There’s never been a black hole, so close to Earth.

Black holes are undoubtedly the most mysterious objects in the universe, hiding in the dark, devouring all the light that enters. All black holes, regardless of size, share common characteristics, which is the event horizon. Once the light crosses the event horizon, it cannot escape.

There's never been a black hole, so close to Earth.

Art concept diagram of the HR 6819 system (Photo: ESO and L. Cal?ada)

Writing . . . Jonathan O’Callaghan

Compilations . . . Wu Fei

Black holes that the naked eye can “see”

However, the black hole still reveals the horse’s feet, so that we capture the trace: when the black hole is not far from a star, the star’s material is attracted by the black hole, ultra-high temperature dust and gas form around the black hole’s rapidly rotating accretion disk, the release of X-rays can “light up” the black hole. What if there’s not such a close enough companion star around a black hole? Although not visible directly, scientists can indirectly detect these mysterious objects through the gravitational effects of black holes on other objects.

In a new study published in the Journal of Astronomy and Astrophysics, astronomers at the European Southern Observatory (ESO) made a remarkable discovery by finding the closest black hole to Earth to date. If the conclusion holds, people in the southern hemisphere could even see the star system in which the black hole is located without the use of observation devices.

The star system HR 6819 is located in the constellation of telescopes in the southern sky, 1,000 light-years away. This is an unobtrusible, ordinary binary system that barely sees with the naked eye in the southern hemisphere, but the researchers found that the spectral lines of one of the stars showed periodic swings. Therefore, in this system, there must be an undiscovered object.

Further analysis suggests that one of the stars appears to orbit the invisible object at a 40-day cycle; The object is 4.2 times the mass of the sun. If this is a star, observers on Earth will surely be able to see it, given its mass and distance. Therefore, the study suggests that at the center of the HR 6819 system is a black hole.

Buried data for 15 years

Thomas Rivinius, of ESO, the study’s lead author, said: “We initially thought HR 6819 was a binary system, but we looked further at it and found out that it was actually a system of three celestial bodies. “

The team made the discovery using eSO’s 2.2-meter telescope at the La Ula Observatory in Chile. It should be noted, however, that this observation was not made recently. Astronomers obtained the data in a months-long observation as early as 2004. But the data didn’t come to the attention of astronomers — as mentioned above, they thought it was just a normal binary system.

Until last year, Liu Jifeng’s team at the National Observatory of China used the Guo Shoujing telescope to discover the largest mass star-level black hole 70 times the mass of the sun. It was through further analysis that Liu’s team noticed the abnormal spectral line in a star that it was orbiting an “invisible object” in an approximate circular motion.

The study, published in the journal Nature, caught Rivinius’s attention: “I think, wait, I have some unused data in my drawer that is very similar to LB-1, the double-star system of stars found by Liu Jifeng’s team. So the Rivinius team began to reanalyze the dusty data. (Note: Just last week, two articles in Nature opened a space-proof conversation about star-level black holes in the LB-1 system. Scientists at the University of Leuven in Belgium believe that Liu’s team’s interpretation of the hydrogen spectrum is incorrect, so the source of the hydrogen emission line is not a black hole, while Liu’s team responded in a separate study that the problem of hydrogen emission lines is more complex than previously thought, and that, combined with the latest data, the mass of the black hole in LB-1 could be between 23 and 65 times the mass of the sun. )

Based on the age of two stars in the HR 6819 system, Rivinius et al. suggest that the black hole in the system is a relic of a supernova explosion thousands of years ago. In general, black holes in binary systems are able to abulk the material of the companion star, and the resulting amount of X-rays that make up the disc sending the black hole is surrounded. Interestingly, in the HR 6819 system, the distance between the two companion stars and the orbit of the black hole is far enough to avoid being “eaten” by the black hole. Because of this, the “double star” system was once forgotten by astronomers for years after it was observed.

Astronomical Meaning and Controversy

If black holes in the HR 6819 system do exist, the discovery has a range of astronomical implications, in addition to updating the closest distance between the black hole and Earth. It was previously thought that supernovae would affect the orbits of significant surrounding stars and even “kick” stars into interstellar space. And this stable Three-Body Problem system tells a completely different story. “We know from this case that black holes can form without ‘kicking’ the surrounding stars. Rivinius said.

Another significance of the study is that it shows that such “quiet” black holes are more common than previously thought, so there are still a large number of similar unknown black holes waiting to be discovered. Even LB-1 may belong to this previously unknown black hole system. Of course, because of the distance and the weaker signal, the observation of THE LB-1 is more difficult, but it is not impossible. Rivinius says it has plans to study the LB-1 system.

HR 6819 also provides an enticing clue to the mechanism serise of the mechanisms of the black hole system that produces gravitational waves. When two black holes, or black holes, coincide with neutron stars, the resulting space-time ripples have been detected by astronomers. But until the rendezvous, it is an open mystery how such a system was born.

The scientific significance of the discovery is seductive, but some scientists disagree. Kareem El-Badry of the University of California, Berkeley, who was not involved in the study, said the findings of the study were “clearly questionable.” El-Badry notes that this conclusion is based on a series of assumptions, especially for stars in systems that are closer to black holes, about five times the mass of the sun. In his view, this assumption is not reliable enough. Once the star’s mass is not as assumed by the Rivinius team, the mass of the invisible object son at the center of the system will decline. As a result, the object may not be a black hole at all, but a star of insufficient mass to be observed. “There must be a celestial body there, but it seems unwise to say it’s a black hole, ” Says El-Badry. “

Edward van den Heuvel of the University of Amsterdam questioned it from another angle, arguing that it was not possible to tell whether the object identified as a black hole was a single object 4.2 times the mass of the sun or two stars that were close to each other, with an average mass of 2.1 times the mass of the sun. “It could also be a quadruped system, with many bright stars in the universe in such a quadruped system,” van den Heuvel said. But if we never see an X-ray signal, the question arises: Is it a black hole or two stars orbiting each other? “

In response, Rivinius argues that if this is a quadruped system, we can find features that identify it in the light released from HR 6819. To identify themselves, more telescopes are needed to make longer observations. A number of observatories are closed due to a new corona outbreak that is spreading around the world. Rivinius said they would try it immediately after the observation restart. For now, we can say that an unknown “dark” companion lurks in the “backyard” of the solar system.