Seeing the Universe with both old and new eyes… with a boost from the cosmos itself

December 28, 2023   Issue #662

About this newsletter

Ooo, meta

This is my last issue of BAN for 2023, so I figure why not run a cool image that is equal parts jaw-droppingly beautiful and mind-expandingly sciencey? The theme here is seeing things in new ways to et a better view, and that also seems like a good moral for the fin d’année. There will be changes coming in the new year, even as last year brought so many. For me personally; regular readers know I moved from Colorado to Virginia, and I’m still getting used to trees and leaves and different birds and humidity and being able to hop in a car and visit family and old friends who used to be half a country away.

There’s a lot of work to do for 2024. But that’s still a few days away, so in the meantime take a deep look into the distant Universe and revel that we can do the things we do. Oh — and in the spirit of once-more-around-the-Sun, I’ve made this article free for everyone. Enjoy.

[Edited to add: D’oh! Due to a fumbly finger on my part, this was NOT sent to everyone on Thursday. Sorry about that! To fix that, I’m republishing it today, Friday, Dec. 29, 2023, so that everyone gets it. My apologies to paying subbies who got it twice!]

Pic o’ the Letter

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

One great way to learn more about some object out there in the Universe is to look at it with telescopes that look at different kinds of light. For example, stars and gas clouds emit a lot of their light in visible wavelengths, the kind our eyes see, but warm dust is much brighter in infrared. Combining observations like this can tell you where stars are forming, where they’re dying, and much more. Also, galaxies that are extremely far away are so redshifted that much of their light gets to us at infrared wavelengths, so looking at that kind of light can help us understand those distant galaxies better.

So what could be better than combining the might of Hubble Space Telescope and JWST? Especially when you point them at a huge galaxy cluster, and take a bunch of images using filters that capture light across a huge swath of the electromagnetic spectrum?

Especially especially when it makes an image as cool as this:

MACS 0416.1-2403 (or just MACS 0416 for short) is a huge cluster of galaxies about 4.3 billion light-years from Earth. It’s actually two such clusters that are colliding, and may merge into a single larger cluster eventually. Hubble has taken observations of this cluster several times, and JWST twice, in general to look at very distant galaxies to see how they form and change over time.

The cluster itself isn’t really the target! But it’s critical: The gravity from the cluster bends space around it, and as light from even more distant galaxies in the background passes through that warped region of space it bends, too. This can distort the images of those background galaxies, but, importantly, it can also magnify them, making them brighter. They’d be too dim to see otherwise. So, this gravitational lensing is like a free pass to the distant cosmos.

In the image, the colors you see are assigned to observations through different filters. So, for example, Hubble’s F435W filter (which lets through a wide range of light centered around 0.435 microns, in the blue part of the spectrum) is shown as deep cobalt blue. The F814W filter is shown in teal.

The JWST observations are colored more toward the red end of the spectrum (though not entirely; some of the shortest wavelength observations are also colored blue and green, making this a bit confusing… but don’t sweat it too much). So what you see as yellow is actually light at a wavelength of around 2 microns, well outside what the human eye can perceive. The reddest light shown here is from 4.44 microns.

The reddest galaxies you see are, in general, so far away their light is massively redshifted. Some, though, may just have lots of dust that also blocks bluer light and makes galaxies look red. You have to be an expert to tell the difference (or have observations which can separate the two effects).

To be honest, I kinda dig the esthetic. I like the colors, and how different objects show up so vividly in different wavelengths. But that’s not the reason this image was taken.

It’s that gravitational lensing I mentioned above. As you can see, there are arcs scattered all over the image. These are al lensed background galaxies, their light twisted by the cluster’s huge gravitational well. Some of them, though, look like they’re being warped by individual galaxies in the cluster more than the overall cluster, too. One in particular is very interesting indeed…

Follow-up observations indicate that this galaxy is so far away from us its light took over 10 billion years to reach us so it’s well in the background of the cluster. It also has several clumps of brighter stuff in it, possible regions where stars are being born.

But one bright spot, indicated by an arrow in the image above, is likely a single star system, a binary star made up of two massive stars. The official name of it is LS1, but they nicknamed it Mothra, because it’s a monster star, and they also found a similar star in a different galaxy they had already nicknamed Godzilla, so why not (link to research paper).

One star is likely a blue supergiant and the other a yellow super- or hypergiant, meaning truly massive stars that blast out light at rates thousands of times the Sun’s. That’s one reason we can see them at all; they probably outshine any other star I that galaxy.

But the lensing is amplifying that light as well. Here things get even more interesting. Given how bright the stars are intrinsically (how much light they give off) and how bright they should be at that distance, the amplification by lensing can be calculated… an it’s a factor of about 4,000.

That’s a lot. Like, a lot a lot. Weirder, the star is seen (barely) in the Hubble image in 2014, which means it was being amplified back then too. That’s unusual, since the magnification depends strongly on how closely the star is aligned to the lensing foreground galaxy as seen by us at Earth, and over ten years that alignment would’ve changed enough to lower the amplification significantly.

To explain this, the astronomers think a second lens is acting here, too! Something in the MACS cluster with a mass of roughly a million times the Sun may also be in that alignment, too faint for us to see. If so, it may be a globular cluster, a collection of stars that usually has about that mass. That would be amazing, since at that distance it would be completely invisible.

This is a lot, I know, but it’s pretty cool: A star we wouldn’t be able to see has its light amplified by an intervening galaxy cluster, as well as a star cluster that itself is too faint to see!

Amazingly, a total of 14 objects in this field were seen to change brightness over time, so there’s still a lot of info to mine in the data (link to research paper). And that’s just one aspect! We can learn more about the cluster, other galaxies, how they formed, and how galaxies tend to evolve over time as well.

It’s an aspect I really love about astronomical observations: You can look for one thing, and find a treasure chest opening up loaded with more fun science. People will be studying these data for decades, and I wonder if we’ll ever fully tap their potential.

Et alia

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