New study indicates our galaxy weighs 1.5 trillion solar masses

We know that our galaxy of the Milky Way is big, but its size is an open question. In the past, estimates of total mass ranged from 500 billion to 3,000 billion solar masses. It was hard to pin down because of the unmeasurable dark matter that makes up the bulk of the galaxy's mass. Researchers at the European Southern Observatory (ESO) have successfully measured the mass of the galaxy, including all dark matter. They say that the Milky Way weighs 1.5 billion billion solar masses.

The problem that scientists have always encountered when trying to measure the galaxy is that dark matter could account for up to 85% of all matter. We can not detect dark matter with any known mechanism because it neither emits nor absorbs energy on the electromagnetic spectrum. But we know that this is because of the gravitational effects on the surrounding matter. For example, calculations show that galaxies would move away instead of turning without the hidden mass of dark matter.

The ESO team proposed a clever solution for measuring the mass of the Milky Way without directly observing the dark matter. They used NASA's Hubble Space Telescope and the European Gaia satellite to study the movement of globular clusters around the Milky Way. These star clusters are part of the Milky Way in some respects, but they also gravitate independently. The team examined 46 globular groups, including 34 with Gaia and 12 with Hubble. The farthest was about 129,000 light-years away from Earth.

The globular cluster 47 Tucanae photographed by the Hubble Space Telescope.

The speed of the clusters being directly related to the mass of the Milky Way (more mass makes the clusters gravitate faster), the team has therefore reached a total mass of 1.5 trillion suns. Technically, it's the total mass within 129,000 light-years of the galactic center. The Milky Way disk is about 100,000 light-years in diameter, but it is in the middle of the range predicted by previous studies.

Having a precise measure of the mass of the galaxy is necessary to better understand the universe. The Milky Way is just a galaxy, but it's the one we study best. The distribution and effects of dark matter are related to the formation of structures in the universe such as the Milky Way, but also distant galaxies dating back to the dawn of time. These objects should work as our own galaxy. Knowing his mass is therefore an essential piece of the puzzle.

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