The SDSS 1557 is a binary star system that is quite unlike other binaries.
The two companion stars are not quite “stars”.
One of them is a white dwarf, a remnant of a star that exhausted its hydrogen fuel and turned into a scalding hot husk that is incredibly dense.
The other one is a so-called brown dwarf, a massive object that does not have the prerequisite mass to fuse hydrogen into helium. They are slightly smaller than a main sequence star but still far bigger than gas giants – their minimum mass is 13 times that of Jupiter.
Trailing rocky asteroids are sucked in by the white dwarf and after orbiting it for a while they fall on it.They appear to be made from metals rather than ices and other lighter materials, which points to formation of planets in the system’s past.
The planets may still lay there intact, but there is a huge obstacle that impedes their finding- the system’s brown dwarf. It was hiding because it gave little light, but its large mass caused a gravitational tug on the white dwarf.
“The brown dwarf was effectively hidden by the dust until we looked with the right instrument,” said coauthor Steven Parsons of University of Valparaíso and University of Sheffield, “but when we observed SDSS 1557 in detail we recognised the brown dwarf’s subtle gravitational pull on the white dwarf.”