whatnot that might enjoy having me come speak about astronomy, please let me know! Or better yet, my speaking agent Beth Quittman ([email protected]) of Samara Speakers Agency, that would be lovely. Thanks!

I’ve written about the Sombrero Galaxy many times before. It’s relatively nearby (30 million light-years away), and bright enough to be a favorite target for astronomers. It’s a nearly edge-on spiral with two prominent features: a striking dark lane of dust across the midplane of the disk, and a vast smooth halo of stars surrounding it. It’s been imaged in detail by Hubble, JWST, and many more observatories. It’s gorgeous.

I’ve also written about DECam before: an insanely huge 570-megapixel (!) camera mounted on a 4-meter telescope, designed in a way to see a staggering 2.2° on a side of the sky — the moon is about 0.5° across, so this is an immense chunk of sky to see at one time for such a camera. It’s designed to look at millions of galaxies to understand better how dark matter and dark energy have sculpted the cosmos.

So, combining these two, here is a very cool and somewhat unusual view of the Sombrero with DECam:

Daaaaang. Most images show the galaxy itself filling the frame, but I love this one because it puts the Sombrero more in context, surrounded by stars and faint galaxies.

In the profoundly huge 14,000 x 9,000 pixel version several things stand out. One is that the halo of stars around the galaxy goes for a long way, stretching far outside the main disk. This is true for most big galaxies, including our own, but the Sombrero’s halo is much brighter than most. This is likely due to a collision with another galaxy, which can strip stars away and put them on far-flung orbits. The dark lane of dust across the middle is likely from that collision as well; most galaxies don’t have such an intense lane like that. It may have collided with a dust-laden galaxy; the gravity of the bigger galaxy then stripped out that dust which went into orbit around the big galaxy’s center.

There’s also a faint loop of material to the lower right as well, and that too is from a collision; it’s made of stars stripped from a smaller galaxy that came too close to the much larger spiral. There’s a hint of it at the upper left as well.

It’s well known that the Sombrero is also surrounded by about 2,000 globular clusters, ancient collections of hundreds of thousands of stars held together by their own mutual gravity. Compare that to our Milky Way, which only has 160 known! I’m starting to think the Sombrero is something of an overachiever. Anyway, I searched the high-resolution image of the Sombrero to look for them, but honestly there are so many stars and so many small fuzzy background galaxies I couldn’t positively identify any. Maybe you’ll have better luck. 

But this new image got me thinking about the Sombrero. I’ve actually never seen it for myself through a telescope. It’s part of the Virgo Cluster of galaxies, and is getting higher in the southeast part of the sky after sunset as summer approaches. I’ll have to try for it; I have dark skies here in nowheresville Virginia, so I bet I can spot it with binoculars. I’ll put it on my todo list! 

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Speaking of big, nearby spiral galaxies…

You’ve probably heard that in some billions of years time, our Milky Way Galaxy and the Andromeda Galaxy are due to collide, merging into a single larger galaxy as chaos ensues in them both.

I’ve written about this event many times, and (to toot my own horn) I’ve been one of the few voices out there throwing some skeptical cold water on the conclusions. Back when the results were first announced the merger seemed inevitable, but papers started coming out showing that that may not be the case; Andromeda’s approach toward us (or the two of us approaching each other if you prefer) has some sideways motion to it as well. If that tangential velocity is high enough, the two galaxies will miss each other.

The slide to the side is very difficult to measure, because you have to physically see the stars in the Andromeda Galaxy move over time. Given they’re 2.5 million light-years from us, that motion is teeny tiny, and you have to observe the galaxy over many years to see any motion at all. Even then, uncertainties in the measurement make it really hard to know exactly how fast the galaxy is moving. The last time I wrote about this, for Scientific American in August 2024, researchers looking at the gravitational influence of other galaxies around us on the collision concluded there was a 50/50 chance of a collision, and if it does occur it’ll be in about 8 billion years.

Welp. New research has just been published that builds on that. Starting with the same assumptions, these scientists used updated measurements from the Gaia spacecraft of stars’ motions in both Andromeda as well as the Triangulum Galaxy, the third largest in our Local Group of galaxies and the one with the strongest outside gravitational influence on the potential collision. With these new data they find the collision probability goes up to 90%, with a median merger time of 6.5 billion years from now.

BUT! They also show that this depends sensitively on their input assumptions, and the probability can range from 64% to 100%, depending on what parameters they use. So, aggravatingly, even after all this we can’t be completely sure a collision will take place! It’s probably the way to bet, but certainty still eludes us. 

The thing is, our understanding will get better over time, because the longer we do observe Andromeda the more the stars will move, and the easier it gets to see that motion (think of it like seeing a distant bird flying; its apparent motion is small so it’s hard to know what direction it’s moving, but if you wait long enough that gets easier to see).

So the jury is still out on any future existence of Milkomeda, but time will tell.

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!