Primordial black holes have remained certainly one of astronomy’s most intriguing ideas for many years. Now, researchers on the University of Miami consider a recent gravitational wave detection may bring scientists closer to confirming that these ancient objects are real, a breakthrough that might also help solve the enduring mystery of dark matter.
Primordial black holes are thought to have formed through the first fraction of a second after the Big Bang, long before the primary stars or galaxies existed. Unlike the black holes created by collapsing stars, these hypothetical objects could range in size from something as small as an asteroid to much larger bodies.
Although no primordial black hole has ever been confirmed, scientists consider they might answer several major questions on the universe. One in every of the largest is the character of dark matter, the invisible substance that makes up about 85 percent of all matter and provides the gravitational pull that helps hold galaxies together.
“We consider our study will aid in confirming that they really do exist,” said Nico Cappelluti, an associate professor within the University of Miami’s Department of Physics, referring to research he conducted with Ph.D. student Alberto Magaraggia.
An Unusual LIGO Signal
Their work builds on a possible discovery reported by the Laser Interferometer Gravitational-Wave Observatory (LIGO), which late last yr detected an unusual gravitational wave signal. Gravitational waves are ripples in spacetime produced by among the universe’s most violent events, including collisions between black holes.
Most known black holes form after massive stars explode as supernovas. Their masses typically range from several times the mass of the Sun to billions of solar masses.
“Essentially the most common black holes form as the results of a supernova, the death of an enormous star. So, their masses can range from a couple of times the Sun’s mass to billions of solar masses,” Cappelluti explained.
But in November, LIGO issued an automatic alert for a merger during which no less than one object appeared to have lower than one solar mass. Such a small black hole could be difficult to elucidate through conventional stellar evolution and as a substitute could point to a primordial black hole.
Not everyone seems to be convinced. Some astrophysicists have suggested the signal may simply be noise inside LIGO’s extremely sensitive detectors relatively than evidence of a remarkable recent discovery.
Could This Explain Dark Matter?
Cappelluti and Magaraggia argue that the detected object is best explained as a primordial black hole that formed within the dense conditions of the early universe, long before stars existed.
To check that concept, the researchers estimated what number of primordial black holes might exist throughout the cosmos and the way often LIGO should detect them.
“We attempted to estimate what number of primordial black holes may exist within the universe and the way lots of them LIGO should find a way to detect,” Magaraggia said. “And our results are encouraging. We predict that subsolar black holes just like the one LIGO can have observed should indeed be rare, consistent with how infrequently such events have been seen to this point.”
Their findings, published in The Astrophysical Journal, suggest that the mysterious LIGO signal has no conventional astrophysical explanation and is most consistent with a primordial black hole.
The study “suggests that probably the most plausible explanation for the LIGO signal, which lacks any conventional astrophysical explanation, is the detection of a primordial black hole,” Cappelluti said. “And our research indicates that these primordial black holes could account for a good portion, if not all, of dark matter.”
Even so, each researchers emphasize that one detection just isn’t enough to settle the query.
For now, scientists must wait to see whether LIGO and its international partners record additional events that match the identical pattern.
“LIGO picked up what may be very strong evidence that some of these black holes exist. But we’ll must detect one other such signal and even several others to get the smoking-gun confirmation that they’re real,” Cappelluti said. “But what is evident is that they can’t be excluded as being real.”
A Theory A long time within the Making
The concept of primordial black holes dates back to the Cold War era, when Soviet scientists Yakov Zeldovich and Igor Novikov first proposed their existence. Within the early Seventies, Stephen Hawking expanded on the thought, arguing that these objects might be abundant throughout the universe, emit radiation, and possibly explain dark matter.
LIGO later provided the primary opportunity to go looking for evidence supporting those theories. On Sept. 14, 2015, the observatory made history by detecting gravitational waves for the primary time, confirming a serious prediction of Albert Einstein’s general theory of relativity and opening a completely recent option to study the universe.
The Way forward for Gravitational Wave Astronomy
LIGO consists of two observatories situated in Hanford, Washington, and Livingston, Louisiana. Along with the Virgo detector in Italy and the underground KAGRA observatory in Japan, they form the international LVK collaboration, which searches for black holes, regions of space where gravity is so strong that not even light can escape.
Planned upgrades will make LIGO much more sensitive, increasing its probabilities of finding additional candidate primordial black holes. Nevertheless, the observatory’s two L shaped detectors, each with 2.5 mile long vacuum arms, were designed to detect the high frequency gravitational waves produced by relatively recent cosmic collisions, not the waves generated directly through the Big Bang itself.
Future observatories will extend that reach much farther back in time. The European Space Agency’s Laser Interferometer Space Antenna (LISA), scheduled for launch in 2035, is anticipated to detect gravitational waves from the universe’s earliest epochs after the Big Bang.
One other planned facility, Cosmic Explorer, is currently within the design phase in america. Researchers expect it to be about 10 times more sensitive than LIGO, allowing it to detect black hole and neutron star mergers stretching back to the era when the primary stars formed.