Futura-sciences (France): the discovery of earth closest to the black hole

A team of astronomers at the European southern Observatory and other institutions quite by accident I discovered the existence of a black hole at a distance of 1 000 light-years from Earth. During observation system called HR 6819 in the study of systems with two stars the team of Thomas Rivinius (Thomas Rivinius) established the presence of a third object, a black hole.

It is located only 1,000 light-years from us and is thus closest to the solar system among all known. Thanks to the 2.2-meter telescope MPG/ESO Chilean Observatory ESO scientists were able to track the motion of two stars companions and calculate the existence of this invisible object. According to them, this system may be just the tip of the iceberg. In other words, in the near future can be open to a lot of similar holes.

The first triple system with a black hole, visible with the naked eye

As emphasized by study co-author Peter Hadrava (Petr Hadrava) of the Czech Academy of Sciences, “we were very surprised to discover that we are talking about the first star system with black hole, visible with the naked eye”. This triple system is indeed so close to the Ground that members of her stars can be seen with the naked eye in the night in clear weather in the southern hemisphere. A black hole is by definition invisible.

To determine the existence of a black hole, scientists have used observations with the spectrograph of the telescope MPG/ESO, which showed that one of two stars that revolve in a period of 40 days around the invisible object, while the second is at a greater distance from the inner pair. Scientists have determined its presence and established its mass by studying the orbit of the stars from the inner pair. “Invisible object with four times the solar mass can only be a black hole,” — said Thomas Rivinius. We are talking about one of the first open to date black holes of solar masses, which do not interact with the environment in an aggressive way and, as a consequence, appear to us truly black.

The discovery supports the theory that the milky way has much more than a few tens of open to date of black holes. Scientists believe that since the formation of our galaxy, much larger number of stars turned into black holes at the end of its existence. The opening of the silent and invisible black hole in HR 6819 makes it possible to detect many other black holes in the milky way. “There must be hundreds of millions of black holes, but we know only a few of them. Knowing what to look for, should help us to more efficiently find them,” adds Thomas Rivinius.

Let us give the floor to Thomas Rivinius, research associate of ESO and the main author of the study in the journal Astronomy & Astrophysics.

“Futura”: This finding surprised you, surprise?

Thomas Rivinius: Absolutely. We were looking for something else entirely, expect to see a perfectly normal dual system. We had hoped that the observations will allow us to understand the reason for such large differences between the two stars. One (external) spins so fast that it almost shatters (it loses the substance mainly because of this rapid rotation), and the second rotates very slowly.

Then we realized that actually we were talking about three sites. I would like to clarify that initially the study was our colleague Stan Stefl (Stan Štefl, was tragically killed in an accident in 2014, which is job one didn’t). Now we have continued it because I recently found a system which appears to be a similar triple system with a black hole LB-1. To confirm our conjecture will require new observations.

— A black hole in the ternary system — how rare is that?

Yes. A true marvel! Most of the models of stellar evolution and the supernova explosion was suggested that such a system will be shaken, and some objects will disperse. But HR 6819 continues to exist as a triple system, and therefore it is not always the case.

— Should we be concerned about the discovery of a black hole so close to Earth?

To care for the Land is not worth it. Since we are talking about black hole solar masses, its diameter is only several tens of kilometers. That is, at this stage, it does not pose a threat even to the immediate neighbor, the inner stars. They are apart the same distance as the Sun and Earth. Anyway, in the course of evolution the inner star it will begin to grow, and the black hole will absorb at least part of its weight. But before that, there are still millions, maybe even tens of millions of years.

The other question is, is there a danger for the Earth primordial explosion of a supernova that spawned the black hole. It is unlikely, given that it all happened 15-75 million years ago. Besides, the star was within a few hundred parsecs from us, much closer than it is now. It reads safe distance in the explosion of a supernova.

— What does the discovery of this black hole?

— The interesting thing is that it’s probably nothing special! It’s pretty close to us and, if we do not consider our immediate environment as an exception, there must be many others. Yet we know only a few dozen scattered throughout the galaxy of black holes. Usually it is because they have accumulated a large mass of matter from their environment, leading to strong radiation in the x-ray spectrum. We believe that the milky way should be from hundred million to a billion black holes that resemble the one that was found in this ternary system: they are calm because they have nowhere to accumulate weight, and they are very difficult to detect.

— The proximity of this system will allow you to make more detailed studies than in more distant systems?

— Proximity and illumination of this system means that we will probably be able to decompose it into separate components. This can be achieved only with interferometry, which is to combine multiple telescopes to get the same crisp image as if you had a giant telescope the size of all together. As soon as our paralysie Observatory will resume and my team will be able to use the VLTI (Very Large Télescope Interferometer), we will try to do it. I can’t wait.

The second possibility is the observation of HR 6819 x-ray spectrum. Although x-rays tells about the tranquility of the black hole, this does not mean that nothing is happening. Black hole probably collects something from the inner circle, but since its density is small, its ability to absorb substances is severely restricted. All of our other observations are associated with a much more active black holes. It remains to prove that it works and at a very low level of absorption of a substance, as in the case of the black hole.