About the role of superclusters and voids in our cosmic web.
Many major scientific discoveries and exciting missions have marked 2019. One of the most awe-inspiring moments was the first picture of a black hole which we will all remember. We also spotted the first insterstellar comet “Oumuamua” which visited us from another star system. The first man-made objects named Voyager 1 and 2 ventured into interstellar space. The legendary Voyager probes have officially left our solar system and they discovered that the heliopause is not just a theoretical border, but an actual shield-like phenomenon, where the sun’s plasma bubble deflects most of the incoming cosmic radiation. This is good because it’s how our star keeps our faces from melting, funny as that might sound..
More news and further understanding of the universe awaits us as current missions continue. The Japanese spacecraft Hayabusa 2 is on its way home to earth, carrying samples from far away asteroid Ryugu. We are also closely following NASA’s Parker solar probe as it continues to get closer and closer to our sun. On the 29th of January it approached our star’s surface to a distance of 18.6 million kilometers. Next to this, we continue to watch SpaceX and Boeing while they prepare their rocket fairing capsules for the actual transport of astronauts to the international space station, and eventually to Mars.
Though this is all amazing and inspiring I was struck by an impressive YouTube video last week. It once again showed the vastness and emptiness of space while discussing our planets’ place in it. Understanding our solar system’s position in the grander scale of things will make you feel unbelievably tiny and insignificant. The amount of effort it takes us to map and visit the planets and objects within our own solar system is already enormous, could you imagine going beyond our solar system into interstellar space? (Matthew McConaughey & Anne Hathaway can). Without further ado, let’s talk about galaxies, clusters and groups.
When we talk about these subjects, a key definition is that these systems we call “clusters” or “groups” are gravitationally bound. To start out small, our galaxy, the Milky Way is a system of gas, dust and billions of stars. A step further and we see a galaxy group, these usually contain around a dozen galaxies. Our Milky Way is a part of the so-called Local Group which contains around 30 galaxies and was first discovered by Edwin Hubble in 1936. Within this group, the Milky Way and the Andromeda galaxies are the heaviest members. These two galaxies are expected to eventually collide and form one massive elliptical galaxy. During this collision, our solar system would probably survive as objects within these galaxies are still very far apart. What a sight it would be..
Moving further into space. In the 1950’s Mr. Gérard de Vaucouleurs found out that our Local Group is part of the Virgo Cluster. This cluster contains somewhere over a thousand individual galaxies. As the author of Universe Today, Fraser Cain describes: “these galaxies are all connected together by mutual gravity. Astronomers estimate that it contains a total mass of about 1.2 quadrillion times the mass of the Sun. It covers a total volume of space with a diameter of 15 million light-years across.” These volumes and masses are already hard to imagine, but let’s push even further. The most recognizable member of the Virgo Cluster is Messier 87, we know this galaxy because it holds the supermassive black hole of which we have recently seen the first-ever picture, which is truly awesome..
Something remarkable is that out of the center of Messier 87, a plasma jet forms. This jet of sub-atomic particles and electrons travelling at nearly the speed of light stretches out about 5000 light-years into space. The image above and to the left is taken by the Hubble Space Telescope. In the picture above and to the right you see the black hole at the center of Messier 87 which is responsible for blasting this jet into space.
Feeling small yet? Let’s move further out past the Virgo Cluster into the Virgo Supercluster..
That’s right, the Virgo Cluster is part of the even bigger Virgo Supercluster which is estimated to contain over a million galaxies. The Virgo Supercluster spans over 110.000.000 light-years in size and is just one of the millions of superclusters out there. Other famous superclusters are the Perseus-Pisces, Centaurus, Hydra and Coma superclusters.
These superclusters are forming the filaments of space, they act like curtains in space, shrouding the very large voids that are out there. These voids are areas in space where almost no galaxies or other massive objects are found. All together the superclusters are pulling all objects with mass, like planets, galaxies, clusters and such, towards them leaving huge voids in their midst. The balance between voids and superclusters is the largest visible way of how to perceive our Universe today. A very exciting role in this cosmic play, and the cosmic expanse, is reserved for dark matter and dark energy, but let’s discuss these topics in later articles.
The most impressive discovery where I wanted to talk about in this article is the Laniakea Supercluster. You might be thinking, yet another supercluster? Yes indeed, the Laniakea Supercluster is a gravitationally bound structure where our Virgo Supercluster is a small part of. I said small because Laniakea is about 100 times bigger, and heavier compared to the Virgo Supercluster. A team of scientists, led by R. Brent Tully of the University of Hawaii, found that Laniakea is where we can draw the line. Where we previously thought our supercluster ended with Virgo we found out we were part of an even bigger structure. Laniakea which means “immense heaven” is pulling all objects within its domain towards itself. With many galaxies drawn to an especially dense region within the supercluster called “The Great Attractor”.
Everything outside Laniakea is not gravitationally bound to the supercluster and is moving away from it as our cosmic web keeps expanding. Moving away from Laniakea we see the neighbouring supercluster called Perseus-Pisces as seen below.
Zooming out even further, we see that the structure of space as we know it is made out of voids and superclusters and is looking something like the image below. This cosmic web that we see in the image is expanding but the speed at which that happens is still heavily debated. The speed of the expanding of our Universe is very fundamental to many scientific theories, constants and statements some of which are:
- How old is our Universe?
- Which objects are ultimately bound together, and which are destined to drift away?
- What lies ahead for the eventual state of our Universe?
In my following article I shall explain more about the Universe’s expansion, the role of General Relativity and Hubble’s Law herein.
Further reading on this topic: