Answer by Raziman T.V.:

These are Diffraction spikes.

The shared image was taken by the Hubble Space Telescope which is a reflecting telescope. Reflecting telescopes have a secondary mirror which stands right in the path of the incoming light.

Schematic of a Cassegrain telescope [1].

This is required to take the light collected by the primary mirror out of the telescope system where it can be read. But this creates a problem since the secondary mirror can’t clearly be floating in space. It is thus held in place using a support structure.

Support structure for the secondary mirror of a Newtonian eflector [2].

Light from strong point sources diffracts around the supporting structure, causing diffraction lines in the image which depend on the shape of the support arrangement.

Diffraction spikes produced by various support arrangements for the secondary mirror [3].

This is what happens with the Hubble images as well [4]:

The cross shape visible on bright objects (such as stars) in Hubble  images is a form of distortion that is visible in all telescopes that  use a mirror rather than a lens to focus light rays. The crosses, known  as diffraction spikes, are caused by the light’s path being disturbed  slightly as it passes by the cross-shaped struts that support the  telescope’s secondary mirror. It is only noticeable for bright  objects where a lot of light is concentrated on one spot, such as stars.  Darker, more spread-out objects like nebulae or galaxies do not show  visible levels of this distortion.

If you look closely, you can see that the lines emanating from the stars in the four directions are not of uniform intensity but show intensity oscillations typical of diffraction.

Sources
[1] Source: Wikimedia Commons. Author: Krishnavedala. License: Creative Commons Attribution-Share Alike 4.0 International
[2] Source: Wikimedia Commons. Author: SvonHalenbach. License: Creative Commons Attribution-Share Alike 3.0 Unported
[3] Source: Wikimedia Commons. Author: Cmglee. License: Creative Commons Attribution-Share Alike 3.0 Unported
[4] FAQ – Frequently Asked Questions. Hubble Europeans Space Agency Information Centre

Why do stars in pictures very often have four perfect beams?