Under Italian Skies, The Comet and the Galaxy Trio

December 18, 2023   Issue #657

Subscribers mi rendono felice (I think; I used Google translate)

My book

This is about Under Alien Skies, isn’t it? Yes. Yes it is.

I am very pleased to announce my book, Under Alien Skies, is now available in Italian! Sotto Cieli Alieni is through Bollati Boringhieri, an Italian publishing house that publishes books on science, mythology, ethnology, and humanities. It’s available at Amazon and probably all the other usual online booksellers.

I assume the translation is fine, but the only Italian I can say is “sono ferito”, which is what happens when your dad has a bunch of Navy World War II pocket-sized translation booklets and you’re bored one day. I used to be able to ask, “Where are you bivouacked?” in Polish. Anyway, it’s fun for me to poke through the book, and also to see the back cover blurbs by John Green and Laura Helmuth in Italian. I assume they said nice things.

And remember, Christmas is coming (it’s probably too late for Hanukkah) so you can get it for your loved one who speaks or is learning Italian. Buon Natale! I think!

Pic o’ the Letter

A cool or lovely or mind-bending astronomical image/video with a description so you can grok it

Damian Peach is an amazing astrophotographer who specializes in ridiculously amazing shots of solar system objects. But sometimes he catches some rather more distant objects at the same time.

Wow, that’s pretty, isn’t it? The comet in the shot is C/2020 V2 (ZTF), and the galaxies are collectyively called the Grus Triplet, because they’re close together in the constellation Grus (the Crane). The galaxies are NGC 7590, 7599, and 7582, and they’re about 70 million light-years away. NGC 7582 is an active galaxy, with a central supermassive black hole that’s gobbling down matter. This stuff forms a huge, hot disk around the black hole, so hot it launches a powerful wind of gas away so hard it plows into the galaxy around it. Winds like this can enhance star birth by compressing clouds, but if they’re too powerful they can push that material clean out of the galaxy, quenching star formation.

The comet is interesting, too. It was discovered in 2020 by the Zwicky Transient Facility, which scours the sky looking for objects that move or change brightness. The orbit of this comet is hyperbolic, which means it’s moving too quickly to stay bound to the Sun. Objects that are bound to the Sun gravitationally have elliptical orbits, and ones that are just barely not bound move along a parabola. If they have too much energy, are moving too quickly, the orbital shape is a hyperbola.

In some cases the object is moving far too quickly to stick around, and we surmise it came from outside the solar star, from another star. ‘Oumuamua and Comet Borisov are very hyperbolic interstellar objects. But many times the orbit is jussssst barely hyperbolic, which is unlikely for something coming from interstellar space. I talk about the math of all this back on The Old Blog; we measure the shape of an orbit by its eccentricity, a mathematical quantity. E=0 is a circle, and E greater than 0 but less than 1 is an ellipse. E=1 is a parabola, and E>1 a hyperbola. The orbital eccentricity of 2020 V2 is 1.001. Very close to 1.

That indicates to me that it came from a long way out in the solar system, so far out that it might have been given a very small extra kick of energy from a passing star or even the galactic tides long ago. That was just enough to push it into an orbit that means it will only be passing the Sun this one time. It’s already on its way out, and it will very likely never return.

As an aside, something I’ve been meaning to write about for a long time is hyperbolic meteors. If a shooting star is caught by multiple cameras, the trajectory can be triangulated and its pre-meteoric orbit measured. Some are hyperbolic, just a bit, indicating they are either interstellar or come from very far out in the solar system past Neptune. For at least one such case, astronomers find the meteor may have come from an Oort Cloud object (a repository of icy bodied far, far past Neptune) that may have been perturbed by a passing star, consistent with Scholz’s Star, which passed the Sun about 70,000 years ago. Pretty cool, and I hope we get more examples of these so we can figure out where they’re coming from.

When Damian took the shot of C/20202 V2, it was about 500 million kilometers from Earth, a fair distance, and well south of the plane of the solar system. It’s faint, around 10th magnitude, so you need a decent telescope to see it by eye, even from a dark site. He used a 50-cm. telescope, with a total of 39 minutes of exposure (30 with no filter and three minutes each in a red, green, and blue filter). The green color is common, and due to diatomic carbon: two carbon atoms bound together. The tail near the comet head looks like it may be a little blue to me, which is likely from carbon monoxide molecules glowing, excited by sunlight. The extended tail might be faintly yellow or red — I can’t tell — but if so it might be form dust shed by the comet. If you look closely you can see there are two tails, one ions and one dust. That’s common.

I love seeing shots of nearby objects — if half a billion klicks is “nearby” — with cool deep sky objects, far, far in the background… in this case, those galaxies are about a trillion times farther away than the comet!

Perspective. Comes in handy in astronomy, and life in general.

Et alia

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