Complex sentence: A total of five supernova remnants (SNRs) have been observed in NGC 5585 and a 1997 paper estimated that the galaxy probably has about one supernova every 1,000 years.
Split into simpler sentences: A total of five supernova remnants (SNRs) have been observed in NGC 5585 to date. A 1997 paper estimated that the galaxy probably has about one supernova every 1,000 years.