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Mystery of Gravitational-Wave Astrophysics --"How Two Black Holes Can Come Together and Merge"




Astrophysicists at the University of Birmingham have made progress in understanding a key mystery of gravitational-wave astrophysics: how two black holes can come together and merge. Senior author Ilya Mandel added: "This work makes it possible to pursue a kind of 'palaeontology' for gravitational waves. A palaeontologist, who has never seen a living dinosaur, can figure out how the dinosaur looked and lived from its skeletal remains. In a similar way, we can analyse the mergers of black holes, and use these observations to figure out how those stars interacted during their brief but intense lives."

During its first four months of taking data, Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) detected gravitational waves from two mergers of pairs of black holes, GW150914 and GW151226, along with the statistically less significant black hole merger candidate LVT151012.

The first confirmed detection of gravitational waves occurred on September 14 2015 at 5.51am Eastern Daylight Time by both of the twin LIGO detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. It confirmed a major prediction of Albert Einstein's 1915 general theory of relativity and opened an unprecedented new window onto the cosmos. However, we still do not know how such pairs of merging black holes form.

A new paper, published in Nature Communications, describes the results of an investigation into the formation of gravitational-wave sources with a newly developed toolkit named COMPAS (Compact Object Mergers: Population Astrophysics and Statistics).

In order for the black holes to merge within the age of the Universe by emitting gravitational waves, they must start out very close together by astronomical standards, no more than about a fifth of the distance between the Earth and the Sun. However, massive stars, which are the progenitors of the black holes that LIGO has observed, expand to be much larger than this in the course of their evolution.

The key challenge, then, is how to fit such large stars within a very small orbit. Several possible scenarios have been proposed to address this.

The Birmingham astrophysicists, joined by collaborator Professor Selma de Mink from the University of Amsterdam, have shown that all three observed events can be formed via the same formation channel: isolated binary evolution via a common-envelope phase.

In this channel, two massive progenitor stars start out at quite wide separations. The stars interact as they expand, engaging in several episodes of mass transfer. The latest of these is typically a common envelope - a very rapid, dynamically unstable mass transfer that envelops both stellar cores in a dense cloud of hydrogen gas. Ejecting this gas from the system takes energy away from the orbit. This brings the two stars sufficiently close together for gravitational-wave emission to be efficient, right at the time when they are small enough that such closeness will no longer put them into contact.

The whole process takes a few million years to form two black holes, with a possible subsequent delay of billions of years before the black holes merge and form a single black hole.

The simulations have also helped the team to understand the typical properties of the stars that can go on to form such pairs of merging black holes and the environments where this can happen. For example, the team concluded that a merger of two black holes with significantly unequal masses would be a strong indication that the stars formed almost entirely from hydrogen and helium, with other elements contributing fewer than 0.1% of stellar matter (for comparison, this fraction is about 2% in the Sun).

First author Simon Stevenson, a PhD student at the University of Birmingham, explained: "The beauty of COMPAS is that it allows us to combine all of our observations and start piecing together the puzzle of how these black holes merge, sending these ripples in spacetime that we were able to observe at LIGO."

The Daily Galaxy via University of Birmingham



Dear friends. Can someone explain to me, how we can talk for merge of two black holes, when up to date we have not found a single black hole. Did we are moving too fast?

I`m not brite enough to understand how 2 Black Holes can get close to each other, i hope you can enlighten me. So a Black Hole is basically like a huge vacuum cleaner. Let`s admit it`s movin in an orbit through space, around another object, be it another Black Hole. Suddenly a ginormous cloud of gas arrives in the area. The vacuum cleaner does it`s job eating instantly the gas in front himself. So normally the Black Hole should accelerate it`s move , as it`s nothing emitting out of it`s back side. I know there are 2 jet stream forming at the poles , but they do not affect the movement as they are opposed, equal and at 90 degrees to the movement, so i will allow myself to not consider them 2. Now please, as i am not brite enough, explain me how the increasing speed will allow the Black Hole to come close to the attracting other, when increasing speed in an orbit will ALWAYS get your in a higher orbit.

By the way, please don`t mention me about tidal forces, as these 2 objects are the size of pin-heads (actually smaller they say, we`re talking about Black Holes, not Neutron Stars), so no tides will form on their "surface" ...Also we are losing our fuking Moon because of the tidals , not the other way around.

Gaugain. The article says gas is ejected from the system because of the violent interaction between the two stars (i.e. mass is lost not gained); there is no mention of extra gas coming along. Whether that results in the effect described I have no idea.

Your description of black holes as vacuum cleaners is slightly misleading as you have to get fairly close to a black hole for its gravitational field to be any different from a massive star. Most of the stuff that reaches the extreme gravitational field closer to the event horizon gets ejected in the way you describe because of the huge acceleration it causes.

That leads on to your second comment. If you take an object just light enough to be a neutron star and an object just heavy enough to be a black hole, the gravitational field around them would be almost the same. It is only when you approach beyond where the surface of the neutron star used to be that the gravitational field will be significantly different. Although black hole singularities are infinitely small the gravitational fields around them are not. The tidal forces would definitely be there.

"A palaeontologist, who has never seen a living dinosaur, can figure out how the dinosaur looked and lived from its skeletal remains. In a similar way, we can analyse the mergers of black holes, and use these observations to figure out how those stars interacted during their brief but intense lives."

No similarity whatsoever: paleontologists do not have to rely on advanced mathematical gymnastics to demonstrate that dinosaurs existed... Black holes, dark matter and dark energy are all numerical figments of our imagination to try to shore up a theoretical cosmology which ever increasingly is shown by observations to be untenable. Evidence which does not fit the Big Bang model family is cherry-picked and discarded as being "in error."

I see the usual 'Cosmology is wrong' & 'it's all lies' gang is here.
What next? Electric Universe theory is correct? BULLS**T!!!!!!
Go take your nonsense to the conspiracy forums with the rest of the ignorant buffoons.

This universe is like a huge aquarium of dark matter pingpong balls, the weak force exerted on an intrusion "matter" over millions of miles of space becomes a strong force as the intrusion displaces the ping pong balls less and less in distance but the combined force is insistent to squeeze out the intruder of matter and the weaker area is between them so they are drawn together . The holes in time-space to another larger slower time-space interval "black hole" also get pushed around by this dark matter but they will not be sucked through them.

@Talios Actually the claimed detection of gravitational waves by LIGO relies on imputing the signal to the merger of two black holes. If you smell circularity, you're not alone.

@Robert J. Baran Well said.

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