The Largest Known Things in the Universe

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Podcast Transcript

The universe is big. Really, really big. So big that it is hard to intuitively grasp its size because we have nothing in our lives that we could compare it to. 

Not only is the universe big, but within it are things that really big as well. 

The discovery of these big things have been some of the biggest discoveries in the history of science, and the discoveries will probably keep continuing into the future. 

Learn more about the largest known things in the universe on this episode of Everything Everywhere Daily.

If you are going to talk about the biggest things in the universe, you have to start the discussion with the biggest thing there is and the biggest thing there can be, the universe itself. 

Before I get into that, I should note that when it comes to the size of the universe, there is much we simply do not know and in fact, that we cannot know. 

We are ultimately limited by the speed of light. In a previous episode, I addressed the age of the universe and how we can estimate its age.

As we have developed better telescopes, such as the James Webb, we have been able to gather more and better information. However, we can only see what we can see. That means our knowledge is limited to the observable universe. 

The observable universe is the part of the universe that is close enough to us that light has had time to reach us since the universe began. 

If we take the generally accepted age of the universe at 13.8 billion years, and this number has come into dispute in the last few years, then the furthest we can see would be 13.8 billion light years away. That is the size of the observable universe. 

However, that isn’t quite true. The universe is expanding, so if the furthest light that we can see is 13.8 lightyears away, that means the light was emitted 13.8 billion years ago. We are literally looking into the past. 

In the 13.8 billion years since the light was emitted, space has expanded, which means we are seeing something that is currently much further than 13.8 billion lightyears away. 

The best estimate, based on the expansion of the universe, is that the edge of the observable universe that we can see is now actually about 46.5 billion light-years away. 

As the edge of the observable universe can be seen in all directions, and because the universe appears to be expanding equally in all directions, the diameter of the observable universe would be about 93 billion light years. 

Of course, that is only what we can see. There is no reason to believe that what we can see is all there is.  The problem is there is no way to know what or how much is beyond what is in the observable universe. Because it is beyond the limit light can travel, there is no way for any information from this part of the universe to reach us. 

It is entirely possible that the universe is infinite in size, but there is no way to know. 

So, if we take a step back from the entire universe, what is the biggest….thing inside it?

Astronomers have done a mapping of the observable universe, and what they’ve found is that the universe is not equally distributed. There are enormous areas that are seemingly devoid of anything. Then, there are vast chains of galaxies known as Galaxy Filaments and Walls

Filaments are long stretches of galaxies, and walls are the same stretched-out-like a sheet. 

The largest of these is the Hercules-Corona Borealis Great Wall. It is literally the largest structure in the universe, measuring about 10 billion light years in length.

These large filaments and walls are not necessarily held together by gravity. They are too large. 

The largest gravitationally bound objects are galaxy clusters and superclusters. They are collections of hundreds to thousands of galaxies that are gravitationally bound to each other. 

The largest known galaxy supercluster is the Laniakea Supercluster. 

The Laniakea Supercluster consists of approximately 100,000 galaxies, including the Milky Way. 

The diameter of the Laniakea Supercluster is about 520 million light years.

The fundamental unit of a cluster or supercluster is the galaxy. A supercluster is a collection of galaxies gravationally bound, just as a galaxy is a collection of stars that are gravitationally bound. 

There are many different types of galaxies. There are spiral, elliptical, lenticular, and irregular galaxies.

The largest galaxy observed is IC 1101. It is a supermassive lenticular galaxy located in the Abell 2029 galaxy cluster. It has a diameter of approximately 500,000 lightyears. 

It is located approximately 1.15 billion lightyears from Earth. The galaxy is so big that it was discovered in 1790 by William Herschel, the discoverer of the planet Uranus. 

Galaxies are collections of stars, and at the center of most galaxies are supermassive black holes. 

If you remember back to my episode on black holes, they are created when large stars collapse on themselves. The result is something so massive with a density so great, that light itself can’t escape. 

So far everything I’ve mentioned in this episode, even the universe itself, I’ve been able to provide an estimate using some measurement of length. 

You can’t really do that with a black hole. Once a black hole starts to collapse on itself, there isn’t any known force in nature that can stop it. That is why they are often called singularities. We have no clue if they have actual length, width, or depth because it is impossible to observe them. 

So, when determining what the largest black hole is, we can measure it in one of two ways, either through the size of its event horizon or by its mass. 

The largest black hole that has ever been found is known as TON 618. 

It was first observed in 1957 as it powers an incredibly powerful quasar, but at the time, astronomers didn’t know what it was. 

TON 618 has a mass 40 billion times the mass of the sun, and the quasar that it powers has a luminosity 140 trillion times that of the sun.

Black holes are ultimately made up of stars. So, as we step down our cosmic ladder, what is the biggest star that we know of?

A few things about stars. For starters, it is difficult to observe individual stars outside of our own galaxy. Other galaxies are so far away that all of the stars in them tend to blend together, making it difficult to identify individual ones.

So, for the most part, what we know of individual stars are stars located in our galaxy, the Milky Way. 

There is a limit to how large a star can get in terms of mass. Beyond a certain point, the star will explode. 

However, stars can grow quite large in terms of volume. If you remember back to my episode on stars, depending on the mass and age of a star, they can become red giants. 

The largest known star in terms of volume in UY Scuti. 

UY Scuti is classified as a red supergiant and a pulsating variable star. A pulsating variable star is a star whose brightness, as seen from Earth, changes over time.  

UY Scuti is way larger than the sun. The radius of UY Scuti is 909 times greater than that of the sun. The volume of UY Scuti is 750 million times that of the sun. 

If UY Scuti were to be placed in our solar system in the current location of the sun, it would completely swallow up Mercury, Venus, Earth,  Mars, the asteroid belt, and Jupiter. 

Eventually, UY Scuti will wind up as a massive supernova millions of years from now. 

As we take a step down from stars, we encounter the things that orbit stars, aka planets. 

You are probably pretty familiar with the planets orbiting the sun and know that Jupiter is the largest planet in our solar system. 

However, just because something is big in our solar system doesn’t mean that it is big in galactic terms. 

It has been almost 30 years since the discovery of the first exoplanet. As of the time of this recording, 5,653 exoplanets orbiting other stars have been discovered. 

While everything I’ve mentioned in this episode is subject to change pending new discoveries, the thing most likely to change is probably the largest exoplanet. 

As of my recording of this episode, the largest exoplanet that has been discovered so far is PDS 70b.

PDS 70 is the name of the star, and b indicates that it is the second planet discovered around that star. 

It has a mass of about three times that of Jupiter. If it were any more massive, it would become a brown dwarf star. 

While it is the most massive, it isn’t the largest exoplanet by volume. The largest exoplanet by volume is HAT-P-67 b. 

HAT-P-67b is known as a hot gas giant. It is a gas giant like Jupiter or Saturn, but it is extremely close to its star, like Mercury. The mass of the planet is only about 60% that of Jupiter, but it is 2.08 times the diameter of Jupiter. 

Given its mass and volume, it makes it the least dense exoplanet ever discovered. 

As we get below planets, we have to look closer to home because we can’t observe anything smaller further away.

What is smaller than a planet? Well, that was resolved with the whole “Is Pluto a planet?” controversy, which provided the currently used definition in astronomy. 

The largest thing we know of smaller than a planet would be a transneptunian object. 

The largest transneptunian object ever discovered is named Eris. Eris is slightly larger and more massive than Pluto, which is also a transneptunian object. 

It is, on average, 67.8 astronomical units from the sun, an astronomical unit being the average distance from the Earth to the Sun.

However, transneptunian objects are not the only sub-planetary objects in the solar system. There are also moons that orbit around planets. 

The largest moon that we know of, is Jupiter’s moon, Ganymede. 

Ganymede has a diameter of 5,268.2 kilometers, which is larger than the Earth’s Moon and the planet Mercury. 

As we shrink in size, a host of rocks fly about the solar system in erratic orbits. These are known as meteoroids. When they strike the surface of the Earth, they become meteorites. 

The largest meteorite that is believed to have hit the Earth did so 2 billion years ago. Known as the Verdfort Meteorite, it hit what is today South Africa. It was over twice the size of the meteorite that hit the Yucatan Peninsula in Mexico, and it is estimated to have been 12.4 to 15.5 miles or 20 to 25 kilometers in diameter.

There are a lot of very big things in the universe, and obviously, this list only scratches the surface. 

But the next time you ponder something that you think is big, just remember that there is always something much, much bigger.