Editing Lambda-CDM model (section)

==== Galaxy morphology problem ====
If galaxies grew hierarchically, then massive galaxies required many mergers. [[Galaxy merger|Major mergers]] inevitably create a classical [[Bulge (astronomy)|bulge]]. On the contrary, about 80% of observed galaxies give evidence of no such bulges, and giant pure-disc galaxies are commonplace.<ref name="kormendy2010">{{cite journal |last1=Kormendy |first1=J. |author1-link=John Kormendy |last2=Drory |first2=N. |last3=Bender |first3=R. |last4=Cornell |first4=M.E. |title=Bulgeless giant galaxies challenge our picture of galaxy formation by hierarchical clustering |year=2010 |journal=[[The Astrophysical Journal]] |volume=723 |issue=1 |pages=54–80 |doi=10.1088/0004-637X/723/1/54 |arxiv=1009.3015 |bibcode=2010ApJ...723...54K|s2cid=119303368 }}</ref> The tension can be quantified by comparing the observed distribution of galaxy shapes today with predictions from high-resolution hydrodynamical cosmological simulations in the ΛCDM framework, revealing a highly significant problem that is unlikely to be solved by improving the resolution of the simulations.<ref name="Haslbauer2022">{{cite journal |last1=Haslbauer|first1=M|last2=Banik|first2=I|last3=Kroupa|first3=P|last4=Wittenburg|first4=N|last5=Javanmardi|first5=B|title=The High Fraction of Thin Disk Galaxies Continues to Challenge ΛCDM Cosmology|date=2022-02-01|journal=[[The Astrophysical Journal]]|volume=925|issue=2|page=183|doi=10.3847/1538-4357/ac46ac|issn=1538-4357|arxiv=2202.01221|bibcode=2022ApJ...925..183H|doi-access=free}}</ref> The high bulgeless fraction was nearly constant for 8&nbsp;billion years.<ref name="sachdeva2016">{{cite journal |last1=Sachdeva |first1=S. |last2=Saha |first2=K. |title=Survival of pure disk galaxies over the last 8&nbsp;billion years |year=2016 |journal=The Astrophysical Journal Letters |volume=820 |issue=1 |pages=L4 |doi=10.3847/2041-8205/820/1/L4 |arxiv=1602.08942 |bibcode=2016ApJ...820L...4S|s2cid=14644377 |doi-access=free }}</ref>