An­dromeda galaxy smaller than an­tic­i­pated

Sky at Night Magazine - - BULLETIN - www.icrar.org

The Milky Way’s ‘big­ger’ brother may be more of a twin The An­dromeda Galaxy might not be as large as we thought, as a new method of mea­sur­ing its size sug­gests that it is roughly the same mass as the Milky Way. The team be­hind the dis­cov­ery mea­sured the speeds of stars in An­dromeda to find the es­cape ve­loc­ity of the galaxy, which is de­ter­mined by its mass.

“By ex­am­in­ing the or­bits of high-speed stars, we dis­cov­ered that this galaxy has far less dark mat­ter than was pre­vi­ously thought, and only a third of that un­cov­ered in pre­vi­ous ob­ser­va­tions,” says Dr Pra­jwal R Kafle from the Uni­ver­sity of Western Aus­tralia who led the study.

An­dromeda and the Milky Way are the two most prom­i­nent mem­bers of the Lo­cal Group of gal­ax­ies, and this find­ing will have big im­pli­ca­tions for our ideas about our near­est neigh­bours.

“It’s re­ally ex­cit­ing that we’ve been able to come up with a new method and sud­denly 50 years of col­lec­tive un­der­stand­ing of the Lo­cal Group has been turned on its head,” says Kafle.

With An­dromeda no longer con­sid­ered the Milky Way’s big brother, new sim­u­la­tions are re­quired to pre­dict what will hap­pen when the two gal­ax­ies col­lide An­dromeda

Milky Way

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