Science - gas-cloud

Mar

2013

11:28am, EST

A chance to watch Milky Way's black hole gobble up 'snack'

European Research Media Center

This still photo from a computer animation shows a simulation of a giant space cloud falling into Sagittarius A*, the supermassive black hole at the center of our own Milky Way galaxy, in mid-2013.

By Clara Moskowitz
Space.com

The giant black hole at the center of the Milky Way is preparing to gobble up a tasty gas cloud in a cosmic meal astronomers are eager to witness.

Most galaxies are thought to host humongous black holes at their cores, and the Milky Way's, which is called Sagittarius A* (pronounced "Sagittarius A-star") contains about 4 million times the mass of our sun.

It's about to add a tiny bit more mass to its girth, when it swallows a cloud on a collision course with it. Scientists think it will take the black hole about a year to completely devour the cloud, with the peak of its feast occurring around September of this year.

"This is the first chance we've had to witness such an event in nearly 40 years of monitoring the galactic center, so this is a rare privilege," said P. Chris Fragile, an astrophysicist at the College of Charleston who works on computer simulations of the cloud's fall. The phenomenon, he said, "will be one of the most carefully observed astronomical events ever."

In contrast to the enormous size of the black hole, the cloud is just about three times the mass of Earth — "just a tiny little snack," said Stefan Gillessen, an astronomer at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. [Milky Way Black Hole Eats Gas Cloud (Video)]

Gillessen and his colleague Reinhard Genzel have been observing the cloud and plan to ramp up their observations soon to catch its descent toward the black hole. Observing the event will require some of the most sensitive observatories on Earth, such as the Very Large Telescope in Chile, where Gillessen and Genzel will be making their observations.

"It's at the limit of what telescopes can do," Gillessen told Space.com. "It's very faint, and we have to look for quite some time to see it."

Already, scientists have seen the cloud speed up and stretch out as it gets pulled closer and closer to its doom. Gravitational tidal forces from the black hole have caused it to morph from a roughly circular shape, in 2004, into a thin, oblong object in 2012. And while eight years ago the cloud was moving about 620 miles per second (1,000 kilometers per second), it is now zooming at a brisk 1,500 miles a second (2,500 km/s).

The upcoming cosmic spectacle should offer scientists a chance to test some of their theories about how black holes pull in, or accrete, mass.

"It might be a very unique opportunity to see how it is accreting," Gillessen said. "The most exciting thing would be if Sagittarius A* changes its accretion state. If the accretion rate increases, you might expect that Sagittarius A* itself will turn significantly brighter, and it might also change its structure. There's a slight chance that radio telescopes can actually catch that."

Scientists also hope to learn more about the cloud and where it came from. For example, some theories suggest there could be a hidden star buried beneath the gas that is currently invisible, but which is feeding the cloud with gas from within.

"We can obviously learn more about the nature of the cloud itself, we can learn about the conditions of the background gas, and ultimately we can learn more about how the black hole at the center of our galaxy is really fed," Fragile said.

Follow Clara Moskowitz on Twitter @ClaraMoskowitz or Google+. Follow us @Spacedotcom, Facebook or Google+. This article was first published on Space.com.

Jan

2013

6:50pm, EST

Baffling star birth mystery finally solved

NASA/Spitzer/Benjamin et al., Churchwell et al.

In this image, taken by NASA's Spitzer Space Telescope, the mysterious gas cloud G0.253+0.016 is the black object on the left. The Milky Way's center is the bright spot at right.

By SPACE.com

Astronomers have finally solved a longstanding cosmic mystery — why a super-dense gas cloud near our Milky Way galaxy's core isn't churning out many new stars.

The gas cloud, known as G0.253+0.016, is simply swirling too fast, researchers said. And it lacks the requisite pockets of even denser material, which eventually collapse under their own gravity to form stars.

The results suggest that star formation is more complex than astronomers had thought and may help them better understand the process, researchers said.

An oddly barren cloud
G0.253+0.016, which is about 30 light-years long, defies the conventional wisdom that dense gas glouds should produce lots of stars. [ 8 Baffling Astronomy Mysteries ]

The cloud is 25 times more dense than the famous Orion Nebula, which is birthing stars at a furious rate. But only a few stars are being born in G0.253+0.016, and they're pretty much all runts.

"It's a very dense cloud and it doesn't form any massive stars, which is very weird," study lead author Jens Kauffmann, of Caltech in Pasadena, said in a statement.

Kauffmann and his colleagues determined to find out why. Using the Submillimeter Array, a set of eight radiotelescopes atop Mauna Kea in Hawaii, they found that G0.253+0.016 possesses very few ultra-dense nuggets that could collapse to form stars.

"That was very surprising," said co-author Thushara Pillai, also of Caltech. "We expected to see a lot more dense gas."

Spinning out of control
The researchers then probed the cloud with another network of telescopes, the Combined Array for Research in Millimeter-wave Astronomy in California.

CARMA data showed that gas within G0.253+0.016 is zipping around 10 times faster than gas in similar clouds. G0.253+0.016 is on the verge of flying apart, with its gas churning too violently to coalesce into stars.

Further, the team found that the cloud is full of silicon monoxide, a compound typically produced when fast-moving gas smashes into dust particles. The abnormally large amounts of silicon monoxide suggest that G0.253+0.016 may actually consist of two colliding clouds, whose impact is generating powerful shockwaves.

"To see such shocks on such large scales is very surprising," Pillai said.

G0.253+0.016 may eventually be able to churn out stars. But its position near the center of the Milky Way could make it tough for the cloud to settle down, as it may smash into other clouds or be ripped apart by the immense gravitational pull near the galaxy's central black hole, researchers said.

The study has been accepted for publication in the Astrophysical Journal Letters. The team also presented the results last week at the 221st meeting of the American Astronomical Society in Long Beach, Calif.

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