Chinese researchers have presented an impossible black hole - now German researchers have another explanation for this discovery.
- Chinese researchers report in "Nature" the discovery of an "impossible" black hole
- For a stellar black hole, it is much too heavy at 70 solar masses - should not exist
- Contradictions quickly arise, and now German researchers are presenting a different solution
Update of January 24, 2020: In November 2019, Chinese researchers announced a discovery that caused astonishment and unbelief in the professional world: They had discovered a stellar black hole with a mass of 70 suns. Such a black hole should not actually exist - scientists assume that stellar black holes cannot have more than 20 solar masses . Criticism quickly came from experts, three works dealt with the unusual black hole that the Chinese researchers had not seen directly, but found about a star that orbited the black hole.
German astronomers publish study on “impossible” black hole
It has been some time since the first papers were published and a new study has been published in the journal "Astronomy & Astrophysics". The authors are a team of researchers from the Friedrich Alexander University of Erlangen-Nuremberg (FAU) and the University of Potsdam. They had looked at the black hole that is currently being debated and come to the conclusion that the object does not necessarily have to be a black hole.
The astronomers looked at the companion star of the black hole, which the Chinese researchers had also examined. The researchers were particularly interested in the frequencies of the chemical elements on the surface of the star, who found that the measured frequencies of helium, carbon, nitrogen and oxygen do not resemble those of normal, massive stars. “At first glance, the spectrum actually looks like that of an ordinary young massive star - apart from a few strange details. That's why we took a closer look at the data, ”explains Dr. Andreas Irrgang from the Dr. Karl Remeis observatory Bamberg, the FAU astronomical institute.
"Impossible" black hole could be a massive neutron star
The unusual chemical pattern of the star could be the result of an interaction between the star and its companion, the researchers suspect. The star may have lost its outer layers due to the interaction, only its shellless core remains. However, this shellless core would have significantly less mass than a normal star. The Chinese researchers assumed for their study that the star has the mass of eight suns.
The German researchers combined their results with new distance measurements from the Esa "Gaia" satellite and estimated the mass of the star at 1.1 solar masses. These new results also affect the black hole that Chinese researchers presented in their 2019 study. Based on the results of the German researchers, it no longer has 70 solar masses, but in the smallest case only about two to three solar masses, as the German researchers have determined. In this case, it could simply be a massive neutron star or an ordinary star, the researchers conclude.
“Impossible” black hole: Researchers have doubts about the Chinese study
Update from December 10, 2019: After Chinese researchers have announced the existence of an actually impossible - because too massive - stellar black hole in the journal "Nature", there is a contradiction between colleagues. Three works published on the arXiv.org portal deal with the unusual black hole "LB-1". Six authors write in their study "It is very unlikely that the black hole in this system has this extreme mass". Instead, it is more likely that it is a typical black hole, as you would expect in our galaxy (arXiv: 1912.03599).
In a further study (arXiv: 1912.04092), 16 researchers argue that the values from which the Chinese researchers derived the mass of the black hole actually come from the movement of the star orbiting the black hole. They write: "As a consequence, there is no evidence of a massive black hole in the data." Another study (arXiv: 1912.04185) by two researchers also concludes that it is "unlikely" that it is the stellar black hole with a mass of 70 suns actually exist. "The shape of the invisible companion remains unclear," it says. However, a "normal" stellar black hole with a mass of 5 to 20 solar masses is the most plausible.
Chinese researchers discover “impossible” stellar black hole
First announcement from November 30, 2019: Researchers estimate that there are 100 million stellar black holes in the Milky Way, the home galaxy of our solar system. These objects are created when a star collapses at the end of its life. They are so massive that not even light can escape them. So far, researchers have assumed that a stellar black hole cannot have more than 20 solar masses - unlike the super-massive black holes that are found in the center of galaxies.
But now researchers led by Jifeng Liu from the Chinese Academy of Sciences have discovered a much larger black hole - and are thus turning all assumptions about stellar black holes upside down. The researchers discovered a stellar black hole with a mass of 70 suns. This monstrous black hole is 15,000 light years from Earth and has been named "LB-1" since its discovery. The Chinese scientists describe their discovery in the journal "Nature" (doi: 10.1038 / s41586-019-1766-2)
A newly discovered stellar black hole should not actually exist
"Black holes with this mass should not exist in our galaxy according to the common models of star development," explains Liu. So far, researchers have assumed that large stars in the Milky Way lose most of their gases in strong stellar winds - and therefore cannot leave behind such massive remains. However, the discovered black hole is twice as massive as the researchers thought it was possible, Liu continued. "Now theorists will have to face the challenge of explaining that."
The researchers discovered the stellar black hole with a new method of observation: with the help of the largest Chinese telescope, the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), they looked for stars orbiting an invisible object because they were attracted by its gravity become. This technique was developed as early as the end of the 18th century, but was only practically possible with modern telescopes. Nevertheless, this method involves searching for the needle in a haystack, according to a statement by the Chinese Academy of Sciences: only one in a thousand stars could circle a black hole.
How do stellar black holes arise? Researchers have to revise models
The researchers were successful - but in fact they did not see the black hole *, but rather a star that is eight times larger than our sun and orbits the black hole with a mass of 70 suns every 79 days. “This discovery forces us to revise our models of how stellar black holes are created.” This is how David Reitze, who heads the LIGO observatory in the USA, which first detected gravitational waves, reacts to the Chinese discovery.
"This astonishing result and the measurement of collisions between black holes in recent years indicate a renaissance in our understanding of astrophysics of black holes," continued Reitze. The Chinese researchers see a connection between the gravitational wave measurements by the detectors LIGO and "Virgo" and the black hole "LB-1", which they discovered: In all cases, the black holes have significantly more mass than previously suspected.
How did the stellar black hole “LB-1” come about?
But how did the stellar black hole “LB-1” come about? The researchers have several theories:
- The black hole could be the result of two stars merging. The star that orbits the black hole every 79 days could then be the third (surviving) star of a triple system.
- However, it could also be that there are two black holes that circle around one another. Then each black hole would have about 35 solar masses - a value that comes significantly closer to previous research.
Black holes exist in different classes
There are different classes of black holes:
- Stellar black holes arise when a certain size star collapses. The outer shells are repelled in a supernova, while the core collapses into a very compact body - the black hole. Until now it was thought that these could only have about 20 solar masses - this theory must now be revised.
- Super-massive black holes are found in the center of galaxies. They have significantly more mass than stellar black holes: the black hole in the center of the Milky Way has a mass of 4.3 million solar masses - and there are even larger black holes, some with a mass of several billion suns.
- Primordial black holes are black holes that already formed during the Big Bang. This is the theory of Stephen Hawking, who first thought about it in the early 1970s. Theoretically, the primordial black holes are tiny and can hardly be located optically. Most recently, primordial black holes were a topic when researchers were looking for a theory that could explain the mysterious “planet 9” in our solar system: They put forward the theory that “planet 9” was a primordial black hole in our solar system ,
Current research on black holes
Three black holes that are about to merge * - researchers found this rare phenomenon with the help of a trick. Now they hope to find more black hole systems.
A black hole is so massive that it attracts everything that comes too close to it. Now researchers have observed for the first time how a black hole tears apart a star *.
Black holes have a dangerous reputation: they swallow matter - with no chance of return. But a newly discovered black hole defies this stereotype.
The black hole with the largest mass that astronomers know so far is located in the galaxy cluster “Abell 85”. Its mass compared to our sun is gigantic.
Researchers have discovered a source of black hole food in the early universe. This will help you to find out how black holes grew so quickly in the early days of the universe.
A previously inconspicuous star system in the constellation arrow is on the best way to merge. Researchers have calculated a not too distant period for this.
By Tanja Banner
* fr.de is part of the nationwide Ippen-Digital central editorial office.
Rubric list image: © Jingchuan YU, Beijing Planetarium, 2019