How many galaxies make up the universe?

Antoine Ducarre

We had long believed that the universe contained between 100 and 200 billion galaxies. However, this figure is very low compared to recent estimates.

our galaxy, The Milky Way, is far, very far from being the only representative of its category in the infinity of the universe. Until recently, scientists estimated that there were between 100 and 200 billion galaxies. A figure that makes you dizzy, but which would be very far from reality. In fact, there would be at least 10 times more.

What is a galaxy?

To know how many galaxies make up the vastness of the universe, it is important to know what we are talking about. According to NASA’s definition, a galaxy is thus a set of stars, gas and dust bound together by gravity. At its center there is very often a supermassive black hole around which it orbits. There is to date three types which was defined by Edwin Hubble, an American astronomer.He therefore distinguishes spiral galaxies, elliptical galaxies and irregular galaxies.

The spiral galaxies

Spiral galaxies are very easily recognizable. Take effect, The Milky Way is about to be one, just trace its shape to try to find similar formations. It is thus a rotating disk with a set of very old stars in the center, which is called a bulge. From the latter relatively light arms emerge. The solar system is also in one of the arms of the Milky Way, far from the center and its supermassive black hole called Sagittarius A*.

Artist’s impression of the Milky Way, a spiral galaxy Science Photo Library – Mark Garlik/GETTY_IMAGES

In this category there are also barred spiral galaxies. We recognize them because their arms do not start directly from the central bulb, but from a star bar located in their center, giving the impression that they have been crossed out.

Satellite image of NGC 1300, a barred spiral galaxy located 55,000 light years from Earth Stocktrek / GETTY_IMAGES

Elliptical galaxies

These galaxies are ellipsoidal often huge formations where very few stars are born. These are determined very old galaxies which took this form after colliding with other galaxies during their lifetime. The best known elliptical galaxy today is for sure M87. It lies 60 million light years from Earth in the constellation Virgo. Its supermassive black hole M87* had been photographed in 2019 by the Event Horizon telescope ensemble. It was that time the first ever image of a black hole.

Illustration of an elliptical galaxy Science Photo Library – Mark Garlik/GETTY_IMAGES

Irregular galaxies

These are often the smallest galaxies present in the universe. Since they have no regular shape, they are estimated to contain far fewer stars than their counterparts. Indeed, in these formations, the number of stars would not exceed a billion between 100 and 400 times smaller than in the Milky Way.

NGC 4449, a Magellanic irregular galaxy located in the constellation Hounds approximately 12.6 million light-years from Earth Stocktrek / GETTY_IMAGES

How many galaxies in the universe?

Now that the different galaxy types have been identified, we can focus on their numbers. From the 90s to 2016, the scientific community agreed that the observable universe contained between 100 and 200 billion galaxies. However, the work of Professor Christopher Conselice from the University of Nottingham in England published in October 2016, made it possible to review this estimate upwards.

According to his research conducted by observing the various readings of the Hubble Space Telescope and with the help of ESA, the European Space Agency, he was able to estimate that the number of galaxies present in the universe would be 2000 billion or10 times more than previous estimates. For the curious and bilingual, his entire study can be found in English,just here.

This figure will certainly change or be clarified thanks to future images, whichJames Webb Space Telescopecan send us.

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