Primordial black holes and dark matter are linked: NASA

Washington: A NASA scientist has suggested a possible link between primordial black holes -- formed during the first second of our universe's existence -- and dark matter, a mysterious substance composing most of the material universe.

According to astrophysicist Alexander Kashlinsky at NASA's Goddard Space Flight Centre in Maryland, this interpretation aligns with our knowledge of cosmic infrared and X-ray background glows and may explain the unexpectedly high masses of merging black holes detected last year.

“This study is an effort to bring together a broad set of ideas and observations to test how well they fit, and the fit is surprisingly good," said Kashlinsky.

“If this is correct, then all galaxies, including our own, are embedded within a vast sphere of black holes each about 30 times the Sun's mass,” he added. The nature of dark matter remains one of the most important unresolved issues in astrophysics.

NASA is currently investigating this as part of its Alpha Magnetic Spectrometer and Fermi Gamma-ray Space Telescope missions.

“The previous and new studies are providing increasingly sensitive results, slowly shrinking the box of parameters where dark matter particles can hide," Kashlinsky added.
The failure to find them has led to renewed interest in studying how well primordial black holes -- black holes formed in the universe's first fraction of a second -- could work as dark matter.

Physicists have outlined several ways in which the hot, rapidly expanding universe could produce primordial black holes in the first thousandths of a second after the Big Bang. The older the universe is when these mechanisms take hold, the larger the black holes can be.

Because the window for creating them lasts only a tiny fraction of the first second, scientists expect primordial black holes would exhibit a narrow range of masses. In September last year, gravitational waves produced by a pair of merging black holes 1.3 billion light-years away were captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana.

This event marked the first-ever detection of gravitational waves as well as the first direct detection of black holes.

The signal provided LIGO scientists with information about the masses of the individual black holes, which were 29 and 36 times the sun's mass, plus or minus about four solar masses. These values were both unexpectedly large and surprisingly similar.

"Depending on the mechanism at work, primordial black holes could have properties very similar to what LIGO detected," Kashlinsky explained.

In his new paper published in The Astrophysical Journal Letters, Kashlinsky analyses what might have happened if dark matter consisted of a population of black holes similar to those detected by LIGO.

“Future LIGO observing runs will tell us much more about the universe's population of black holes, and it won't be long before we'll know if the scenario I outline is either supported or ruled out," Kashlinsky added.