Air carrier Captain reported a NMAC at PVU after the Tower had closed and while on approach with an opposite direction non-communicating aircraft. The Captain suggested the PVU Tower extend operating hours to provide increased safety margins for the increasing volume of traffic.

Narrative

There were three IFR arrivals inbound to PVU after the Tower had closed. We were number 2 following Aircraft Y. We had been slowed from about 150 miles out to provide arrival spacing into PVU because the Tower would be closed. Aircraft Y flew over FFU at around 9000 accepting a night time visual over terrain and canceling IFR in the air. Aircraft Y then transitioned to PVU CTAF without clearance from SLC approach. We were monitoring PVU CTAF from approximately 80 miles out an making arrival position calls as able noting at least 3 aircraft in the pattern at PVU; we did our best to let them know that three turbo jet IFR arrivals were inbound. Because Aircraft Y had changed frequencies without being handed off by SLC; SLC asked us to relay their cancellation of IFR and asked us to tell them to squawk 1200. Because it was night and the Tower was closed we then asked SLC that after TAYTR if they could vector us toward point of the mountain for an intercept with the ILS course for a visual approach backed up by the ILS.I was the pilot monitoring and after given an intercept for the ILS course we called the airport in sight. Traffic was called at our 1 o'clock position by SLC at 500' below opposite direction not in communication with him. We had the traffic in sight and asked if we could switch to CTAF to try to communicate. We were handed off by SLC and reminded to cancel so he could get the following Aircraft Z in after us. Immediately after being handed off to CTAF we tried to raise the opposite direction traffic but had no luck and immediately got a TA. My First Officer (FO) responded according to SOP. I asked for any traffic to please advise and called a 6 mile final for full stop in PVU. Still no response or course change from the opposite direction traffic. At this point we were less than a mile and at the same altitude as the opposite direction traffic. The aircraft generated an RA; the FO and self responded according to SOP.Once clear of conflict we re automated the aircraft and continued our approach. I made a plea on CTAF for the aircraft in the pattern to please communicate for the safety of all of us flying in the valley. This was heard by the inbound Aircraft Z. I also let CTAF know that a RA had been generated.ATC has also expressed a shared frustration at the lack of 24 hour Tower in the PVU valley and expressed concern at the frequency of near collisions and traffic saturation between GA and 121 aircraft in the PVU Valley making it increasingly hard to do their job safely when none of the GA aircraft will talk with them. It should be noted there was a highly elevated amount of GA traffic this evening because for this entire week PVU Tower is not allowing any pattern work. Because of this the flight schools are having their students go out before and after Tower closing making a uncontrolled environment even more congested and challenging. I understand we probably have more TCAS events at other airports; however in those environments there is still a Tower proving position reporting and reducing the need for frequency chatter and providing alerts. Even if PVU has less TCAS events these uncontrolled events in a CTAF environment are incredibly dangerous and hard to manage creating undo risk to our passengers and the GA traffic in Utah county. It is highly recommended that the FAA reviews this airspace.Even ATC has expressed their frustration at the unsafe situation in the Provo Valley with the increased volume of flight training and 121 operation side by side. The quickest and easiest solution for increased safety margins would be increased hours of the PVU Tower and changing from contract to FAA personnel. Other mitigations could be the inclusion of ADSB in or ADSB receivers in our aircraft so we can see N numbers for traffic in uncontrolled airspace to allow us to better communicate with unidentified aircraft on CTAF frequencies.