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Biggest thing in the universe?

John Healy

So, on the 10^n scale, today Space.com posed the interesting question “What Is the Biggest Thing in the Universe?”

Scientists have created the first map of a colossal supercluster of galaxies known as Laniakea, the home of Earth’s Milky Way galaxy and many other. This computer simulation, a still from a Nature journal video, depicts the giant supercluster, with the Milky Way’s location shown as a red dot.

What’s bigger than a galaxy? Well, groups or clusters of galaxies and then superclusters.

[Wiki] A supercluster is a large group of smaller galaxy clusters or galaxy groups, which is among the largest-known structures of the cosmos. The Milky Way is part of the Local Group galaxy cluster (that contains more than 54 galaxies), which in turn is part of the Laniakea Supercluster. This supercluster spans over 500 million light-years, while the Local Group spans over 10 million light-years. The number of superclusters in the observable universe is estimated to be 10 million.

On the scale of space and time, the Space.com article notes:

The biggest supercluster known in the universe is the Hercules-Corona Borealis Great Wall. It was first reported in 2013 and has been studied several times. It’s so big that light takes about 10 billion years to move across the structure. For perspective, the universe is only 13.8 billion years old.

But what really struck my interest was a point about the existence of such structures and cosmology’s guiding principle of universal homogeneity — the cosmological principle.

A 2013 article from Discovery News (a partner site to Space.com) pointed out that this structure appeared to go against a principle of cosmology, or how the universe formed and evolved. Specifically, this principle says that matter should be uniform when seen at a large enough scale. The cluster, however, is not uniform.

That caveat about the cosmological principle — “when viewed on a large enough scale” — has always seemed fuzzy to me. It boggles the mind when galaxies are viewed as pixels on a cosmic map, eh.

 

4 thoughts on “Biggest thing in the universe?”

  1. This Space.com article (June 28, 2018), “Huge Galaxy Cluster Found Hiding in Plain Sight,” discusses the ongoing search for galaxy clusters.

    … the researchers have discovered a Phoenix-like cluster located about 2.4 billion light-years from Earth around a quasar named PKS1353-341. They estimated that the cluster has a mass equal to about 690 trillion times that of Earth’s sun; in comparison, recent estimates of the Milky Way’s mass range between 400 billion and 780 billion times that of the sun.

    The central galaxy of this cluster is incredibly bright: about 46 billion times more luminous than Earth’s sun. The most likely source of all this energy is an extraordinarily hot disk of matter whirling into a supermassive black hole millions of times the mass of the sun, the researchers said.

  2. Biggest star?

    The largest known star in the universe is UY Scuti, a hypergiant with a radius around 1,700 times larger than the sun.

    If UY Scuti replaced the sun in the center of the solar system, its photosphere would extend just beyond the orbit of Jupiter. The nebula of gas stripped from the star extends even farther out, beyond the orbit of Pluto to 400 times time the Earth-sun distance.

  3. Speaking of “big” and the universe, this Forbes.com article “How Long Would It Take To Travel From One End Of The Universe To The Other At Light Speed?” (August 6, 2018) asks a question which takes us on an impossible voyage.

    Answer by Jack Fraser, Master’s Physics, University of Oxford, on Quora:

    It would take an infinite amount of time to traverse the universe.

    At the current time t=13.7bn years, and using the current best measured values of the cosmological parameters, the cosmological event horizon is at a radius re≈16bn light years — which is well within the radius of the observable universe (46 bn light years). Hence, there are regions of the observable universe which are sealed off behind this event horizon.

    Because of this, you cannot travel to these regions, even travelling at the speed of light, as by the time you get to where they are now, they will have expanded to a point further away.

    General Relativity is weird.

  4. Visualizing the observable universe.

    • NASA > APOD > “The Observable Universe” (March 16, 2022)

    Visualization scale varies
    Illustration Credit & Licence: Wikipedia, Pablo Carlos Budassi

    Explanation: How far can you see? Everything you can see, and everything you could possibly see, right now, assuming your eyes could detect all types of radiations around you – is the observable universe.

    In light, the farthest we can see comes from the cosmic microwave background, a time 13.8 billion years ago when the universe was opaque like thick fog.

    Some neutrinos and gravitational waves that surround us come from even farther out, but humanity does not yet have the technology to detect them.

    The featured image illustrates the observable universe on an increasingly compact scale, with the Earth and Sun at the center surrounded by our Solar System, nearby stars, nearby galaxies, distant galaxies, filaments of early matter, and the cosmic microwave background.

    Cosmologists typically assume that our observable universe is just the nearby part of a greater entity known as “the universe” where the same physics applies.

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