photography - What causes horizontal and vertical lines coming out of pictures of stars?

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.