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Interstellar visitor 'Oumuamua could still be alien technology, new study hints

 
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08/22/2020 02:26 AM
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Interstellar visitor 'Oumuamua could still be alien technology, new study hints
'Oumuamua — a mysterious, interstellar object that crashed through our solar system two years ago — might in fact be alien technology. That’s because an alternative, non-alien explanation might be fatally flawed, as a new study argues.

But most scientists think the idea that we spotted alien technology in our solar system is a long shot.

In 2018, our solar system ran into an object lost in interstellar space. The object, dubbed 'Oumuamua, seemed to be long and thin — cigar-shaped — and tumbling end over end. Then, close observations showed it was accelerating, as if something were pushing on it. Scientists still aren't sure why.

One explanation? The object was propelled by an alien machine, such as a lightsail — a wide, millimeter-thin machine that accelerates as it's pushed by solar radiation. The main proponent of this argument was Avi Loeb, a Harvard University astrophysicist.

Most scientists, however, think 'Oumuamua's wonky acceleration was likely due to a natural phenomenon. In June, a research team proposed that solid hydrogen was blasting invisibly off the interstellar object's surface and causing it to speed up.

Now, in a new paper published Monday (Aug. 17) in The Astrophysical Journal Letters, Loeb and Thiem Hoang, an astrophysicist at the Korea Astronomy and Space Science Institute, argue that the hydrogen hypothesis couldn't work in the real world — which would mean that there is still hope that our neck of space was once visited by advanced aliens — and that we actually spotted their presence at the time.

Here's the problem with 'Oumuamua: It moved like a comet, but didn't have the classic coma, or tail, of a comet, said astrophysicist Darryl Seligman, an author of the solid hydrogen hypothesis, who is starting a postdoctoral fellowship in astrophysics at the University of Chicago.

'Oumuamua was the first object ever seen flying into our solar system and back out again. That's opposed to most solar system objects that turn circles around the sun, never leaving the celestial neighborhood. Its journey and the fact that it was accelerating suggested 'Oumuamua, which is estimated to be about 1,300 to 2,600 feet (400 to 800 meters) long, was a comet. And yet, "there was no 'coma' or outgassing detected coming from the object," Seligman said. Normally, comets come from regions more distant from the sun than asteroids, and ice on their surface turns straight into gas as they approach the sun, leaving behind a trail of gas, or what we see as a beautiful comet tail, Seligman said.

That outgassing changes how the comet moves through space, he said. It's a bit like a very slow rocket engine: The sun strikes the comet, the warmest part of the comet bursts with gas, and that gas flowing away from the comet sends it tumbling faster and faster away from the sun.

In a paper published June 9 in The Astrophysical Journal Letters, Seligman and Yale astrophysicist Gregory Laughlin proposed that the object was a comet made up partly or entirely of molecular hydrogen — lightweight molecules composed of two hydrogen atoms (H2).

H2 gas freezes into a puffy, low-density solid only when it's very cold — minus 434.45 degrees Fahrenheit (minus 259.14 degrees Celsius, or just 14.01 degrees above absolute zero) in Earth's atmosphere. Researchers had already proposed the existence of "hydrogen icebergs" out in the very cold reaches of space, Laughlin and Seligman wrote in the study. And outgassing hydrogen wouldn't be visible from Earth — meaning it wouldn't leave behind a visible comet tail.

The numbers worked out neatly; while a few other substances (like solid neon) could potentially explain the coma-free acceleration, hydrogen was the best match for the data.

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Re: Interstellar visitor 'Oumuamua could still be alien technology, new study hints
The debate over the origins and molecular structure of ‘Oumuamua continued with an announcement in The Astrophysical Journal Letters that despite earlier promising claims, the interstellar object is not made of molecular hydrogen ice after all.

The earlier study, published by Seligman & Laughlin in 2020—after observations by the Spitzer Space Telescope set tight limits on the outgassing of carbon-based molecules—suggested that if ‘Oumuamua were a hydrogen iceberg, then the pure hydrogen gas that gives it its rocket-like push would have escaped detection. But scientists at the Center for Astrophysics | Harvard & Smithsonian (CfA) and the Korea Astronomy and Space Science Institute (KASI) were curious whether a hydrogen-based object could actually have made the journey from interstellar space to our solar system.

“The proposal by Seligman and Laughlin appeared promising because it might explain the extreme elongated shape of ‘Oumuamua as well as the non-gravitational acceleration. However, their theory is based on an assumption that H2 ice could form in dense molecular clouds. If this is true, H2 ice objects could be abundant in the universe, and thus would have far-reaching implications. H2 ice was also proposed to explain dark matter, a mystery of modern astrophysics,” said Dr. Thiem Hoang, senior researcher in the theoretical astrophysics group at KASI and lead author on the paper. “We wanted to not only test the assumptions in the theory but also the dark matter proposition.” Dr. Avi Loeb, Frank B. Baird Professor of Science at Harvard and co-author on the paper, added, “We were suspicious that hydrogen icebergs could not survive the journey—which is likely to take hundreds of millions of years—because they evaporate too quickly, and as to whether they could form in molecular clouds.”

Traveling at a blistering speed of 196,000mph in 2017, ‘Oumuamua was first classified as an asteroid, and when it later sped up, was found to have properties more akin to comets. But the 0.2km radius interstellar object didn’t fit that category, either, and its point of origin has remained a mystery. Researchers focused on the giant molecular cloud (GMC) W51—one of the closest GMCs to Earth at just 17,000 light years away—as a potential point of origin for ‘Oumuamua, but hypothesize that it simply could not have made the journey intact. “The most likely place to make hydrogen icebergs is in the densest environments of the interstellar medium. These are giant molecular clouds,” said Loeb, confirming that these environments are both too far away and are not conducive to the development of hydrogen icebergs.

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Re: Interstellar visitor 'Oumuamua could still be alien technology, new study hints
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