score:14
The spacing divides the 'half-lines' of the poem. This is fundamental to Old English metre, where each line of the poem consists of two half-lines, connected by alliteration.
If you are interested, the Electronic Beowulf edition, that you have linked in the question, has a section describing the meter of the poem.
By clicking the Meter option, the student may choose to have tooltips for any or all of the five different prevailing metrical theories.
The meter option can be selected from the Options pane on the left of the viewer: