Astronomers have made a new estimate of the total weight of the Milky Way: the galaxy that includes the Sun. They come in at a weight of about 200 billion suns. This makes the Milky Way four to five times lighter than expected.
Scientists regularly try to determine the weight of the Milky Way. This is difficult, because in addition to all the stars, black holes, nebulae and gas piles, they also have to include dark matter in the calculations. Canadian scientists came out in 2017 at a weight of 700 billion suns. In 2019, another research team arrived at a different weight: 1.54 trillion (!!) suns.
Now scientists have used data from Gaia to accurately estimate the weight of our host galaxy. The Gaia catalog contains 1.8 billion stars. Thanks to this data, researchers have gained a good picture of the so-called rotation curve of our galaxy. The rotation curve is a representation of the speeds at which matter – such as stars – revolves around the center of a galaxy at different distances. This is often outlined in a graph, as you see below.
In this graph of the rotation curve you see the speed (y-axis) and the distance from the center (x-axis). The white points and error bars show Gaia’s measurements. The blue curve connects these points. It is noticeable that in the outer regions of the Milky Way the speed decreases rapidly. This decrease is also called the Keplerian decrease. This may be because there is little dark matter present.
Scientists have always assumed that there is six times more dark matter than normal matter in the Milky Way. However, the strong Keplerian decline is clear evidence that our galaxies harbor much less dark matter. The researchers write in the new paper that about a third of all matter in the Milky Way is normal matter. The rest is dark matter.
This seems obvious, but it is not. Other spiral galaxies in the area do not have Keplerian decay. Our Milky Way therefore appears to be unique. How come? One possible explanation is that the Milky Way has not had many collisions with other galaxies in the past. The last major merger with another galaxy was nine billion years ago: more than four billion years before the birth of our solar system. Another explanation could be the different measurement methods. To determine the rotation curve of other galaxies, scientists look at neutral hydrogen gas. In the case of the Milky Way, a six-dimensional data set was used. Is it a matter of comparing apples and oranges?
The search for the true weight of the Milky Way will undoubtedly continue. Fortunately, because thanks to this kind of research we learn more about our own galaxy and the distribution of dark and visible matter.
2023-09-30 17:04:19
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