In this universe, we are just a drop in the cosmic ocean.
This image, taken from the International Space Station by astronaut Karen Nyberg in 2013, shows the two largest islands in the southern part of the Mascarene Plateau: Reunion, in the foreground, and Mauritius, partially covered in clouds. To see a human on Earth from the altitude of the ISS would require a telescope the size of Hubble. The scale of a human is less than 1/5,000,000 of the scale of the Earth, but the Earth is just a proverbial drop in the cosmic ocean.
Everything mankind has ever known is confined to a spheroid only 13,000 km in diameter.
This view of Earth is brought to us by NASA’s MESSENGER spacecraft, which had to fly by Earth and Venus in order to lose enough energy to reach its ultimate destination: Mercury. The round and rotating Earth and its characteristics are undeniable, because this rotation explains why the Earth bulges in the center, is compressed at the poles and has different equatorial and polar diameters. Yet the average diameter of the Earth is just under 13,000 kilometers and differs by less than 1% in the polar and equatorial directions.
Even other planets regularly occupy thousands of times the volume of Earth.
The planets of the solar system are shown here to scale in terms of physical sizes, but not in terms of distances between them. Jupiter and Saturn are each more than ten times the diameter of Earth, and some giant planets can be ~twice the size of Jupiter.
Stars start out as small as the largest planets, but grow much larger.
Brown dwarfs, between about 0.013 and 0.080 solar masses, will fuse deuterium + deuterium into helium-3 or tritium, remaining at the same approximate size as Jupiter but reaching much larger masses. Red dwarfs are only slightly larger, but Sun-like stars are not shown to scale here and would be several times larger.
The largest supergiant stars have diameters exceeding billions of kilometers.
This illustration shows some of the largest stars in the Universe, along with the orbits of Saturn (brown ellipse) and Neptune (blue ellipse) for comparison. The stars, from left to right, are the largest blue hypergiant, the yellow hypergiant, the orange hypergiant, and then the two largest stars of all: the red hypergiants UY Scuti and Stephenson 2-18. The largest stars are about 2,000 times the diameter of our Sun.
They are comparable in size to the event horizons of the most supermassive black holes.
This diagram shows the relative sizes of the event horizons of the two supermassive black holes orbiting each other in the OJ 287 system. The larger, at about 18 billion solar masses, is 12 times the size of the orbit of Neptune; the smallest, at 150 million solar masses, is about the size of the asteroid Ceres’ orbit around the Sun. There are few precious galaxies, all much smaller than ours, that have a supermassive black hole of “only” ~4 million solar masses.
But even the largest individual objects are no match for cosmic collections of objects.
The solar system, seen on a logarithmic scale, highlights how far away some of the objects are. The planets, Kuiper Belt, Oort Cloud and nearest star are all represented here, with Voyager 1, currently 155.5 AU from the Sun, our furthest man-made spacecraft.
Around each star system, the Oort clouds extend for several light years: tens of trillions of kilometers.
An illustration of the inner and outer Oort cloud surrounding our Sun. While the inner Oort cloud is torus-shaped, the outer Oort cloud is spherical. The true extent of the outer Oort cloud may be less than 1 light-year or greater than 3 light-years; there is enormous uncertainty here. Comet Bernardinelli-Bernstein has an aphelion of just under a light year, suggesting that the Oort Cloud is at least as large.
The stars themselves come together in large galactic assemblages.
Only about 1,000 stars are present in the entire dwarf galaxies Segue 1 and Segue 3, which have a gravitational mass of 600,000 Suns. The stars making up the dwarf satellite Segue 1 are circled here. As we discover smaller, fainter galaxies with fewer stars, we begin to recognize how common these small galaxies are; there are nearly 100 in our local group alone.
At a minimum, they have thousands of stars, spanning hundreds of light years.
The cluster of giant galaxies, Abell 2029, hosts the galaxy IC 1101 at its heart. With a width of 5.5 to 6.0 million light-years, more than 100 trillion stars, and the mass of nearly a quadrillion suns, it is the largest known galaxy of all according to many metrics. It is unfortunately difficult for the Universe to make a single object significantly larger due to its finite age and the presence of dark energy.
The largest galaxies contain more than 100 trillion stars, with Alcyoneus, a record, spanning an unprecedented 16 million light-years.
In a one-of-a-kind image, the scale of galaxies including the Milky Way, Andromeda, the largest spiral (UGC 2885), the largest elliptical (IC 1101) and the largest radio galaxy, Alcyoneus, are all displayed together and, accurately, to scale.
At even larger scales, galaxies cluster together, forming structures up to hundreds of millions of light-years in diameter.
The impressive galaxy cluster MACS J1149.5+223, whose light took more than 5 billion years to reach us, is one of the largest bound structures in the entire Universe. On a larger scale, nearby galaxies, groups, and clusters may appear to be associated with it, but are distant from this cluster due to dark energy; superclusters are only apparent structures, but the largest clusters of related galaxies can still be hundreds of millions or even a billion light-years in extent.
The largest superclusters, voids and filaments – although not gravitationally bound – span billions of light years.
The Great Wall of Sloan is one of the largest apparent, presumably transient, structures in the universe, at around 1.37 billion light-years in diameter. It may just be a fortuitous alignment of several superclusters, but it’s certainly not a single gravitational related structure. Sloan’s Great Wall galaxies are shown on the right.
Overall, our observable universe spans 92 billion light-years.
The size of our visible Universe (yellow), as well as how much we can reach (magenta). The limit of the visible Universe is 46.1 billion light-years, because that is the limit of how far away a light-emitting object reaching us today would be after moving away from us for 13.8 billion years. However, beyond about 18 billion light-years away, we can never reach a galaxy even if we are traveling through it at the speed of light. Beyond the limits of the observable Universe lies more Universe, up to the limits imposed by where inflation did not stop at the same time as it happened where our hot Big Bang has occurred. This limit, if it exists, has not been discovered.
But the unobservable Universe must be at least hundreds of times larger.
This simulation shows the cosmic network of dark matter and the large-scale structure it forms. Normal matter is present, but only represents 1/6th of the total matter. Meanwhile, matter itself only makes up about 2/3 of the entire universe, with dark energy making up the rest. The unobservable Universe must span at least ~400 times the extent of the visible Universe we can see, which means our 92 billion light-year-diameter Universe is less than one 64 millionth of the minimum volume of what exists.
For all we know, the Universe may even be infinite.
While many independent universes should be created in expanding spacetime, inflation never ends everywhere at once, but rather only in separate, independent areas separated by continuing expanding space. This is where the scientific motivation for a multiverse comes from, why two universes will never collide, and why we expect the unobservable universe to grow to infinite size over time.
Mostly Mute Monday tells an astronomical story in pictures, visuals and no more than 200 words. Talk less; smile more.