Free Astronomy Magazine March-April 2016

GALACTIC EVOLUTION their lives). Entirely comparable results were observed in the second and more re- cent study, conducted by a mainly Italian team, led by Enrico Maria Corsini (Depart- ment of Physics and Astronomy “Galileo Galilei”, University of Padua), on the bar- red lenticular galaxy NGC 1023, located in Canes Venatici and distant about 35 mil- lion light-years (visual magnitude 10.6). By processing Hubble’s archival data together with the spectra collected by the Multi- Pupil Field Spectrograph of the historic Russian telescope BTA-6, Corsini and col- leagues succeeded in separating the light contribution (and thus the properties) of the stars of the nuclear disk from that of the stars of the hosting spheroid. Thanks to this, the team found that while NGC 1023 is about 12 billion years old, its nu- clear disk exists ‘only’ from 3 billion years, an era to which can be dated back the last, big merging event for this specific particu- lar galaxy. The objective of those involved in the two works is now that of dating a growing number of nuclear disks and, once gath- ered a statistically significant sample size, ascertain whether the galaxies with great- er size and mass are indeed those which have undergone most mergers. R ight, the giant dome of BTA-6 (53 metres high). [SAO RAS] Below, the posi- tion of the dwarf satellite galaxy PGC 10139 (aka NGC 1023A) with respect to NGC 1023. The two galaxies are con- nected by a neu- tral hydrogen bridge, probably generated by an interaction cur- rently underway. [STScI/NASA] those of the surrounding stars. While the galaxy’s age was calculated in 12 billion years, the stars of its nuclear disk were in- stead found to be at least 6 billion years old and to have an obviously greater metal content (the gas from which they originat- ed had meantime been enriched by the metals released from previous generations of massive stars that reached the end of n