One of the great things about the scientific study of the universe is that many times we do not know what we are discovering. There are plenty of things that we can observe without understanding, and we certainly cannot predict their future importance in understanding the universe we live in. Fermi bubbles are one of those fantastic things that we find in our universe that inspire curiosity and further study. Since their discovery in 2010, by a team from the Harvard-Smithsonian Center for Astrophysics, there has been a strong desire to understand their origin.
The first question that many may have is, “What is a Fermi Bubble?”. Fermi Bubbles are a pair of balloon shaped structures in the middle of the Milky Way that are made up of energetic gamma rays, which are the most powerful rays in the universe. They were first observed using the Fermi Gamma-Ray Space Telescope, which is why they are named after Fermi. Upon observation, scientists see that they are sharply shaped structures, almost like gigantic footballs made of gamma rays in the middle of our galaxy. They are also gigantic! They are about 30,000 light years long. They are a puzzling and vast part of our solar system that has sparked our intrigue.
So what started these Fermi bubbles? Is there any way to know? As with most space discoveries, the answer is complicated. Scientists have estimated that whatever event caused the bubbles happened between two and a half and four million years ago. Right after the bubbles were discovered theorists began trying to put the puzzle together. Some think that the bubbles were created when a black hole consumed an enormous amount of gas and dust in the middle of the galaxy. Others believe that it could have been a massive amount of stars experiencing a supernova at the same time, creating the energy necessary to create these Fermi bubbles. None of the current theories are perfect, and at this point, we cannot say for sure which is more likely. The one thing we do know is that something big happened and left us with an incredible mystery.
Using a Hubble Space Telescope, astronomers observe distant a quasar that lies behind the bubbles and tracks how much energy from the quasar the bubble absorbs. These observations have shown that the gas that is outflowing from the center of the Milky Way is flowing in all directions at about 2 million miles per hour. This gas outflow is connected to whatever event created the Fermi bubbles several million years ago. Since the first quasar that astronomers observed, they’ve since added over 20 other quasars that send gamma rays through the bubbles. Since these different quasars send energy flows in various directions through the bubbles, the observation of their speed might tell us something. It might give us some great insight into how these bubbles got started in the first place. Either way, this has led to a massive amount interest about what exactly is happening at the center of our galaxy.