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Giant gas cloud 'resembles spaghetti' as it plunges toward a black hole

A giant gas cloud is on a suicide mission to the black hole at the center of our galaxy. As the cloud spirals into oblivion, the black hole's extreme gravity is stretching it thinner and thinner.

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Astronomers have been watching G2's slow spiral towards destruction for over a decade. When Gillessen and his colleagues published their findings last year, they described it as a "a dusty cloud" with three times as much mass as Earth, but four times bigger than our solar system – the whole loop of Neptune's orbit. Even then, this unthinkably enormous but mostly empty cloud of gas was en route to the center of our galaxy, heading for the encounter that has now begun. Over the years, the German astronomers measured G2 accelerating: its front end doubled in speed from 2004 and 2011, rushing headlong towards its date with destiny. (Or at least density.)

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The latest measurements, made in April, show that the front end is moving over 7 million miles per hour (3,000 km/s) – and it's heading back towards us, say the German scientists.

"The most exciting thing we now see in the new observations is the head of the cloud coming back towards us at more than 10 million km/h along the orbit – about 1% of the speed of light," said Reinhard Genzel, leader of the research group that has studied this region for nearly twenty years, in a press release. "This means that the front end of the cloud has already made its closest approach to the black hole."

Gillessen and Genzel won't give a particular date to the moment when the gas cloud rounded the bend, like a comet slingshotting around the sun. "The cloud is so stretched that the close approach is not a single event, but rather a process that extends over a period of at least one year," said Gillessen.

G2's origins are still unknown, though there are plenty of theories, which these new observations have been testing. Some astronomers thought that the gas cloud could have been created from stellar winds blowing from stars near the black hole. Others argued that the gas came from a jet at the galactic center. Many theorized that there must be a star at the heart of G2, like the frozen slushball at the heart of a comet. This last theory predicted less stretching than appears in the new observations, so Gillessen and his colleagues argue that it now seems unlikely. 

Hundreds of astronomers around the world are watching to see what happens next. Will the accelerating gas cloud create a bow shock, like the bow of a boat? Will it fall into the black hole with '"a nice firework show?" asks Frail, whose radio telescopes are making monthly observations of the galactic center to watch the whole, slow-motion show.

With G2 spiraling toward its glorious demise, astronomers have a once-in-a-lifetime chance "to make predictions and actually test them," says Frail. "You get to make the measurements in real time to see if you were right or you were wrong. It's just a great opportunity."


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