The Milky Way has gained weight

Science Illustrated - - SCIENCE UPDATE -

Our galaxy is at least 28 % heav­ier than we thought. That is the con­clu­sion of a re­search project by the Univer­sity of Ari­zona, USA, and the Univer­sity of Cam­bridge.

Un­til now, astronomers have used ob­ser­va­tions from satel­lite gal­ax­ies to cal­cu­late the mass. Satel­lite gal­ax­ies are bound by the grav­ity with which the mass of the Milky Way in­flu­ences them, and when astronomers know the dis­tance to the gal­ax­ies and the speed at which they or­bit the Milky Way, they can cal­cu­late the mass of our galaxy. In re­cent years, cal­cu­la­tions have shown re­sults of 600-750 bil­lion times the Sun’s mass. How­ever, those re­sults are doubt­ful, as rather than cir­cu­lar, the satel­lite gal­ax­ies have el­lip­ti­cal or­bits, and so, their speeds vary, de­pend­ing on their po­si­tion in the or­bit. When they are the fur­thest away from the Milky Way, they travel more slowly than close by.

In­stead of us­ing the speed of the satel­lite gal­ax­ies, the sci­en­tists use their an­gu­lar mo­men­tum, which is the same all through the or­bit, be­cause it de­pends on both speed and dis­tance. Ac­cord­ing to the new method, our galaxy weighs 960 bil­lion times more than the Sun, or 28% more than ear­lier cal­cu­la­tions. The new knowl­edge helps astronomers seek­ing dark matter, which we can only mea­sure by look­ing at the grav­ity, with which the matter in­flu­ences its sur­round­ings.

The mass of the Milky Way can be cal­cu­lated by ex­am­in­ing the mo­tion of the gal­ax­ies that or­bit it – such as the Large Mag­el­lanic Cloud (in­sert).

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