Black holes remain a contentious issue among stellar scientists. While their existence is all but confirmed, debate continues about exact mechanisms of operation, size and impact on general relativity. However, we are close to having some answers. As noted by National Geographic in 2017, a global team of researchers completed the first ever “photo shoot” of Sagittarius A*, the supermassive black hole at the center of the Milky Way, using the Event Horizon Telescope (EHT). These pictures are close to being developed by the MIT Haystack Observatory and the Max Planck Institute for Radio Astronomy, Mother Nature Network said.
Then there will finally be hard evidence — one way or another — of the existence or absence of mega-sized black holes.
According to general relativity, massive objects curve or “warp” space–time and create gravity. Conceptually, the easiest visual is stretching out a blanket and then dropping a ball in the middle — the heavier the ball, the bigger its depression.
Smaller objects will naturally fall “down” toward the ball, but if they’re moving at high speed — like planets orbiting the sun — they roll around the massive center. Einstein’s theory also predicts that the closer objects get to massive objects, the more gravity affects their orbit. As noted by New Scientist, this is evident in Mercury’s orbit, which is odd enough that scientists once argued for the existence of another planet inside its orbit to explain the disturbance.
General relativity also predicts the existence of black holes at the center of galaxies that are orbited by all mass in that galaxy. And while repeated testing has yielded results consistent with black hole formation and existence, researchers have never been able to directly observe a black hole. If the EHT worked as intended, a close-up may soon be available.
There’s a sizable amount of research that suggests that black holes are out in the cosmos warping space-time and consuming all matter that comes their way. In January 2017, for example, the Laser Interferometer Gravitational-Wave Observatory detected gravitational wave distortions that indicated a black hole–to–black hole binary collision. In 2015, LIGO spotted these black holes on a collision course; the current measurement lines up with predictions about their impending crash.
Or consider the work of Aurelien Hees of the University of California. In the 1990s, Hees and other scientists began tracking the orbits of stars close to Sagittarius A* — S0-2 and S0-38 take 16 and 19 years, respectively, to complete full revolutions. Now Hees and his team have tracked their entire orbits and found that general relativity accurately describes their path and movement. Next year, S0-2’s elliptical orbit will take it just 111 AUs from the black hole, for an even better chance to view potential deviations. So far, however, relativity and the four fundamental forces hold up, with no sign of the mysterious “fifth force” posited by some experts.
Teams at the University of Texas and Harvard University, meanwhile, tackled another question: What happens when a black hole “eats” stars that stray too close? The accepted theory is that they’re trapped by the event horizon — the point past which even light cannot escape — and then simply “vanish.” But other theories postulate the existence of a hard surface, something stars would crash into once they’re trapped in the gravity well. Researchers determined what would happen if the hard surface theory were true — the star’s gas would envelop the black hole and create a glow. Researchers then sought evidence of these so-called “transients” using current data on star masses. The result? No transients and further affirmation of Einstein’s theory.
All this goes to show why the work of the EHT is so critical. Using five telescopes in Hawaii, Arizona, Mexico, the South Pole and Spain — combined with the acuity-enhancing Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, researchers may finally have taken the first picture of black-hole event horizons. It was a grueling process, since the telescopes needed clear weather at all locations simultaneously to gather solid data. While there’s no guarantee that the end result will be usable, and even if the images aren’t ideal, astronomer Heino Falcke said they “will turn black holes from some mythical object to something concrete we can study.”
Let’s just hope we caught Sagittarius A*’s good side.
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