Only one merger of neutron stars and five incredible issues

17 Aug Earth made up both light and gravitational-wave signals from merging neutron stars. For the first time in the history of the pair of signals was registered by the people. Phase spiral whirling was observed by the detectors LIGO and Virgo for 30 seconds, 100 times longer than previous gravitational wave signals. Also, this signal was the closest we've seen is only 130 million light-years from us. While the Observatory was recovered from the signals of huge amount of information, created a new task: to bring all this to the theoretical meaningfulness.

Relatively speaking, we heard the sound but did not know where he is.

Ethan Siegel sat down with Chris FYROM National laboratory Los Alamos, an expert on supernovae, neutron stars and gamma ray bursts, which works on the theoretical side of these objects and events. Nobody expected that LIGO and Virgo will be able to register the merger at such an early stage of the project, only two years after the first successful registration well before reaching the planned sensitivity. But they not only saw the signals, but were able to pinpoint their source and confluence that brought us a lot of surprises.

Here are five of the biggest new issues raised by this discovery.

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How often are the merger of neutron stars?

Before we saw this event, we had two ways to assess the frequency of mergers of neutron holes: measurements of binary neutron stars in our galaxy (like pulsars) and our theoretical models of star formation, supernovae and their remains. All this gives us a rating of 100 such mergers occurs annually within a cubic gigaparsec of space.

Watch for a new event has provided us with a first evaluation of the observed frequency of the Aurora, and she's ten times more than expected. We thought that we need LIGO, has reached the limit sensitivity (halfway) to see something, and then another, and three additional detector to determine the exact location. And we managed not only early to see him, but also to localize the first attempt. So the question is: we were just lucky to see this event, or the frequency thereof is much higher than we thought? If above, then what is incorrect with our theoretical model? Next year LIGO will be spent on modernization, and theorists will have a little time to think.

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That causes the substance to be disposed of in the process of merging in such numbers?

Our best theoretical models predicted that the merger of stars of this kind will be accompanied by bright light in the UV and optical parts of the spectrum during the day, and then will fade and disappear. But instead, the glow lasted two days before beginning to fade, and we, of course, have questions. Bright glow, which lasted so long suggests that the wind disk around the stars threw 30-40 Jupiter masses in a substance. According to our data, the substances should be less than twice or even eight times.

What is so unusual about these emissions? To simulate such a merger, you need to include many different physics:

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• hydrodynamics
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• GTR
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• magnetic field
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• equation of state of matter at nuclear densities
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• interaction with neutrinos

...and much more. Different codes model these components with different levels of difficulty, and we don't know which of the components responsible for these winds and emissions. Find the right is a problem for theorists, and we have to accept the fact that we were the first to measure the merger of neutron stars... and got a surprise.

In the last moments of the merger of two neutron stars emit not only gravitational waves, but also the catastrophic explosion that reverberates throughout the electromagnetic spectrum. And if the product is a neutron star, a black hole or something exotic secondary, the transition state is unknown to us

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Produced whether the merger of a supermassive neutron star?

To get enough of lost weight from the merger of neutron stars, it is necessary that the product of this merger generates sufficient energy of the appropriate type to blow away the mass from the surrounding disk stars. Based on the observed gravitational wave signal, we can say that this merger has created an object with a mass of 2.74 solar, which is much higher than the solar maximum mass that can be non-rotating neutron star. That is, if nuclear matter behaves as it is expected, the merging of two neutron stars would lead to the emergence of a black hole.

a Neutron star is one of the densest collections of matter in the Universe, but its mass is an upper limit. Exceed it — and the neutron star collapses again with the formation of a black hole

If the nucleus of this object immediately after the merger had shrunk to a black hole, no release would not exist. If, instead, it became a supermassive neutron star, it would have to rotate extremely rapidly, since a large angular momentum would increase the maximum mass by 10-15%. The problem is, what if we got so rapidly rotating supermassive neutron star, it would have to be a Magnetar with an extremely powerful magnetic field that is a quadrillion times more powerful than the field on the surface of the Earth. But Magnetar quickly stops spinning and needs to collapse into a black hole in 50 milliseconds; our own observations of magnetic fields, viscosity and heating, which threw the weight, show that the object has existed for hundreds of milliseconds.

Something's not right here. Either we have a rapidly rotating neutron star, which for some reason is not a Magnetar, either we have to be emitted for hundreds of milliseconds, and our physics does not give us the answer. Thus, even for a short while, most likely, we had a supermassive neutron star, followed by the black hole. If both are true, we are dealing with the most massive neutron star and most low-mass black hole in the history of observations!

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If these neutron stars would be more massive, it would merge invisible?

There is a limit to how massive may be the neutron star, and if you add weight, you get exactly the black hole. This limit is 2.5 solar masses for non-rotating neutron star means that if the total mass of the merger will be lower, you will almost certainly be left with a neutron star after the merger, which will lead to strong and long ultraviolet and optical signals, which we saw in this case. On the other hand, if you go up to 2.9 solar masses, immediately after the merger will form a black hole, it's probably no ultraviolet and optical variations.

Anyway, our first merger of neutron stars was in the middle of this range, when you may receive a supermassive neutron star that generates the emissions and the optical and ultraviolet signals for a short time. If Magnetar formed with less massive mergers? And more massive — just come to black holes and are invisible at these wavelengths? How rare or common these three categories of merger: ordinary neutron stars, supermassive neutron stars and black holes? A year LIGO and Virgo will search for answers to these questions, and theorists will be the year to bring their model in line with forecasts.

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That leads to the fact that gamma ray bursts are so bright in many directions, and not in the cone?

This question is very complicated. On the one hand, the discovery confirmed what had long been suspected but could not prove that merging neutron stars produce gamma-ray bursts. But we always believed that gamma-ray bursts emit gamma rays only in a narrow conical form, 10-15 degrees in diameter. Now we know, because of the provisions of the merger and the value of gravitational waves, gamma-ray bursts go at a 30 degree angle from our line of sight, but we observed a powerful gamma-ray signal.

The Nature of gamma-ray bursts needs to change. The task of theorists is to explain why the physics of these objects is so different from predicted by our models.

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a Separate line: how opaque/transparent heavy elements?

When it comes to the heaviest elements in the periodic table, we know that they are produced for the most part not a supernova, namely the mergers of black holes. But to get the spectra of heavy elements from a distance of 100 million light years, you need to understand their transparency. This includes the physical understanding of the atomic transitions of electrons in the orbitals of an atom in an astronomical environment. First we have the environment to test how astronomy overlaps with nuclear physics, and follow-up merger should allow us to answer the question of opacity and transparency in particular.

It is possible that the merger of neutron stars happens all the time, and when LIGO will reach the planned level of sensitivity, we will find tens of mergers per year. It is also possible that this event was extremely rare and we are lucky to see only one for the year even after the settings are updated. The next ten years, theoretical physicists spend searching for answers to the above questions.

The Future of astronomy lies before us. Gravitational waves — a new, completely independent way of exploring the sky and mapping the sky with gravitational waves with the traditional astronomical maps, we are ready to answer the questions they never dared ask a week ago.

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