A terrifying black hole was discovered thanks to the material it pulls from its partner

This unique system will end its life in a violent collapse of the partner into the black hole * In the discovery, which was made with the Chandra space telescope and will be published today (18.10.2007) in the journal Nature, Israeli researchers are also involved * Interview with Prof. Zvi Mzaha

An international team of astronomers with the participation of Israeli astronomers managed to measure the mass of a black hole moving around its partner in the neighboring galaxy M33, which is about 3 million light-years away from Earth, and it turns out that it is a body with a huge mass 15.7 times that of our Sun. Until now, such a large mass has not been measured in a stellar black hole, and this discovery was made possible due to the proximity of the black hole to another huge star - which has a mass of 70 solar masses. The two bodies orbit each other at a distance equal to a tenth of the distance between the Earth and the Sun, that is, almost within touching distance, from a cosmic point of view.
The Israeli team includes Professor Zvi Maza, director of the Sackler Institute for Astronomy of Tel Aviv University, and research student Avi Shaforer. A report on the groundbreaking research appears in the October 18 edition of the prestigious scientific journal Nature.

Black holes moving together with their partners have been known for about 40 years. According to the accepted theory, such a system began its life as a system of two stars moving around each other in space. The heavier star of the two ended its life in a massive explosion called a supernova, which is created by the collapse of the star into its center, and shines with a bright light billions of times stronger than the sun's light. At the end of the explosion, a black hole remains in the core of the exploding star, which continues to surround its partner. Material passing from the companion to the black hole falls at enormous speeds to the rim of the black hole, heats up to a temperature of millions of degrees, and before entering the black hole succeeds in emitting X-rays (X-rays) that were picked up by the Chandra spacecraft.

"I am thrilled by the fact that we are able to study black holes, which only because of Einstein's theory of general relativity could we hypothesize their existence," says Professor MZA: "The latest spacecraft and giant telescopes allow us to study systems in space that look as if they were taken from a science fiction movie. The reality revealed to our eyes surpasses any human imagination."
A black hole is formed as a result of the collapse of a star at the end of its life (when most of the hydrogen in it has already turned into helium). Although all stars collapse, if they are small, on the order of our Sun, they end their lives as white dwarfs after experiencing a period of inflation of their atmosphere as red giants. Stars whose mass at the time of collapse is greater - several solar masses, collapse under their own weight to such an extent that the atoms are no longer able to surround the nucleus and the neutrons in the nucleus come closer to each other, leaving a compact star - the size of the Earth and with a mass greater than that of the Sun. If the star is larger, from 10 solar masses or more (although the exact limit has not been measured) the self-gravity of the collapsing star is so great that even the neutrons collapse and it actually collapses into one point in space - a black hole. Such a black hole is simply called a stellar black hole. There is another type of black holes, more common at least in terms of the ability to detect them - black holes located in the centers of most galaxies. The mass of these black holes is millions of solar masses, and the hypothesis is that they were formed from the merger of stellar black holes that also swallowed stellar and interstellar matter that came their way.
Stellar black holes are very difficult to detect. So far no more than 10-15 of these have been discovered. If such a black hole were standing on the outskirts of the solar system, we would not feel it until some stray comet fell into it, and when it reached the threshold of the black hole it would emit radiation in the X-ray range. Therefore, most of the stellar black holes that have been discovered are those that are members of a binary star system, meaning that they orbit another star (or it orbits them) in such proximity that the solar wind from that star hits the black hole, and when swallowing this material, the black hole emits X-rays.
The circumstances of the discovery are somewhat reminiscent of the discovery of planets outside the solar system - it was discovered thanks to the fact that the star it orbits hides it once every three and a half days for a few hours.
The mass measurement was made with the help of observations made by the space telescope in the X-ray field, Chandra (Chandra) belonging to the American space agency, NASA (NASA), and the giant telescope Gemini (Gemini), located on the heights of the highest mountain in Hawaii. This measurement makes M33 X-7 the heaviest black hole known so far in a binary system.

The conventional theories of the evolution of massive stars struggle to explain the properties of the M33 X-7 binary system. The star from which the black hole was formed had to be heavier than its partner for the former to become a black hole. The radius of such a heavy star is larger than the current size of the binary system. Hence, the original stars probably formed at a greater distance than their current distance and came closer to each other while in a shared outer atmosphere. This process usually results in a large amount of material being thrown out of the system. Therefore, we do not fully understand how the exploding star managed to create a black hole that is 15.7 times the mass of the Sun. "This discovery raises questions about how such a black hole could have formed," says Jerome Uros from the University of San Diego in the US, the first author of the paper.

"This is a giant star that has a partner that is a giant black hole," says Jeffrey McClintock, another author of the paper, from the Center for Astrophysics of the Smithsonian Institution and Harvard University in Cambridge, Massachusetts. "Eventually, the stellar partner will also end its life in a supernova explosion and then a double system will be formed with two black holes."

Wolfgang Fich of the Max Planck Institute near Munich, Germany, another author of the paper, was the first author of a previous paper that discovered the black hole using observations made with the Chandra Space Telescope. M33 X-7 is the first black hole discovered in a binary system where anomalies occur, where the partner obscures the black hole and its surroundings cyclically. These defects make it possible to measure the masses of the black hole and its partner very precisely. "Because the black hole is defective and because it has such a large mass, it is a unique opportunity to test accepted astrophysical theories" says Fitch.

How was the discovery made?
Prof. Maza: "The spacecraft looked at the area containing part of the M-33 galaxy for 26 consecutive hours. The scientists on Earth received the observation data and divided the individual stars between them to analyze them. The analysis showed that the X-radiation intensity of this source, this X-7 source, its X-radiation intensity drops to almost zero, wait a few hours and suddenly it rises again. That is, there is a defect here. When you see something like this and it repeats itself, you realize that there is some kind of cyclical phenomenon here - two stars that rotate around each other and the source of the X-ray is hidden by the partner. This is how we discovered that there is an eclipse here - a double system that rotates around itself and this is the most unique thing about the unique system - that the source of X-radiation undergoes an eclipse every three and a half days, disappears for a few hours and then returns to radiate X in full force.
How do you know it's actually a black hole?
Mainly according to the mass. We made very detailed observations with optical telescopes to follow the partner and from the cycle time and the measurement of the speed the partner moved and the eclipse, we can estimate the mass of the X-ray source and it comes out to be 15.7 solar masses, and it cannot be any other compact star that we know, not a white dwarf, Not a neutron star, all of these things have a mass of 3/XNUMX and XNUMX solar masses. The nature of the X-rays also shows us that such X-rays are usually emitted very close to the rim of the black hole.

Does he threaten to swallow his partner?
They go around each other very close but safe. At the current rate to consume all the mass will take hundreds of millions of years. Long before the companion will swell and spill dramatically into the black hole, the system will be much louder than today.

In the illustration taken from the article appearing this week in the prestigious journal Nature, the stages of development of the double star are described. Star number 1 begins to swell (phase a) until its envelope engulfs star number 2 (phase b). During the movement of star 2, the envelope of star 1 is thrown away and the two stars approach (step c).

Then star 1 explodes, creating the newly discovered black hole.