Gravitational waves could shed light on the origin of black holes

November 30, 2017 by Kevin Stacey, Brown University
Gravitational waves could shed light on the origin of black holes
The LIGO experiment has made several detections of colliding black holes. Future gravitational wave experiments might detect such events much further back in time, which could shed light on how black holes form. Credit: The SXS (Simulating eXtreme Spacetimes) Project

A new study published in Physical Review Letters outlines how scientists could use gravitational wave experiments to test the existence of primordial black holes, gravity wells formed just moments after the Big Bang that some scientists have posited could be an explanation for dark matter.

"We know very well that black holes can be formed by the collapse of large stars, or as we have seen recently, the of two neutron stars," said Savvas Koushiappas, an associate professor of physics at Brown University and coauthor of the study with Avi Loeb from Harvard University. "But it's been hypothesized that there could be black holes that formed in the very early before stars existed at all. That's what we're addressing with this work."

The idea is that shortly after the Big Bang, quantum mechanical fluctuations led to the density distribution of matter that we observe today in the expanding universe. It's been suggested that some of those density fluctuations might have been large enough to result in black holes peppered throughout the universe. These so-called primordial black holes were first proposed in the early 1970s by Stephen Hawking and collaborators but have never been detected—it's still not clear if they exist at all.

The ability to detect gravitational waves, as demonstrated recently by the Laser Interferometer Gravitational-Wave Observatory (LIGO), has the potential to shed new light on the issue. Such experiments detect ripples in the fabric of spacetime associated with giant astronomical events like the collision of two black holes. LIGO has already detected several black hole mergers, and future experiments will be able to detect events that happened much further back in time.

"The idea is very simple," Koushiappas said. "With future gravitational wave experiments, we'll be able to look back to a time before the formation of the first stars. So if we see black hole merger events before stars existed, then we'll know that those black holes are not of stellar origin."

Cosmologists measure how far back in time an event occurred using redshift—the stretching of the wavelength of light associated with the expansion of the universe. Events further back in time are associated with larger redshifts. For this study, Koushiappas and Loeb calculated the redshift at which black hole mergers should no longer be detected assuming only stellar origin.

They show that at a redshift of 40, which equates to about 65 million years after the Big Bang, merger events should be detected at a rate of no more than one per year, assuming stellar origin. At redshifts greater than 40, events should disappear altogether.

"That's really the drop-dead point," Koushiappas said. "In reality, we expect merger events to stop well before that point, but a redshift of 40 or so is the absolute hardest bound or cutoff point."

A redshift of 40 should be within reach of several proposed gravitational wave experiments. And if they detect merger events beyond that, it means one of two things, Koushiappas and Loeb say: Either primordial black holes exist, or the early universe evolved in a way that's very different from the standard cosmological model. Either would be very important discoveries, the researchers say.

For example, primordial black holes fall into a category of entities known as MACHOs, or Massive Compact Halo Objects. Some scientists have proposed that dark matter—the unseen stuff that is thought to comprise most of the mass of the universe—may be made of MACHOs in the form of primordial black holes. A detection of primordial black holes would bolster that idea, while a non-detection would cast doubt upon it.

The only other possible explanation for at redshifts greater than 40 is that the universe is "non-Gaussian." In the standard cosmological model, matter fluctuations in the early universe are described by a Gaussian probability distribution. A merger detection could mean matter fluctuations deviate from a Gaussian distribution.

"Evidence for non-Gaussianity would require new physics to explain the origin of these fluctuations, which would be a big deal," Loeb said.

The rate at which detections are made past a of 40—if indeed such detections are made—should indicate whether they're a sign of or evidence for non-Gaussianity. But a non-detection would present a strong challenge to those ideas.

Explore further: Did the LIGO gravitational waves originate from primordial black holes?

More information: Savvas M. Koushiappas et al, Maximum Redshift of Gravitational Wave Merger Events, Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.221104

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milnik
1 / 5 (7) Dec 01, 2017
If we want to find out what is happening in the infinite universe, we must first of all understand the structure of the universe and learn how to form matter and form it.
All previous explanations do not rest on natural laws, but on some indicators derived from some fictitious models and formulas.
Who are those people who think that everything is created out of nothing, and this is "proven" by the appearance of some kind of BB, taken as the "divinity" of these supernatural scientists. SVAŠTA !!
The black holes are formed in the process of the disappearance of matter and its return back into the form of AETHER, from which the matter forms and which fills the infinite universe. Therefore, there is neither BB nor the black hole collision, nor GV. The formation of celestial bodies is a process that is renewable and cyclical (from magnetars to black black holes).
antialias_physorg
5 / 5 (7) Dec 01, 2017
Erm...what you just wrote is:

"in order to know we must first know"

That's....stupid?
Captain Stumpy
5 / 5 (4) Dec 01, 2017
That's....stupid?
@A_P
it doesn't get any better, either - see for yourself: https://phys.org/...ent.html

it's about religion, aether and Kepler's law, and none if it makes any sense

TheGhostofOtto1923
5 / 5 (2) Dec 01, 2017
In 50 years or so we will be mapping the universe in detail with our neutrino and graviton telescopes.
SVAŠTA !!
Borat: "This is my country of Kazakhstan. It locate between Tajikistan, and Kyrgyzstan, and assholes Uzbekistan."
milnik
1 / 5 (4) Dec 02, 2017
How can one speak and draw conclusions about the existence of GW, if nothing is gentle about what is gravity and how it arises.
And you again show that you better understand the meaning of "stupid", of the meaning of gravity and magnetism
Whydening Gyre
5 / 5 (2) Dec 03, 2017
How can one speak and draw conclusions about the existence of GW, if nothing is gentle about what is gravity and how it arises.
And you again show that you better understand the meaning of "stupid", of the meaning of gravity and magnetism

milnik,
Gravity IS gentle on a small scale. It just gets stronger as more of it accumulates, subsequently makes its effect on a smaller scale seem - "un-gentle"...
milnik
1 / 5 (4) Dec 03, 2017
@WG,
Does any one of you try to think, what could it be gravity, if science has so far not given a response that agrees with occurrences in nature.
Again, I'm trying to enter a science virus in tycoon science, which will teach the science the right way.
The gravity is left unbalanced between the AETHER and the "solid aggregate state" of matter, which is a 3kg (3 quark and 3 gluon binder) particles.
For easier understanding, compare gravity with the cohesion force of the liquid droplet. Why does a liquid droplet tend to get a spherical shape?
milnik
1 / 5 (4) Dec 03, 2017
Because the intrinsic forces outside the liquid can not equalize with the air forces, and therefore the surface stress occurs, which fluid balances from the center of mass to the end of the liquid. The same is the phenomenon of gravity. The substance "submerged" in Aether has a relationship with Aether in the form of attracting particles with each other, and Aether is a "means of transport" for connecting matter at any distance in the space.
The rest is related to the electromagnetic properties of Aether, which causes light and magnetism and heat, but the science did not find an answer to the eagerness of these phenomena.
Captain Stumpy
5 / 5 (1) Dec 03, 2017
@milking a bull
The gravity is left unbalanced between the AETHER and...

The rest is related to the electromagnetic properties of Aether, which causes light and magnetism and heat, but the science did not find an answer to the eagerness of these phenomena
you cannot find the properties and define something that doesn't exist, like the aether: https://www.natur...omms9174

Whydening Gyre
not rated yet Dec 03, 2017
@WG,
Does any one of you try to think, what could it be gravity, if science has so far not given a response that agrees with occurrences in nature.
Again, I'm trying to enter a science virus in tycoon science, which will teach the science the right way.
The gravity is left unbalanced between the AETHER and the "solid aggregate state" of matter, which is a 3kg (3 quark and 3 gluon binder) particles.
For easier understanding, compare gravity with the cohesion force of the liquid droplet. Why does a liquid droplet tend to get a spherical shape?
Water drop is probly Van der Waals type or EM cohesive - prob'ly even a combo of both. Not to mention the weak, strong, EM AND gravity combo. An aggregate. Gravity is mass derived. Aggregation, again.
The Universe only adds...
milnik
1 / 5 (3) Dec 03, 2017
None of you has any opinion, but use some "proofs from the past, which have never been proven true and that agree with natural laws. And I know and own many of the work of scientists from the past, but I do not serve their evidence.

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