What causes the horizontal and vertical lines coming out of pictures of stars, instead of them simply appearing as circles? For example, this picture from Wikipedia: .
They are called diffraction spikes, and they're artifacts from a supporting structure inside a reflector-type telescope.
sometimes you can get these spike artifacts from the microlenses over the CCD's sensor array as well.
also if your CCD does not have antiblooming logic, a very bright star can cause neighboring pixels to saturate as they are being read out, leading to a "spike" only along the readout axis. here's a good document with some common artifacts, from the hubble team: HandoutIIIc.
the spikes in the OP's image are likely caused by the spider vanes which hold the secondary mirror in place, as Russell says.
(I'd make this a comment, but no reputation yet.)
Minute Physics has a good video on this! Filtering light through any lens causes spikes that identify what kind of aperture was used. That looks like a Hubble picture because of the diamond spikes.