At center of the star

what is it inside the star?

http://legacysurvey.org/viewer?ra=119.9798&dec=34.9036&zoom=16&layer=decals-dr2

Do you mean this bright star? If so – the centers of bright stars often saturate, and those pixels are flagged as bad, so the image processing code doesn’t know what to put there. Those two orange funny-shaped things on either side are called “ghosts” from reflections inside the telescope. Nice!