Astronomers have uncovered new evidence for rogue planets that fly freely in space rather than revolving around their parent stars. They found four new candidates whose mass is comparable to the mass of rocky planets similar to Earth. This is reported in an article published in the Monthly Notices of the Royal Astronomical Society.
The researchers analyzed data obtained in 2016 during the two-month K2 mission of NASA’s Kepler Space Telescope, which observed stars in an area 3.7 degrees in the bulge (central bright ellipsoidal component) of the Galaxy. They found 27 transient microlensing signals, when an invisible object distorts the light of background stars and galaxies, while simultaneously increasing their brightness. The duration of the events ranged from an hour to 10 days, with the four shortest signals corresponding to objects the size of the Earth.
Short signals were not accompanied by longer ones, which could indicate the presence of a parent star. Thus, events can refer to freely flying planets. Such objects may have originally formed in a protoplanetary cloud before being thrown away by the gravitational pull of other, heavier planets.
About one in a million stars in the Milky Way are subject to microlensing at any given time, but only a few percent of these events are caused by planets. Although the Kepler telescope itself was not a good instrument for observing microlensing in a dense field of objects in the center of the Galaxy, the researchers used new software to process photometric data, which made it possible to detect both known microlensing events and new ones.