Solution to Exploration by Arcadia

 Exploration by Arcadia - SOLUTION

Nine galaxies (four elliptical, three spiral and two irregular) with all non-galactic entries attracted towards the central barred cell, itself at the centre of an irregular galaxy spelling [BLACK HOLE STAR]*. Answers to galactic clues, appropriately entered, filled the whole grid, with answers to the non-galactic clues allowing sufficient checks to enable the solver to deduce unchecked letters making real words.

Derivation	Answer	type
R in GO+USERS, SHOO(t)	GROUSERS; SHOO	E
TIER after MY(homph), AN+AN	MIGHTIER, ANAN	S
POND in SEES, ARE+S	SPONDEES, ARES	S
REIN round (ROAD*), (h)IKE+A	REORDAIN, IKEA	S
DECIDES about I; double def. of SEAL	DEICIDES; SEAL	E
PAR+VENUE; ON round (s)CEA(t)	(PARVENUE+OCEAN)*	I
(GP round NIPPER)<; double def of SALE	PREPPING; SALE	E
LES(t) round SLADE*; (c)RISE(s)	LEADLESS; RISE	E
B+LACK+WHOLE (homph) ARTS*	(BLACK HOLE+STAR)*	I
(b)OUNDARIES [almost extinct = archaic]	DEINOSAUR	7
PAIL+L+E+T+T+(win)E	PAILLETTE	1
(j)DVANCE after RE+A	READVANCE	8
[NINES+SEL(f)]+G	LESSENING	2
EC+(s)ARDINES	ECARDINES	11
PALEBRASS*	SPARABLES	10
INTRO*+HO(rr)ID	ORNITHOID	4
IN+(RIT in HEED)	INHERITED	5
L in CUE	CLUE	9 i
(b)ELIA(l)	ELIA	18I
GALE(na) [ “cover” = “hide” per Chambers]	GALE	12i
RICE*	ICRE	20I
(EH in OR)<	RHEO-	3i
S(p)ADE	SADE	6i
S+(g)EAR [in WP “kit's” is “kit has”, SR “kit is”]	SEAR	13I
K after SEE	SEEK	15I
O after SEP	SEPO	16I
&lit (i)S(s)U(e)R(e)A(d)	SURA	14I
&lit Hidden word< [“reserves” = “holds back” per Chambers	TANA	19I
(h)URLS [“fail” = “omit” per Chambers]	URLS	17I