Question about Objects in Ultra Deep Field

phyzguy

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The objects with crosses are stars in our galaxy. The crosses are caused by diffraction of light around the supports that hold the telescope's secondary mirror.
 
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The objects with crosses are stars in our galaxy. The crosses are caused by diffraction of light around the supports that hold the telescope's secondary mirror.
not necessarily all of the objects with diffraction spikes are stars in our own galaxy. some may be quasars or QSO's shining from across the visible universe. after all, they're called what they're called b/c of their star-like appearance, even though they are not stars. they can often be bright enough (even over cosmic distances - that is, several billions of light years) to cause diffraction spikes. you have to remember that, even though its virtually impossible to find even the smallest patch of sky without stars of our own Milky Way in it, the Hubble Deep Field was taken from one of the least star-inhabited patches of sky the Hubble team could find. so while it may be impossible to find a patch of sky completely devoid of Milky Way foreground stars, it doesn't necessarily mean that all objects with diffraction spikes in the HUDF are stars in our own galaxy.
 

Chronos

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There are also artifacts from the camera. They are famous for producing horizontal lines.
 

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