In 2018, amazing news spread around the world: planets were discovered outside the Milky Way for the first time. Now researchers from the same scientific group have found similar objects in two more galaxies. They can be planets or primordial black holes that astronomers have been hunting for for a long time.
Details are set out in a scientific article published in the Astrophysical Journal.
Let us recall what the authors' method consists of. Scientists are analyzing X-rays from quasars that have undergone gravitational lensing. The movement of bodies of different masses in the lens galaxy affects the spectrum of this radiation. Therefore, the spectrum can tell how many and what objects are hidden in the star system. More precisely, astronomers can calculate what proportion of the mass of a galaxy's halo is occupied by objects of one size or another.
In this study, the authors focused on galaxies Q J0158-4325 and SDSS J1004 + 411. They are part of a cluster of galaxies, in contrast to RXJ 1131-1231, where planets outside the Milky Way were first detected. The radiation received by the telescope was emitted when the age of the universe was about seven billion years, that is, half of the present.
Lens Galaxy SDSS J1004 + 4112 (bright spot) and four X-ray images of the background quasar due to lensing (blue dots).
Illustration by the University of Oklahoma.
Scientists have analyzed the data accumulated over ten years from the X-ray observatory ^ Chandra and performed calculations on a supercomputer. They found that objects with masses from the Moon to Jupiter make up 0.03% of the mass of the halo Q J0158-4325 and 0.01% of the mass of the halo SDSS J1004 + 4112. Moreover, these celestial bodies do not revolve around the stars, like ordinary planets, but freely drifting in space.
The authors believe that at least some of them are orphan planets. Another explanation is primordial black holes. The latter would be no less remarkable discovery, since these objects, left over from the first moments of the life of the Universe, have not yet been discovered. There are only upper limits of their number, meaning that if there were more primordial black holes, we would have noticed it.
“Finding objects of planetary mass, whether freely drifting planets or primordial black holes, is extremely valuable for simulating the formation of stars, planets, or the early universe,” notes co-author Xinyu Dai of the University of Oklahoma. The [upper] limit for the abundance of primordial black holes is already several orders of magnitude lower than the previous limits in this mass range."
Note, however, that the discoveries of Dai and colleagues can be considered valid only after independent experts confirm the correctness of their methods.