Meet our newest neighbor in the galaxy - a black hole was discovered, and it is the closest one to our solar system yet! The exciting findings were published in a study in the journal Astronomy & Astrophysics, as recently as this Wednesday. The black hole is about 1,000 light-years away, and each light year is 5.9 trillion miles away (or 9.5 trillion kilometers). It may not sound all that close but in terms of the cosmos and even the galaxy, it’s considered practically next door according to European Southern Observatory astronomer Thomas Rivinius, who led the study.
For proportion, the black hole that was previously considered the closest one is about three times further - 3,200 light-years away. The black hole at the center of the Milky Way lies more than 25,000 light-years away, and another black hole which astronomers managed to capture in unprecedented detail in April last year is a whopping 55 million light-years away, in another galaxy altogether.
So if this newly discovered black hole is so close, how come it was wasn’t known to us until now? Black holes are regions in space that exert a force of gravity so strong that nothing can escape, not even light. Because no light is reflected, black holes are invisible, and the only way for astronomers to discover them is by noting the luminous bodies that orbit them. Most of the black holes we know of were detected because they were devouring nearby stars. Astronomers believe most black holes don’t have anything close enough to swallow, and so they remain undetected.
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Interestingly, this was exactly the case for the newly discovered back hole. It is a part of a two-star system called HR 6819, which has been examined by astronomers for years. When they analyzed the data, they noticed that there was something unusual about the behavior of the inner star of HR6819. Its velocity was so extreme, the team started suspecting that a third object existed in the system, which was flinging the inner star around.
They concluded it could only be a black hole. It was powerful enough to change the star's course, but not close enough to swallow it. “An invisible object with a mass at least 4 times that of the sun can only be a black hole," Rivinius explained in a press release.
Another unusual aspect is that this star system is actually close enough for people in the southern hemisphere to actually be able to spot it on a clear night. This is the first-ever stellar system containing a black hole that can be seen with an unaided eye.
The video below shows what the astronomers saw: a star (blue) orbiting an invisible black hole (red), with another star (also blue) orbiting the inner pair. That makes this star system, called HR 6819, a triple system, and not double-system, as was believed thus far.
This discovery could help scientists progress and expand the knowledge of black holes immensely. "There must be hundreds of millions of black holes out there, but we know about only very few. Knowing what to look for should put us in a better position to find them," Rivinius said. Dietrich Baade, another astronomer on the research team called it “the tip of an exiting iceberg”.
The more we learn about the universe surrounding us, the more we realize how vast and mysterious it is, and despite being difficult, the process of studying it is certainly gratifying.