The largest and brightest galaxies are those that contain

Quasars

Explanation:

 Quasars are the brightest and the largest in the galaxy and it is also known as the bright center of the galaxy. In the year 2015, the quasars was declared as the brightest in the galaxy and it is observed with the help of WISE telescope.

The quasars word is basically derived from the radio source in the quasi-stellar as this type of the object are mainly identified in the form of radio resources. The quasars are also known as QSOs (Quasi stellar object).

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