“Dark matter” mystery deepens

Like all ga­lax­ies, most as­tro­no­mers be­lieve ours is filled with a strange, in­vis­i­ble sub­stance that be­trays its pres­ence only through its gravita­t­ional pull. The gal­ax­y’s stars would fly apart with­out this so-called dark mat­ter hold­ing them to­geth­er.  But the na­ture of “dark mat­ter” is a riddle—and a new study has only deep­ened the mys­tery.