The Supernova and Cepheids of Spiral Galaxy UGC 9391
What can this galaxy tell us about the expansion rate of the universe?
Perhaps a lot because UGC 9391,
featured,
not only contains Cepheid variable stars (red circles) but also a recent
Type Ia supernova (blue X).
Both types of objects have standard brightnesses, with
Cepheids typically being seen relatively nearby, while supernovas are seen much farther away.
Therefore, this spiral is important because it allows a calibration between the near and distant parts of our universe.
Unexpectedly, a
recent analysis of new Hubble data from UGC 9391 and several
similar galaxies has bolstered previous indications that Cepheids and supernovas are
expanding with the universe slightly
faster than expected
from expansion measurements of the early universe.
Given the
multiple successes of early universe
concordance cosmology, astrophysicists are now vigorously speculating about possible reasons for this discrepancy.
Candidate explanations range from the
sensational,
such as the inclusion of
unusual
cosmological components types such as
phantom energy and
dark radiation, to the
mundane, including statistical flukes and underestimated sources of
systematic errors.
Numerous future observations are being planned to help resolve the conundrum.