Baxters novels are nice but he always takes this incredible long term view which is just depressing - in the incredible long term everything becomes cold and dark. He invents quark beings which had their time when the universe was a lot hotter; and whose seeds germinate when you light up certain types of engines which operate with these temperatures of old.
He also invents neutrino birds and lots of other beings. Take them for what they are, don't take them too serious. They're like Q in Star Trek: unexplained storyline drivers.
So this is my answer - They are not explainable, but they do their part in the context of the story.
The rest below is just nice to read.
There are some more nice energy beings in other stories which have equally unfeasible physics but which drive their respective storyline equally well.
other energy beings
Commonwealth Series, Peter F. Hamilton
Hamilton let's his humanity discover a way to store information in the sub-quantum-level of physics. They then shrink in size and energy consumption to less than a atom size; while their intelligence and abilities (in the virtual world) grows immensely.
In order to influence the real world, however, they have to clone or manufacture a real body and download a human-sized conciousness into it; which takes away the superintelligence but gives the ability to deal with the real world.
Hamilton mainly uses this storyline device to put some "canned characters" back on the plate hundreds or thousands of years after their real life time, just because he and probably his readers love those characters.
Ender's Game, Orson Scott Card Spoiler alert
In the first book (and film) Ender fights a race of beings who live in their interstellar mind connections more than in the real world. In the later books of the series, (spoiler alert) humanity discovers that it is possible to have an entire conciousness living only inside those connections; and that they have their own one which is made up of computer networks (thought) and interstellar connections (soul). There are even more strange beings, but I don't want to go spoil the entire book series.
Orson Scott mainly uses all of this to explore the different possible styles of life, possibilities of "what's that, a soul" and to set some arrogant humans back to their real place in the world. First contact novel, written large.
The "Energy beings" are mostly generated by dreams of psychic active species, live in a separate plane of being or dimension or whatever. They either come through the head of a psyker or they scratch through the walls of a ship during interstellar flight - because faster than light flight is literally through the dimension of nightmares in that background story. Being a wargame, the only thing they do is attack someone or generate unrest so that other species attack each other.
Again, these are mainly style drivers and storyline drivers, and they're great at that.