Imagine that you have never left your house. What could you draw better? Your own building or the building across the street? The answer is simple. If we look out the window, we can see the building in front in detail, but we have no idea What is it like where we live?. The same thing happens with galaxies. There is data that is easier to analyze from neighboring galaxies than from the Milky Way. Therefore, for a long time, its appearance has been a mystery and its size a very cursory estimate. Thanks to the Gaia missionfrom ESA, we were able to have the most precise map of our galaxy and, with it, understand its structure much better. We know, for example, that it consists of 4 arms, instead of two, as we used to think. Now, through a collaboration between ESA and NASA, we have also discovered the size of the Milky Way.
10% bigger. NASA and ESA scientists have achieved measure the size of the Milky Way through its two X-ray observatories: the XMM-Newton, of the European Space Agency, and the Chandra, of the American one. This type of observatories have been used because the measurement has been carried out through the analysis of X-rays released by gamma ray bursts in other galaxies. Thus, they have seen that the distance between the two outermost arms of the Milky Way is 10% greater than what had been calculated until now.
What do X-rays have to do with it? Gamma ray bursts They are the most energetic explosions in the Universe. Although the rays that give it its name stand out, these explosions are usually followed by an emission in the rest of the electromagnetic range known as afterluminescence. Here X-rays stand outwhich can be measured thanks to the ESA and NASA observatories. These X-rays from neighboring galaxies shoot out in all directions, so some can reach the Milky Way and, of course, also the Earth.
In the latter case, there are some that arrive directly and others that arrive after being dispersed by the dust clouds in the arms of our galaxy. Detecting these two types of X-rays is what allows us to determine the size of the Milky Way.
The importance of angle. The X-rays that travel directly to Earth are the first ones captured by observatories. Next come those that have been dispersed by the dust clouds. As they come from many directions, in the detectors it is seen as a circle in the center of which are the X-rays that arrive directly and, around them, the scattered ones. Although in reality they are several concentric circles. Each of them corresponds to X-rays that have been scattered at the same distance. In the case of galaxies, from the same arm.
With all this, calculations can be inferred that allow us to detect how far some arms are from each other. Until now, only estimates had been made, but in this case the distances have been measured thanks to three gamma ray bursts measured in three of the four arms of our galaxy: Perseus, the outer one, and the outer Scutum-Centaurus. To know the size of the Milky Way you only have to measure the distance between the outermost arms. It was observed that the distance between them and the center is 10% greater than what had been measured until now, so the galaxy is larger than we believed.
Far from retirement. So much Chandra as XMM-Newton They were launched in 1999. We might think that they are already outdated, but they continue to give us data as important as the size of the Milky Way. The key is knowing how to use the information they can capture. In this case, the calculations have been based precisely on looking out the window towards the neighbor’s house. Because until now we had not seen that we could draw our own building by observing the shadow on the one in front.
Images | Magnificent | ESA/Gaia/DPAC, Stefan Payne-Wardenaar, ESA/XMM-Newton and NASA/Chandra
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