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Judging the size of a thing is often better done when compared to other things, but this way of thinking tends to collapse when you start talking about objects in space. The Earth is huge, but not if you compare it to something like Jupiter, and Jupiter is tiny compared to our Sun, and our Sun is tiny compared to … well, you see the idea.
So, when you try to measure the weight of something the size of a galaxy, it may seem too abstract to be understood. We have barely seen a fragment of what the Milky Way contains, but scientists are doing their best to provide a global estimate of what our galaxy contains and its weight.
Researchers using Hubble Space Telescope data and ESA's Gaia galaxy mapping mission now estimate that they have a true picture of the Milky Way mass. As you would have suspected, it's very, very big.
For non-astronomers to have a better chance of understanding, the team determined the mass of the galaxy in terms of comparison with our own Sun. It is estimated that the Sun weighs a little more than 330,000 times that of the Earth and that the Milky Way now weighs about 1.5 trillion times as much as the sun. For those who are wondering, it is thought that the Earth weighs about 13.1 billion to 170,000,000,000,000,000,000 pounds.
This new estimate of the weight of the Milky Way is in the best previous hypotheses, ranging from 500 billion to 3,000 billion solar masses. But the science behind this new figure is considered as accurate as possible with current technology.
You may be wondering why it is so difficult to determine the mass of the galaxy, especially when we can see and measure many nearby stars and have detected thousands of exoplanets from which we can derive an estimate. In the end, it is dark matter, which scientists can not observe directly but which represents 90% of the mass of our galaxy.
Without being able to see the dark matter, the researchers proposed a workaround. As ESA notes in a new blog post, astronomers have measured the speed at which the star clusters at the edge of the galaxy are moving. Their speed gives an idea of the total mass of the total galaxy, dark matter included, allowing them to calculate the total mass without having to see everything that is hidden in the Milky Way.
Image Source: ESA / Hubble, NASA, L. Calçada
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