Monsters of the Universe: The VLT super telescope first spotted a dormant black hole that spooked scientists

Where is the largest telescope

On July 18, a team of scientists announced the discovery of a system consisting of a quiescent black hole with the mass of nine suns and a hot blue star. The unique object is located outside the Milky Way, 160 thousand light years from Earth. The results of the study are published in journal natural astronomy.

This is the fruit of six years of observations with the FLAMES (Fiber Large Array Multi Element Spectrograph) instrument at the VLT (Very Large Telescope) at the European Southern Observatory. The focus is on the sleeping black hole itself, labeled VFTS 243. This is the only such object outside the Milky Way known to science today. Conventional methods to identify a dormant black hole would be unrealistic. But fortunately the VLT telescope came to the rescue.

FLAMES (Large Array Multi-Element Spectrograph). Photo © ESO.org

The unit belongs to the MegaScience class, that is, a research complex with a fundamental scientific program, an international staff of researchers and colossal funding. Although the VLT is the largest European project, it is located in Chile, in the driest desert – Atacama, there is almost no precipitation, interference with observation is minimal. From the idea of ​​creating a VLT to combining the four mirrors of the VLT complex into a single system, 59 years have passed, it took 10 years to find a site for construction alone. Among optical telescopes, the VLT is the largest on the planet in terms of total mirror area and has the highest resolution in the world. The Very Large Telescope is equipped with a wide range of instruments to observe wavelengths from near ultraviolet to mid-infrared, where it can take images four times as sharp as the Hubble Telescope. Well, for reference: the VLT weighs 350 tons, its rotating dome is comparable in size to a football field, and the cost is about 1 billion euros. Although the largest optical telescope to date, the E-ELT (“Extremely Large Telescope”) is scheduled to open in 2027, but that’s another story.

The VLT telescope studies the processes of destruction of protoplanetary discs, in 2016 it was used to obtain ultra-clear images of Jupiter, in 2018 – photographs of the planet Neptune, as well as the globular star cluster NGC 6388, in 2019, for the first time in history, an optical telescope made it possible to observe an exoplanet (planet outside the solar system). Two years ago, with the help of the VLT, scientists obtained an ultra-high-resolution image of the planetary nebula NGC 2899. A new discovery is the first black hole in the history of astrophysics outside the galaxy.

Comparison of images of the planet Neptune obtained with the VLT telescope and with adaptive optics MUSE.  Photo © ESO/P.  Weilbacher (AIP)

Comparison of images of the planet Neptune obtained with the VLT telescope and with adaptive optics MUSE. Photo © ESO/P. Weilbacher (AIP)

Black holes in the universe beyond the Milky Way

Black holes were predicted by Einstein’s general theory of relativity. These objects are extremely difficult to identify (after all, they are from the “blacker than black ink” category) due to the fact that light quanta cannot leave their boundaries due to the monstrous gravity acting in a black hole. Stellar mass black holes form when stars ten times larger than the Sun collapse under their own gravity. Their appearance is preceded by the formation of a supernova. A black hole bends space and time and thus affects the movement of stars and light. In fact, black holes marked the transition from the universe, where the laws of mechanics dominate, to the universe, where the laws of space-time curvature are put first.

A black hole cannot be identified by optical radiation – it is not there, but it can be with X-rays (Hawking radiation). It is formed due to the work of the accretion disk. These are the remnants of matter captured by the black hole from the surface of nearby stars, and the remnants of broken stars and other space objects that were absorbed by the black hole.

Hawking radiation.  Photo © Wikipedia / Alain r.

But the fact is that the black hole VFTS 243, which exists in a binary system paired with a blue star, is unique. The star that gave birth to it collapsed without much noise and a powerful explosion. But most importantly, VFTS 243 does not emit Hawking radiation. That is, if you follow the usual logic, it was impossible to open it. Optical scope – earlier, X-ray – earlier. How to identify her? The ESO team used the “spectral unraveling” method. This is when the radiation from several pairs of stars is studied (it usually merges into one image), and then it is revealed by the method of elimination which of the stars does not have radiation, that is, it is asleep. Sleeps, but affects the properties of the other star in its pair, in this case a hot blue star.

Thus, VFTS 243 is a black hole. To prove this, the spectra of 1,000 massive stars in the Tarantula Nebula within the Large Magellanic Cloud had to be unraveled.

The mass of the blue star is 25 times the mass of the Sun, the mass of the black hole VFTS 243 is equal to the mass of nine suns. This object is unique, according to researchers.

The minimum mass of the satellite means it is a black hole. No other black hole that does not emit X-rays is unequivocally known outside our galaxy, Tomer Shenar, researcher at the University of Amsterdam, notes.

How many black holes are there in the universe

If black holes themselves are one of the most mysterious objects in the universe, VFTS 243 breaks all records. In fact, its formation contradicts the generally accepted model of stellar evolution, according to which massive stars flare up as supernovae, the process is accompanied by an explosion, and then either a neutron star or a black hole emerges. VFTS 243, apparently, did not form as a result of a supernova explosion, but went according to the “direct collapse” scenario. During this collapse, no more than 0.5 of the Sun’s mass was ejected in the form of stellar matter. This is very little. It was once thought that direct collapse was an exceptional phenomenon in the formation of black holes, and that a massive star of 200–250 solar masses was needed for such a scenario.

This is a unique case, not only in terms of the fact that VFTS 243 is the first such object discovered outside our galaxy, but also in that scientists have previously rejected many more obvious black hole candidates. And here, after six years of observation, they are absolutely sure that the conclusions are correct.

This proves the assumption that most black holes yet to be discovered are elusive, and what lies on the surface can be misleading. In January of this year, Italian scientists concluded that in the observable universe there are at least 40 quintillion (a number with 18 zeros. — Note. Life) stellar mass black holes. And at least a third of them were formed by direct collapse, past the supernova stage. Some joke: “If VFTS 243 is a sleeping black hole, what happens when it wakes up?”

When a dormant black hole awakens, a powerful ejection of hot plasma is induced. Three and a half million years ago, a supermassive black hole woke up in the center of the Milky Way, after the ejection of hot plasma from which a giant trail was formed. It can be seen at a distance of 200 thousand light years. In the case of VFTS 243, in about 5 million years it will absorb the companion star and turn into a double black hole, but the process could take another dozen million years. But if you think about it, there are a billion billion black holes in the universe, some of which are inactive, closed to scientists. But since a black hole is a dynamic system, it tends to wake up, expand, absorb everything that falls into the gravitational zone and also violate the laws of physics. With all the colossal efforts that science is making to study black holes, humanity is only one step closer to understanding them, but has not yet decided whether they are dangerous to humanity or not. Bringing in new methods, as in the case of “spectral resolution”, as well as the involvement of telescopes such as the E-ELT, can allow us to put together a puzzle that will either throw people in horror or turn the minds of humanity. Or all at once.

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Are black holes dangerous to humanity?

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