Dark matter was &quot;invented&quot; because there wasn&#x27;t enough observable mass in galactic-scale objects to account for their behavior. In other words, they acted like they had more mass than we could observe. Dark matter is basically characterized by not responding on the electromagnetic spectrum, which is what we use to do these observations. Since all the matter we know of generally <i>does</i> respond on this spectrum, that&#x27;s why dark matter is considered to be &quot;exotic&quot;.