Police stand guard in front of the Supreme Court on March 27, 2013 in Washington, DC. The US Supreme Court tackled same-sex unions for a second day Wednesday, hearing arguments for and against the 1996 US law defining marriage as between one man and one woman. After the nine justices mulled arguments on a California law outlawing gay marriage on Tuesday, they took up a challenge to the constitutionality of the federal Defense of Marriage Act (DOMA). The 1996 law prevents couples who have tied the knot in nine states -- where same-sex marriage is legal -- from enjoying the same federal rights as heterosexual couples. TOPSHOTS/AFP PHOTO/Jewel Samad