Is a cyst on the aorta dangerous?

Vascular surgeon. Any growth or swelling or cyst or aorta is of great concern. This must be checked out with vascular surgeon.
Check with your doc. Typically the aorta does not develop cysts. The aorta, or main blood vessel leading from the heart to the neck, arms and abdomen / legs can develop an aneurysm or enlargement. This is not normal and can be dangerous if it gets too large. There are several ways to image the aorta depending on what part of the body is involved including ultrasounds and ct scans.
Unclear question. A cyst on the aorta is not a medical condition, unless you mean aneurysm. If you are asking about aneurysm, it depends on the location, size and etiology of aneurysm.