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Mysterious behavior of a black hole: swallowed a star and spit it out 3 years later



Astronomers have discovered a black hole mysteriously spewing out pieces of an engulfed star a few years after it was consumed.

The event, which scientists have classified as AT2018hyz, began in 2018 when astronomers saw a black hole grab an unfortunate star with its strong gravitational pull before tearing it apart.

Then, three years later, in 2021, a radio telescope in New Mexico picked up a signal indicating unusual activity – a black hole began to erupt a star at half the speed of light.

Black holes have previously been seen to devour stars before regurgitating them, but so far, the ejection has only occurred during the “eating”. The researchers used four ground-based observatories around the world and two space-based observatories to record the event.

The scientists’ work was published in The Astrophysical Journal.

“It took us by surprise — no one had ever seen anything like it before,” said the lead author, an astrophysicist at the Harvard and Smithsonian Center for Astrophysics, Yvette Sendes.

The absorption of a star by a black hole is called a tidal disruption event (TDE) because of the powerful tidal forces that act on the star due to the black hole’s gravity.

As the star pulls closer and closer to the black hole’s mouth, the black hole’s tidal forces strip and stretch the star layer by layer; turning it into a long, noodle-like thread that wraps tightly around the black hole like spaghetti around a fork, forming a ball of hot plasma. This is known as spaghettification.

This plasma rapidly accelerates around the black hole and turns into a huge jet of energy and matter, which produces a characteristic bright flash that can be detected by optical, X-ray and radio wave telescopes.

But AT2018hyz is unusual: not only has it waited three years after swallowing a star to emit a flare, but the speed of material ejected from its mouth is staggering. Most TDE streams move at 10% the speed of light, but the ejected stellar matter of AT2018hyz moves at 50% the speed of light.

“We have been studying TDEs with radio telescopes for over a decade and occasionally find them glowing in radio waves as they erupt material when the star is first being swallowed up by the black hole. But there was radio silence in AT2018hyz for the first three years, and now it has brightened up dramatically and has become one of the brightest TDEs ever observed,” said Edo Berger, co-author of the study, professor of astronomy at Harvard University.

Scientists aren’t sure what causes the flash delay, but they think the delay may be more common than previously thought. To test if this is the case, astronomers will need to look at the sources of other TDEs previously thought to be out of commission to see if they can catch their flare again.

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Extraterrestrial life may be hiding in “terminator zones”




In a study published in the Astrophysical Journal, astrophysicists set out to find out if exoplanets could support life.

Astronomers have come to the conclusion that on the surface of some exoplanets there is a strip that may contain water, necessary for the existence of biological life. The terminator zone is the dividing line between the day and night sides of an exoplanet.

Many exoplanets are planets outside the solar system held by gravity. This means that one side of the planet is always facing the star they orbit, while the other side is in constant darkness.

The water on the dark side will most likely be in a frozen state, while on the light side it will be so hot that the water should just evaporate.

The terminator zone would be a “friendly place” – neither too hot nor too cold – in which liquid water could support extraterrestrial life.

Dr. Ana Lobo of the University of California, said: “The day side can be scalding hot, much uninhabitable, while the night side will be icy, potentially covered in ice. You need a planet that’s the right temperature for liquid water.”

“We’re trying to draw attention to planets with more limited amounts of water that, despite not having widespread oceans, might have lakes or other smaller bodies of liquid water, and that climate could actually be very promising.”

“By exploring these exotic climate states, we are improving our chances of finding and correctly identifying a habitable planet in the near future.”

The researchers created a model of their climate by analyzing different temperatures, wind patterns and radiative forcing, and found the “correct” zone on exoplanets that could contain life-supporting liquid water.

Researchers who are looking for life on exoplanets will now take into account the fact that it can hide in certain areas.

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Astronomers discover the strongest evidence for another Universe before the Big Bang




The notion of the Big Bang goes back nearly 100 years, when the first evidence for the expanding Universe appeared.

If the Universe is expanding and cooling today, that implies a past that was smaller, denser, and hotter. In our imaginations, we can extrapolate back to arbitrarily small sizes, high densities, and hot temperatures: all the way to a singularity, where all of the Universe’s matter and energy was condensed in a single point. 

For many decades, these two notions of the Big Bang — of the hot dense state that describes the early Universe and the initial singularity — were inseparable.

But beginning in the 1970s, scientists started identifying some puzzles surrounding the Big Bang, noting several properties of the Universe that weren’t explainable within the context of these two notions simultaneously. 

When cosmic inflation was first put forth and developed in the early 1980s, it separated the two definitions of the Big Bang, proposing that the early hot, dense state never achieved these singular conditions, but rather that a new, inflationary state preceded it. 

There really was a Universe before the hot Big Bang, and some very strong evidence from the 21st century truly proves that it’s so.

Although we’re certain that we can describe the very early Universe as being hot, dense, rapidly expanding, and full of matter-and-radiation — i.e., by the hot Big Bang — the question of whether that was truly the beginning of the Universe or not is one that can be answered with evidence. 

The differences between a Universe that began with a hot Big Bang and a Universe that had an inflationary phase that precedes and sets up the hot Big Bang are subtle, but tremendously important. After all, if we want to know what the very beginning of the Universe was, we need to look for evidence from the Universe itself.

Read the full article here.

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