The dwarf galaxy problem is one that arises from numerical cosmological simulations that predict the evolution of the distribution of matter in the universe. Dark matter seems to cluster hierarchically and in ever increasing number counts for smaller and smaller sized halos. However, while there seems to be enough observed normal-sized galaxies to account for this distribution, the number of dwarf galaxies is orders of magnitude lower than expected from simulation. For comparison, there were observed to be around 38 dwarf galaxies in the Local Group, and only around 11 orbiting the Milky Way, (for a detailed and more up to date list see Milky Way's satellite galaxies) yet one dark matter simulation predicted around 500 Milky Way dwarf satellites.
This problem has two potential solutions. One is that the smaller halos do exist but only a few of them end up becoming visible because they have not been able to attract enough baryonic matter to create a visible dwarf galaxy. In support of this, Keck observations in 2007 of eight newly discovered ultra-faint Milky Way dwarf satellites showed that six were around 99.9% dark matter (with a mass to light ratio of about 1000) Other solutions may be that dwarf galaxies tend to be gobbled up or tidally stripped apart by larger galaxies due to complex interactions. This tidal stripping has been part of the problem in identifying dwarf galaxies in the first place, which is an extremely difficult task since these objects have low surface brightness and are highly diffused, so much that they are virtually unnoticeable even in our own backyard.
Famous quotes containing the words dwarf, galaxy and/or problem:
“When I lie down to love,
old dwarf heart shakes her head.
Like an imbecile she was born old.”
—Anne Sexton (1928–1974)
“for it is not so much to know the self
as to know it as it is known
by galaxy and cedar cone,
as if birth had never found it
and death could never end it:”
—Archie Randolph Ammons (b. 1926)
“The thinking person has the strange characteristic to like to create a fantasy in the place of the unsolved problem, a fantasy that stays with the person even when the problem has been solved and truth made its appearance.”
—Johann Wolfgang Von Goethe (1749–1832)