Using target="_blank" to make links open in a new window has several unwanted security and performance side effects due to the way this is implemented in browsers. There is a great explanation on Google's Chrome Audit resources page:
On top of this, target="_blank" is also a security vulnerability. The new page has access to your window object via window.opener, and it can navigate your page to a different URL using window.opener.location = newURL.
Here is a proof of concept detailing and demonstrating the vulnerability.
At the very least, DSpace should use target="_blank" rel="noopener" for links to external resources that are meant to open in a new window.