

The Aloof control the galactic core and prevent all attempts by the Amalgum to enter the core. The galaxy is controlled by two groups, the Amalagum and the Aloof. I would guess the second book is Incandescence by Greg Egan. Lizards identified themselves as belonging to one of three groups, which were named for the actions of spiraling inward, spiraling outward, and, the clear majority, following a circle. The lizards had no apparent social hierarchies, and as hermaphrodites they exhibited no sexual dimorphism, but the scouts identified one curious form of division. They find a sentient life form that look like lizards, and these have the three philosophies, Spiral In, Spiral Out and Circle:

The two travellers are Azaz and Shelma, who are sent to investigate the planet. a planet drifting alone through space, so it should have cooled to only a few degrees Kelvin but instead it is warm enough to have liquid water.

I read it in the 2010 anthology Godlike Machines. The first story is the novella Hot Rock by Greg Egan. Thus they are revealed to be the mysterious keepers of the core. Realizing how much the core sucks, they vowed to always push away others who try to enter the core. It turns out the aliens are the source of the DNA and they evolved in the galactic core. The story alternates between their investigations and strange tale of weird alien life. In the second one, two travellers are invited to the galactic core as a planet is found that has DNA on it. Most people are in the circle faction but some are spiral in and others are spiral out. The heat is caused by them figuring out how to turn themselves into little quantum strings or something that can run simulations and produce energy. On the planet/rock they find an aquatic species. The main character, while she is on the trip, her whole planet slows down so that they will only experience a few years subjectively like her, as is there custom. In the first one, two travellers from different planets meet at a hot rock passing between their two solar systems. Anyone that tries to enter the galactic core mysteriously finds themselves turned around.

The outer galaxy is united in a largely digital civilization. A couple years ago I read two novellas/novels set in the same universe.
