As one might imagine a massive, collapsed star in which the laws of physics seem to break down, black holes hold a special place in human culture – fueling all manner of creative science fiction, creative real-world physical theories, and creative metaphors. Yet even as we gaze in awe at the astronomical bodies first known to theorists as “dark stars,” we still could not envision the impossibly massive black hole at the center of our own galaxy and around which the rest of the galaxy’s stars revolve itself.
Until now, that is.
Scientists from the Event Horizon Telescope Collaboration (EHT) announced Tuesday that they coordinated eight synchronized telescopes around the world to capture an image of Sagittarius A*. Four million times more massive than our own Sun, Sagittarius A* has long been theorized as a supermassive black hole, but experts couldn’t know for sure because it was difficult to image this part of the sky with great precision. The new image shows a ring of orange and gold light, growing particularly bright in three places. In the center and colored black, there is a slightly bean-shaped hole.
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“Although we can’t see the black hole itself because it’s completely dark, the glowing gas around it shows a telltale signature: a dark central region (dubbed the ‘shadow’) surrounded by a bright annular structure,” the astronomers explained in a statement. One of them, EHT project scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics in Taipei, added in the statement: “We were amazed at how well the ring’s size agreed with predictions from Einstein’s general theory of relativity. These unprecedented observations have greatly enhanced our understanding of what is happening at the center of our galaxy and offer new insights into how these giant black holes interact with their surroundings.”
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The first-ever direct image of a black hole was captured in 2019 and was the culmination of years of astrophotography and research. That black hole was the supermassive black hole at the center of the galaxy M87, which has a mass about 6.5 billion Suns and is 50 million light-years away. Sagittarius A* is only 27,000 light-years away, much, much closer; However, due to its position in the night sky and relatively clear field of view, it was easier to visualize a distant galaxy’s black hole before we saw our own.
It must be emphasized that while in one sense we see the black hole, in another sense the concept of “seeing” one of these objects is absurd. The term “event horizon” is more than the title of a classic 1997 sci-fi horror film. It refers to the threshold surrounding every black hole through which nothing can escape. The gravitational force is so strong that anything that falls into it stays in the black hole forever.
This includes, of course, light itself. Therefore, in order to “see” a black hole, you are actually observing the objects orbiting it, sometimes very close and very fast. These include the accretion disk, the accumulation of space debris — gas and dust — that whips around most black holes near the event horizon, creating a faint aura of light from the heat of collision and motion.
“Some of it falls in, some of it just forms this disk around itself and the stuff glows,” Seth Fletcher said Scientific American Editor-in-Chief who has written a book on EHT recently stated. “The black hole casts a shadow on this glowing matter due to the way it distorts the space and time around it due to the incredible gravity — and that’s what we see in this image.”
To say this is a long-distance photo would be a gross understatement. We live in a barred spiral galaxy, or one that twirls around with waving arms and has a rod-shaped structure at its center made mostly of stars. Our planet is in one of these spiral arms, and Sagittarius A* is 27,000 light-years away. This means that if we traveled at the speed of light, it would take us 27 millennia to reach Sagittarius A* from our heavenly home.
The EHT research team that made this discovery published their findings in The Astrophysical Journal Letters. Concluding the announcement of their discovery, they noted that more than 300 people from around the world have participated in this effort and EHT has more ambitions.
“Since these observations, the EHT has continued to monitor and expand its capabilities by adding new stations, expanding bandwidth and introducing higher frequency capability,” they wrote. “Existing and new observations with the EHT of Sgr A* and M87*, coupled with innovations in analysis and theoretical modeling, will propel discoveries in these unique black hole physics laboratories.”
While black holes weighing at least four times the mass of our Sun routinely form in supernova explosions of massive stars, supermassive black holes like Sagittarius A*, weighing millions or billions of solar masses, form differently: either through a bizarre process of gas fusion in the early Universe ; or when thousands of stellar black holes merge over billions of years; or a combination of both. Supermassive black holes have unique properties compared to their much smaller counterparts. Some scientists theorize that due to the large distance between its event horizon and its central singularity, if one plunges into a supermassive black hole, one would not be immediately oblivious to one’s immense tidal forces, as would be the case with an everyday black hole 4 up to 100 solar masses. Rather, an observer falling into a supermassive black hole could have a few hours or more before being killed by tidal stretching. If they were to look back out of the black hole and toward the event horizon in this span, they would see future near-space events at a hyper-accelerated pace, as outer time appears to be speeding up as they approach the singularity. Unfortunately, this observer would never be able to transmit this information as there is no escape.
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