(ORDO NEWS) — It has long been known that the Milky Way has a distinct spiral structure, but our position in the interior has so far prevented astronomers from determining the diameter of the Galaxy with any degree of accuracy.
Various models of what the Milky Way might look like from the outside have estimated a diameter of about 100,000 light-years. But according to one curious study , the size of our galaxy could be about twice that.
Like other spiral galaxies, the Milky Way is a relatively flat disk consisting of a spiral structure surrounded by a rarefied outer halo. The bulk of the stars of the Milky Way are concentrated in the disk, flowing into the halo, and the point of contact of these regions is the rough boundary of the galactic disk itself.
Traditionally, the diameter of spiral galaxies is measured from the center of the disk to the point where the stellar “population” begins to thin out.
However, in the case of our own Galaxy – in which we ourselves are located – it is extremely problematic to measure the exact distance from the center to the edge of the galactic disk, so mathematical and theoretical modeling has to be used to determine the diameter of the Milky Way.
A new way to measure the diameter of the Milky Way
Since most of the stars in the galactic disk are much younger than the average age of halo stars, teams of researchers from the Canary Institute for Astrophysics and the Beijing National Astronomical Observatory came up with the exciting idea of using spectroscopy to determine which distant stars belong to the disk and which belong to the halo.
Working together, the two teams obtained the spectra of 4,600 stars, which was necessary to implement the idea that involves using the individual chemical composition of the stars to determine their age. As a general rule, the younger a star is, the more complex its chemical composition becomes, as each successive generation of stars contains heavier and heavier elements.
Thus, dividing the sample stars into discrete groups, the researchers found that young, “chemically mature” stars occur about 81,000 light-years farther from the galactic center than thought just ten years ago.
It was previously believed that our solar system is located approximately in the middle of the radius of the galactic disk (approximately 26,000 – 27,000 light years from the center of the Galaxy), which means that the stars most distant from the center of the disk are at a distance that is twice as large as the distance from center to the sun.
From this it follows that the radius of the Milky Way is 52,000 – 54,000 light years, and the diameter is 104,000 – 108,000 light years.
Allowing for all sorts of errors, the diameter was roughly rounded off to 100,000 light years. According to a study by the two teams, stars farthest from the center of the Galaxy are at least 100,000 light-years away (81,000 + 26(27) 000 = 107(108) 000).
“Of course, one would expect the existence of young stars at very large distances from the galactic center, as part of a halo,” comments Martin López Corredoira, physicist and lead author of the study.
“However, to the best of our knowledge, no one has previously been able to say that stars [beyond 81,000 light-years from the galactic center] spectroscopically confirm their belonging to the [Milky Way] disk.”
The extra 100,000 light-years added to the Galaxy’s span add almost no extra mass to its disk. Objectively, a small number of young stars is less than the proverbial drop of water in the oceans. This means that the mass of the disk of the Milky Way remains basically unchanged, but the distribution model of the stellar population has been revised.
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