“If you take a picture of the sky, you’ll find a lot of white dots. Almost all of them are stars, but there are also quasars,” says Peter Barthel, professor emeritus of astronomy at the University of Groningen. “We call that a quasar, which stands for A quasi-stellar object.’
Quasars are billions of times brighter than a star
Dutch astronomer Martin Schmidt discovered the existence of quasars in the 1960s. He saw bright points of light in the sky, which he initially thought were stars. However, it turned out that something special was happening: these “stars” were billions of light-years away, but they were still extremely bright. Such bright stars do not exist. And so it had to be a different kind of being.
What is a quasar?
So a quasar is not a star, but what is it? “Black holes are located at the heart of active galaxies. When such a black hole consumes a lot of matter from the environment, it produces a massive explosion of energy. “A kind of explosion,” Barthel explains. This explosion of light is so bright that it can be seen billions away. Light years: a quasar.
A quasar forms because a black hole consumes an enormous amount of matter from its environment. But not all black holes are active. What exactly causes a quasar to form in a galaxy or not remains a mystery.
We know that there are likely billions of quasars in the universe. They are usually found in the cores of galaxies very distant from us. Even the nearest quasar is millions of light-years away.
A quasar is a look back into the history of the universe
This means that the light from the quasar has been on its way to us for many years. So we look back in time and get a lesson in the history of the universe.
“Quasars were more common in the past,” Barthel says. “The universe was smaller then, and there were more encounters between galaxies. They impacted each other more, and black holes ate more matter, creating quasars. It’s a little quieter in the universe now.”
The bright quasar we now see in the universe may have already disappeared. Because a quasar is a temporary phenomenon. A supermassive black hole swallows a lot of matter from its environment for a period of time, causing a light explosion. This can continue for thousands or millions of years, but it can also stop again. Then the quasar comes out.
Can a quasar form in the Milky Way?
Also at the center of the Milky Way is a black hole, Sagittarius A*. Could quasars form there too? “Our Milky Way Galaxy is in a dormant state, which means the black hole is not feeding,” Barthel says. “But in theory, the core of the Milky Way could also return to the active phase.”
Such a quasar would then send huge amounts of ultraviolet radiation and X-rays into our galaxy. What we will observe on Earth is difficult to predict. The good news? Sagittarius A* is located 26,000 light-years from Earth. As a result, the light from a potential quasar also takes a long time to reach us. It’s possible we’ll see such a quasar coming in advance, says astronomer. But for now, things seem quiet in our part of the universe.
“The chance of quasars is getting smaller and their impacts are going to be smaller too. Things used to be denser in the universe, because it was more compact and had more structure. Everything is much more relaxed now.”
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