Washington DC: Two undergraduates have discovered two galaxies that are known to be densest.
The first system discovered by the investigators, M59-UCD3, has a width two hundred times smaller than our own Milky Way Galaxy and a stellar density 10,000 times larger than that in the neighborhood of the Sun. For an observer in the core of M59-UCD3, the night sky would be a dazzling display, lit up by a million stars. The stellar density of the second system, M85-HCC1, is higher still: about a million times that of the solar neighborhood. Both systems belong to the new class of galaxies known as ultracompact dwarfs (UCDs).
The study, led by San Jose State University's Michael Sandoval and Richard Vo, used imaging data from the Sloan Digital Sky Survey, the Subaru Telescope, and the Hubble Space Telescope, as well as spectroscopy from the Goodman Spectrograph on the Southern Astrophysical Research (SOAR) Telescope, located on the Cerro Tololo Inter-American Observatory site.
The SOAR spectrum was used to show that M59-UCD3 is associated with a larger host galaxy, M59, and to measure the age and elemental abundances of the galaxy's stars.
While the nature and origins of UCDs are mysterious, Michael Sandoval favoured the tidally stripped dwarf galaxies hypothesis, and said that one of the best clues was that some UCDs host overweight supermassive black holes. This suggested that UCDs were originally much bigger galaxies with normal supermassive black holes, whose fluffy outer parts were stripped away, leaving their dense centers behind.
To test this hypothesis, the team will investigate the motions of stars in the center of M59-UCD3 to look for a supermassive black hole.