Mystery Cloud Heading for the Milky Way’s Black Hole Hints at Planet Formation at the Galactic Center


A new study by an international team of astronomers led by Stefan Gillessen of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, announced that they had spotted dusty gas cloud about three times as massive as Earth, possibly heading toward a close encounter with Sagittarius A* (Sgr A*), our centraal supermassive black hole, which has as much mass as four million suns. They believe that the object was belched out as stellar plasma winds from the young stars that orbit the black hole.

In a followup analysis, Ruth Murray-Clay and Abraham Loeb of the Harvard–Smithsonian Center for Astrophysics concluded that the newfound cloud Gillessen and his colleagues discovered could be the disrupted remnants of a planet-forming disk surrounding a star that used to orbit Sagittarius A* at a safe distance but is now being pulled toward the black hole. 

“This cloud of gas naturally originates from a proto-planetary disk surrounding a low-mass star, which was scattered a century ago from the observed ring of young stars orbiting Sgr A*,” they wrote.
Sagittarius A* has distortion field has generated a debris stream around the star that telescopes can detect.

If the young stars orbiting Sagittarius A* host protoplanetary disks, that “implies that planets form in the Galactic center,” bombarded by intense radiation emitted by material swirling around the outside of the black hole, which gets compressed and heated as it falls inward into the balck hole's event horizon.

The cloud is on schedule to swing past Sagittarius A* in mid-2013 where  it will get torn apart and partly consumed by the black hole, temporarily brightening the radiation from around Sagittarius A* if it's dust cloud. Biut, if the cloud is debris from a protoplanetary disk, the star itself should cruise past Sagittarius A* largely intact.

Another recent study highlighting planet formation near the Galactic Center, "A Model of Habitability Within the Milky Way Galaxy," led by the University of Hawaii's Michael Gowanlock, used computer models to 'find' habitable planets – and to weigh the possibly devastating effects of supernova explosions. The rapid formation of planets at the galaxy's core would 'outweigh' the negative effects of repeated supernova explosions – providing a haven for life, said the researchers. 

Common wisdom has it that the galactic habitable zone is a torus about 30 lightyears in diameter around the center of the galaxy lessening the likelyhood that habitable planets will form close to the galactic centre or very far away from it. In contrast, however, Michael Gowanlock at the University of Hawaii in Honolulu and colleagues, developed a new map of the galactic habitable zone in which challenges this convention and suggests that the galactic habitable zone is much more complex than a simple torus.

The new map uses the latest findings about exoplanets to determine galactic habitability. The oldest stars in the early universe were formed entirely from hydrogen and helium but generated heavier elements when they ran out of fuel and exploded. The next generation of stars formed from the debris of these supernovas and so have higher levels of heavier elements or metallicity.Astronomers have recently discovered that exoplanets are much more likely to form around  those stars that contain heavier elements.

These heavier stars are most likely to form in areas where there are lots of supernovas and in our galaxy that's near the centre (at distance of about 9 light years), and are more likely to have planets and therefore more likely to have a planet in the habitable zone

The Gowanlock team say that habitable planets are so common towards the center of the galaxy that even if many are wiped out by supernovas, there should still be plenty that survive for long enough for complex life to evolve.

"We find the majority of stars in our galaxy will be bathed in flux by a nearby supernova event during their lifetimes,' the team concluded – but even if a planet was irradiated, it could evolve life at a later stage, or even re-evolve life after a supernova blast.  Planets that might support avanced life could be more common than we realize."

Their model suggests that 2.7 per cent of stars in the inner galaxy should have habitable planets. And there should also be habitable planets further away too. Gowanlock and team say about 0.25 per cent of stars in the outer galaxy should have habitable planets.

"We predict that ∼1.2% of all stars host a planet that may have been capable of supporting complex life at some point in the history of the Galaxy," says Gowanlock. But, their model also predicts that 75 per cent of these habitable planets will be tidally locked around their mother star, meaning that one side of this planet would burn under a scorching sun while the other would freeze. 

Whether life could exist anywhere on a planet such as the superEarth around Gliese 581, which is close enough to the star to be in the habitable zone but is also probably tidally locked, is unknown.

Currently, arguments rage over what, precisely, constitutes a 'habitable' planet. Early statistical analysis of the Kepler results provoked furious debate when one researcher concluded that one-third of planets round sun-like stars (stars with the classifcation F, G or K) could have 'earth-like' planets, while other experts say that many of the "habitable" worlds would be shrouded in clouds of freezing gas

The Daily Galaxy via Max Planck Institute for Extraterrestrial Physics,   and Ref: A Model of Habitability Within the Milky Way Galaxy


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