The dramatic, serendipitous discovery in 1987 of an extremely massive but almost invisible galaxy, dubbed Malin 1, shows how much our picture of the universe may be biased by what astronomers can readily observe (SN: 5/16/87, p.308).
Subsequent observations revealed this unusual, dim object, now labeled Malin 1, as the largest galaxy yet detected.
"You get to discover something you didn't expect." He and his collaborators have since found a second distant, faint galaxy similar to Malin 1 but only half as large.
Malin 1 is dark because most of its mass still exists in the form of hydrogen gas rather than luminous stars.
Malin 1 and its more recently discovered sibling are unusual in that they both contain an enormous amount of diffuse hydrogen gas.
In the June 1 ASTROPHYSICAL JOURNAL, Impey and Bothun propose that Malin 1 is a quiescent, nonevolving disk galaxy -- a faint giant that has quietly lurked in the background for billions of years without changing very much.
Known as Malin 1, the dark galaxy is located in the direction of the famous cluster of galaxies in the constellation Virgo, but it does not belong to that cluster, and lies in fact some distance beyond it--715 million light-years from earth--in one of the recently discovered voids of space, where few or no galaxies appear to be.
Indeed, when first discovered late in1985 as the group was using the United Kingdom Schmidt telescope to survey the Virgo cluster for dark dwarf galaxies, Malin 1 was thought to be part of the cluster.
This means that Malin 1 is also much bigger than the observers initially believed.
Malin 1 thus has plenty of the materialout of which stars form.
Photo: In normal photo (right) Malin 1 looks like a dwarf member of the Virgo cluster.