With a diameter of about 100,000 light years – that is, a trillion and a half kilometers – and a mass between 600,000 and 750,000 million times that of the Sun according to the latest measurements, the Milky Way is not a huge galaxy (there are until fifty times larger), but it is a respectable size . The question was whether it is growing or shrinking. Or neither.
The Spanish scientist Cristina Martínez-Lombilla, from the Instituto de Astrofísica de Canarias (IAC), in Tenerife, and her collaborators believe that yes, she is of a growing age . For this, it has been based on the behavior of other groupings of stars with similar characteristics, since we cannot study our space home from the outside, as if we were external observers. They have presented the results of their research at the European Astronomy and Space Science Week, held in Liverpool.
Martínez-Lombilla’s team has based on the information collected by the GALEX and Spitzer space telescopes , which capture rays near ultraviolet and infrared respectively, and the Sloan Digital Sky Survey (SDSS) , an optical observatory capable of making detailed three-dimensional maps. of the universe. Thus they were able to analyze the movements and color of other spiral galaxies comparable to ours.
The peculiarity of this type of galactic formations is that the most massive stars with the most ephemeral life accumulate in their central disk ; astronomical models say that the edges of this disk, with its characteristic arms, is where you have to look if you want to know if the galaxy is growing.
500 meters per second
The observations of the Canarian group of astronomers indicate that, according to the changes in brightness detected at the edges of other disks, the galaxies of the Milky Way family increase in size at a rate of 500 meters per second. At that speed, it would take us around twenty minutes to get from Madrid to Barcelona . Or put another way, as Martínez Lombilla has stated: “if we traveled in time of 3,000 million years, we would see our galaxy 5% larger”. This data puts the increase in perspective, which is rather slow, says the astronomer.
In addition, shortly after (4,000 million years from now), this stellar rejuvenation will be conditioned by the foreseeable collision and fusion of the Milky Way with the Andromeda galaxy , which will create a new cosmic monster with its own personality and rhythm of increase. It should also be borne in mind that the study is limited to the visible part of our cosmic home, since it is believed to be enveloped by a gigantic spherical halo of dark matter that can make up up to 95% of its mass.
In 2015, an investigation in which the CSIC participated demonstrated the presence of this invisible entity –which is only detected indirectly, due to its gravitational effects– in the innermost part of the Milky Way. There, the rotation values of gas and stars did not match those calculated taking only luminous matter into account.
