Notes on a supercluster

Today I'm going to focus on outer space, because if I don't I'll be forced to deal with events down here on Earth, and it's a little early to start drinking.

The James Webb Space Telescope just posted information on a structure called the Saraswati Supercluster,  which at a diameter of 650 million light years and a mass of twenty quadrillion times the mass of the Sun, is one of the largest gravitationally-bound structures known.  If you look toward the constellation Pisces, visible in the Northern Hemisphere from August to early January, you're staring right at the Saraswati Supercluster.

Not that you can see it with the naked eye.  Its center is about four billion light years away, meaning not only that it's extremely faint, the light from it has taken about a third of the age of the universe to get here, so it's really red-shifted.  Here's the rather mind-blowing image the JWST team just posted on their site:

[Image licensed under the Creative Commons Pablo Carlos Budassi, Extended universe logarithmic illustration (English annotated), CC BY-SA 4.0]

On this diagram, the Sun and Solar System are at the center, and as you move outward the scale increases exponentially, allowing us to visualize -- or at least imagine -- the astonishing vastness of the universe.  (Saraswati is just slightly to the left of top center on the diagram.)

The name of the supercluster is from a Sanskrit word meaning "ever-flowing stream with many pools," which is appropriate.  It's made of forty-three galaxy clusters -- not galaxies, mind you, but galaxy clusters -- of which the largest, Abell 2631, is thought to be made up of over a thousand galaxies (and something on the order of a hundred trillion stars).

If your mind is not boggling yet, you're made of sterner stuff than I am.

Because of its distance and faintness, we haven't known about Saraswati for all that long.  It was discovered in 2017 by a team of Indian astronomers led by Joydeep Bagchi from the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune, India, and since has been the object of intense study by astrophysicists for two main reasons.  First -- although it's phenomenally massive, its vast diameter makes it remarkable that it hangs together gravitationally.  (Remember that gravitational attraction falls off as the square of the distance; it never goes to zero, but it does get really weak.)  The fact that it does seem to be acting as a single structure could give us valuable information about the role of the elusive dark matter in making large objects stick together over time.

Second, it might provide some insight into solving another mystery, the question of how (or if) dark energy, the strange force that seems to be making the expansion of the universe speed up, is changing over time.  You may recall that just this past August, a pair of papers came out suggesting that the strength of this peculiar phenomenon might be decreasing; that instead of heading toward the rather ghastly prospect of a "Big Rip," where dark energy overpowers every other known force and tears matter apart into a soup of subatomic particles, the expansion might eventually stop or even reverse.  The old "oscillating universe" idea, that the universe goes through an endless series of expansions and collapses -- popularized by such brilliant luminaries of physics as Paul Steinhardt and Roger Penrose -- might have legs after all.  Studying Saraswati might give us more information about how the strength of dark energy has changed in the four-billion-odd years it's taken the light from the supercluster to arrive here.

So next time you look up into a clear night sky, think of what lies beyond the bit you can actually see.  Every individual star visible to the naked eye lives in a (relatively) tiny sphere in the Orion Arm of the Milky Way.  The few bits that visible but are farther away -- the smear of light that is all we can discern of the rest of our own galaxy, as well as the few other galaxies we can see without a telescope (like Andromeda and the two Magellanic Clouds) are so distant that individual stars can't be resolved without magnification.  What we think of as the impressive grandeur of the night sky is, basically, like thinking you're a world traveler because you drove around your own neighborhood once or twice.

But I guess I need to come back down to Earth.  Unfortunately.  On the whole, I'm much happier looking up.  It makes the current horror show we're living through at least seem a little less overwhelming, and puts our own place in the universe into perspective.

Maybe if our so-called leaders spent more time stargazing, it might provide them with some much-needed humility.

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